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Randomly Discharging Battery


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#1 jseabolt

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Posted 21 March 2011 - 07:46 AM

Hello, this is my first posting. I hope this vehicle belongs here since it's based on a full size Chevy truck. It's a 1998 Chevy 1500 Express "Explorer" conversion van. 1/2 ton, V8 (305 or 350 not sure). Around 120,000 miles. This vehicle belongs to my father and I've been trying to figure out why it discharges batteries for no apparent reason.

He bought this vehicle when it was 2 years old and since then I bet he has put 6 batteries on this thing. Whenever the battery goes dead he will recharge it a couple of times then just take it back and get a new one since it's under warranty.

I'm not so convinced he's getting a string of bad batteries.

It seems the battery just goes dead for no apparent reason. It can be winter or summer. It can sit for 2 months and start right up or drive it one day then the next day it's flat.

Here's what I have done so far.

Since this was a conversion van, the company added some wires that overlapped the side posts with split ring terminals so they were never getting a real good connection from day one. I could wiggle the cables and get the van to start. So initially I thought it was just a poor connection at the posts.

So I got him to get a dual post battery and I got some top post adapters and use them for the added-on wires and use the side posts just for the original cables. I put new bolts in the battery cable connectors, etc.

I have also unplugged the engine bay bulb to rule out the mercury switch.

Well that seemed to work for about a year but then a couple of days ago it wouldn't start.

I did a rudimentary diagnostic on it. With the engine not running, the battery is producing 12.5 volts. With the engine running I'm getting 14 volts at the posts. To me that sounds like the alternator is working properly and the battery does not have a dead cell.

I've been trying to figure out if the battery is going dead from the alternator not working at times or if some component is draining the battery just from being parked.

I asked dad if he has ever seen the voltmeter gauge drop to the red zone. He says at one time or another the gauge dropped to the middle white mark with the headlights on. With a span of 9 to 14 volts that sounds like 12.5 volts (or battery voltage). When I checked this, the gauge never dropped below 14 volts.

Looks to me if this was happening, it wouldn't take long to drain the battery to the point it wouldn't even run with the amount of electrics on a modern vehicle (fuel injection, etc.) He was having randomly discharging batteries on his 76 Chevy truck so I drove it for a week to see if I could figure it out and at times saw the gauge drop to 8 volts with no headlights burning. And all that was pulling power on that vehicle was the radio and ignition coil. That turned out to be a slipping V-belt.

Since I don't normally drive this van, I'm not real sure what's going on with it. So I've tried to instruct him on what to do. Like monitor the voltmeter gauge. I gave him a digital voltmeter and told him the next time the battery goes dead to test the battery voltage and get back with me. Just in case the problem is not actually the starter. I mean you never know, he says the starter is clicking which is normally associated with a dead battery but I just want to be sure the battery is in fact discharged.

I seem to think the battery is being discharged just from sitting. I'm curious if a bad diode in the voltage regulator can drain the battery randomly. Is this possible? I've heard alternators either work or they don't but I'm not so sure.

Just wanted some advice as to how I could go about troubleshooting this problem. I'm thinking about just getting a rebuilt alternator since we have pretty much ruled out a string of bad batteries and a poor connection. A guy at work says unlike the old AC Delcos, the voltage regulators are built into the alternators so replacing the entire unit sounds more like it.

Thanks!
1976 Chevrolet 454 big block trailering special
1968 Ford Fairlane 500
1980 Fiat 124 Spider (turbo)
1987 Yugo 1500 (turbo)
1980 Fiat 131 Brava
2003 Subaru Baja
2008 Mustang GT

#2 Wires

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Posted 21 March 2011 - 08:22 PM

I doubt a guy could get that many bad batteries. :lol:

I'd suspect either a bad alternator, or you have a wire grounding somewhere, or something is staying on when it's not supposed to.

You can swap the regulator in the alternator and see if that fixes it. It's not that hard to do. Does that unit pre-date that cool GM feature that kills power to the accessories after so long? My '00 Chevy did that.

#3 jseabolt

jseabolt

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  • Location:Hawkins County, TN
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Posted 22 March 2011 - 06:57 AM

I doubt a guy could get that many bad batteries. :lol:

I'd suspect either a bad alternator, or you have a wire grounding somewhere, or something is staying on when it's not supposed to.

You can swap the regulator in the alternator and see if that fixes it. It's not that hard to do. Does that unit pre-date that cool GM feature that kills power to the accessories after so long? My '00 Chevy did that.


I'm not sure, I'll have to check. I wonder if it's possible to retrofit this device on earlier models? I'll have to do some research on that.

I've been doing a search and allot of people claim the most common reason for discharging batteries on GM trucks is a faulty switch on the vanity light mirrors. I find that hard to believe. I left the dome light on my 96 Explorer for about 12 hours and it never ran the battery down.
1976 Chevrolet 454 big block trailering special
1968 Ford Fairlane 500
1980 Fiat 124 Spider (turbo)
1987 Yugo 1500 (turbo)
1980 Fiat 131 Brava
2003 Subaru Baja
2008 Mustang GT




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