Foretravel Owners' Forum

I'm in the market for fresh engine start batteries, and looking at two options.  I have researched this subject in the Forum archives, and found some excellent info...especially Don's more recent posts on his battery system re-do.  But I'm still unsure which way I want to go, so looking for input.  I don't want to get into debates about battery type, or brand.  I'm just interested in weighing the pros and cons of 2 different setups.

My current battery arrangement is two O'Reilly AGM8D house batteries (installed Dec. 2013, haven't been abused, still in good shape) and two Optima Model 34/78-980 Red Top start batteries, which were in the coach when we bought it in Nov. 2013 - actual install date is unknown.  The Red Tops have been working fine up to now, but are starting to get tired, hence my search for replacement.

I am looking at two options.

Option #1:  Replace the Red Tops with 2 fresh AGM group 34 batteries of similar CCA rating (at least 800 CCA).  I will decide on the actual brand later - don't want to go off on that tangent right now.  This option provides total CCA of 1600 (two fresh fully charged batteries wired in parallel), which has always been sufficient for my C8.3 Cummins.  My engine manual calls for a minimum of 1280 CCA at 32 degrees F, and minimum of 1800 CCA at 0 degrees F.  In our 5 years of ownership we have only started the engine perhaps once or twice in below freezing temps, and both those times I simply used the boost switch + block heater = no problem.

Option #2:  Replace the Red Tops with a single O'Reilly AGM8D.  This battery is rated at 1450 CCA, which is less than the dual Red Top combo.  However, it still meets the Cummins CCA requirement for 32 degrees, and if it was colder than that I would just use the boost switch.  Where the AGM8D has a big advantage over the Red Tops is in its capacity: 245 Ah versus 100 Ah (50Ah x 2).  I am thinking this would come in handy when dry camping.  I could use the boost switch to connect both battery banks and increase my useable capacity (staying above 50% drawdown) from 245 Ah to 367 Ah.  Yes, I know, I would have to closely monitor voltage to avoid getting in a bind, but I do that anyway.  We have always been able to get along with our two 8D house batteries, but I usually have to start the generator in the mornings to use the microwave.  I'm thinking the extra 122 AH of capacity might JUST allow us to avoid using the generator in the mornings and wait for the sun to come up and start powering our PV battery charging system.

The price of the two different options (depending on what brand "small" batteries I buy) could be close.  The AGM8D battery weighs twice as much as the (2) group 34 batteries, so there would be a weight penalty, but it also seems like the coach would be better balanced (side to side) if I used the "big" 8D battery.  I THINK the AGM8D would fit in the existing start battery rack, but it would be very tight in the width dimension.  The start battery cables would hook up just fine either way.

One thing I wondering about (with Option #2) is the problem of mixing old and new batteries.  If I were to combine (with boost switch) both battery banks to extend our dry camping time, I would have one new battery tied to two old batteries.  Would this be a problem, or harmful to the new start battery?  If all three batteries were fully charged (normal condition at end of driving day) then I would think when they were combined that they would just equally "share the load" as they were drawn down overnight.  But I could be wrong...

One other thing - if I decided to use the AGM8D as a start battery, I would probably replace our (OEM) diode isolator with either a manual switch or some kind of "smart" combiner, and connect the alternator directly to the start battery.  This would give me more control over the way the batteries are being charged, especially when in extended dry camping situations.

Welcome any thoughts/ideas/comments from the Collective.  I highly value the wisdom and experience of those who have gone before!

I replaced the shot three 34 series when we purchased our used U300 nine years ago with threeAutozone 34 series Duralast batteries for the chassis/engine batteries. They lasted for 8 years until one was a bit low so I replaced all of them with 31-950 series Duralast batteries. Almost exactly $300 total for all three. After asking for a discount, Autozone dropped the price 10%. They have 950 CCA or 2850 CCA total. What may seem like overkill in summer is a good resource to have available at high altitudes and sub feezing weather in wintertime.
https://www.autozone.com/batteries-starting-and-charging/battery/duralast-battery/97512_721426_25698

Using a boost switch makes the solar system less efficient as it has a constant power draw. It's not a latching solenoid/relay. This heats the solenoid and will decrease it's lifespan even though it's rated "continuous duty." Plus, anytime you use anything to combine banks and only have deep cycle batteries on the house batteries, the conventional or AGM batteries on the engine side will see reduced life.

We shut off the inverter at night. Not a big deal, just flip the switch. Even with only 400ah on our six 68ah AGM deep cycle house batteries, we have plenty in the morning to run the microwave and latte maker. I never use the boost switch. I consider it only for use in emergencies.

The start batteries don't lose much in dry camping for a week so I don't worry about them. If longer while plugged in at home, I  tie both banks together lighter plug to lighter plug for charging. Voltage stays 13+V on both banks that way.

Pierce

I like the idea of using an 8d agm for start with a battery combiner to connect to house
batteries. The only problem I see is that the combiner would disconnect at 12.7 volts which means that the start battery would not share the load at any voltage below that. You could use a manual switch as well, but would have to keep eye on voltages so start battery does not get too low.

Yes, if using a battery combiner, one would need a dash switch in addition to the combiner's normal "automatic" feature.  But,  there should already be a switch and wiring to the OE combiner (solenoid). 

OR

One could just add the combiner and leave the OE boost switch.

Pierce,

Thanks for your comments, to which I would make the following responses:

1.  The Duralast Group 31-950 batteries sound like a good deal, but they are 13" long, where my battery rack is sized for Group 34 batteries, which are 10" long.  31's would not fit without some modification to the rack, which I was trying to avoid.

2.  Good point on the boost switch drawing constant power.  I could avoid that by doing what Brett said in his comments: add a manual switch.

3.  In my Option #2, all three batteries would be identical in size and type and capacity.

4.  We can't shut off our inverter cuz we have a residential fridge.  I could add a separate smaller dedicated inverter for just running the fridge, but so far haven't seen that as a high priority.  Our Magnum MS2812 isn't too bad a power hog when in standby mode.

