Battery Isolator - doing exactly what it should shouldn't?

[toyotaspeed90]

So this is a relatively new vehicle to me. The wiring is somewhat nightmare'ish... both from the factory and from what others have done.

1984 E350 Fleetwood Jamboree.

2 batteries, an isolator, and 2 solenoids.

Battery on the passenger side appears to be mainly a starting battery for the engine. This is a standard battery for starting. It runs directly off to the starter solenoid and has 2 other wiring connectors on that same post as well (guessing mostly for the chasis needs).

Battery on the drivers side, just replaced, seems to be mainly for the 'house' and the generator. This is a deep cycle battery.

The alternator feeds directly into the isolator.

The isolator is a 3 post. 1 wire feeds to a solenoid on the passenger side. The other feeds into a harness, with a quick look can't tell where too.

The solenoid on the passenger side, on the same post of the solenoid that the isolator is connected to, feeds off to the drivers side battery post.

The generator is wired directly to the deep cycle battery (driver side)

When the engine is running, generator off:
14.4V is read at the center post of the isolator and at the starting battery.
12.28v is read at the other post of the isolator and at the deep cycle battery.

Generator running, engine is of:
13.8v is read at the deep cycle battery
12.(something)v is read at the starting battery

So - in looking online this isn't that atypical of a set up (solenoid and isolator)... I've read that there should be 14.4 on both sides when the engine is running.... but have also read that the purpose of the isolator is to keep the deep cycle separate from the starting battery in the event the deep cycle has voltage spikes and/or running it too low - so you can still start the engine.

So, as the title says.... is my isolator doing exactly what it should be doing or exactly what it shouldn't be doing?

[Grillmeister]

Glad you have everything figured out. I must have pulled out a 100' of wiring from the rats nest under the hood and dash. I still have stuff under the dash that I don't even know what it is for!
Most corrosion I ever saw on a vehicle, especially those ridiculous factory connection plugs. Don't even get me started on the vacuum hoses :E

[toyotaspeed90]

Actually it isn't the isolator, as I found out later.

The solenoid isn't receiving a switched 12V.... if I supply 12v the solenoid switches on and all terminals on the isolator show a high 13v reading.

I've got some wire chasing to do... I doubt it's something as nice and simple as a blown fuse.... none of the glass fuses in the fuse box are bad... there have been numerous pieces of wiring that have been done horribly, for instance:

3 wires for a ground... each have an eyelet... then they were bolted together with a 1" screw, dangling above the battery... enough tape to cover the eyelets but the screw was exposed - with the vibrations it actually tore through the sheathing of one of the grounds connected to it.

Another was.... all within 10" of the battery..... eyelet, way oversized home wiring nut, fuse holder, way oversized home wiring nut, butt connector with 1/8" of wire sticking out on either end (stripped back too long).

I've gone through and replaced all of the additional fuses someone else added with new wires. I've also gone through and replaced many of the shorter run wires along with many of the longer wire connections (due to corrosion).

Today I plan to pull the starter battery out and start going through some of the wiring on that end to see what's actually going on.

For the weekend (plan to head out mid afternoon tomorrow) if I haven't resolved the issue I will bypass it and use a switch with a relay (or something) to ensure both batteries charge while driving.

I do appreciate the comments, though.

[ScottG]

I agree the Iso has died and in the most common of ways.
I was warned by a mechanic friend that diode based iso's are problematic. So I bought one that was rated at 160 amps for my 120 amp alt. It still died on me one night with the family on board and tt in tow. I swapped it out for a solenoid operated relay (Napa $25) and never had another problem.

[YC_1]

Quote: When the engine is running, generator off:
14.4V is read at the center post of the isolator and at the starting battery.
12.28v is read at the other post of the isolator and at the deep cycle battery.

Your isolator is defective. You should only have a .7 volt difference between the center post and either of the outside posts. Using a voltmeter with the wires off will fool you. Without a load on it you not get an accurate reading. To demonstrate that just put one lead of your voltmeter on the negative battery terminal, hold the other lead in your fingertips of one hand and then touch the positive side of the battery with the other. The meter will show voltage. Not enough current flow to feel or drive an electronic device but enough to drive a meter.

Re-reading the voltages leads me to believe the previous person had an issue with the isolator and bypassed one section already. That is why you have the full alternator voltage on the starting battery. Could be they are now trying to use the solenoid to tie the house battery to the starting battery.And you said that in your last post. So as you suggest, finding the lost 12 volts could be as simple as a blown fuse.

You could replace the isolator but finding the missing 12 volts should be an inexpensive fix.

[ksg5000]

My 92 Jamboree is setup as follows.

The coach battery (drivers side) is isolated from the chassis battery (passenger side) via a 3 prong battery isolator solenoid located on the fire wall. When the ignition key is turned 12 volt power is supplied to the small middle prong of the isolator which energizes the solenoid (it makes a loud click) which connects the two batteries.

