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Topic: Battery Isolator Puzzle (Read 2880 times) previous topic - next topic

Battery Isolator Puzzle

I cleaned up and refurbished the Battery Isolator panel HERE a few weeks ago. When I sketched the panel before disassembly, I found a mystery between what was wired and what was on the drawings. B19 was wired to the 4th post and there was a jumper wire run between the 2nd and 4th posts. I did not find an alternator sense wire (from the drawings). When the coach is running, I am charging but it seems that I'm charging at 14.2, no less.

Looking at the 2 drawings below, the first is from the coach diagrams, the 2nd is what is currently there. When I tried to wire it correctly, I never got a charge from the alternator. I suspect the jumper and B19 move was to compensate for this.

Having to want to get it "period correct", and manufacturer correct, I want to rewire a new alternator sense wire, take the jumper off, and put B19 back to post #2. It appears I have the original 8RG2112 Leece-Neville Alternator. Can't find any documentation on where the sense wire attaches. Does anyone have a drawing or picture of where the sense wire attaches to the alternator?
 

Re: Battery Isolator Puzzle

Reply #1 –
I don't have a schematic but I can tell you from experience that your sense wire is listed on YOUR schematic as B26 coming from the start batt post to the aux solenoid, then comes out as B35 from the solenoid to that lil 15 amp auto reset fuse, then changes again to B71 to the alternator DUVAC connector. On mine which is probably the same as yours, that sense wire is the only small wire on the isolator.

B19 is the + cable from the alternator.

Re: Battery Isolator Puzzle

Reply #2 –
Chuck,

You have fallen victim to the "Owner-modified Custom Wiring" syndrome.  PO changes things, with no explanation of why.  You, the new owner, are stuck with figuring out the puzzle.

Look at your first diagram - the printed one.  See the smaller black line directly above the "B14 2RD" line, connected to the 4th post?  That line is identified on the diagram as "59 RD ALT EXCITE".  This notation is incorrect.  If you do have a alternator which requires a "EXCITE" wire, then that wire should only be connected to a "HOT with Ignition" source.  If you have a "Self Excited" alternator, then you do not need a "EXCITE" wire.  In that case, the line on the diagram should be labeled "59 RD ALT SENSE".  The "SENSE" wire from a "Self Excited" alternator should be connected to the 4th post on the isolator.

To solve this mystery, you must first determine what type alternator you have.  8RG2112 is the voltage regulator model - it is not the alternator model.  This regulator is used on several different Leece Neville alternators.

If your alternator is "self excited", then you do not require a separate "EXCITE" wire.  In that case, there will be only one small wire (SENSE) attached to the back of your alternator.  The other end of that wire should connect to the 4th post on the isolator (or to a positive post on a start battery).

If you have a DUVAC alternator, as mentioned above by Twig, then there will be 2 small wires attached to the back of the alternator.  One of those wires (EXCITE) should connect to a "HOT with Ignition" terminal.  The other small wire (SENSE) should connect to the 4th post on the isolator (or to a positive post on a start battery).  EDIT:  this statement is only half right - see next post below.

Your alternator output cable is currently connected to the 4th post, which is the "engine start" battery post.  As you observed, this is incorrect.  First, determine whether you have one or two small wires coming from your alternator.  Then, connect the (one or two) small wires to the proper place.  Once that is done, you should be able to move the alternator output cable back to the 2nd post on the isolator, and remove the extra jumper.  Your actual wiring should then match the factory diagram.

Re: Battery Isolator Puzzle

Reply #3 –
"If you have a DUVAC alternator, as mentioned above by Twig, then there will be 2 small wires attached to the back of the alternator.  One of those wires (EXCITE) should connect to a "HOT with Ignition" terminal.  The other small wire (SENSE) should connect to the 4th post on the isolator (or to a positive post on a start battery)."


With all due respect, this is incorrect. On a DUVAC modification (which I'm sure yours is) the "duvac" connection on the alternator regulator (sense wire) goes thru a self resetting fuse to the 4th post on the isolator by way of the aux solenoid as shown on the schematic.  The other small wire on the regulator goes back inside the alternator to the "duvac" modification. There is no excite wire connected to ignition.

Re: Battery Isolator Puzzle

Reply #4 –
Quote from: Twig –
With all due respect, this is incorrect. On a DUVAC modification (which I'm sure yours is) the "duvac" connection on the alternator regulator goes thru a self resetting fuse to the 4th post on the isolator by way of the aux solenoid as shown on the schematic.  The other small wire on the regulator goes back inside the alternator to the "duvac" modification. There is no excite wire.
Absolutely no problem, Twig, I stand corrected.  This is what makes this whole "Alternator" subject so confusing, both for owners and for the "mechanics" working on these coaches.  So you are saying a DUVAC alternator has only one small wire leaving the alternator going "somewhere else", and that is the "SENSE" wire.  Which would make a DUVAC alternator "Self Excited".

