"Tank" my 91 Crew Cab Dually

chillman88

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That's what I've always been told. I've even seen it happen in golf carts. I know that even with my 1G, the voltmeter will read over 13 volts (can't remember how much) right after I shut the truck off. It will drop back to 12.7 after a time. I do know that batteries can show fine on volts, but still not have much in the way of amps. Since you just shut your truck off and only have a total of 900 CCA, I'd say that it's that time.:cry: If your 3G is working good, it should not overcharge your batteries. It has a regulator for a reason. At least it's summer time and you should be fine running on one battery for a little while. Don't have any extra electrical things (like A/C blower) on until it's running and, of course, get another battery in there before it cools off very much just in case.

Well he was measuring voltage at the batteries, I don't have any real gauges yet :sorry:

I'm going to run the voltage sense wire to the output stud to be sure, it's running somwhere else now, I don't remember. Starter solenoid maybe? Idk it's been a few years.

Check all your cables. Maybe have your starter tested. It’s one of those things that flat batteries will speed the decline of your starter because it has to draw more current to make the same wattage. It just spirals. Same with the starter, if it’s getting weak, it takes longer to start so it’s harder on the batteries.

I'm afraid they would just tell me "yup it spins" I don't think they can load test it. I'll be honest, there have been a few times of impatience and over cranking on my part which I'm sure hasn't helped. I'm considering pulling it apart and looking at it, it is just a parts store reman.

I might be considering a powermaster as one and done to check it off the list though.

Cables look good but can't hurt to clean the grounds up again.
 

IDIBRONCO

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Well he was measuring voltage at the batteries, I don't have any real gauges yet
Last fall, while I was trying to diagnose the bad alternator on my truck, I measured the voltage at the batteries with my DVOM. I only got a reading of .1 volts higher going from post to post on the batteries compared to my volt meter.
 

The_Josh_Bear

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Fast way to tell is to remove the positive from the drivers battery, measure each battery that way. They should be very close-- even a .5v difference is a problem.

Then let them sit overnight like that and test again.

And before all that check your charging voltage if you're worried about them overcharging. Should be 13.8-14.3. Up to 14.5v is acceptable.
 

chillman88

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Fast way to tell is to remove the positive from the drivers battery, measure each battery that way. They should be very close-- even a .5v difference is a problem.

Then let them sit overnight like that and test again.

And before all that check your charging voltage if you're worried about them overcharging. Should be 13.8-14.3. Up to 14.5v is acceptable.

That's a great idea, unhooking them and testing them in the morning. Thanks!

Probably wouldn't be a bad idea to run a headlight off one for 5-10min and retest after as sort of a load/drain test too.
 

chillman88

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Is the factory voltmeter as useless as the rest of the gages?

Blower motor on engine running:

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Blower motor off engine running:

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Seems like it shouldn't drop that far if the alternator is working correctly?


I bit the bullet anyway. Holy crap this thing weighs a ton!

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It is a stud type but I got post adapters. I'd like to rework my cables for the studs eventually though.
 

BrianX128

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Somehow the dash either grounds or gets power through the same wires as the blower motor. When I was messing with mine from my other thread I noticed the factory gauge move like that with both motors but my real volt meter between battery and alternator dropped by .1
 

chillman88

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Somehow the dash either grounds or gets power through the same wires as the blower motor. When I was messing with mine from my other thread I noticed the factory gauge move like that with both motors but my real volt meter between battery and alternator dropped by .1

I considerd that as a possibility, thanks!
 

IDIBRONCO

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Yes, a million times yes. And it's annoying!!!!!
It's so simple to install an aftermarket voltmeter that it's a real shame that more people don't run them. Just hook them to a 12v source and a ground and they work. I think that it's too bad that ammeters are next to useless today since the ones that I've seen are usually only good for around 70 amps or so. They give you a better idea on what your alternator's actually doing right now.
 

chillman88

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It's so simple to install an aftermarket voltmeter that it's a real shame that more people don't run them. Just hook them to a 12v source and a ground and they work. I think that it's too bad that ammeters are next to useless today since the ones that I've seen are usually only good for around 70 amps or so. They give you a better idea on what your alternator's actually doing right now.

Indeed, I would like an ammeter as well but can't think of a good way to install one on a dual battery system. I've seen some that can handle high amperage but can't figure out how to install a shunt properly to accurately capture full system load. My limited understanding says they are supposed to be installed between the ground and the battery.
 

chillman88

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Well I will probably replace the batteries anyway but we'll have to see how they look after sitting unhooked. I'll feel alot better if there's a significant voltage difference after sitting unhooked because I don't see anything wrong.

Charging voltage is roughly 14.20 with no accessories running

Charging voltage is roughly 13.80 with lights on and AC running full blast

Voltage was around 12.68 when I started after sitting all night (fully connected)

I left lights and blower on for a minute after I had shut off the truck. Voltmeter read 12.50. I then unhooked the batteries and tested them. They read 12.91 and 12.94. They have gone up to about 12.95 and 12.98 in the last couple minutes. I'll leave them for at least a few hours and check again.

She's been starting just fine since I bought the new battery. Go figure. Just don't want to put it in if I can't confirm it's the problem.
 

IDIBRONCO

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Indeed, I would like an ammeter as well but can't think of a good way to install one on a dual battery system. I've seen some that can handle high amperage but can't figure out how to install a shunt properly to accurately capture full system load. My limited understanding says they are supposed to be installed between the ground and the battery.
This is completely different, but what I've done in the past (with 1G alternators) was to extend the charge wire that comes off of the alternator. I'd run a 8 or 6 gauge wire into the inside and hook the ammeter inline. Run the incoming wire to one side, the other side would go back into the engine compartment and attach to the spot that the charge wire originally hooked to. Now that I'm older and wiser(?) I do understand that I probably didn't do the fusible link any justice by doing this, assuming that the charge wire is a fusible link like on our trucks. The only time that I had any trouble was on my 1984 Mustang with a CFI 3.8. That was a higher amp alternator and I actually burned out a gauge while driving on a dark, cold, rainy morning while running everything on high.
 

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