Battery isolator dual batteries both dead? help

[SevenThree91F250]

Hey please link if there is an other thread about this I tried to search and could not find.

A few weeks ago I unscrewed my battery isolator from where it was mounted and just left the screws out. Havent had any problems until today. I am new to all this electric circuit stuff but from research I found the alternator is supposed to go to the isolator and it charges up both batteries while running, a house battery and engine battery. Well both of my batteries are dead after jumping my truck earlier today and giving it a good 15 minute drive so I am guessing the alternator or isolator isn't working. Do you think I could have broken the isolator by unscrewing it and it jiggling around? Do you think it could just be a loose wire from the alternator? I also read it might just be a ground wire messed up or something but it started up fine this morning and all of a sudden it wouldnt start up until I got it jumped and drove it home, now it wont start and both batteries are at 12.0v. Thank you

Edit: Also i think my alternator is warm even after being shut off for hours. Is there a short in the alternator maybe?

 

[IDIBRONCO]

If the alternator is warm after sitting like you say, then it's probably bad. I think you guessed correctly about the short. That's probably what is draining the batteries. It also may not be charging enough. Just because the batteries are at 12 volts, there still may not be enough amperage in them to start the engine. You can test for a battery drain. Fully charge the batteries and leave them disconnected for a few days. Then test them again. If they're still charged, then you do have a drain on your batteries. If they aren't still pretty close to being charged, then your batteries are bad.
I'm having trouble picturing your battery set up in my mind. These normally have two batteries for starting. Having a house battery and an engine battery doesn't make much sense to me. This is going off of the 1991 F250 in your screen name.

 

[SevenThree91F250]

If the alternator is warm after sitting like you say, then it's probably bad. I think you guessed correctly about the short. That's probably what is draining the batteries. It also may not be charging enough. Just because the batteries are at 12 volts, there still may not be enough amperage in them to start the engine. You can test for a battery drain. Fully charge the batteries and leave them disconnected for a few days. Then test them again. If they're still charged, then you do have a drain on your batteries. If they aren't still pretty close to being charged, then your batteries are bad.
I'm having trouble picturing your battery set up in my mind. These normally have two batteries for starting. Having a house battery and an engine battery doesn't make much sense to me. This is going off of the 1991 F250 in your screen name.

Well thats just what I read about when I googled dual battery isolator. they said the dual batteries work in parallele to start the engine but then the extra battery is for the accessories such as radio and what not. Im no expert. I might have been wrong about the alternator still being warm because the rest of my engine was a little warm I think from the sun. but now the batteries are reading below 12.0 like I think there is a parasitic draw somewhere. I just watched Chrisfix video on diagnosing alternator and parasitic draw. I need to buy a battery charger to know for sure. It is stupid though because it started up good twice this morning then my last stop is when it totally shut down. The batteries were still reading 12.7 and it would barely crank, when I got a jump from my other car it started right up. I drove it home and let it sit for an hour or 2 and tried to start it again and discovered the batteries are sitting at like 12.0 and then I just measured again they are like 11.94


Edit: also guess i need to check all grounding connections everywhere there is so much dirt build up everywhere but I still dont get why it was all of a sudden maybe messing around with my fuse box on the inside of the cab did it

 

[IDIBRONCO]

Well thats just what I read about when I googled dual battery isolator. they said the dual batteries work in parallele to start the engine but then the extra battery is for the accessories such as radio and what not.

Generally, our trucks don't have a battery isolater.

 

[CDX825]

One of the diodes in the alternator is bad if its staying warm after shut down.

I'm not sure why you have a battery isolator either. Is this an RV setup?

 

[G. Mann]

If I understand exactly what you did, you unscrewed the battery isolator and let it hang?

I'm betting when you dismounted the islolator, you removed a necessary ground for that piece, which is part of the charging circuits as it is wired in... thus, it's missing it's ground, so it is not switching internally to isolate as it should and that is causing house batteries to draw energy from start batteries....

You need a schematic for the isolator and determine if it's wired in correctly, then decide what you did to change that wiring.

Was it working before ? and, Why did you change anything if it was?