5.  I don't worry about our starting batteries either.  We have a Trik-L-Start that keeps them topped up all the time.  If I used the AGM8D as a combo start/house battery, when dry camping I would need some other means of recharging it after a big draw down.  A manual switch connecting both battery banks would serve that purpose by allowing either our solar panels or our generator to recharge all 3 batteries simultaneously.

Something else occurred to me whilst pondering this question.  The "standard" starting battery configuration on my coach is two 800 CCA AGM batteries connected in parallel, which yields (optimally) 1600 CCA to the starter.

Cummins says under "normal" temperature conditions (above freezing), my C8.3 engine only requires 1280 CCA to spin the starter.

If I engage my boost switch, I am adding two AGM8D batteries which connected in parallel put out (optimally) another 2900 CCA.

So the total starting power of both battery banks could be (optimally) 4500 CCA!  :o

Is it possible to send TOO many amps to the starter?  What can these diesel starters safely handle without melting down?

In a word, NO.  No such thing as too little voltage drop.  The starter will not draw any more amps if hooked up to 2 or 20 batteries, but the more batteries (amps) the lower the voltage drop and the faster it will start and the longer the starter will last.

You could have a million 12 volt batteries in parallel and it would not make any difference to the starter motor. The voltage drop would be less and the starter would love you for that.

The more voltage drop you have, the harder the starter has to work and since it takes longer to start, the hotter it gets and is more likely to overheat and fail.

It's just like trying to run a roof AC unit on a coach that is supplied by a long extension cord if you don't have enough CCAs to start your coach. You never can have too many CCAs.

Pierce

The single O'Reilly "AGM8D" (This is the part# that O'Reilly uses if you are trying to look it up on their website) that is used in our coach for starting is still spinning it up just fine after 5 years or so. It was probably abused some by not having a charging set up while camped on shore power for long periods for the first 3 years or so of its life (no solar on the roof or shared charge set up), but it does the job without complaint. Usually starts the coach within a couple of seconds. We have the electronic version of the Cummings 8.3, which because of the intake grid heater and ECM, is probably at bit more power hungry at start up. The key is to have good electrical connectivity. When I changed the battery cable set up with new 4-0 marine cable and bus bars, there was a notable improvement in the starter's enthusiasm for cranking the coach. When this 8D reaches the end of its useful life, I will likely by another one. It fits lengthwise the OEM battery tray perfectly where the Red Tops sat sideways. I like the simplified wiring of this set up compared to extra connection points in the multiple parallel OEM method. That said, I wouldn't mind having two of these in parallel for starting :D  Of course, I have four of these O'Reilly AGM8D's for the house batteries and a heavy duty Blue Sea magnetic relay to act as a boost switch. I am embarrassed to admit that I accidentally started the coach with the new boost switch engaged but with the heavy duty Blue Sea chassis battery disconnect in the off position. This meant that there was NO help from the chassis battery, but the starter turned over as it normally does and started the coach no problem. I never intended to do that as it stresses other components in the set up beyond what I would like to see, but it is nice to know that it is possible... at least with the medium duty Cummings 8.3 ISC. Obviously, it would probably be a different story with the bigger ISM or M11.
Don

And the 9 liter 6V-92TA won't do well in winter with a single 8D or two 34 series batteries.

P

Don,

What switch are you using?  (I could look it up in your old posts, but feeling lazy)

I was just looking at the Blue Sea Systems ML-ACR automatic charging relay.  The way I read it, this device could be used to replace my diode isolator and my boost solenoid.  Does that sound right to you?

BLUE SEA SYSTEMS ML-Series Heavy Duty Automatic Charging Relay | West Marine (https://www.westmarine.com/buy/blue-sea-systems--ml-series-heavy-duty-automatic-charging-relay--9369059?recordNum=19)

I just replaced my 3 engine batteries with AGM Deca.  I was told that red tops are not made in the USA anymore.

Chuck,
I went with the Blue Sea 7713 Heavy Duty Remote Battery Switch rather than the ACR version. I don't fully remember why I went with that version as the cost is similar, but I am sure I had a reason ::) I know part of it had to do with my Sterling ProSplit R Zero Voltage Drop Battery Isolator and 12 Volt - 210 Amp Sterling Alternator-to-Battery Charger installation. Potentially, I suppose it could confuse the battery monitors somewhat (I also have one on the chassis battery). Anyway, removing the battery isolator sounds good, but I would have to study the implications to be comfortable with that set up. If and when some part of that battery menagerie needs updating, I will give it some thought. Too busy planning other upgrades and changes to worry about it as the coach DC systems are working harmoniously together at this time...
Don    

Thanks, Don.  Your whole DC setup is MUCH more complicated than our coach, so any resemblance is purely coincidental!

Chuck,

The flaw in this is the boost solenoid and related wiring will limit the amperage that you will really have.

Mike

Mike,

What is the limiting amperage (solenoid) or wiring (what gauge and length)?

I would have though that it was over 250 amps for an instant (i.e. starting) use.

Both,as neither will give you the full 2900 cca potential through them.
250 amps for a short time yes
Just because you have a bigger bucket full of electricity don't mean you have the means to use its full potential. The solenoid and related wiring is the choke point, like the small end of a funnel.
Mike

The ACR combiner uses the stock boost wiring to operate its switch in the rear and uses the boost switches original location. An additional wire would need to be run ,which we did not do,  to light up the switch to positively show the rear switches actual position. 

You have a no load manual connect/disconnect as part of the switch

Chuck, you asked:
One other thing - if I decided to use the AGM8D as a start battery, I would probably replace our (OEM) diode isolator with either a manual switch or some kind of "smart" combiner, and connect the alternator directly to the start battery.  This would give me more control over the way the batteries are being charged, especially when in extended dry camping situations.

