Battery Isolation - Is it working as it should?

My new-to-me 1993 Itasca Suncruiser has the normal battery arrangement of 1 regular automotive battery for the chassis and two deep cycle house batteries connected in parallel.  The power converter seems to be working fine, and there are a couple different 12V-related switches on the dash.  The "Aux Battery" switch appears to work - when I flip it to "off", there's no power for any of the coach's 12V systems as it should be.  The radio power switch works properly, allowing the radio to be powered when the ignition is off.  The Dual Batt switch, however, is confounding me a bit. 

According to the operator's manual, the Dual Battery switch has a momentary position for starting help as well as a "dual" position for connecting the house batteries to the alternator to charge up while driving.  It isn't explicitly stated, but my assumption is that the middle position represents a disconnected state where the automotive 12V system and the house 12V system are isolated from each other.  When I operate that switch, I hear the click of a relay coming from somewhere in the back, so it's doing *something*, I just don't know if it's the right thing.

What makes me question this system is that I was getting a very low reading on my volt meter in the gauge cluster.  Early 90's GM products aren't really world renowned for their accurate readings, so I pulled out my multimeter and did some testing of my own before determining that the alternator had failed.  I do not believe that the Dual Battery switch was in anything other than the "off" position during the time between when the alternator failed and when I started troubleshooting.  With the ignition off, I got the exact same voltage reading on all three batteries.  I would certainly expect that the coach batteries would read identically to each other, but if that switch was in the off position and the automotive battery and house batteries were isolated from each other, shouldn't the house batteries have been reading their normal 13.75 volts while the automotive battery was reading around 10-11 volts since the alternator wasn't charging it?  When I swapped the alternator, I disconnected the negative terminal from the automotive battery only and the engine's systems were dead as a doornail while the house systems continued to work fine.

I'm not familiar with how the isolation system is supposed to work or even where they've physically installed it, so I'm not sure if I have a problem or not.  I'd like to have the peace of mind to know that in the event that I run down my house batteries, the engine will still start without having to fire up the generator or plug the power converter in to shore power to charge the system.  Other than just turning on all the coach 12V systems and waiting for the battery to die, is there a good way to check if the isolator is working as it should?  Will checking continuity between the negative terminals on the house battery and the auto battery tell me anything?  Any good places to look for the isolator so I can verify that it hasn't been bypassed?  The wiring diagram says "bottom leg of front electrical box", but I'm not 100% clear on where that would be.  Thanks in advance!

Hi wae. If your battery isolation switch disables your house 12 volt systems, it seems like it's working as advertised. The switch controls a solenoid, which connects/disconnects power. It also sounds like your combiner switch is working properly. Its purpose is to momentarily tie the house and chassis batteries together, so you can use the house-batteries to assist with starting the engine if the chassis batteries die.

I'm also interested in why the house and chassis battery-banks would have identical voltage readings. I'd expect to see that when the combiner switch is pushed, but not otherwise. That 13.75 volts you saw is the charger's voltage - not the battery's voltage, so you were either plugged into shore-power, running a generator or idling the engine when you took the readings. A fully charged 12 volt battery will indicate 12.6 to 12.7 volts when at rest. That 10 to 11 volts your chassis-battery is putting out means it's, essentially, dead.

When you're plugged into shore-power, your converter powers your 12 volt systems and charges your house-batteries. It probably doesn't charge your chassis battery, which isn't unusual for a coach of that era. The alternator, on the other hand, charges both the house and chassis batteries.

Kev

It only charges the house batteries if the switch is in the duel mode. Chassis battery most likely isn't charged by the converter.

I put together a pretty complete testing regimen and had little charts all ready to fill out as I walked through the steps but it was all for naught because I confirmed the isolation is working with a quick continuity test between the battery posts.  I don't know why the voltages were all the same before, maybe I had the switch flipped for a bit and didn't remember doing that, but I have continuity on the positive side of both systems but not on the negative side, so the isolator is functioning.  I've also got different voltage numbers on the two battery banks now as well.

TL;DR:  No idea what I was doing before to get wonky readings, but everything is working as it should.

Good news! Thanks for the update.

Kev

Hopefully this zombie thread won't want to eat too many brains, but...

