Battery voltage decreases to 10volts - Team Camaro Tech
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post #1 of 20 (permalink) Old Mar 9th, 09, 07:24 AM Thread Starter
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Battery voltage decreases to 10volts

This is an issue that just started happening. I drove the car as usual, parked it overnight and it would not start the next morning.

Battery reads 12.4 volts when tested out of the car. When i connect the battery cables to it, it reads 10.8 volts.

When i try the test light in-line with the negative cable, i get a 'burst' of light then immediately fades to nothing.

I've started reading threads here at work this morning so im looking for things to try when i get home tonight.

When i attempt to start the car, i don't hear the solenoid clicking. The headlights are bright (but i cannot say for sure they are as bright as normally).

My first thoughts are alternator or starter solenoid is doing something to cause it.

Any suggestions? I only have a digital voltmeter at my disposal right now.

Thanks,
Rob

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post #2 of 20 (permalink) Old Mar 9th, 09, 07:32 AM
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Re: Battery voltage decreases to 10volts

I would disconnect any aftermarket electronics and then see what is happening with the test light again.

As I read this thread and symptoms, a capacitor is being charged. A capacitor is a direct short when DC current is applied, as the cap charges up to battery voltage, the current becomes less, hence the light goes out.

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post #3 of 20 (permalink) Old Mar 9th, 09, 07:41 AM
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Re: Battery voltage decreases to 10volts

Possible blown Diodes in the alternator or accessory short to ground. I doubt if it's an internal battery short. Yes it could be the solenoid shorting through the starter field coils. I don't think you would have hot wired anything directly from the + terminal of the battery like an audio amp or something.

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post #4 of 20 (permalink) Old Mar 9th, 09, 08:51 AM Thread Starter
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Re: Battery voltage decreases to 10volts

nothing wired direct to battery except:

3-wire alternator ( large red wire to back of alt (via the lug on the starter solenoid) with a pigtail that goes into the small 2-prong clip on side of case).

Battery positive goes straight to starter solenoid.

Relay for headlamps (via fusible link)

I do have a retrosound stereo that has an all the time drain for the clock/settings. But i disconnnected this first and still had the burst of light then nothing.

I installed an AAW classic Update kit along with the new 3 wire alternator when building the car, it has performed flawlessly until this point (approx. 1 year)

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post #5 of 20 (permalink) Old Mar 9th, 09, 09:16 AM
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Re: Battery voltage decreases to 10volts

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Originally Posted by RockinRob View Post
still had the burst of light then nothing. Rob
Find the reason for the burst of light and the problem has been found.

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post #6 of 20 (permalink) Old Mar 9th, 09, 09:35 AM Thread Starter
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Re: Battery voltage decreases to 10volts

If there was just a burst of light, would that be enough to drain the battery overnight?

what do you make of the battery reading 12v with no cables connected and then 10v as soon as i connect the cables?

Im no electrical genius, so im fishing for stuff right now. I will look at it tonight when i get home and start by pulling fuses like all suggest.

I did put a battery charger on it last night and it only took like 2 minutes before it read it was fully charged.

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post #7 of 20 (permalink) Old Mar 9th, 09, 09:36 AM
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Re: Battery voltage decreases to 10volts

Quote:
Originally Posted by RockinRob View Post
Battery reads 12.4 volts when tested out of the car. When i connect the battery cables to it, it reads 10.8 volts.
That kind of voltage drop is what I see when I hit the starter...what is that, 150-200 amp draw?

Disconnect the power wire from the junction block behind the battery, check voltage, no change that's not it. Disconnect alternator, check voltage, etc, etc...until you find it.

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post #8 of 20 (permalink) Old Mar 9th, 09, 12:21 PM
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Re: Battery voltage decreases to 10volts

Quote:
Originally Posted by RockinRob View Post
If there was just a burst of light, would that be enough to drain the battery overnight?

what do you make of the battery reading 12v with no cables connected and then 10v as soon as i connect the cables? Rob
A battery with no cables connected, should have a lot of potential, just like a garden hose with your thumb over it - lots of pressure, but going no where, as in no volume.

Now, connect the cables, current (volume) flows, pressure goes down.
Release your thumb from the hose and water flows, but pressure has dropped. Place your thumb over the hose and feel the hose grow as pressure builds up.

I would say either the charging system is not outputting enough current or voltage, either one, or the battery itself does not accept a charge.

If you have a battery on an external charger and the voltage is ever over 16 volts as the charger front panel ammeter shows maybe a couple of amps, then battery needs replacing.