Welcome any thoughts/ideas/comments from the Collective.  I highly value the wisdom and experience of those who have gone before!"


And the debate (Isolator vs, Manual vs Gadget) rages on..............
I fail to understand why we continue to complicate this very simple issue:

From a technical and engineering standpoint, these three options are personal choices, with pro's and cons to each. As such, each owner must decide what kind of talents they possess and to what degree of complexity they want to commit, in terms of reliability and bragging rights: 

In my opinion, there are three easily defined and distinct groups:

If one possesses perfect Engineering and Operating skills (as well as focus):  install a "Bank 1, Bank 2, Both, OFF" manual switch (or redesign to a single battery bank design, as Wyatt has done): Because

• You understand electrical engineering theory, design and the operation of your coach components..............without reservation.

• You either have or will replace your current battery instrumentation and install a battery instrument system designed with appropriate accuracy, precision, monitoring and alarms.

• You recognize proper, improper and inconsequential operating conditions without fail

• You remember to operate manually, without fail (can't have memory lapses)

[/list]
If one is a Gadget Guru: install any one of the dozens of automatic battery bank combiner gadgets: Because:

• You believe the advertisement hype.

• You believe that the failure rate of Gadgets is lower than Isolators

• You believe that reliable and unreliable Gadgets are easily sorted out

• You believe that the Gadget engineering has been thorough and complete for all batteries and operating conditions

• You believe that Gadget complexity improves system reliability

• You do not realize that improper Gadget operation can instantly ruin a Gadget and, left uncorrected, can quickly and irreversibly damage entire sets of batteries

• You feel that partial or complete Gadget failure will be easily detected and corrected

• You do not believe that Gadgets risk your battery investment

[/list]
If one is a KISS advocate: Continue to use the current ISOLATOR/BOOST SW design:  Because

• You understand that while it may be more expensive than a manual switch, it is the next least expensive and (by far) poses the least operating risk (highest operating return value) of the three options.

• You understand that an Isolator has ZERO, meaningful, negative operating characteristics.  And, if you don't understand that, you keep asking until you do.

• You understand that an Isolator and BOOST Switch design is the most elegant option in coach lifetime application (all owners/all operating conditions).

• You understand that an Isolator is many orders of magnitude more user-friendly and is far less prone to operator error induced damage to battery sets.

• You understand that Isolator/BOOST SW failure characteristics are far easier to detect, understand and correct than a Gadget's will be.

[/list]
HTH,
Neal

Every new coach has a combiner as far as I am told.  No isolators.

Boost switch requires 3amp load to stay on. Combiner consumes zero.  Magnetic.  Silver contacts  100k? Cycle rating?

Isolator consumes power.  Hence the fins. Combiner consumes zero.

Versus a separate charger for the engine batteries? 

Some good info.
Power Distribution Charging Relays (https://www.outbackmarine.com.au/power-distribution/charging-relays/)
Over the years have had many isolator failures. Have replaced them with ACR's [combiners] and have't had a failure on one of them yet.
Not a "gadget guy" but know if one bank 13.8 volts and the other 12.2, we have a problem. I do not necessarily embrace all the new stuff, but if new stuff is working 15 years later, it is okay by me.

Option 3,get 2 new red tops and don't try to re-invent the wheel.We used to have the start battery drain down and about a year
ago I replaced the Isolator,alternator and all solenoids and breakers on the Isolator mounting plate,can go much longer now.

Your Option 3 is the same as my Option #1 (in Post #1).

I appreciate your input, Neal.  Exactly what I asked for.  You obviously have strong feelings about this subject.

I like the KISS concept but the items you listed are not KISS. The isolator and boost solenoid is far from an elegant solution. The isolator has a good chance of failing over the lifetime of the coach and when it does, there is a good chance either the shop or the owner will wire it incorrectly. This was the case when we purchased our coach. The boost solenoid is perhaps the most poorly used/abused item on the coach. If Foretravel had intended it to be used to charge batteries on a regular basis, they would have installed a latching solenoid instead. Latching solenoids have no parasitic draw. The 24213 Cole-Hersee draws/wastes 3 amps. So much for using a trickle charger with the boost solenoid activated. The electrical panel location is also badly placed so as to be exposed to road spray on GVs. Some members have moved the panel to a better location. The corrosion is probably the primary reason a replacement isolator may be incorrectly wired.

I use a mechanical link between the two sets of batteries with my lighter plug to lighter plug cord. This is as KISS as possible. Another option would be to install a latching solenoid like a Cole-Hersee 24200 latching solenoid to tie both battery banks together for charging. Latching solenoids only use a momentary current to activate and generate no heat. It could be used in conjunction with the boost solenoid or because of the 110 amp maximum, two of the 24200 solenoids could replace the 24213 solenoid.

Attached below is the spec sheet for the Cole-Hersee 24200.

Pierce

And, the KISS I chose was to replace the battery isolator with a simple, marine ON-OFF switch at the foot of the bed.  Chassis battery and alternator to one large lug, house battery to the other.

REALLY simple.  No diode-based isolator to fail or turn alternator output into HEAT. No voltage loss-- alternator is not putting out high voltage to have .7 VDC loss to heat.

On or off, chassis battery is charged by the alternator any time the engine is on.

ON and both battery banks charged by either alternator or converter, charger or inverter/charger. And, if you want to use both batteries to start the engine, this makes a heck of a "boost" pathway.

Off, batteries are isolated.  One of my pet peeves was, when going from CG to CG (batteries fully charged), that the alternator would "over-charge" the house bank all day (taking diesel to do it and adding to alternator load).

Lots of ways to wire an electrical system.  Some more complex than others. As with most things, do what meets YOUR needs/desires.

Chuck,  while I have done a lot of augmenting of my 12 volt system I think keeping it simple has a lot of advantages which is what I tried to do.

You can get solonoid switches for the boost that are rated up to 400 amps.  My coach had 4 ga cables to each side of the boost solenoid from the isolator, increase the size to 3/0 or 4/0 for less resistance.

