Foretravel Motorhome Forums => Foretravel Tech Talk => Topic started by: Chuck & Jeannie on August 19, 2019, 11:13:18 am
Title: Dual Alternator Setup
Post by: Chuck & Jeannie on August 19, 2019, 11:13:18 am
From the recent discussion about running air conditioners off inverters and the attendant technical challenges, my thoughts have drifted onto the subject of running dual alternators. I searched the Forum and found one old thread pertaining directly to this subject (link below). I would like to revive the discussion and hear any and all current (ha, ha) ideas, both practical and less so. I know we have some smart folks here - many who have extensive boating experience. Dual alternator systems, I understand, are not unusual in the sailing/boating world.
I'm not trying to fix anything that is broke. My present electrical setup is working well. My old LN alternator does fine keeping the start batteries topped off. My inverter/charger keeps the house batteries happy when we are plugged in. I have a Trik-L-Start that silently does it's job. I have a new very low voltage drop isolator. I have a magnetic latching solenoid that can be used as a "boost" switch, and also can combine my 3 AGM8D batteries into one single battery bank if desired. See photo below.
Our dash air does not work, and I have no plans to get it working. Our personal preference is to run the roof air (or airs) if necessary when driving, so let's not spin off topic as to why I should fix the dash air. Point is - my engine mounted A/C compressor is not required. Seems the logical spot to mount a second alternator. I think one Forum member (maybe more?) has mounted a second alternator in place of the A/C compressor? Would like to hear pros and cons about that.
In my daydreaming mode, here is what I contemplate. Two alternators, running in parallel. I would move the B+ charging cable from the existing alternator to the START battery post on my isolator. I would run the B+ charging cable from the second alternator to the HOUSE battery post on the isolator. So two separate charging systems - one for each battery bank. My reasoning is this: it would be a simple hookup using existing components, and would provide quick and easy redundancy in case one alternator fails. In that event, (at the isolator) I would simply disconnect the B+ cable from the failed unit, and move the B+ cable from the still functional unit back to the isolator ALTERNATOR post.
I am soliciting thoughts on this scheme, and also the answer to a question. With the engine running and both alternators charging their respective battery banks, what would happen if I closed the ML solenoid and combined the banks? Would the alternators play nice with each other? Would the charging current to the combined battery banks be doubled? Would my whole electrical system explode in a ball of fire?
Bring it on. Would this be a total waste of time (and money), or might it actually provide some advantageous benefit?
Title: Re: Dual Alternator Setup
Post by: craneman on August 19, 2019, 11:39:22 am
I don't want to spin off subject on the first post, but to start with you have 2 things doing the same thing in your picture. FET isolator and auto combiner. You only need one of them. As far as the 2 alternators working together I believe whichever one is set to the highest voltage will take over when the voltage of the other one is reached. But let the experts get aboard as I am interested in the ability to run a roof air if needed off batteries.
Title: Re: Dual Alternator Setup
Post by: Chuck & Jeannie on August 19, 2019, 11:43:24 am
..you have 2 things doing the same thing in your picture. FET isolator and auto combiner.
The Blue Sea Model 7701 ML solenoid is not a AUTO combiner...it is a manual combiner. I have a switch on the dashboard that opens or closes the solenoid. It uses zero battery power while in either position, and has a very high current rating, which is why I used it.
ML Solenoid - 12V DC - Blue Sea Systems (https://www.bluesea.com/products/7701/ML_Solenoid_-_12V_DC)
Title: Re: Dual Alternator Setup
Post by: Protech Racing on August 19, 2019, 11:47:36 am
I have two alts The second one runs the refer. And house bats .
Title: Re: Dual Alternator Setup
Post by: Chuck & Jeannie on August 19, 2019, 11:51:43 am
Excellent! I know you are a man of few words, Mike, but could you supply at least a few details? Like specifics on how the second alternator is mounted and driven, and how the charging cables are connected. Photos?
Title: Re: Dual Alternator Setup
Post by: craneman on August 19, 2019, 11:53:57 am
The ML solenoid is not a AUTO combiner...it is a manual combiner. I have a switch on the dash that opens or closes the solenoid. It uses zero battery power while in either position, and has a high current rating, which is why I used it.
