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Battery drains over night
#1376480 Wed Sep 09 2020 12:55 PM
Joined: Nov 2005
Posts: 38
5
Wrench Fetcher
I lose battery charge overnight on my 69 c10. Found out there is a 10 ohm resistance from battery + to ground with key off. This resistance went away when I removed the positive lead from the alternator. I replaced the alternator and have same reading, approximately 10 ohms. Is this possibly a bad regulator? What removes the path to ground through the alternator?


Chevy Pete
Re: Battery drains over night
5253chevyman #1376484 Wed Sep 09 2020 01:42 PM
Joined: Jun 2011
Posts: 3,670
E
Shop Shark
Remove fuses one at a time to find leak. Also brake light if lever type.

Ed


'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.
Re: Battery drains over night
EdPruss #1376492 Wed Sep 09 2020 02:41 PM
Joined: Nov 2005
Posts: 38
5
Wrench Fetcher
Thanks Ed, I pulled all the fuses one at a time and still have leak.


Chevy Pete
Re: Battery drains over night
5253chevyman #1376574 Thu Sep 10 2020 01:38 AM
Joined: Feb 2016
Posts: 431
7
Shop Shark
You have a short to ground somewhere or a non-fused circuit that is energized by mistake.


1957 Chevrolet 5700 LCF 283 SM420 single speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto
Re: Battery drains over night
78buckshot #1376578 Thu Sep 10 2020 01:52 AM
Joined: Nov 2005
Posts: 38
5
Wrench Fetcher
thanks 78buckshot. I have tried to find the short and the only thing I found out is when I remove the b+ wire from the alternator, the short goes away. what would happen if I connected the alternator through the ignition switch instead of straight to battery?

Last edited by 5253chevyman; Thu Sep 10 2020 01:54 AM.

Chevy Pete
Re: Battery drains over night
5253chevyman #1376580 Thu Sep 10 2020 02:03 AM
Joined: May 2015
Posts: 2,969
Housekeeping (Moderator) Making a Stovebolt Bed & Paint and Body Shop Forums
An alternator that draws power when not turning has a bad diode in it.
I would take the alternator off and get it tested.
Fix the problem instead of putting a band aid on it (connecting the alternator through the ignition switch).


Kevin
First car '29 Ford Special Coupe
#2 - '29 Ford pickup restored from the ground up.
Newest Project - 51 Chevy 3100 work truck. Photos [flickr.com]
Busting rust since the mid-60's
Re: Battery drains over night
5253chevyman #1376586 Thu Sep 10 2020 02:36 AM
Joined: Feb 2004
Posts: 21,245
H
Boltergeist
Do you have the original equipment alternator with an external regulator, or has the alternator been upgraded to the later internal regulated type? The older system with the external regulator was notorious for diode leaks and the exact symptoms you're describing. I'd recommend trying another alternator before doing anything else. If you choose to isolate the alternator charging wire, don't run the circuit through the ignition switch- - - -use two Bosch-type 60 amp relays wired in parallel and energized by the ignition switch to be able to handle the alternator current without an excessive amount of voltage drop. Even that will be a band-aid fix, however.
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Battery drains over night
Hotrod Lincoln #1376641 Thu Sep 10 2020 04:31 PM
Joined: Nov 2005
Posts: 38
5
Wrench Fetcher
Thanks Jerry and Kevin. Good points. Update on my efforts. I have the original equipment with the voltage regulator. When I measure the resistance with the positive lead on the positive post and negative lead to chassis ground, I read approximately 20 ohms. If I reverse the leads the resistance goes way up. I removed the alternator and now I measure around 30K ohms. I pulled all the fuses one at a time with no change. I disconnected the connector to the regulator and the resistance shows an open. Is it normal to have 30K ohms across the regulator. UPDATE went to parts store and ordered new regulator, keeping my fingers crossed.

Last edited by 5253chevyman; Thu Sep 10 2020 05:46 PM.

Chevy Pete
Re: Battery drains over night
5253chevyman #1376654 Thu Sep 10 2020 07:23 PM
Joined: Feb 2004
Posts: 21,245
H
Boltergeist
Unless you have the battery disconnected, trying to measure resistance in a circuit such as the alternator is a lost cause. There is no telling what sort of reading the ohmmeter will give. You might try disconnecting one of the battery cables and using the "amps" function of a digital multimeter to measure the parasitic current draw with all the circuits turned off. It should be no more than a few milliamps. Half an amp (500 milliamps) would be a ridiculously high drain. If disconnecting the big alternator charge lead stops the battery discharge, the alternator is bad- - - -no matter how many alternators you have to swap until you find a good one. You could probably resolve the whole problem by retrofitting to a 10-SI internal regulated alternator and tossing that antiquated original equipment unit into the nearest scrap metal bin. GM's first attempt at an AC charging system was a pretty weak one in the 1960's, and those units haven't improved with age. The newest rebuilt external regulator alternator you can buy will be around 50 years old. You can buy a brand new 10-SI at any corner auto parts store.
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Battery drains over night
Hotrod Lincoln #1376673 Fri Sep 11 2020 12:02 AM
Joined: Nov 2005
Posts: 38
5
Wrench Fetcher
I do have the battery disconnected. All my readings were with the negative terminal disconnected from the battery. found a nova conversion kit that will work on my truck to convert to a new style alternator. Hopefully all problems will be solved.
Pete

Last edited by 5253chevyman; Fri Sep 11 2020 12:59 PM.

Chevy Pete
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