If you have an DMM, set it up for current monitioring and with nothing on, OE equipment, 1 or 2 milliamps will flow. Aftermarket stereo head/tuner with clock and station memory, no more than 100 milliamps.
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post #9 of 20 (permalink) Old Mar 9th, 09, 01:00 PM Thread Starter
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Re: Battery voltage decreases to 10volts

Thanks guys, I'll be looking into it tonight when i get home, i'm sure i'll post back with more questions.

thanks again for all the help.

Rob

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post #10 of 20 (permalink) Old Mar 10th, 09, 06:21 AM Thread Starter
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Re: Battery voltage decreases to 10volts

Update: I've narrowed it down to my ignition switch or starter. I will be digging in again tonight.

Anyone know how to test the ignition switch?

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post #11 of 20 (permalink) Old Mar 10th, 09, 01:50 PM
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Re: Battery voltage decreases to 10volts

This is a common issue on old vintage cars with orginal looms...including my 69...
Quick soln is a install a relay on the firewall just above the starter motor...From memory its the purple wire....
As wires age they get resistance...u may find somewhere in the loom the purple wire shows signs of being hot.

The easest way to check is use a long loop temp wire (run it out the window) from the ign to starter by passiing the loom wire.

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post #12 of 20 (permalink) Old Mar 11th, 09, 05:18 PM
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Re: Battery voltage decreases to 10volts

Any bad connection will show a voltage drop accross it when current flows through it. So if you're testing the igntion switch and you see 12.5 volts going in and only 10.5 comming out, you've found a bad switch.

I'm a bit confused about your readings. When you say the battery voltage is dropping to 10. something volts in the car, are you reading the voltage at the battery posts? If so, this indicates a serious short circuit somewhere, or else the battery has very high internal resistance. If you're measuring the voltage somewhere else then you may be finding a bad connection that is allowing the voltage to drop somewhere.

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post #13 of 20 (permalink) Old Mar 11th, 09, 06:41 PM
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Re: Battery voltage decreases to 10volts

Good point, Dave. If you think the ign switch might be bad, it will only show up when its has been used, say for 10-12 minutes of time while current flows through it . This is case when there is a high resistance on the contact points of the switch.

First thing I'd do is to external charge the battery, have dinner, then come back and measure the charging voltage across the battery posts while being charged. if it measures above 16 volts, then battery is bad.

If battery charges up, install it and run the engine. As the battery warms up from charging, less voltage is needed for charging. After 10-12 minutes, I would suspect to see min 14 volts across battery posts. Anything less measured here, as Dave suggests, is a severe short, disconnect the battery post to witness change. Voltage pops up, bad battery - measure the battery cables. Voltage low, either a short in the car or alternator has a low output.

Feel the alt alum case. If hot to the touch, electrical system short, alternator is working its buns off creating current for the demand.

If everything is okay in the engine compartment, meaning you measure the red power supply wire to ground and voltage is 14 volts, good, horn relay buss bar, alt BAT terminal, etc.

Now move into the interior to the fusebox. You will see three spade terminals labelled BAT , IGN, ACC. BAT is supply from the red wire. IGN is from the ign switch, so is ACC, but another ign switch terminal. If BAT & IGN read different, then either a faulty connection to/from fusebox to ign sw or bad ign switch.

After the red supply wire comes through the firewall connector, the red wire continues to the headlamp switch - there is a factory crimp inside the electrical tape for a red wire branched to the ign switch.

So hopefully this helps. With headlights on, and you attempt to start the engine, the headlamps should dim when the starter drive engages and there should be enough power from the battery to start the engine with the lights on. Alternator belt may squeal until battery charge lessens up.

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post #14 of 20 (permalink) Old Mar 11th, 09, 06:52 PM
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Re: Battery voltage decreases to 10volts

I had a very similar problem and it turned out to be my solenoid.

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post #15 of 20 (permalink) Old Mar 12th, 09, 06:33 AM Thread Starter
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Re: Battery voltage decreases to 10volts

I'm still chasing it guys, i have the battery and the starter with me today to take to the parts store to have them test.

Dave, I was measuring at the battery terminals with both the pos. and neg. cables connected.

What I boiled it down to was: I charged the battery and it showed 12 volts, put it back in the car and hooked up the cables. Read the voltage at the battery posts and it still showed 12 volts. Attempt to start car and nothing (but I did hear the relay I have for the neutral safety switch click). Go back out and measure voltage at the battery posts again and now it reads 10v.

So I am guessing that it is either a bad battery or the starter solenoid (I have a mini powermaster starter). I will be stopping by the parts store today to have them test each of those to see if one is the culprit.

I would have done this last night but little did i know that advance now closes at 8:00 PM instead of 9:00.

I'll post back with my results, and thanks to eveyone for chiming in!

Rob

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