ML Solenoid - 12V DC - Blue Sea Systems (https://www.bluesea.com/products/7701/ML_Solenoid_-_12V_DC)
Sorry mine is a different model. Also no draw when locked in auto mode. it also has the remote manual function. Now back to the dual alternators.
Title: Re: Dual Alternator Setup
Post by: Protech Racing on August 19, 2019, 12:05:10 pm
There should be a pic under the fridge thru the door thread . It mounts in the same belt location as the OE AC compressor .
I did not remove the isolator. Just wired to the other batteries. Maybe I should un hook it , but after a year of non issues, I may leave it as is. I also use an E bate 1200 watt Pure sine wave inverter to run my baby refer.
Title: Re: Dual Alternator Setup
Post by: Caflashbob on August 19, 2019, 12:28:01 pm
A dual alternator setup would seem to be a needed thing if you have added additional, non li-ion batteries, to charge the larger bank at the required 1/5th capacity rate.
Remote battery bank on/off switches would seem to be helpful to separate and then recombine the banks as needed to adjust the batteries amp hour capacity you are charging to match the alternator?
Or a li-ion bank separate from a regular batter bank? Switch one bank in while the other is recharging?
Lots of fun.
I bought a heavy duty slide setup from the link posted here a while ago to allow a couple more mk gels to be added to my existing system if wanted..or needed,
With one alternator would seem to need to switch any extra batteries in and out of the system to maintain the 1/5th C charge rate.
I installed several 110 volt alternators long long ago in several coaches to run roof air(s?) off the engine while driving.
Customers said it worked ok but definitely took away some motor power back then.
4400 watt and 5500 watt were the options long ago,
Title: Re: Dual Alternator Setup
Post by: prfleming on August 19, 2019, 01:51:56 pm
Our Roadtrek has dual alternators and no generator. Roadtrek calls this their "underhood generator". After experiencing this I would not want it any other way.
The house alternator is 280 amps and controlled by a Balmar MC-614 multi-stage regulator. There is no connection between house and engine battery systems. We could run the house AC driving, but our dash air still works so don't typically do this.
Title: Re: Dual Alternator Setup
Post by: prfleming on August 19, 2019, 02:33:04 pm
Chuck, just a couple of thoughts, from when I was running my roof air driving in the 1991 U300.
You will need an inverter with enough overload capacity to handle the AC locked rotor amp draw, or put in a soft start system. My 4000 watt AIMS inverter had a 12000 watt overload capacity, which worked fine.
My front roof air would draw about 16 amps at 120V, this converts to about 180 amps at 12V (with inverter efficiency). You will need a healthy alternator, maybe 250 - 300 amp capacity with a little margin for charging the batteries. I had put in a Delco 40SI 300 amp with good results.
This should be an interesting project.
Title: Re: Dual Alternator Setup
Post by: Chuck & Jeannie on August 19, 2019, 03:10:51 pm
1. You will need an inverter with enough overload capacity to handle the AC locked rotor amp draw, or put in a soft start system.
2. My front roof air would draw about 16 amps at 120V, this converts to about 180 amps at 12V (with inverter efficiency). You will need a healthy alternator, maybe 250 - 300 amp capacity with a little margin for charging the batteries. I had put in a Delco 40SI 300 amp with good results.
Thanks for joining in, Peter. I was hoping you would show up, since you have already been down this road.
1. I only have a Magnum MS2812, so marginal there...but I ordered a EasyStart 364 (3 ton) soft start module from Micro-Air, which should be here today. I am hoping this will sufficiently ease the strain on my inverter. Won't know for sure until I get it installed.
2. If I decide to pursue this project, I will get the best alternator I can afford. One thing I have noticed while looking at the high powered models online: the big output amp numbers only occur at RPM levels we never see with our diesel engines. The 300 amp 40Si, for instance, makes less than 150 amps at 2000 RPM, which is where my engine feels happiest when cruising. This is why I am interested in running two alternators. I am hoping that if I combined my start and coach batteries, having 2 alternators would give me double the "normal" (2000 RPM) charging amps, and help support my 3 AGM8D batteries during heavy drawdown situations (like when trying to run a roof A/C unit). I am hoping you smart guys will confirm this theory.