Switch to a zero voltage drop isolator.  I have one like Don's, a Sterling which adds a bit of smarts to the process.  It makes sure the start batteries get charged first and then quits charging them and pays attention to the other batteries coming back to check on the start batteries periodically and adding to them as needed.
Sterling ProSplit-R – Zero Voltage Drop Battery Isolator (https://baymarinesupply.com/electrical/isolators-22/sterling-prosplit-r-zero-voltage-drop-battery-isolator.html)

Or use a Victron ArgoFET 200 amp zero voltage drop isolater.
Victron Argofet Battery Isolator (https://baymarinesupply.com/electrical/isolators-22/argo-fet-battery-isolator.html)

There are combiners out there that will disconnect the battery sets if the voltage on one gets below a preset minimum (protects the start batteries) if you need to do it this way. 

Adjust alternator voltage if you use a zero voltage drop isolator or big switch.

Make sure your solar system charges both sets of batteries without providing a combining path between them.  Maybe use a small Victron ArgoFET isolator as I did.

When you make changes from OEM draw out new wiring diagrams, make a parts lists and write down what your thinking is.  It helps you out in a year or two (for me it is often a couple weeks) later when you are wondering why you did it that way, what parts you used and where the parts came from.  Eventually it makes it nice for the next owner too.

I think I like the idea of a single 8D AGM battery for the start battery, just one set of connections.  My coach came with 3 Yellow Tops that were replaced at 10 years with new Yellow Tops which have a deep cycle capability (not in Red Tops) to deal with continuous loads on the start batteries.  They are at 7 years now and seem to be fine. 

Think it through as I konw you will and choose what works best for you.

Roger

Following your line of thought and also Roger's comments, if the current carrying capacity of the BOOST solenoid is a concern, one could easily substitute a Blue Sea Systems 7701 ML solenoid, which has a 500 amp continuous rating and zero draw in "ON" and "OFF" position.  This would work nicely as both a BOOST solenoid, and to allow long-term charging of both battery banks from inverter/charger or solar.

ML Solenoid - 12V DC - Blue Sea Systems (https://www.bluesea.com/products/7701/ML_Solenoid_-_12V_DC)

Brett's solution is probably the best. All our fire trucks had the same marine on-off switch just under the driver's seat. It was in the off position while parked in the station. The rotating knob has 4 positions, OFF, BOTH, A and B. We started using it in opposite letters starting with every shift change but the Detroit Diesels didn't like just one 8D battery so we always went to both. With the mechanical diesel, it could run backwards if it kicked back. Not a problem with Foretravels as the battery CCA is good for starting and the electroinic engines can't run backwards.

You would have to adjust the alternator voltage down to compensate for removing the alternator. Turning the battery selector while the engine is running could also fry the alternator. Nice to have a switch rated for 300 to 500 amps as many are.

Brett's solution is not only KISS but the most elegant in my thinking. Now to get rid of the Allison! :D

Pierce

Follow link to Cole-Hersee and Blue Sea System heavy duty switches: Amazon.com: Cole Hersee M750 Battery Selector Switch: Automotive (https://www.amazon.com/Cole-Hersee-M750-Battery-Selector/dp/B000XBCPD6)

You refer to the one we have (you installed): We leave it in 'off' all the time. If I ever have to use the boost switch on the dash (perish the thought) do I have to remember to turn on the isolator?

Mike,

No, the two (ON-OFF battery combiner/isolator and solenoid-based battery combiner/boost solenoid) are independent of each other.  EITHER ONE can be used to combine the batteries.

There are so many experts and so few electrical engineers!  And it isn't easy to explain some of these electrical things in just one or two sentences.  So Please bear with me as this has some $$$$ gravity to lots of people who have only sketchy ideas of what's right and wrong:

Jim - "Over the years have had many isolator failures. Have replaced them with ACR's [combiners] and have't had a failure on one of them yet." 
ANS. - OK.  But what were the actual root causes of any Isolator/ACR/Combiner failures?  I have replaced defective ACR's/Combiners on a Tiffin Allegro Bus, a Tiffin Phaeton, an American Eagle, and isolators on three different Foretravels.  I also helped investigate why an LXI Blue Bird burned close to a total loss, and it was associated with this subject - more later on that.  The root causes of all three Foretravel isolator failures were due to sensing signal faults, two due to the inadequate FOT OEM design and one due to a DIY error.  Each of the isolator failures ruined one if not several batteries. 

