Electrical troubleshooting : battery drain

[boyt911sc]

My son's '87 Carrera is having some sort electrical problem causing the battery to drain (voltage loss) over-night. The car would start on the first click after the battery has been fully charged but battery drains power after a day. This happened 3 days in a row so I decided to disconnect the battery ground cable to see if the battery would hold power.

The following day, the battery ground cable was connected and started the car. Started the very first try. Disconnected again the battery ground for the day. Two (2) days later, the cable was connected and started the car again. Car ran fine. Cable disconnected again. On the 4th day, the battery (-) cable was hooked-up and engine immediately ran. The battery seems to be holding its power and even after 4 days.

Today, I removed all the fuses in the luggage compartment except fuse #4 (interior lights, clock, radio, and glove compartment) and fuse #6 (fuel pump), and started the car. It started at the first click.

Other information:
1). I tried to get ampere reading across the fuses with the battery connected to the car and failed to find any. Even at the circuit where the clock is connected (???). Why I was not getting any reading? Bad procedure/technique?
2). The current readings across the battery terminals are both 40 UA (ground cable connected and disconnected).

Question:
1). Should the circuit where the drain is occurring register some amperage?
2). Where should I place the probes (multi-tester) to find the drain?
3). What amperage draw at the battery terminals should I expect on a good, normal, 911 car?

Plan of Action:
1). Install the fuses back one at a time and observe when the battery drain starts to occur. This process would take several days to accomplish.

Any suggestion/s how to get this investigation done efficiently and effectively? Thanks.

Tony

[timmy2]

1. Remove battery negative strap.
2. Remove all fuses
3. Connect your digital meter on the 10 amp DC scale between the negative post of battery and the negative (ground strap)
4. insert fuses one at a time until you see a current draw, write down the current value and continue until all fuses installed.
5. if no measureable current on 10 A scale then switch to the mA scale for each fuse before proceeding to the next one.(Remember to switch back for the next one)

With an overnight drain I'd guess there is close to a full amp of draw on some circuit(s).

A meter needs to be in series with the circuit to be able to read the current flow.(Unless it's a clamp on)

[rfuerst911sc]

Does the car have power seats ? Alarm system ?

[schamp]

How well is the alternator charging? You could have a diode out and the alt trying to run like a motor.

[boyt911sc]

Originally Posted by rfuerst911sc

Does the car have power seats ? Alarm system ?

rfuerst911sc,

The car has power seat for the driver-side only and probably an alarm system (????). I bought the car 3 weeks ago and the owner knew very little about the car. As a matter of fact, he taught he has a 915 transmission (early '87 production) when I bought the car and it turned out to be a real G-50 5-speed transmission. He never used the alarm in 8 years of ownership but it has the alarm switch at the door. I have to inspect the door panel and investigate if the alarm system is active.

Tony

[Etarga]

Aftermarket sound system? Sometimes the amplifiers get hooked up directly to the battery (easy) - so they are on all the time.

[Lorenfb]

The first step in determining a 'draw' problem is to measure the battery current with
all fuses 'in' and every system element 'off' (asleep). The maximum 'draw' should be
less then 30 - 60 ma (.03 - .06 amps). This will allow the battery to adequately crank
the engine for a non-charging condition of about two weeks.

[Joeride9]

Pull all fuses and check for continuity from ground to each fuse block. If you have continuity I think you have a short on that circuit

[wwest]

Originally Posted by timmy2

1. Remove battery negative strap.
2. Remove all fuses
3. Connect your digital meter on the 10 amp DC scale between the negative post of battery and the negative (ground strap)
4. insert fuses one at a time until you see a current draw, write down the current value and continue until all fuses installed.
5. if no measureable current on 10 A scale then switch to the mA scale for each fuse before proceeding to the next one.(Remember to switch back for the next one)

With an overnight drain I'd guess there is close to a full amp of draw on some circuit(s).

A meter needs to be in series with the circuit to be able to read the current flow.(Unless it's a clamp on)

Bit of a correction for step 4. As you insert fuses you might see a short/momentary current flow surge due to the charging of the various capacitors throughout the systems.

[porschenut]

You need to follow timmy2's advice. Don't waste time guessing or looking at anything else until you've completed this basic troubleshooting sequence.

If you prefer, you can do it the other way around by first measuring the current draw between the battery negative post and the ground cable, to confirm you have a parasitic draw. Then, one by one, remove the fuses and see which one causes the current measurement to drop after it's removed.

[timmy2]

Originally Posted by wwest

Bit of a correction for step 4. As you insert fuses you might see a short/momentary current flow surge due to the charging of the various capacitors throughout the systems.

Yep, wait for the steady state, not the in-rush current... By the time you look at your paper (right before you start writing it down) the rc time constant will have expired and it will be a steady current...(Look away and look back at your meter)
(after 30 yrs as an electrical technician I forget some of the minor details for others that may not know)

[Lorenfb]

So what's the draw current? There's been 10 posts and no answer.

Bottom line: Remember, when troubleshooting, guessing is not allowed!

[ischmitz]

Originally Posted by Lorenfb

So what's the draw current? There's been 10 posts and no answer.

I think Tony indirectly answered it in his first post: Re-read and think:

Originally Posted by Tony

Other information:
1). I tried to get ampere reading across the fuses with the battery connected to the car and failed to find any. Even at the circuit where the clock is connected (???). Why I was not getting any reading? Bad procedure/technique?
2). The current readings across the battery terminals are both 40 UA (ground cable connected and disconnected).