I remain extremely confused by this whole system.  Most of my camping is done where I have shore power so it hasn't been high on my to-do list, but I do a week long dry camping trip ever year at the end of January and I'm trying to get everything working in time for that.  Last year, we drove part of the way, dry camped in a Walmart lot then drove the rest of the way.  Something like 8 hours a day of driving, plus or minus.  When we arrived in Florida at our destination, it didn't take very long for the house batteries to start showing pretty low voltage.  I thought that the batteries were going out and was all ready to go buy new ones but after running the generator for a while, the voltage was topped off and all was good.  Same thing on the ride home.  So it seems that my battery isolator is doing half of its job REALLY well, but it doesn't seem to be UN-isolating them. 

Today, I did some testing around and when I hit the momentary switch on the dash, I can hear the plunger activating in the solenoid.  When I jump +12 to it, I get continuity across the chassis and house battery terminals on the solenoid itself and when I take the jumper wire off, the continuity is broken.  When I turn the key to "run" I don't hear anything, though, and if I read the wiring diagram correctly, it should be connecting the two banks of batteries at that point -- however, I think I only have about 4 volts on the chassis battery right now.  I'm working on that problem of course, but if that switch was working properly, I would have thought that holding down the momentary switch while turning the key to "start" should have resulted in cranking of the engine.  But it didn't.

Looking at the wiring diagrams, it seems like everything should be working as advertised and the batteries are definitely isolated, but I don't seem to be able to get the two systems to join up.  Any ideas of where I should be looking?  Worst-case, I can put a jumper cable between the batteries while we're driving to top off the batteries, but I'd kind of like the automagical solution to work!

The battery isolation solenoid needs adequate voltage to operate, so if you only have 4v with the key on, it may not be enough. You can check the voltage at the solenoid with the key on to see what, if anything, you are getting there. In any event, I would not leap to any conclusions until you get the chassis battery in operating condition.

Absolutely agree that I've got to get adequate coach voltage before I go too far down any rabbit holes!  The momentary switch, however, is engaging since it is powered by the house batteries.  I can hear it actuate and I am getting continuity across the two posts on the solenoid.  Isn't a dead coach battery the main reason for the momentary switch?  I would think that if it were working as designed I would have been able to start the engine with fully topped off house batteries and a dead coach battery.  Thinking out loud a bit, though, I have had batteries that were dead dead which wouldn't start with a jump, so maybe that's what is up here.  I've had the coach battery on my charger/conditioner overnight so I'll load test it this evening and replace it if it fails.  Then I can do some more testing under better conditions and report back!

I charged up the coach battery and had it load tested at my FLAPS.  With engine off and no shore power connected, I have different voltages on both banks of batteries.  Same with engine running.  I can hear the solenoid actuating and I have continuity across the two posts when 12v is applied and no continuity when there's no 12V.  Can that solenoid fail in such a way that there's continuity but not enough of a connection for the voltage? 

wae said:

  Can that solenoid fail in such a way that there's continuity but not enough of a connection for the voltage?

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From other threads on this topic, yes it can, wae.  Lots of posters state that OEM solenoids usually have copper contacts (cheaper) which can fail in the mode you describe.  A better solenoid is available; most recommend this one (with silver-tungsten contacts) which may well outlast the coach.  https://www.amazon.com/Cole-Hersee-24213-Continuous-Solenoid/dp/B005K2429I/ref=sr_1_2?s=automotive&ie=UTF8&qid=1515473503&sr=1-2&keywords=cole+hersee+solenoid

I plan to replace both the boost/charge solenoid  and the coach battery disconnect solenoid in my rig just because of age/cycles.  Mine are working fine, but I just don't want to have them fail when my daughter and grandkids are out with the coach this summer so I'll install the "upgrade" version....... not that expensive; so, for me, a "preemptive strike" is in order.

Good luck with your "hard fought" fix, and safe travels.

I was actually looking at that very one earlier today and going through the reviews on it.  It is on its way and now I can move on to troubleshooting the fridge!  Thanks for the sanity check -- I can't recall ever working an electrical problem before where continuity didn't mean "it works"!