One combiner failure (root cause) was because a DIY wired the device according to the labels on the device and didn't wire it IAW a highly confusing, revised manual that could only be found on-line. Two ACR's failures (root cause) were because they were not compatible with the application (solar plus alternator plus charger).  In each case, the manufacturers replaced, under warranty (but not through any recall - I had to discover the causes unaided by the OEM).  One ACR failure root cause I never figured out and although they had experienced multiple failures, that coach OEM manufacturer had never been able to determine the root cause either.  Fleetwood (American Eagle) just said replace it, which we did, and since then two more ACR's have failed.  I think the owner has been through at least (5) 8D damaged or ruined batteries, all occurring during storage.
Roger - "There are combiners out there that will disconnect the battery sets if the voltage on one gets below a preset minimum (protects the start batteries) if you need to do it this way."
ANS. - Yes, but, as Barry (Barry and Cindy) has previously pointed out:
http://www.foreforums.com/index.php?topic=33088.msg299563#msg299563
at least two of of the best ACR's and Combiners cannot be made compatible with properly temperature profiled battery chargers.  Isolators and Boost Sw's work much better, providing you use the BOOST SW. for what Foretravel intended it to be (A starting BOOST SW.  Not a Battery Charging SW.) I have used my BOOST SW maybe ten times in the past several years.  And even then, it was ONLY to verify that it still works or to verify that the bulbs still light in the SW.  The 1998 U270 seemed to benefit from the starter having an easier start with paralleled battery banks.  But the U320 ISM, with three Group 31 starting batteries, could care less if the battery banks are in parallel.
Roger - "Adjust alternator voltage if you use a zero voltage drop isolator or big switch."
ANS. - Why would you adjust the alternator voltage when installing a zero voltage drop isolator?  Everyone's alternator voltage needs to be adjusted so that it is putting out what you want the voltage to be AT the start battery output terminals on a hot day, whenever the engine is running at normal, loaded RPM.  AND that is where your voltage sense line should already be located, whether you are using an isolator, ACR, VSR, combiner or trickle charger.
Brett - "And, the KISS I chose was to replace the battery isolator with a simple, marine ON-OFF switch at the foot of the bed.  Chassis battery and alternator to one large lug, house battery to the other."
ANS. - Agree, but for you, and others like you Brett.  One philosophy being that if you can operate a motorhome, you should be able to remember to turn a switch.  But believe me when I say that none of the owners that I worked with in all of my examples above would understand why or would remember when to operate your simple two position switch.  And a four position switch, Pierce, would blow their minds.  They might not be baffled immediately by your two "more elegant" solutions, but give them a week and there would be no way that they could remember what the SW was for.  Sorry, but they would NEVER understand that if they turned the "Break-Before-Make", four position battery switch to anything but OFF while the engine was running, they would be damaging if not ruining alternator diodes, and then wondering why the engine is skipping and nothing works at 60 MPH going down the Interstate.
 Brett - "One of my pet peeves was, when going from CG to CG (batteries fully charged), that the alternator would "over-charge" the house bank all day (taking diesel to do it and adding to alternator load)."
ANS. - Ohm's law says I=E/R.  When the engine is at RPM, electrons are only going to flow where the resistance allows them to flow.  So when the start bank voltage is drawn down some small amount by the engine start, both the start bank's terminal voltage AND resistance have been lowered somewhat and the majority of the electron's will go there rather than to a fully charged house bank.  True, there is a small sympathetic effect from the regulator that oops! start battery voltage is low and I'll increase  my "driving head" to catch the start battery back up faster, but the major effect is a pretty short lived, lowered, starting battery resistance.  Because the House Bank, as you said, is already charged,  it's resistance is much higher and it isn't likely to get abused from overcharging.  The two bank resistances only take as much alternator charging current as their resistance's allow.  Where things go wrong is when the sensing line to the alternator voltage regulator develops a high resistance or fails open entirely.  Then the regulator goes to maximum voltage and current trying to catch the start batteries back up to the regulator's target voltage.  That is what causes most isolator failures, bulges in the sides of batteries and causes lifetime damages in our expensive batteries.  I have my alternator voltage regulator set for 13.7 Vdc so as to not overcharge either bank of batteries (Lifeline 8D AGM's and Exide PX31925C AGM's)  in high temperature driving conditions.
Pierce - "I use a mechanical link between the two sets of batteries with my lighter plug to lighter plug cord. This is as KISS as possible!"
ANS. - Let me tell you a true story about KISS suicide plugs.  Close friends had a new LXI Blue Bird that they thought the world of.  Someone convinced him to use one of your power outlet jumper plugs to trickle charge his start batteries, rather than invest in an "unreliable" Trik l Start.  They had an issue going on whereby the start battery bank seemed to be getting weak.  One day when he had taken the coach out for an exercise run (a very extensive, thorough checklist for his routine monthly PM), he put it back in the barn only to notice smoke rolling out of the building a short while later.  The coach and building did not burn to the ground, but it probably would have been better if they had. I was there when the fire department did the initial investigation.  One of the start battery cables had chafed on the frame and had a low resistance/small leakage to ground (the frame).  Hence the weak starting battery symptoms from the previous few weeks.  The exercise session had aggravated the short to ground (located before fuses) and the short eventually started a fire in the battery compartment.  Over several weeks, the suicide jumper at the dash had melted considerable wiring inside the dash as the jumper was trying to keep up with the decreasing start battery voltage.  The wiring to the dash power outlets did not have dedicated fuses  During the battery compartment fire, the wires overheated further and melted other wires which started a secondary fire in the dash.  Fuses eventually stopped feeding Vdc power to the power buses in the dash so the dash fire was relatively easy to put out but the nest of dash wires was a nightmare to rebuild.  The battery cables in the battery compartment had to be chopped off with axes to stop the feed at the batteries.  The "Welding Damage" from the batteries was more expensive than the water and smoke damage inside the coach.  It took them years to rebuild and sell the coach at a tremendous loss.
Bob - "Every new coach has a combiner as far as I am told.  No isolators."
ANS. - Yes, and every new coach has multiple slides.  But, like others, I don't want slides that take up any of my Fulltimer's precious space and enjoyment, so I won't have any, thank you very much.  There are lots of ways to save money on components, like isolators, refrigerators and heating systems (and dozens more), and to "Keep up with the Joneses", but I would rather have my sixteen year old, higher quality coach.
Bob - "Boost switch requires 3amp load to stay on. Combiner consumes zero.  Magnetic.  Silver contacts  100k? Cycle rating?"
ANS. - As others have already pointed out, I didn't take the time before to include the options to the OEM Cole-Hersee (marginal )100 Amp BOOST SW Solenoid.  The Blue Sea 9012 and Blue Sea Blue Sea 7701 ML, 1,000,000 cycle and 100,000 cycle, 250 and 500 continuous BOOST amp rating, respectively are much more acceptable in the Foretravel intended function as a BOOST SW
Bob - "Isolator consumes power.  Hence the fins. Combiner consumes zero."
ANS. - Really?  So does the resistance in the wires and studs, nuts, and the diodes (at least a dozen or more) in the alternator that generated the voltage to begin with.  But the .5 to .9 Vdc dropped across the Isolator diodes is meaningless if you are properly sensing battery voltage at the start battery terminals, as originally intended.
Bob - "Versus a separate charger for the engine batteries?"
ANS. - Got me.  I have a sixteen year old Trik-L-Start charging my start battery bank when the coach is sitting still and it is doing that just fine.  I also have a sixteen year old device from the same company feeding power to the Jeep battery when it is under tow or to the trailer emergency braking system, when using the trailer, which also includes the tongue jack battery plus Goldwing battery when the trailer is full and hooked up to the coach.
Hope all of this helps and hasn't wasted your time.
Neal