Title: Re: Dual Alternator Setup
Post by: craneman on August 19, 2019, 03:14:55 pm
The pulley size on the alternator might be available with a smaller diameter. Just a thought.
Title: Re: Dual Alternator Setup
Post by: Don & Tys on August 19, 2019, 03:18:37 pm
Does the 2000 RPM factor in the pulley sizes with your engine RPM figure? Depending on the ratio between the crank pulley and the alternator pulley, there could be quite a difference in the alternator RPM and engine RPM... Edit: Craneman beat me to it! Don
Thanks for joining in, Peter. I was hoping you would show up, since you have already been down this road.
1. I only have a Magnum MS2812, so marginal there...but I ordered a EasyStart 364 (3 ton) soft start module from Micro-Air, which should be here today. I am hoping this will ease the strain on my inverter. Won't know for sure until I get it installed.
2. If I decide to pursue this project, I will get the best alternator I can afford. One thing I have noticed while looking at the high powered models online: the big output amp numbers only occur at RPM levels we never see with our diesel engines. The 300 amp 40Si, for instance, makes less than 150 amps at 2000 RPM, which is where my engine feels happiest when cruising. This is why I am interested in running two alternators. I am hoping that if I combined my start and coach batteries, having 2 alternators would give me double the "normal" (2000 RPM) charging amps, and help support my 3 AGM8D batteries during heavy drawdown situations (like when trying to run a roof A/C unit). I am hoping you smart guys will confirm this theory.
With the engine running and both alternators charging their respective battery banks, what would happen if I closed the ML solenoid and combined the banks?
Would the alternators play nice with each other?
YES, Each will regulate itself according to the load. Subwoofer nuts have paralleled alternators for years.
Would the charging current to the combined battery banks be doubled?
YES, the sum of the alternators, ie 160 + 240 would be 400 amps total avail.
Would my whole electrical system explode in a ball of fire?
NO
Title: Re: Dual Alternator Setup
Post by: jcus on August 19, 2019, 04:27:14 pm
Believe this is the same frame size and mounting as the units we use now. New Blue Bird Bus Alternator AVI160J2004 A160204 (https://www.urqualitysolutions.com/New-Alternator-Blue-Bird-Bus-AVI160J2004-A160204-A160204.htm)
Title: Re: Dual Alternator Setup
Post by: Pierce & Gaylie Stewart on August 19, 2019, 06:50:56 pm
We also never use the dash air but if it gets too hot, we run the generator. Easy to remove the compressor and install another LN alternator to match the existing one. Wire that one to the engine batteries less than two feet away and separate the two charging systems all together with the OEM alternator just feeding the house batteries. Get rid of the isolator and install a latching relay in case one alternator goes down.
I have two digital voltmeters, one right below the other so this way, if one alternator fails, I can see it quickly. Running both into a common system means that you are much less likely to see if one fails.
With two of the exact same kind, it would be easy to carry common parts or even a spare. The LN alternator is very reliable and not expensive on ebay.
I just plug in my jumper from one dash lighter plug to the other when camping to keep the engine battery up when the solar is active. The latching relay would do the same and they don't use a juice when in either position.
Pierce
Title: Re: Dual Alternator Setup
Post by: Chuck & Jeannie on August 19, 2019, 08:40:39 pm
Believe this is the same frame size and mounting as the units we use now.
Interesting. I will keep an eye on it, but they are back-ordered at this time.
Title: Re: Dual Alternator Setup
Post by: prfleming on August 19, 2019, 09:12:10 pm
As Pierce said, I think IF you intend to occasionally combine battery banks, it is advisable to have 2 identical alternators. This way the alternators will pull together and one won't get overloaded due to slight differences in regulators, etc. In my case with the Roadtrek the battery banks are never combined, and the alternators and regulators are very different. When running the roof air, hit the combine switch, and the alternators will share the load and life will be good. Be sure to match cable size and length as much as possible.
