Low battery reading

[jux]

I have an 86 c10, and recently my battery gauge will read about 10.5 steady sometimes. I have a new napa battery that I don't believe to be causing any issues. It replaced a smaller napa battery about a month before the issue began.

When I have the engine running and it's reading low, when I disconnect the battery and then reconnect it the gauge will read normal. The problem has only been occurring about once or twice a week. I recently moved and cannot find my voltmeter, but I believe the battery is ok and the grounds are fine as well.

I know these oem gauges aren't the best, I was just wondering if anyone else has had this problem. Thanks!

And I forgot to mention, all electronics work ok and the truck starts fine every time.

 

[chengny]

The battery is basically only there to provide power to start the engine. Once the engine is running the alternator takes over the job of supplying power (and recharging the battery so that it can crank the engine the next time). The battery does provide some degree of additional power during times of heavy load but it is mostly the alternator that provides the juice.

If you are getting periods of low voltage (and at other times the gauge reads 13+) - trust the voltmeter.

How old is the alternator? Fluctuating voltage is often a sign that the brushes are just barely keeping contact with the slip rings.

 

[jux]

Thanks Chengny. I realize the job that the battery has is mostly to provide start up power. I did not word it very well, but when I disconnect the battery while running, the power shoots up to 13+ (running only on alt). It stays around 13 when I reconnect it. Would that fit in the diagnosis of a dying alternator?

I don't have any idea how old the alternator is.

Thank you very much!

 

[jux]

Ok, I just came back from advance auto. They checked my system:

Battery-
Voltage: 13.08v
Measured: 965 CCA
Rated: 850 CCA
Temp: 83 F

Results: GOOD

Starter-
Voltage: 11.10V
Amps: 0.1A
Time: 1.8sec

Results: LOW CRANKING AMPS

Charging system-
No Load: 14.54V, 0.1A
Loaded: 14.49V, 0.1A

Results: OUTPUT TEST NORMAL



So, I have low cranking amps. Battery is a month old Napa Prem. Starter is a re-manufactured Napa, about a month and a half old.

Can any of you squarebody wizards point me in the next logical direction? I am about to go out to check all connections.

Thanks to all!

 

[chengny]

If the brushes are barely making contact with the slip rings sudden load changes can momentarily get them back in contact. The rotor moves a bit with aplication or loss of load and the carbons will re-seat just enough to pass power.

Taking the battery in oand out of the circuit could be causing them to set back down again but then they eventually lose contact again.


Here is my advise: let things be as they are now.

If it is the alternator the problem, will soon become evident by lower voltages for longer periods of time.

At some point the brushes will not make any contact and you will be living off the battery.

When that happens the system voltage will start to drop off and continue till the batttery is dead - if you let it get that far.


Sometimes applying a heavy load will make the alternator output drop dramatically if the brushes are on their last legs. Try making the scenario happen by turning on the headlights and wipers at once.

 

[jux]

Ok, I will monitor it for now. Yesterday I did notice that when the headlights and turn signal were on, when I turned the heater fan on there was a sudden ~2 volt drop.

If it is the alt, I have a few rookie questions:
Do I have to replace it with one of a similar amperage?
What are decent alt. brands?
Would it be worth it to order a Bosch or Hitachi?
Re-manufactured alts good or no good?

Thank you very much Chengny, you have been very helpful!

 

[chengny]

Rock Auto has some brand new (not reman) 78 amp ACDELCO's for a real good price - $73 with no core

ACDELCO Part # 3351094 {#88877304} NEW UNIT
GENERATOR WITH A/C; REGULAR CAB; 4 WHEEL DRIVE; DELCO-12SI 78AMP
GENERATOR WITH A/C; CREW CAB; 4 WHEEL DRIVE; DELCO-12SI 78AMP

If I needed an alternator, I would be all over that.

When you buy an internet alternator be sure it got the correct style pulley for your belt. But it's not a deal breaker if the style is wrong - just re-use your current pulley.

 

[jux]

Thanks! Probably a stupid question, but would that alt be ok to use in a non ac truck? and I have a serpentine belt, is it hard to switch the pulley without marring it?

Thanks again

 

[chengny]

Oh yeah, it will be fine. It just has the capability to provide a bit more power if the truck has certain accessories.

Some accessories - like an oversized blower (as in an A/C truck), a massive sound system, a winch, etc - can create a significant drain on the electrical system.

An oversized alternator can meet the demand created by those add-ons during periods of peak loads.

But if the truck has no extra electrical components - like yours - a higher rated alternator just lives an easy life. Matter of fact, due to lower operating temps and the use of heavy duty components, it will most likely last much longer than a standard unit.

 

[jux]

Thanks for all your help chengny! The old alt was on it's dying breath so I picked up a reman (ALL wear parts replaced) delco from (gasp) auto zone. 92 amp for $77 after military discount and core return. Runs great now, thanks.

On a side note, the first one they gave me had the back plate (don't know if there is a term) of the alt 180* backward so the rear mounting bracket didn't line up. Good thing I was doing it in the parking lot so I just went back in and they swapped it.

Funny thing is, before I paid for the faulty unit, I asked the manager "do you have many of these come back?". Shook his head "nope, almost never".

Just thought it was funny.

 

[jux]

Bad news for me, I'm still producing low current. I had 13 amps until I got to work, then it dropped to 10.5 and would sometimes go up to almost 13, then back down again...

The next thing I can think of are the wires to the starter that got pretty hot near the header before I got a heat shield around the wires. I remember them feeling putty-like and soft (also not very thick).

Does anyone have any suggestions about what to look for next?

Thanks

 

[ScottyB]

Hot wires mean something is drawing current. Are these your starter wires that are staying hot? The wires may be shot but it sounds like your starter is still calling for power.

(I'm sure someone will be along soon to say I'm on the wrong track though. Damn rookies!)

 

[jux]

Thanks for the reply. I just finished doing the "big 3" wire upgrade. Still losing power, I'm down to around 10-10.5 on the gauge.

I just found my multimeter, does anyone know what to check and what I should be looking for?

This could be just another issue altogether, but on my way home after upgrading the wires I would feel the truck surge. As in acting like I'm pushing the gas pedal up and down slightly. Could this be related?

This issue is driving me nuts, thanks so far for the help.
One of these days I'll get'er "squared" away.

 

[towjoe]

I have a 80 K30 that reads low voltage when it runs by the gauge. when I check it by the charging tester it checks fine. I think the gauge in dash is shot in mine, truck only has 430k miles on it tho.

 

[jux]

An update:

Took the c10 to my mechanic, he found that the charging system is in great working order and that it must be my gauge malfunctioning. I hope he is right.

The stumble I was recently experiencing was just a fouled spark plug.

Thanks to everyone that helped, and a special thanks to chengny!