Neal, we are certainly fortunate to have a talented electrical engineer on the forum.
I am sorry you have had so many problems with ACR's. I do not have your knowledge, but I have replaced 3 or 4 isolators that had bad terminals or other physical damage, and 3 that did not pass current one way or the other. I have only used Blue Sea combiners and have never had to do anything after installation. I suppose you could wire them wrong and cause problems, but with only 4 wires, you would have to be pretty inept. Wish I could agree with your conclusions, but in this case, I will stick with my own favorable experiences with relay type combiners.
Makes you wonder why major manufacturers and bus conversion folks would switch from "reliable" isolators to, ACR's.

Sort of took a left turn somewhere along the way here.

"Roger - "Adjust alternator voltage if you use a zero voltage drop isolator or big switch."
ANS. - Why would you adjust the alternator voltage when installing a zero voltage drop isolator?  Everyone's alternator voltage needs to be adjusted so that it is putting out what you want the voltage to be AT the start battery output terminals on a hot day, whenever the engine is running at normal, loaded RPM.  AND that is where your voltage sense line should already be located, whether you are using an isolator, ACR, VSR, combiner or trickle charger."

With a conventional diode based isolator the LN alternators are set to about 0.7 volts more than you want to see at your start battery to acomodate the voltage drop across the diode based isolator.  With a zero voltage drop isolator adjusting the voltage down on your LN to get what you want at your batteries will be beneficial to battery life.

I am not using a LN alternator.  I have a brushless Delco.  LIke Neal I rarely use the boost switch.

I appreciate Neal's passionate arguments but there are many ways to accomplish these tasks.  Everyone has the opportunity to create their own successes or make their own mistakes. Whether they learn from them or not or take into account the experience of others is up to them.

Like so many of these systems with multiple choices, learn all you can from every source possible, apply your own needs and expectations, choose wisely and execute carefully. And then evaluate how well you did, adjust as needed.  Someone else's opinion or belief is simply that. As is mine. 

Roger

Nice discussion lots of valuable information. In 12 years I have replaced one isolator, one set of start batteries, one set of house batteries. Had the old LN alternator freshened up 5 years ago. I'll just leave mine like FT built it. But as always do what makes you feel good 😎

Thank you, Neal for taking time to tell it how it is. As you noted we gave up on voltage-controlled combiners (ACR's) and now keep both banks lasting 10 years or so with a good charger, diode isolator combiner & diode Trik L Start. I found I had to 'monitor' things more when I had ACR's installed.

It does seem that everything has advantages and disadvantages. I will say that several years ago I saw an IH45 with a humongous curved diode isolator, although I have no idea what they are using on current IH production.

My gut feeling is that if one understands the pros and cons and has some conceptual electrical charging experience of alternative ideas why not try to 'improve' things. But when one 'follows' without understanding the big picture, the outcome may be less than optimal. With old-fashioned tried and true concepts, generally one can not go wrong.  'Reinventing' may put more responsibility on the installer.

Our C8.3 mechanical engine was built with 2 Optima red-tops and on our last changeout, we decided the starter and battery bank would have a longer life by adding a 3^rd red-top. Our battery tray is the same as used with U320 and has space for 3 batteries, so it was an easy decision and a small cost over 10 years.

Long ago we got rid of the OEM parallel automotive post cables, and now use 'military' terminals with short jumpers bolted between batteries. All automotive battery cable terminals wear/stretch out or crack and it is a simple fix to replace a single 'military' terminal. Using OEM parallel cables often means continuing to use a 'worn-out' terminal as all the terminals are integrated in one string.

Would anyone here recommend removing a installed ACR?  And then install a diode based isolator?

Without a continuous source of power to the house batteries the advantages of the combiner are lessened.

So I added a 270 watt solar panel set just to power the batteries through the ACR.

At 13.6 volts from the solar at the batteries both battery banks have stayed fully charged for the last year without me touching or doing anything.  13.54  volts on both circuits on the dash power outlets day or night.

Serms pretty KISS to me.  Been playing with motorhome charging systems as a Foretravel employee since 1984.

Hooked through the undersized refer wires drops the volts perfectly for the storage maintenance needs.

IMO you need all the pieces to maximize the idea.

Perfect batteries to start with to not need more amps than my simple system has and good condition cabling.

I am not plugged in.  Outdoor storage. 

Same idea if powered as the std wiring charges the house same as my solar. 

If I had the time I would do what the ACR does exactly only manually.

The ACR is 100% reliable.  I have learned I am not.

Technology finally won after 34 years.

The magnums float is 13.6 for gels.  Same idea. 

Hated buying new expensive batteries as one deep discharge permanently lowered the engine batteries CCA  capacity.

Much better in my experience to never have the engine AGM's run down?  Never. 

Had several trickl  chargers fail. Green light on.  No power output.

Killed a 30amp magnum unit also.  Past thirty amp the internal faze blew.  No indication other than low batteries and lost capacity.

Started over twice.  New batteries. Added solar. Added ACR. 

Solar not needed for storage if plugged in. 

That being said various posters here have reported unknown storage power failures.

Sun shines enough here in so cal that this works great.

Buddy installs these regularly without issues,  minimum 500 Watts solar from him and four 8g8d's for refers and a ACR. 

Neal,

I think everyone really appreciates the time and effort you took to delve into this subject. In relating to my "suicide jumper" I have running from lighter outlet to lighter outlet, almost all plugs sold today have user replaceable 5 amp fuses built in so the scenario you describe cannot occur and in fact, have nothing to do with the jumper I have made up. The lighter plugs are also fused but at a higher amperage.