When will you be posting pics? 😎
Title: Re: Dual Alternator Setup
Post by: Chuck & Jeannie on August 19, 2019, 09:20:47 pm
Won't be this week fer sure. Temps here at or over 100 degrees every day. Barely cools off enough to walk the dog at 08:00hrs.
I'll see about matching the alternators. Might depend on what they will cost. Maybe I'll find a "2-for-1" special!
I need to look at how to mount the "extra" alternator in place of A/C compressor. At first glance, doesn't look like it would be "Plug & Play". The compressor mount is a kinda odd shape and size...
Title: Re: Dual Alternator Setup
Post by: AncloteJoe on August 19, 2019, 09:40:35 pm
heres how to do it.
Title: Re: Dual Alternator Setup
Post by: prfleming on August 19, 2019, 09:47:39 pm
Give Nations Alternator a call. They specialize in custom alternator brackets and installations. They did the dual alt system in our Roadtrek.
Title: Re: Dual Alternator Setup
Post by: Pierce & Gaylie Stewart on August 19, 2019, 10:49:03 pm
Our LN has two belts but the AC compressor has only one. Just a few things like that including the pulley ratio. I expect a little different problems with each engine but depending on DIY experience, a 2 or 3 hour job plus a trip to a wrecking yard for possible parts. Just need a secure way of mounting it so it can pivot and a way to tension the belts without resorting to a pry bar.
Pierce
Title: Re: Dual Alternator Setup
Post by: jcus on August 19, 2019, 11:38:21 pm
This truck is set up for a CB competition(I was told). I dont know if they still do those. I dont know much about the competitions or why they would use so many alternators but I would guess that the more amps your cranking out the stronger the signal. The big alternator at the top left appears to be a delco 50DN 24volt 270 amp, the rest look like leece nevilles similar to the ones in our coaches but, I would assume all to be 24V.
Title: Re: Dual Alternator Setup
Post by: DavidS on August 20, 2019, 10:03:26 am
This truck is set up for a CB competition(I was told). I dont know if they still do those. I dont know much about the competitions or why they would use so many alternators but I would guess that the more amps your cranking out the stronger the signal. The big alternator at the top left appears to be a delco 50DN 24volt 270 amp, the rest look like leece nevilles similar to the ones in our coaches but, I would assume all to be 24V.
Maybe a Mobile welder or emergency mobile home power center
Title: Re: Dual Alternator Setup
Post by: prfleming on August 20, 2019, 11:38:50 am
The subwoofer guys also compete to see who has the most alternators. It's all for show, what they don't realize is the high current audio peaks are supplied by the batteries, one healthy alternator (say 250 amps) can easily keep up with the total average power use over time - but who wants to show up with a whimpy looking sound system with just one alternator...🤣
Title: Re: Dual Alternator Setup
Post by: Roger & Susan in Home2 on August 20, 2019, 11:41:19 am
If someone wants a LN 160 amp alternator I have one I took out of my coach, make me an offer, pay shipping, it is yours.
Title: Re: Dual Alternator Setup
Post by: Chuck & Jeannie on August 20, 2019, 11:42:24 am
If someone wants a LN 160 amp alternator I have one I took out of my coach, make me an offer, pay shipping, it is yours.
PM sent.
Title: Re: Dual Alternator Setup
Post by: Journey, Roam, Explore on August 29, 2019, 02:35:46 am
Seems to me that 2 alternators running thru a Balmar MC 612 dual feeding the house bank with a charge to the start bank via your inverter/charger if yours has that capability like the Victrons do would feed quite a few amps into the bank. You would need enough of a inverter to run the AC or other stuff. 2 victron multiplus would supply 240 amps into the house bank and 8 into the start bank, while supplying 6000 watts and 12000 watts peak. You would need a big bank or Lifepo4 batteries to power this. Would be a sizeable investment. But it is possible. These (https://www.qualitypowerauto.com/item_159/Leece-Neville-4800--4900-Series-style-Alternators.htm) Leese Neville 320 amp alternators with the pulley sized to highway speeds to provide 80% of the rated power would give alot of amps. I can run my front AC via inverter for around 5-6 hours I think it was off the inverter. With this setup I could run 2 ac's down the road and have room to spare. I think.
