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Isolator/Alternator/Battery Issues

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Hi Everyone,

I'm a newbie to the RV thing and I recently went in on an 84 Huntsman with a friend which we picked up in NY and drove to CA. I'm quickly falling in love, but on her maiden voyage across the country we ran into a few electrical problems...

It started with us having problems keeping the coach battery charged, then over the course of a couple days the electrical system was on the fritz then eventually the alternator went out, engine stalling at low RPM, battery and brake dash lights on. A new alternator seemed to fix the problem and got us to CA where I've since done a quick and dirty investigation. The battery isolator (3 terminal) is charging the chassis battery but not the coach battery: 14.5 V across chassis battery, 11.9 V across the (probably bad) coach battery.

My theory for why this happened:

- The coach battery was damaged after sitting around for years with infrequent charging (the RV went through ~5 years of very little use before we got our hands on it)

- We killed the battery for good after a couple charge cycles

- The dead coach battery started putting a big load on the alternator causing it to overheat and burn out

- At some point one of the diodes in the isolator also burnt up due to the high load

Does that make sense?

I have also read a few other threads about battery isolators and it seems like "Toyota RV's need a 4 terminal isolator" is a common theme, but the isolator in there is a 3 terminal. Could that be part of the problem? Do I need to replace my old 3 terminal with a 4 terminal? I still don't fully understand why the 4 terminal isolators are preferable.

My other worry is that some other short/electrical issue caused the alternator to go in which case replacing the battery and the isolator won't actually fix the issue.

Any and all help is appreciated,

John

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I'd start by fully charging the coach battery with a battery charger, if it'll take a charge. Then I'd use a multimeter to see what's going in to and out of the isolator with the engine stopped and running. There's often a circuit breaker or fuse installed to protect the coach battery.

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The 4 terminal solid state isolator is not a preference it is the only way you'll get it charge unless some one has put some thing other then a Toyota alternator on it. The solenoid type does have 3 wires one for each battery and a smaller one that goes to a power source that comes on with the key (no diodes inside). They are different animals but they are both isolators. Like Derek said get your coach battery charged and load tested first and see what happens.

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Although the solid state isolator has advantages over the mechanical solenoid, The Solenoid (the three wire relay) will be just fine in most situations.

If I ever need to replace mine, I'll probably go with the solid state., but for now, the mechanical its OK.

Anyway, if you know how to use a voltmeter, measure the voltage at the truck battery, and the coach battery. (with the engine shut off)

Make sure the coach battery is OK, i.e no shorted cells, no signs of swelling, fluid level OK. f the battery had internal shorts, this could have blown line fuse,it should not have fried the alternaor.

OK, If you know the Battery is OK,

Now start the engine and then measure them again, Voltages should be in the upper 13.5 - 14.5 volts on both batteries The voltage on both batteries should be almost identical.

If the truck battery is OK, but the coach battery is down around 12.0, then the isolator solenoid is either not energizing, or you have a defective breaker/ fuse.

Probably start by measuring voltage on both sides of the isolator with the engine running. If you see a big difference, then either the isolator isn't energizing, or the isolator is defective.

On my Dolphin, there are actually two fuses, one on the truck firewall, just before power enters the isolator (trace the wires from the isolator and you'll see the fuse/breaker.

The other is mounted to the ouside of the coach battery box, need to remove the seat cushion and seat bottom to see it.

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After a couple days waiting for a new fuel pump last night I was able to fire up the engine again…

First of all, my isolator has 3 terminals but is solid state (big and blue, mostly a heat sink) and is aged to the point where the labels have worn off and the terminals are pretty corroded.

At the moment I have no easy way to charge my dead battery, but I did wire another good spare battery in place of the coach battery and at the isolator I measured:

12.5 V @ coach battery terminal (coach battery voltage)

15 V @ truck battery terminal

15.5 V @ alternator terminal

@ the truck battery I measured 14.7 V

Then I also continuity checked the isolator and got an open (in both directions) between the alt and coach battery terminals, but got continuity between the alt and truck battery terminal. This sounds to me like a burnt out diode in the isolator.

So I think I should pick up a new 4 terminal solid state isolator and run a few new wires. At the moment there definitely isn't a fuse/CB between the isolator and the coach battery, is it a good idea to add one there?

I'm still wondering why the 3-terminal isolator worked in the first place? Different type of alternator?

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What are the readings on the three terminals with the truck running, and the truck OFF.

Be aware, if you change from three wire to four wire, this will require a significant modification to the wiring. I would stick with what you have.

My initial thought is that the isolator is bad.

Heres a PDF file from SurePower that might help.

http://www.surepower.com/pdf/180012n.pdf

At the moment I have no easy way to charge my dead battery, but I did wire another good spare battery in place of the coach battery and at the isolator I measured:

12.5 V @ coach battery terminal (coach battery voltage)

15 V @ truck battery terminal

15.5 V @ alternator terminal

@ the truck battery I measured 14.7 V

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With it OFF both batteries are ~12.5 V, which is also what's measured at the isolator terminals. Of course this is with the spare battery not the original dead coach battery.

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Does it look like this??

http://www.rvpartsco...m/70AmpIsolator

Shop around, you can pick these up for under $30. If your measurements are indeed at the Isolator terminals, then Start shopping, looks like the Aux battery side of the Isolator is blown out.

As for differences between three and four wire.

Review the PDF file from my ealier post, Pay particular attention to the "Special Instruction for Toyota, Honda's, and Imports".

Is your three wire original, or did someone attempt to install it, and it has never worked correctly?? Thats the question you'll need to answer by tracing the wiring.

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Does it look like this??

http://www.rvpartsco...m/70AmpIsolator

Shop around, you can pick these up for under $30. If your measurements are indeed at the Isolator terminals, then Start shopping, looks like the Aux battery side of the Isolator is blown out.

As for differences between three and four wire.

Review the PDF file from my ealier post, Pay particular attention to the "Special Instruction for Toyota, Honda's, and Imports".

Is your three wire original, or did someone attempt to install it, and it has never worked correctly?? Thats the question you'll need to answer by tracing the wiring.

Looks exactly like that.

The new alternator looks to me like a Nippondenso, but I have no idea about what the old one. I'm pretty sure the old isolator worked at one point, but that was also before the new alternator was installed. My worry is that my new alternator won't work with the 3 terminal isolator.

If I go with a 4 terminal it looks like I only need to run one new wire with a 6 amp breaker between the E terminal of the isolator and the ignition wire in the alternator harness.

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Looks exactly like that.

The new alternator looks to me like a Nippondenso, but I have no idea about what the old one. I'm pretty sure the old isolator worked at one point, but that was also before the new alternator was installed. My worry is that my new alternator won't work with the 3 terminal isolator.

If I go with a 4 terminal it looks like I only need to run one new wire with a 6 amp breaker between the E terminal of the isolator and the ignition wire in the alternator harness.

That is correct it's marked "ign" and I believe it's red it will work fine, if it's a ND it needs that wire. If the isolator is showing open both directions on the coach side the diode is toes up. The missing wire very will could have been the demise of your alternator the open diode could have been reversed battery connections at some point.

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Review the diagrams and double/triple check the wiring, If your confident you can do the 4, then go for it. Otherwise, stick with the three.

Pay attention to the sense and also the IGN. Sounds like you're getting this under control.

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hello,

I am currently working on an 83 huntsman any idea why the ground wire for the vehicle battery has three wires coming off it? Was trying to jump start it and the insulation on the right wore started to burn? Any help would be great

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Poor ground.

 

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