 

[Cubey]

Generally, our trucks don't have a battery isolater.

It's probably a generic solenoid like this.

You must be registered for see images attach

12v tied to key-on goes to the small pole, starting batteries on one side, batteries to be isolated on the other. It passes alternator current to the extra batteries when running, and isolates them with key-off. That's what RVs used to get, and it's a cheap universal part. The one my IDI RV went bad, but it just quit activating, rather than sticking on and failing to isolate the house batteries from the starting ones.

 

[Cubey]

If I understand exactly what you did, you unscrewed the battery isolator and let it hang?

I'm betting when you dismounted the islolator, you removed a necessary ground for that piece, which is part of the charging circuits as it is wired in... thus, it's missing it's ground, so it is not switching internally to isolate as it should and that is causing house batteries to draw energy from start batteries....

That's opposite from how they work. It would never link the batteries if it lacks ground, since 12v being applied is what activates it to link the batteries. Remove ground or positive and it will deactivate/isolate, unless it's stuck "on" due to failure.

 

[SevenThree91F250]

If I understand exactly what you did, you unscrewed the battery isolator and let it hang?

I'm betting when you dismounted the islolator, you removed a necessary ground for that piece, which is part of the charging circuits as it is wired in... thus, it's missing it's ground, so it is not switching internally to isolate as it should and that is causing house batteries to draw energy from start batteries....

You need a schematic for the isolator and determine if it's wired in correctly, then decide what you did to change that wiring.

Was it working before ? and, Why did you change anything if it was?

Yes it was working before. I unscrewed it because I thought maybe there was some antifreeze underneath after my hose blew off the engine so I cleaned it up trying to get it started, so I unscrewed the isolator from the chasis. But it was still resting on the little shelf spot. didnt realize that was grounding it but shouldnt it have been grounded to the solenoid via negative wires? anyway I just sold the truck because I wasn't trying to deal with it anymore

Edit: I got the truck started back up after charging the batteries. While it was running I put the volt meeter on the terminals and it didnt increase over 12.8 so maybe the alternator just gave out or it was the ground thing you were talking about, either way I sold the truck, thanks for the advice from everyone.

 

[SevenThree91F250]

Generally, our trucks don't have a battery isolater.

It looked something like this


https://www.waytekwire.com/item/800...85581968864693&utm_content=EGIS- Fuse Holders

 

[CDX825]

I'm still not sure why you have an isolator on your truck. Guys will run them when they have a camper to charge the camper battery and keep it isolated from the truck batteries. But there is no reason to keep the truck batteries isolated from each other.

 

[Cubey]

It looked something like this


https://www.waytekwire.com/item/80067/Sure-Power-12023A-Mult-Battery/?msclkid=d9f9c4ed0f3f17927e2aa465b75596ed&utm_source=bing&utm_medium=cpc&utm_campaign=BSHOP-EGIS-Mobile-Electric-B&utm_term=4585581968864693&utm_content=EGIS- Fuse Holders

Ah, the fancier kind.

Do you have a gen1 alternator on the truck? If so, make sure your 2 wire plastic connector has a good connection. The plastic spring on the connector is weak/bad on my RV's, so I used a zip tie under the spring part and that makes it stay when pushed in. It was backing itself out when running, making the alternator not activate.

 

[Cubey]

I'm still not sure why you have an isolator on your truck. Guys will run them when they have a camper to charge the camper battery and keep it isolated from the truck batteries. But there is no reason to keep the truck batteries isolated from each other.

Maybe someone had a slide in or towable camper that they used it to charge the house batteries from.

 

[SevenThree91F250]

Ah, the fancier kind.

Do you have a gen1 alternator on the truck? If so, make sure your 2 wire plastic connector has a good connection. The plastic spring on the connector is weak/bad on my RV's, so I used a zip tie under the spring part and that makes it stay when pushed in. It was backing itself out when running, making the alternator not activate.

Yeah the guy I bought it from said they used to have a hot tub in the back of the truck. I sold the truck today. Yeah I noticed that plastic thing did not look very reliable, it could have been that exciter wire wasnt working. Oh well it is gone and maybe one day I can buy another truck to work on