Other than being wrong about the DUVAC wiring, I think the rest of my statement to (the other) Chuck is still valid.

For basis of comparison, on my coach, there are 2 smaller wires attached to the 4th post on the isolator.  I have been through this process of trying to figure out the alternator wiring, because mine was also screwed up when we bought our coach.  I do have the "B26 RD" going from my 4th isolator post to the AUX START SOL, exactly as you describe.  But, I also have another small wire attached to the 4th isolator post, and on my coach this is the SENSE wire (59 RD on the factory diagram) coming from the alternator.  I have verified this by physically tracing the wire, and by checking continuity.

Photo below of my isolator.  On the 4th post: two big battery cables, smaller red wire from post to AUX START solenoid, and the alternator sense wire in black plastic sheath.  (Disregard the blue wire - it's for the Trik-L-Start)  I do not know if my wiring is factory original, but the way everything is tied together and routed makes me think it is.  At any rate, my alternator (8LHA2070VA) seems to function correctly.  ^.^d

Re: Battery Isolator Puzzle

Reply #5 –
Foretravel!........sometimes I'd like to slap 'em upside the head.

Re: Battery Isolator Puzzle

Reply #6 –
Quote from: Twig –
Foretravel!........sometimes I'd like to slap 'em upside the head.
Agree...X2!

At the risk of confusing things further, I will add a link to my old thread where I was trying to figure out MY alternator puzzle.  My classic "journey to enlightenment" might actually help (the other) Chuck better understand his current situation.  Some of the assumptions that I made back then about the original alternator fitted to our coach may not have been totally correct, but the modification I made (suggested by Brett Wolfe) to the replacement alternator did solve my problem.

Brain Teaser (Electrical)

Re: Battery Isolator Puzzle

Reply #7 –
Thanks to Chuck and Twig!

Based on the above, will be crawling into the compartment this afternoon (replacing fuel filters/separators). Will get a pic of the alternator connections and see if I can get wire identifications before proceeding. Duvac vs Leece-Neville is odd, but will look for other identifications. I included a pic of the "extra" jumper wire in my Original pic.

After priming the system and getting it running again, I'll hunt out this mystery and hopefully find something I may have missed.

Re: Battery Isolator Puzzle

Reply #8 –
While I'm doing something else, here are pics of the alternator. There is a screw missing (literally) on the back of the alternator.

Re: Battery Isolator Puzzle

Reply #9 –
Chuck,

The alternator you have was the replacement model for the one I have on my coach.  The back of it looks exactly like mine.  If I am correct, then you may find that there aren't any small wires coming off your alternator and going to the isolator panel.  In other words, you have a 2-wire alternator - it does not have a external "EXCITE" wire or a "SENSE" wire - both these functions are handled by the small jumper wires attached to the regulator.  It only has a big cable (NEG) going to ground (engine block), and a big cable (POS) going to the battery isolator.

Prestolite - Leece Neville

A 2-wire alternator output cable would normally connect directly to the POS terminal on the start battery.  This is probably why whoever installed it connected the output cable to post #4 on the isolator - that was the only way it would fully charge the start batteries.  This is also why, when you moved the alternator output cable to isolator post #2, the alternator would not work.  It was not "seeing" any battery voltage on the #2 post, so it would not turn on.

With the alternator connected to post #4, I'm trying to get straight in my head what is the result of having the jumper from isolator post #4 to post #2.  Here's how I see it.  The jumper would allow the alternator to also charge the coach (house) batteries, so both battery banks are being charged when engine is running.  The problem is, the "isolation" function of the battery isolator is being bypassed, at least in one direction.  With the jumper in place, as you discharge the house batteries, the start battery bank would also be discharged.  It would be like having your BOOST switch on all the time.  Obviously not a good situation.

To fix this, one solution is the modification I described in the old post linked above.  On the back side of my alternator, I cut the little jumper wire that went from the voltage regulator to the POS output post.  I spliced my existing "SENSE" wire onto the cut wire where it entered the voltage regulator.  The other end of my "SENSE" wire was already connected to the #4 post on the isolator.  This simple mod converted my 2-wire alternator to a "external sense, self-excited" 3-wire alternator.  It has worked fine for the last 3 years.

If you don't want to modify your alternator, then you might want to do away with the diode based isolator, and perhaps go with one of the more sophisticated smart battery charging relays, such as the Blue Sea SI-ACR (see link below).  I think it would work fine with your 2-wire alternator.

SI-ACR Automatic Charging Relay - 12/24V DC 120A - Blue Sea Systems

Re: Battery Isolator Puzzle

Reply #10 –
Ya, without an external sense wire, do NOT use a diode-based battery isolator, as they "charge" .7VDC that they turn into heat (hence the fins on the isolator).