To put a bow on this one for future searchers:. The new isolator linked above has solved the issue.  I got my hopes up when I went to remove the old one because the coach battery connection was pretty loose, but torquing that down didn't solve the problem.  My guess is that it's the loose connection that may have caused the failure.  The only difficult bit (other than the fact that this is the first component installed and the rest of the coach is built around it, of course) was that the old one was grounded through the body of the solenoid and the replacement has a ground terminal.  Not a big deal, just had to run a ground wire and route it such that it doesn't have a chance to rub up against anything and short.

The answer to the question, however, is that a solenoid can absolutely fail in a manner where there is continuity across the terminals but no voltage.

youracman said:

From other threads on this topic, yes it can, wae.  Lots of posters state that OEM solenoids usually have copper contacts (cheaper) which can fail in the mode you describe.  A better solenoid is available; most recommend this one (with silver-tungsten contacts) which may well outlast the coach.  https://www.amazon.com/Cole-Hersee-24213-Continuous-Solenoid/dp/B005K2429I/ref=sr_1_2?s=automotive&ie=UTF8&qid=1515473503&sr=1-2&keywords=cole+hersee+solenoid

I plan to replace both the boost/charge solenoid  and the coach battery disconnect solenoid in my rig just because of age/cycles.  Mine are working fine, but I just don't want to have them fail when my daughter and grandkids are out with the coach this summer so I'll install the "upgrade" version....... not that expensive; so, for me, a "preemptive strike" is in order.

Good luck with your "hard fought" fix, and safe travels.

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This is the solution to your problem. Indeed on the View/Navion Forum on Yahoo, practically everyone with a rig over about 6 or 7 years old has replaced the solenoid, the original being a 85 amp rated minimal quality part. Mine was bad when I bought my 18K mile rig in 2015 (2007 model). They clunk nicely, just don't pass any current.

Charles
2007 Winnebago View 523H on a 2006 Dodge (Daimler-Chrysler aka Mercedes) Sprinter 3500 chassis (T1N). Bought Sept 2015 with 18K miles on it, Prog Ind HW30C, Prog Dymanics PD4645, Coleman Chill Grille, PML/Yourcovers.com deep alum trans pan, AutoMeter 8558 trans temp gauge, Roadmaster sway bar, Koni Red shocks (front & rear), Fantastic Ultra Breeze hood, added OEM parabolic mirrors and RH aspherical mirror, MB grill conversion.

What is being called a momentary switch is just one way to connect the battery banks together.  The real reason for the "charge solenoid" is to connect the battery banks together when the engine is running.  This allows the alternator to charge both sets of batteries then driving.  The easiest way to test the charge solenoid is to start the engine and measure the voltage on both large terminals on the solenoid.  The voltage should be the same with the engine running.  Any mechanical switch being subjected to large currents will fail with time--some sooner than others.  Replacing this solenoid is common enough that many of us carry an extra.  The White Rodgers is a superior solenoid to what is found on most (especially older) rigs.  But it costs $50 or so not $15.

wae said:

To put a bow on this one for future searchers:. The new isolator linked above has solved the issue.

Click to expand...

The Cole-Hersee 24213 is almost universally recommended for a replacement in this application. It is rated at 200 amp continuous, and has a silver-tungsten plated contact disc in it, unlike the plain bare copper one in the original cheapie relay installed by the RV manufacturer. WIth the OEM relay, its not IF, but rather WHEN the solenoid will fail.

Charles

You keep saying you have continuity across the two posts. How are you measuring continuity across the two posts when you still have the battery banks hooked up? To measure continuity across the two posts, you need to have both battery banks disconnected. You need to be measuring the voltage on each side of that solenoid. Not running or being plugged in, measure the voltage on both sides. May be different voltage depending on the state of charge on both batteries. Start the coach, measure the voltage again, should be different, the chassis battery should be getting charged by the alternator. Toggle the switch for the solenoid, battery voltage should be the same on both sides if the solenoid is working. Shut it down.

Now plug the coach in to shore power, check the voltage on both sides again. The house battery SHOULD be charging at this point, and should read a higher voltage than the chassis battery. Throw the switch again and the chassis battery should be equal to the house battery.  If it is working correctly.