Title: Re: Dual Alternator Setup
Post by: Chuck & Jeannie on August 29, 2019, 06:41:56 am
Thanks Bob,
No plans here for anything like what you are describing. Way beyond my modest ambitions...but feel free to try it on your coach! 8)
Title: Re: Dual Alternator Setup
Post by: Journey, Roam, Explore on August 29, 2019, 08:02:20 am
Nah. Not cost effective. Easier to just run the genny! But if I planned to drive a lot on hot days it's a thought. :D But my dash air sucks too.....
Title: Re: Dual Alternator Setup
Post by: John Haygarth on August 29, 2019, 01:33:31 pm
Nah. Not cost effective. Easier to just run the genny! But if I planned to drive a lot on hot days it's a thought. :D But my dash air sucks too.....
Your dash air is supposed to blow, maybe fan is running in reverse?? lol JohnH
Title: Re: Dual Alternator Setup
Post by: Journey, Roam, Explore on August 30, 2019, 10:23:01 am
Hmmm... never thought of that John.... 8)
Title: Re: Dual Alternator Setup
Post by: Chuck & Jeannie on August 30, 2019, 05:13:20 pm
Continuing my investigation of the original subject of this thread (feasibility of running dual alternators) I have made a interesting discovery. The old LN alternator that has been faithfully serving our coach since we took possession is a pretty weak player. I always assumed it was rated at 160 amp max output. Turns out it is only 130 amp. This alternator was not the original factory installed unit. It was a replacement installed by a previous owner. I decided no matter what else I did, I should at least improve my battery charging setup with a fresh new alternator.
Found a good deal on a Delco Remy Model 8600307. This is a 28SI series, 200 amp, J180 mount with optional remote sense input. It has dual internal fans for extra cooling capability. Good price at $250 and free shipping. Arrived in perfect condition. Looks pretty cool with the radically "vented" casing. Should be a big improvement in my battery charging capability.
8600307 by DELCO REMY - NEW ALT (https://www.finditparts.com/products/635859/delco-remy-8600307)
Title: Re: Dual Alternator Setup
Post by: Roger & Susan in Home2 on August 30, 2019, 07:06:55 pm
You should be able to pull the old pulley and use it, That is what I did with mine.
Title: Re: Dual Alternator Setup
Post by: Caflashbob on August 30, 2019, 08:25:59 pm
The batteries will only take so much input. At 130 vs 200 I would be surprised if your batteries charge any faster.
The 130 amp LN you removed does not appear to have the adjustable voltage regulator output that the oem one did?
If you hook up the optional sense wire to make the alternator, for sure, to output 14.15 volts at the battery you may be overcharging both your battery banks on long warm weather drives.
I noticed my replacement LN alternator does not have a adjustable voltage output like the oem.
Brett and Foretravel recommend and set 13.6 volts to lessen the overcharging at warm weather.
Hmmm. Now what?
Using a isolator there is no way to fix the summer overcharging issue that I know of.
My thought was that after i start a drive and both banks are fully charged and the voltages stabilize i would use my combiner to manually disconnect my house mk gels from the alternator.
At that point my solar ,if daylight outside, would output its 13.6 volts output to the house batteries to maintain the house useages while driving and having the inverter on.
So my thought is that a high voltage alternator would benefit from a ability to disconnect it from the house batteries and have a lower voltage, maybe multi staged and /or temp controlled charging like the house does of the inverter?
Of course this requires a combiner that has a remote panel allowing a manual disconnect for the battery banks.
Foretravel had no such thing in 97 when our coach was made so they used an adjustable voltage LN and turned it down as Brett recommends to 13.6 volts.
If you leave the optional sense wire off the delco you start out at 14 volts like my LN and end up around 13.8 at the dash gauges.
Is the Delco made for DUVAC systems?