You could go either with a better isolator as Chuck posted OR you could just use a simple marine ON-OFF battery switch.  With the switch (can be mounted at foot of bed for easy control) alternator B+ and chassis battery to one lug (so chassis battery is always charged) and house battery to the other lug.

OFF, chassis battery is charged by the alternator.
ON, both banks are charged by the alternator.

Also makes a bomb-proof battery combiner for charging or starting the engine.

And, a lot less $$.

Re: Battery Isolator Puzzle

Reply #11 –
I'm not a wiring guru, and this is all pretty foreign to me. "trons" weren't my gig in the Navy, if something broke, the FC's and ET's were the tron chasers.

I have done electrical, and installed switches and the like. The "bomb proof" setup sounds enticing, and would have to ask someone to draw it up for me. Guessing here, sounds like remove all the wires from the isolator, and connect all the terminal 4 wires to A side, and all the terminal 1 wires to B side.

Or, another way of saying, Coach batteries + and Alternator wire to A, and house +to the B side?

And what of the Boost relay?

Re: Battery Isolator Puzzle

Reply #12 –
Perhaps Mike Leary has the diagram from when I did this many years ago.

Re: Battery Isolator Puzzle

Reply #13 –
Many have problems with alternator battery sense wire as originally wired from breaker on isolator panel.  Best results are found with running new wire directly to start battery positive post.  Put a fuse on the end of the new wire at the battery end.  On our coach we used a PVC pipe to carry wire from street side alternator to coach side start batteries.

Re: Battery Isolator Puzzle

Reply #14 –
If he only took the wiring off the isolator panel, why would he have to do ANY thing to the alternator?

Re: Battery Isolator Puzzle

Reply #15 –
Quote from: Twig –
If he only took the wiring off the isolator panel, why would he have to do ANY thing to the alternator?

Because SOMETHING is not correct. That is NOT how it was originally wired and will not work properly.

No way to use an internally regulated alternator (no external sense wire) with a diode-based isolator.

Alternator would put out its design voltage, say 14.0 VDC.  The isolator would loose .7 VDC so the most the batteries would see is 13.2 VDC.  And, as the alternator heats up, it would be even lower.

So, either change the alternator, alternator wiring or isolator.

Re: Battery Isolator Puzzle

Reply #16 –
Quote from: Balcanthez –
Guessing here, sounds like remove all the wires from the isolator, and connect all the terminal 4 wires to A side, and all the terminal 1 wires to B side.

Or, another way of saying, Coach batteries + and Alternator wire to A, and house +to the B side?

And what of the Boost relay?
Yes, I think that is what Brett is proposing.  It would be essentially the same hook-up as you show in your pencil drawing in your first post, with the isolator being replaced by a "2 position (ON-OFF)" switch.  Everything you show (in your drawing) connected to isolator post #4 would connect to A on the switch.  Line B16 would connect to B on the switch.  I think you would leave the BOOST solenoid in place.  That way, you would actually have two ways of combining battery banks - the new manual switch at the foot of the bed, or the existing BOOST switch up front.

Then, as Brett says, using the new switch at the foot of the bed:
OFF, chassis battery bank is charged by the alternator, and your AUX START solenoid and everything attached to it is powered.
ON, both battery banks are charged by the alternator, and your AUX START solenoid and everything attached to it is powered.

Re: Battery Isolator Puzzle

Reply #17 –
Apparently this alternator has not been modified for the duvac and needs to be. Once modified, the schematic is exactly correct and no other apparatus need be used. Here is a picture of the exact schematic. You can see that the alternator is connected to post 2 (covered by wire harness in photo) and the jumper from 3 to 1 is to charge house batteries even when the start battery is full (which is always). Underneath the cable to the start battery on #4 you can see a smaller wire which is the sense wire. It runs to the post on the aux solenoid and then it continues over to the 15 amp self resetting fuse which looks new because I had to replace it. From there it goes to the duvac post of the regulator. This is how it has to be to use the isolator.

And that makes the wheel go round.

Re: Battery Isolator Puzzle

Reply #18 –
Attached is pic of the isolator and solenoid which I have intentions of replacing with a cole hersee  24213 12V 200A Continuous Solenoid and Cole Hersee 48160 Battery Isolator. Can you tell from the photos attached if I have the right replacements? (your topic of the duvac(??)  alternator requirements have me thinking....)

Re: Battery Isolator Puzzle

Reply #19 –
Just by the pics. any isolator will be better than what you have now as that one is coming apart. That isolator will be fine as your alternator should be a 160amp  I run a 200 amp also.

Make sure you have a good clean cable ends and make sure your sense wire to the alternator is in good shape.

Mike