Does the solenoid make a "click" when you turn the ignition key on? These solenoids tend to "stick" as they get older - sometimes rapping it with a hammer is all it takes to fix but they aren't expensive and replacement isn't hard.

[RoyB]

You have discovered why the DIODE ISOLATORS are not used anymore for charging DEEP CYCLE batteries. The high current diodes in the ISOLATOR have a .7VDC voltage drop across them and when it is really important to have 14.4 VDC for charging the deep cycle batteries and only getting 13.7VDC due to the voltage drop then it will be the difference of three hours charge time to more than twelve hours charge time to get the deep cycle batteries to their 90% charge state.

Today they use smart solenoids instead of diode based isolators to get the job done. The diode based isolators work great with your truck standard start battery but not so good feeding a deep cycle type battery unless you got a lot of time on hands to get it charged.

This is probably why you are finding both an isolator and solenoids in your setup.

just my thoughts
Roy Ken

[JaxDad]

I'm sure I missed a solenoid somewhere in your description, I only saw one on pass. side.

Regardless, just to be sure we're on the same page, you are sure you're using the correct term "isolator"? As in a solid state block with cooling fins and 3 posts? I ask because it makes for a slightly more complicated system.

Basically it sounds like yours is like this; Alternator output feeds into center terminal of isolator, that splits it to each battery. The solenoid creates a temporary by-pass of the isolator in the case that you need to either start the generator off the chassis battery, or the m/h engine off the house battery.

I say more complicated because all you really need is a "constant duty" solenoid in the positive lead between the alternator and the house battery. The trigger terminal is then wired to a wire that is powered only when the ignition is in the run position. A simple momentary contact switch to close the solenoid at any time it's needed completes the system.

I wouldn't get too hung up on voltages yet, an isolator does just that, the different charge state or condition of two batteries will be reflected in different voltages.

[toyotaspeed90]

Interesting to hear... the deep cycle is brand new (purchased and installed yesterday, was load tested at the battery shop yesterday and passed with flying colors). I'll go plug the system into the house.

I've figured out the problem... haven't figured out why it's happening but that it is.

The 12v switched signal for the solenoid isn't reading voltage when the key is set to on... when running if I jumper the solenoid switch to 12v then I get a high 13v reading (it's cold and this motorhome isn't cold blooded.... a similar issue as I don't think the electric choke is getting a 12v switched signal either) for both batteries....

There's an obvious non original relay under the hood... 3 of the 4 connections are mediocre at best (read, ugly wiring harness & someone who knows enough to get in trouble and not much else)... There's continuity between the relay switched 12v and the solenoid switched 12v.... so will do some wire chasing tomorrow to try and find the problem.

Worst case scenario I can find a working 12V switched and run a new relay for the weekend.

I appreciate the help & responses.

[hmknightnc]

Hard to tell on a 84 Class C chassis but typically that kind of setup will do the following:

Engine on: Alternator, starting battery, and house battery at same voltage, your 14.4 sounds right for an alternator source

Engine Off and using generator/shore power: House battery at converter voltage (13.8 in your case) and engine battery resting (call it 12.6). Typically the converter does not charge the engine battery. You might have a boost switch to help the starting battery by manually connecting your house and starting battery together if the starting battery is low.

Sounds like your isolator has failed is not working (i.e not connecting house to alternator when voltage > than house battery voltage)

Also getting a reading of 12.28 on the house battery at rest is very low (approaching 50%). You need to fully charge that as soon as possible. With a converter operating at 13.8 that couuld take a couple contineous full days. You need to plug in for a while.

[CloudDriver]

From your voltage readings, IMO your isolator isn't pulling in when you start the engine. If it were, the voltage on both large terminals would be the same.

I would expect the generator to only charge the house battery.

I have replaced the battery isolator twice on our Minnie. Disconnect the ground wires from both the chassis and house batteries before replacing the isolator as a safety precaution.

[toyotaspeed90]

ran out again....

pulled the wires from the deep cell (except the generator cable as I just changed that to a post connector and it's extremely tight)...

also pulled the wire from the isolator that runs into the harness...

continuity runs from the isolator wire to 2 similar sized wires that run to the deep cell, but not to the main 4ga cable that runs off the deep cell.

With that wire pulled from the isolator there is no discernible voltage across the isolator. Once I reconnected that cable to the isolator (keeping the other 3 larger wires off the deep cell, but the generator cable still connected) there was voltage across all 3 posts of the isolator.

[toyotaspeed90]

Ran out into the rain to go check...

The other side of the solenoid in which the isolator is connected to... only feeds to the starter battery.

The only thing I can think of... is that that 3rd post of the isolator actually feeds to the deep cycle battery and that the isolator is toast...