Title: Re: Dual Alternator Setup
Post by: Roger & Susan in Home2 on August 30, 2019, 09:54:16 pm
There is no reason to not use a Delco Remy or any other alternator in your FT or any DUVAC system. These DUVAC systems are simply dual battery systems with a single charging source. The old isolators used big diodes to do the isolating task. There is a significant voltage drop across the diodes so the voltage output of the LN was pushed up to compensate. That is the DUVAC part. The isolators were like a water hose with a Y connection with a check valve in each direction. All things being equal the same amount of water would go in each direction. If one side can accept more water (like a battery that needs more charge, less resistance) then more water goes that way. If you want to push more water faster then you turn up the pressure (voltage). Nothing magic or special here.
The LN is an externally excited version of a common LN alternator. It needs an external excitation (ignition source) to start charging. It uses a sense wire connected to the start batteries as does the Delco Remy to tell the voltage regulator in the alternator to adjust voltage up to increase early amps to speed up charging of the start battery when its voltage is low (after a start).
Today there are lots of zero voltage drop isolators and several zero voltage drop smart isolators (Sterling ProSplitR for example) that manage charging between multiple battery banks. And other smart charging systems that charge the start batteries and manage charge to the house batteries using a multi-stage charge profile.
A properly installed and working alternator will be putting nearly nothing into a fully charged start battery whether the voltage is 13.6 or 14. something. At 13.6 v it will just take a lot longer to charge. The voltage at the battery using the sense wire helps the alternator increase its voltage to what it is capable of producing to reduce the time to charge.
Strategies for managing your batteries have changed considerably in the last 20+ years. As have batteries and available equipment.
Title: Re: Dual Alternator Setup
Post by: Caflashbob on August 30, 2019, 10:50:24 pm
If you are charging your batteries for hours at over 14 volts unless you are at zero degrees you are definitely overcharging your batteries. Seriously lowering your batteries life's, anyone disagree? Please post your opinion and facts.
Why would FMCA's tech director (Brett) mention 13.6? It's an rv. Not a car. Built for the use.
If you buy less expensive everything in the battery system for your coach why would you overcharge the parts to shorten their service life? You could have bought oem grade parts and had them last twice or more as long in my experience.
Why save money then damage it quicker by overcharging the parts?
Title: Re: Dual Alternator Setup
Post by: Journey, Roam, Explore on August 31, 2019, 08:41:12 am
RV stuff is relatively new to me, but on a boat, the alternator output is controlled by a regulator that adjusts the voltage based on a number of factors, including temp of the battery, the alternator, the battery type, voltage, and state of charge. Not sure what my coach has on that front. Since I have a lot of solar up there, the victron mppt puts them charge back into the batteries pretty quick when its sunny out, and the victron inverter/charger when its not and the genny is running or hooked up to mains. The volts will depend on the type of battery you have and where it is in the charging cycle, bulk. absorption or float. It also has a pretty cool belt load manager that will derate the power to protect your alternator. For a little over 300 bucks its a great way to charge and protect your batteries and alternator. Bob
Title: Re: Dual Alternator Setup
Post by: Chuck & Jeannie on August 31, 2019, 09:00:30 am
To address Bob's concern about "over charging on long hot drives", and to satisfy my own curiosity, I plan to do a little experiment when I install my new 28SI alternator. The installation instructions say it will work fine with or without a SENSE wire connected. After making sure all my big battery charging cables are clean, tight and in good shape (I may elect to install fresh cables) I will try two different connections to see what the new alternator actually puts into the batteries.
But first, to establish a "baseline" I will check to see what my old LN alternator has been sending to my batteries. I will pull the start battery down by running the headlights on bright along with the fog lights and the spot light. Then crank the engine and observe the charging output of the old LN alternator with my handy DC clamp ammeter around the charging cable, and my multimeter on the start battery posts.
Next, I will do the same test with the new 28SI alternator, using two different charging cable connection points.
First connection: I will hook the charging cable from alternator B+ post to the ALT post on my isolator, and connect the existing SENSE wire from the START battery isolator post to the alternator. I will then repeat the test.
Second connection: I will hook the charging cable from alternator B+ post to the START battery post on my isolator, and remove the SENSE wire from the alternator. This is basically the same as connecting the alternator directly to the start battery. I will then repeat the test.