In wiring my HID headlights, I installed a fuse next to the ignition solenoid that I tapped into and there is also a circuit breaker down by the headlight power supply.

When I installed my solar system, I installed circuit breakers on the panel side of the controller as well as on the battery side. This is how I turn the system on and off. And if that was not enough, exactly where the system connects to the coach electrical bus, I installed a 250 amp fusible link. Photos of my complete installation can be seen in old posts from about eight years ago.

So, just because an acquaintance of yours did a incompetent job of wiring his coach and had a fire does not mean everyone is lacking the "little grey cells" Agatha writes about. I did see a member who thought his solar converter could be used at a much higher rating than advertised. Seems as if that could be called a "suicide controller."

Pierce

I think this has been a very interesting discussion!  And for me (a dumb English major), quite educational.

As I see it, a conventional diode based isolator is proven technology.  It does the job for which it is designed without human intervention, but at the expense of some "wasted" voltage (turned into heat).  This "deficiency" can be compensated for by employing a DUVAC alternator with properly connected sense wire.  The standard isolator can also be upgraded with more efficient diodes, or by using FETs, to almost eliminate lost voltage.

Argo FET Battery Isolators - Victron Energy (https://www.victronenergy.com/battery-isolators-and-combiners/argo-fet-battery-isolators)

The isolator is, by design, a "one-way" charging controller.  It works fine if you only have one charging source (like the alternator) for two battery banks.  When you add a second and third charging source, like a inverter/charger and a PV system, then the isolator needs help in keeping both battery banks topped off.  The simple solution is a add-on charging "diverter", such as the Trik-L-Start, which is fine as a battery maintainer, but lacks the ability to do heavy recharging.  If you want to allow automatic high amperage recharging in both directions between two battery banks, then a "smart combiner" would seem to be the appropriate device.

If the coach owner is willing to actively monitor the condition of the battery banks, and is clever enough to make the right adjustment at the right time, then a manual switch can take the place of either a isolator or a combiner.  It is up to each individual to decide how much time/effort/thought they want to devote to operating and managing their battery charging system.  The cost of inattention or making a mistake could be considerable (up to and including loss of life), so accepting this responsibility should not be taken lightly.

Do What Makes You Happy! (But Acknowledge Your Own Limitations)

Chuck,

And at only $120 for the 200 amp model, the Victron FET isolator is a bargain. Victron Energy Argo FET Battery Isolators | eBay (https://www.ebay.com/itm/Victron-Energy-Argo-FET-Battery-Isolators-/172312529316)

Have you found a source for 200 amp ACRs? I only see 120 amp Blue Sea Systems ACR. Good price but our alternators are all over 120 amps. SI-ACR Automatic Charging Relay - 12/24V DC 120A - Blue Sea Systems (https://www.bluesea.com/products/7610/SI-ACR_Automatic_Charging_Relay_-_12_24V_DC_120A)

Pierce

Thanks, Pierce for the link. Just bought one.

Here's a link on the big one.
ML-ACR Automatic Charging Relay - 12V DC 500A - Blue Sea Systems (https://www.bluesea.com/products/7620/ML-ACR_Automatic_Charging_Relay_-_12V_DC_500A)

Here is the 500 amp ACR

ML-ACRs - Blue Sea Systems (https://www.bluesea.com/products/category/35/91/Automatic_Charging_Relays/ML-ACRs)

Nice Bob and Chuck! Less than $200 on ebay with this one at $159.99 delivered: Blue Sea Systems 7622 ML-Series Heavy Duty Auto Charging Relay | eBay (https://www.ebay.com/itm/Blue-Sea-Systems-7622-ML-Series-Heavy-Duty-Auto-Charging-Relay/302747140529?hash=item467d22c1b1%3Ag%3AvMAAAOSwEeFU6L7-&_sacat=0&_nkw=blue+sea+7622&_from=R40&rt=nc&_trksid=p2380057.m570.l1313.TR1.TRC0.A0.H0.Xblue+sea+7622.TRS0)

Pierce

Pierce's EBay Victron ArgoFET isolator comes from Bay Marine Supply, same price as the link I provided that actually goes to Bay Marine.  Alan's prices on Victron equipment are most often very competitive.  if you find it for less ask and he may discount a bit.  and if you have questions he is there for support.  These days that is worth more than saving a couple of bucks.
Victron Argofet Battery Isolator (https://baymarinesupply.com/electrical/isolators-22/argo-fet-battery-isolator.html)

My method of just one battery bank with 1400 watts of solar seems to be as "KISS" as is possible.
It does require being aware of the charge state of the batteries, especially when an engine start is required before the sun is shining.
I have used this system for 10 years but did have to boost with my car battery on two occasions.
No isolator required.
I also moved all the wires from behind the rear driver side wheels to under the bed and connected the alternator sense wire to a common "+" post rather than the OEM A/C relay. 

Wyatt,

I have no problem with your "one battery" solution.  BUT (read that a BIG BUT) I suspect less than 5% of RV'ers are "electron savvy" enough to do it correctly (proper discharge/recharge cycle).

Having spend many, many months on a sailboat (ya, no shore power) there ARE those of us who know how to manage 12 VDC.  However, I would not recommend that for very many folks.

OH, and Purket would be proud of you. 

I find Wyatt's comment about the sense wire very pertinent to this whole thread.  With his setup of a single (big) battery bank, and no isolator, one might think that the alternator sense wire is no longer required.  I took this idea one step further, wondering if a "ONE WIRE" alternator could be used to replace the DUVAC unit.  At least that's what I was thinking...but I was wrong.