Connecting the meter across the poles of the battery with the leads connected to the Amp either input blows the internal fuse in an instant and he won't be reading anything. Most DVM have two fuses. One protects the 10 or 20 Amp range and the other the lower ranges. Fuses are pretty expensive.

[ischmitz]

For the electrically challenged: Think of voltage and current as water pressure and water flow:

The water pressure is equivalent to voltage. Both pressure and voltage are always differential measurements. A voltage usually gets measured with reference to GND. Measuring the battery voltage is analog to measuring water pressure on your main line with reference to the sink pressure (ambient).

Flow is equivalent to current. For a current to flow you need to open the faucet a little bit. A faucet acts like a variable resistor. The more you open it the higher the rate of flow if main pressure stays the same.

When measuring a current the DVM meter gets inserted into the circuit. It act like an almost perfect connector or wire (pipe with very large diameter). So when you connect the voltmeter in AMP setting to the battery terminals you short out the battery. The DVM has a super-fast fuse and that bows to protect the internal shunt.

As others pointed out, repair the meter before using it. To measure drain disconnect the GND lead from the battery. Then connect the positive lead of the DVM to the GND lead and the negative lead to the negative terminal of the battery. Make sure the meter is in the coarse setting since your draw could easily exceed the meter (fuse) when set to the 200mA range. Most meters have a separate input for the coarse setting. To test if the meter works set your turn signal to left with ignition off. This will activate the parking light. In addition the interior light will come on with the door open once you connect the meter. This should register maybe 1 Ampere.

If pulling all fuses doesn't reduce the drain to near zero you might have a bad diode in the alternator. The alternator is not fused and always connected to the battery. Let us know how things work out.

Ingo

[Lorenfb]

"2). The current readings across the battery terminals are both 40 UA (ground cable connected and disconnected)."

Do what, across the terminals?

"Re-read and think"

Right! So as was said in the other post, what is the TRUE draw current.
A clock alone draws 10-15ma. The standby current in most late radio
is .5ma (500ua) to a few milliamps.

[boyt911sc]

Before doing the the test, I started the car with fuses # 4 (interior lights) and #6 (fuel pump) installed and the car started instantly. Next, the 2 fuses were removed and a multi-tester was connected between the battery (-) pole and the ground cable. Individual fuses were install one after the other and readings were taken. Here are the results:

Fuse #:
No fuses connected------------------ 2.43 mA
1 (power windows, sunroof)----------- 2.43 mA
2 (A/C and power seat)--------------- 2.43 mA
3 (Headlight washer)------------------ 2.43 mA
4 (clock int. lights, radio, etc)--------- 2.43 mA
5 (Emergency flasher)----------------- 2.43 mA

From fuses #6 to 24------------------- same as above.

A second test was made to confirm the results by repeating the above procedure and got exactly the same results. I've been told by a member that -2.43 mA drain lost is not significant to drain the battery power over-night. Based from the above data, there seem to be no 'battery drain' occurring in the system.

So I left everything tonight as they are and will try to start the car tomorrow morning. New set of fuses were installed to replace the old fuses. Any comment, suggestion, recommendation are highly appreciated.

Additional information & observation:

1). The battery voltage was 12.4 volts (engine off) and registered 14.0 volts with engine running. So alternator is working fine.

2). After leaving all the fuses installed, the voltage reading changed from 12.4 to 12.2 volts after an hour. Voltage seems to be degrading and will continue to take reading until bedtime.

3). Every time the negative battery cable is attached to the battery, there comes a faint buzzing sound from underneath the car (front end) in the vicinity of the fuel pump that lasted about 2 or 3 seconds. It sounded like a FP being energized (???) or something else. Will investigate when I put the car on the lift.

4). How come I'm not able to get a change in the amperage draw during the test?

Thanks.

Tony

[ischmitz]

Tony,
did you check whether your meter in AMP setting and AMP configuration works? Does any of the lights work with the meter inserted into the ciruit. If not your meter is damaged (blown fuse or worse).

What is the model and maker of your meter?

Ingo

[timmy2]

Ok, I'll ask the obvious question, how old is the battery and have you taken it and had a load test done to it.
It may be on it's last legs and that small draw is enough to discharge it 2 or more volts overnight so that it won't start the car.
I had one that was doing that to me. Drove me crazy until I changed it.

[boyt911sc]

Originally Posted by ischmitz

Tony,
did you check whether your meter in AMP setting and AMP configuration works? Does any of the lights work with the meter inserted into the ciruit. If not your meter is damaged (blown fuse or worse).

What is the model and maker of your meter?

Ingo

Ingo,

I wished I read your earlier post how to connect the DVM for the test. I did the test before I read your instruction. First help me in Electrical 101. I have no idea what AMP setting/configuration are!!!! Plus I could not locate the test light I left in the kitchen last night after my wife did some house keeping. So this was a set back in my investigation. Could you elaborate what you meant by 'does any light work...........'

The meter could still read voltage after the tests. How do I check if the DVM is good or bad? Below is the Craftsman multi-tester I used. Thanks.



Tony

[timmy2]

Move the red lead to the green 10A hole. Turn the dial to the green 10A stop on the switch. You should be good to go.
I believe he was referring to the digital display as the lights. If that picture was taken since doing your tests then it is working.
Then if you get no or low readings on the 10A scale you should move the red plug back to the red hole and switch the selector to the mA scale for your readings.