Running these tests will give me some valuable info. I will find out what my old alternator has been feeding my batteries for the last 6 years. It can't be too bad because my batteries have not shown any obvious signs of suffering. Or perhaps I just don't ever drive long enough in very hot conditions to cause a problem. One thing to take into consideration: when traveling we mostly stay at places with full hookups, so both battery banks are usually fully charged (start battery by Trik-L-Start) when we pull out in the morning. Our alternator normally only needs to maintain our battery banks when driving, rather than laboring to recharge deeply discharged batteries.
(We also have a PV system that constantly tries to charge the batteries on most sunny days, which adds another confusing factor)
I will also find out if my Victron Energy ARGOFET (low voltage loss) isolator is living up to it's billing. If it does, there should be very little difference in voltage observed at the isolator posts (ALT and START BAT) in the test using the SENSE wire..
Finally, I will find out what voltage the new alternator actually puts into my start battery. This will tell me if I need to worry about Bob's concern.
I'll update this thread when I get around to installing the new alternator. Gonna have to cool off a bit here before that happens.
Title: Re: Dual Alternator Setup
Post by: Caflashbob on August 31, 2019, 12:08:10 pm
The engine batteries location in the hot engine compartment negates the use of a temp compensating alternator to charge them. Close to 13 volts is correct for them.
Judging by many 10-12 year battery life reports here the 13.6 volts and mk gels and optimas were a excellent system
Title: Re: Dual Alternator Setup
Post by: Roger & Susan in Home2 on August 31, 2019, 10:16:52 pm
A quick look at Optima's website for charging recommendation for yellow top and red top batteries.
14.5 volts from an alternator with no amperage limits looks OK to me for either. 13.6 volts looks like it is at the very low end of acceptable alternator charging for a yellow top.
Title: Re: Dual Alternator Setup
Post by: Caflashbob on August 31, 2019, 10:36:59 pm
The float voltage mentioned on the redtops matches what Foretravel shipped our coaches set at.
The limits are to be strictly adhered to.
Title: Re: Dual Alternator Setup
Post by: krush on September 03, 2019, 08:17:19 pm
1. I only have a Magnum MS2812, so marginal there...but I ordered a EasyStart 364 (3 ton) soft start module from Micro-Air, which should be here today. I am hoping this will sufficiently ease the strain on my inverter. Won't know for sure until I get it installed.
I can attest that the Easy Start from Micro-Air works great. I installed two new A/C units on my boat (15,000 and 20,000 btu/hr) both with EasyStart. My 2000wat harbor freight generator can start either one on eco mode!
Title: Re: Dual Alternator Setup
Post by: Roger & Susan in Home2 on September 03, 2019, 09:52:26 pm
The float voltage mentioned on the redtops matches what Foretravel shipped our coaches set at.
The limits are to be strictly adhered to.
My 2001 U320 was shipped with YellowTop Optimas. RedTops are not recommended or warranted in deep cycle applications which is why FT went to YellowTops in 2001. Long term parasitic loads cause deep cycle discharges. The limits are to be strictly adhered to. Whose rule is this?
Title: Re: Dual Alternator Setup
Post by: Caflashbob on September 03, 2019, 11:30:11 pm
Charging OPTIMA® Batteries | Support | OPTIMA® Batteries (https://www.optimabatteries.com/en-us/support/charging/charging-tips)
Yellow, red and blue all state that float voltage is to be strictly adhered to at 13.2 to 13.8.
Plus the optima website prominently mentions the red top are the ultimate start AGM battery.
Maybe an availability issues or a deal on yellow tops? I understand the factory went back to redtops later?
If you have optimas of any color float charging them over 13.8 volts is not recommended.
After a long drive coming up if both the mk gels and my redtops show over 13.8 volts I may remove the new alternator and put back on the adjustable oem rebuilt lN unit I took off.
Almost every rv and bus manufacturer used the adjustable LN alternator.
And set them at 13.6 volts at the batteries like Brett recommends at his FMCA diesel seminars.
