Chassis batteries

[BCRacing24]

If you have 14.1-14.4v at the chassis battery terminals while engine is running your alternator is working fine.....

[okcnewbie]

Originally Posted by babybeaver

I am experiencing battery drain on my chassis batteries. 2000 beaver coach. Appreciate any ideas. Just bought two new batteries last week at camping world, dead today??

You have two new "chassis" batteries?

Have you fully charged them yet?

Have you used your meter in series with the positive lead to check the draw?

[twinboat]

My thought is you have bad or loose connections on the batteries.

#1, It didn't start, without boost. Low current thru connections.

#2, Your alternator did not sense true voltage of batteries and started overcharging.

Low batteries slowly climb to 14 volts as they charge. That takes an hour or so, from 11 volts.

#3, Always look where the last guy worked. Even yourself.

[Mr_Fixit]

The only thing I would note here is a good many alternators immediately jump to 14 volts or slightly more. But I agree with what Twinboat posted. Anytime I fix something and it doesn't work, the first place I check is where I worked last.

Steve

[Smitty77]

Bad new batteries do happen too.

Best,
Smitty

[Mr_Fixit]

For sure, but two at the same time? The odds seem long.

Steve

[twinboat]

Originally Posted by Mr_Fixit

The only thing I would note here is a good many alternators immediately jump to 14 volts or slightly more. But I agree with what Twinboat posted. Anytime I fix something and it doesn't work, the first place I check is where I worked last.

Steve

An alternator can not jump to 14 volts charging a low ( 11.7 volt ) battery bank.

An alternator will output high amps in an effort to reach the voltage regulators, set point of 14 volts on a deeply discharged battery.

Sure they will reach 14 volts soon after starting an engine but that's because the battery has only been slightly discharged.

I believe the OPs alternator was seeing the fully charged "house bank" and not the start batteries, causing it to cut back its output.

[Mr_Fixit]

Need to tell my Ford dually that. Let me elaborate as I don't want to sound flippant. On my dually, batteries so dead I can't start it, have never seen less than 13.8 volts momentarily, but output is virtually constant at 14.1-14.2. Given the alternator is "smart charging" I am assuming amps are being regulated at a higher voltage, but I have never tested that using my clamp meter. Since it all is working, I don't believe in fixing what isn't broken.

I love electricity and given the option, would never troubleshoot anything else.

Steve

[soneil422]

Originally Posted by BCRacing24

If you have 14.1-14.4v at the chassis battery terminals while engine is running your alternator is working fine.....

This is not entirely true. I just changed the alternator on my Powerstroke truck. While at idle, the alternator would put out 14.4v. The truck never had a dead battery. The alternator light would flash while under load and the light would go out at idle again. Went to the auto store for battery and alternator check. They said everything was fine. I asked to test again while holding the throttle wide open. Parts guy checked it again and while under higher rpm's, the diode was dying and turning the charge off. Bad alternator. Replaced it and all is well, charges at 14.4v and alternator light no longer is flashing while under high rpm's.

This time it payed to check it more than once. I have never seen an alternator good and bad at the same time. First time for everything.