In a perfect world, where 100% of the output from the alternator flows unimpeded to the end of every circuit on the coach, you might do OK without a sense wire.  However, it is not a perfect world, and there is always something trying to "resist" the flow of electricity.  Might be dirty terminals, or corroded connectors, or under sized cables, or poorly designed overly long wiring runs.  No matter what the reason, it is very likely that what your alternator puts out is NOT what your batteries (all of them) will see.  Hence the need for a sense wire.

I always thought that the closer you can connect the sense wire to the actual battery post, the better.  You DO want to induce the alternator to do whatever is necessary, so that the full optimum charging voltage is delivered to where it is required: at the POS battery post.  However, the article below makes a case for connecting the sense wire at some central wiring junction, rather than directly to the batteries.  Sounds more like what Wyatt did.  I'm not smart enough to know if the article's logic is applicable to our coaches, but it seems to make "sense" (Ha, Ha) to me.

Interesting article (written by Hot Rodders) that got my mind right on this subject:

Catalog (http://www.madelectrical.com/electricaltech/onewire-threewire.shtml)

I did the same on the sailboat.  Wired the sense wire (external smart regulator) to the battery itself. That way the small loss in connections and wire are "made up for" and the batteries see the full voltage they are capable of absorbing without harm.  A good thing, since the 4 cylinder diesel auxiliary is run twice a day while at anchor just to recharge the batteries.

My Delco 40si brushless alternator needs no excite wire.  The 40SI uses a Remote Sense wire that reads the actual voltage at the start battery. This signals the alternator to boost its output to compensate for the voltage drop and the actual voltage of the start battery to reduce charge time.

http://www.delcoremy.com/getmedia/f651dcc3-60db-4186-80eb-154b8111fdf0/Delco-40SI-Single-Page-Brochure-3-16.pdf.aspx

If you have multiple battery sets the amps that can be pushed into each set depends on the the overall resistance of the batteries and connections and the voltage of the batteries in each set.  The higher the charge level in the batteries the harder it gets to add more charge.  It is like filling a water tank from the bottom.  It is easier when it is 1/2 full and harder to push water in as it gets fuller. It takes more pressure (voltage) to push water (amps) into the tank when it gets close to full.

So if your house batteries are pretty well charged and you start the coach you just pulled a bunch out of the start batteries.  You will push more amps into the start batteries than the house batteries for a while until the two sets are closer to being equally charged.

Maybe a simplified way of looking at it but it works for me.

My understanding is that most smart alternators output 14.15 volts? 

"Most"  is a big corral to be generalizing.  Not so on the Delco.

Seems this thread has run its course, so I will wrap it up with my conclusions (for what they are worth).  I have considered the info presented here (thanks to all) and believe the following plan will work for our crew, the way we use our coach, and based on our level of technical expertise.

1.  I will replace our two old Red Top start batteries with a new O'Reilly AGM8D.  It will (hopefully) fit in the existing battery rack, and will work just fine with the existing cables.  I will use fresh "military" style battery connectors to hook up the cables.

2.  I will replace our still functional 25-year old Hehr Powerline diode isolator with a new Victron ArgoFet 200 amp 2-bank isolator.  By doing so, I retain the original factory alternator-to-battery charging layout, while enjoying the benefits of more modern technology.  The new isolator should be a bolt-in swap, and will be connected to the existing battery cables, which are in good shape.

3.  I will retain the Trik-L-Start "thief" battery maintainer that has served us so well for 4 years.  It does a fine job of keeping our start batteries topped off when our coach is parked (plugged in to 50 amp) in our driveway and when camping at full hookup parks.

4.  I will replace the existing boost solenoid with a Blue Sea Systems 7701 ML solenoid, which has a 500 amp continuous rating, 1450 amp 30-second cranking rating, and zero power draw in "ON" and "OFF" position.  Doing so will retain the OEM boost circuit design and function, while providing me with additional battery charging options when in dry camping mode.  If I wish to utilize our augmented battery storage capacity, I can simply activate the 7701.  Combining the battery banks will increase my available amp hrs by 50%, and will allow rapid recharging of both banks using our solar panels and/or generator + inverter/charger.


I believe the above plan will add extra capability and options to our battery system, while retaining the elegance and KISS-ness of the original FOT factory design.  I hope this will meet with the approval of the electrical gurus on this Forum.

Sounds like a good plan Chuck. We have certainly well chewed this subject. Please keep us informed of your progress and results. 😎

Chuck, you might want to replace the 4 ga cables from the two battery posts on the isolator to the two sides if the boost solenoid with bigger cables.  The 4 ga cables are probably the minimum size for the amps for that length of wire but bigger would not be a bad thing.  Your alternator to the isolator is perhaps a 2 ga cable, this would be a good size to go from the isolator to the solenoid.

If you have an easy source for cables great but you can order any size and length cables from Bay Marine Supply with the lugs you need on both ends.

Thanks, Roger, for the tip.  My OEM wiring schematic shows the wires to be "2RD" from alternator to isolator, and also "2RD" wires from both of the isolator battery posts to the boost solenoid.  I assume "2RD" means a red 2 gauge wire?  If so, I should be good?

I will verify the actual wire sizes next time I'm under the coach, just to be sure.

My OEM cables from the boost solenoid to the batteries, and all my battery cables, are shown to be "000" which I think is called "triple-aught"?  When AM Solar installed my solar system and Magnum inverter, they used "000" and "0000" cables for the high amperage circuits.

I think your isolator may have originally been over by the wheel well?  If so then the longer cables from the isolator to the boost relay would make a 2 ga cable make sense.  At the head of the bed box the cables were maybe 16" long so 2 ga was probably sufficient.  Yes 4RD means 4 ga Red.  With a bigger alternator I just didn't want those smaller wired to be choke points.

Here's my isolator panel as it is now, in factory stock configuration (plus the add-on Trik-L-Start).  The big fat muffler is long gone...

Chuck,my panel looked exactly like yours,redid the whole thing,all new components and put back in the same spot,after sanding and painting all rusted frame parts.We went with the smaller 28si alternator,keeps the 13.8 even at low idle.