Edit: mk on their technical page on gels states:
No recharge current limitation@13.8volts
Title: Re: Dual Alternator Setup
Post by: Roger & Susan in Home2 on September 04, 2019, 11:28:23 pm
I got the coach out today. We have a Delco Remy 40si 240 amp alternator with a sense connection to the start batteries. 14.5 v possible depending on charge demand from the batteries. No isolator, alternator is connected directly to the start batteries. I checked the voltage at the start batteries about 5 minutes after I started it up. 13.6 volts from the alternator. Alternators have voltage regulators. At least Delcos do.
The idea that you are going to be pushing 14.5 volts into your start batteries all day while you drive is not based in reality.
Title: Re: Dual Alternator Setup
Post by: Caflashbob on September 05, 2019, 12:58:54 am
According to the Delco website you may not have the sense wire hooked up?
Title: Re: Dual Alternator Setup
Post by: Roger & Susan in Home2 on September 05, 2019, 09:59:59 am
The sense wire is connected and the alternator is working as expected. Do what ever you want, Bob.
Title: Re: Dual Alternator Setup
Post by: Caflashbob on September 05, 2019, 10:39:53 am
So the Delco drawing and website is not what actually happens all the time at the battery? It's only till charged?
Most non gel or non optimas could and should have 14 volts constantly at a battery I would think?
All optimas and mk gels are made to have a max of 13.8 volts to them continuously. Better slightly less like the 13.6 recommended.
My Cummins dealer owner/shop foreman wanted to put in the delco sense alternator and he said I would always have 14 volts to my batteries.
Not being contrary just trying to make sure for my own possible personal choices how things work.
I would temporarily clip or add an additional wire from the sense to the batteries just to see if the volts go up to the 14 volts the drawing shows?
What does the delco show at its output terminal? With and without its sense wires?
Could the delco be defective?
Seems like a lot of volts gone somewhere?
Did you set up your system to pull power from the start batteries?
You would think the sense system if working would compensate for any loads?
Title: Re: Dual Alternator Setup
Post by: krush on September 05, 2019, 10:41:10 am
If trying to run the A/Cs off the alternator, why would you still use a diode type isolator? The reason those big heat sinks are on the isolator is because they consume power (they have a voltage drop which makes heat). This means your alternator is working harder to make power that isn't charging the batteries.
Title: Re: Dual Alternator Setup
Post by: Chuck & Jeannie on September 05, 2019, 11:13:40 am
B. If I DO attempt to run my front A/C off the inverter, I will connect my 200 amp Delco 28Si directly to the coach batteries, bypassing my isolator.
Title: Re: Dual Alternator Setup
Post by: Roger & Susan in Home2 on September 06, 2019, 10:24:36 pm
I checked my start battery voltage right after we started the coach this morning and it getting charged at 14.2 volts. 30 minutes later at a rest stop the start batteries were getting charged at 13.2 volts (at normal idle speed) monitoring start battery voltage over 4 1/2 hours at highway speeds showed 13.6 to 13.8 volts with the headlights on. Works exactly as expected.
The Delco alternator has a a smart voltage regulator. It is not constant voltage and constant amps output
Title: Re: Dual Alternator Setup
Post by: prfleming on September 06, 2019, 11:34:43 pm
The Delco regulator is temperature compensated. In the Delco literature the voltages and performance graphs shown are at cold startup temperature (say 70 degrees). At startup the Delco sense adjusted charge voltage is approx 14 volts as Roger mentioned. As the alternator warms up the voltage reduces to approx 13.2 to 13.8 volts depending on alternator temperature. The Delco in my Roadtrek does the same thing. At startup I see approx 14.2 volts, going down the road I see approx 13.6 volts on my battery monitor. In the winter at freezing temps I have seen up to 15 volts at startup and it reduces as the alternator warms up. Roger's alternator is working as it should.
Title: Re: Dual Alternator Setup
Post by: Chuck & Jeannie on September 07, 2019, 08:50:59 am
I think the apparent reduction in charging voltage that Peter and Roger are describing is actually due to a little known fact: as electricity "heats up" the volts expand in length and circumference. Because the volts are "bigger" (or "longer" depending on how you look at it) fewer of them can flow down a wire at any given time. We observe this reduced flow rate as a smaller number on our voltmeter.
Although fewer volts are reaching the end of the wire, because they are "bigger" they each contain more "energy", so it's all good. :thumbsup: