electrical and ignition Voltage while car off? parasitic draw?

[josh72ooh2]

I've been coming out to a dead battery way too often.  A jump or a charge and i can drive my 2002 like normal.

I had issues with the internal voltage regulator on one of those 85 amp Ebay alternators that are a direct replacement for your 2002 alternator.

When the car was warm, the voltage was all over the place... mostly much too low.   

I replaced the alternator (got a 95 amp) and problem solved while car is running.

Still coming out to a dead battery though.

It seems that I still have an electrical issue that i need some clarity on.

Battery is in the trunk.  There is a terminal that goes from the trunk to the engine bay. On that terminal is a series of wires for the headlamp relay upgrade, stereo, and of course, the fat wire that goes to the starter.

I am showing a 12.8v and 20 milliamps when I put the meter between the negative cable and the negative terminal on the battery. 

The only thing that stops that current is when I disconnect the fat positive wire that goes to the starter. 

I am showing a constant 12.8 volts through the alternator when the car is off (by connecting the power lead of alternator to the ground that goes to the engine block).

 

Electrical gurus... any ideas?  need more testing info?  if so, let me know and I'm happy to test more. 

 

-Josh

 

 

[esty]

maybe this will help - How to Find a Parasitic Battery Drain

[josh72ooh2]

I did all that and concluded that the draw ceases when the cable is disconnected from the starter. 

[Mike Self]

There should be no parasitic draw on a stock 2002--such things didn't really exist back when our cars were new--except for clocks.  Presuming you have a modern radio, there should be a small parasitic draw from the radio's memory.  But that should take weeks to draw down a healthy battery.

 

Presume you have tested your battery with a load tester (measures amps, not volts) and it checked out OK.  A bad battery can show 12.8 volts but virtually no amps when load tested.  Once you've cleared the battery of guilt, then the easiest way to find the problem is to remove a fuse a night, and see if it cures the problem.  Once you've determined the guilty circuit, then you'll need to disconnect each item in the circuit until you find the current draw.  Or you can do this by looking for a current draw on each circuit on that fuse with a milliammeter. 

 

BTW, a 20 milliamp draw shouldn't run down a healthy battery overnight...

 

mike

 

 

[TobyB]

If you're only seeing 12.8v running, the battery's not getting fully charged.  It's getting a bit of a charge, but not enough to equalize all the cells at a healthy level.

 

There should be no parasitic draw on the starter- it's either drawing 100+ amps, or it's open, completely.

 

The one place that gets people, and it got me 25 years ago, is the alternator itself- it's always connected to the battery directly,

and the diodes in it can get 'leaky' and draw anywhere from 50-500 mA.  Enough to kill your battery in a couple of days.

It's hard to find, since it's a direct, unfused connection.

 

fwiw,

 

t

[Simeon]

1 hour ago, TobyB said:

If you're only seeing 12.8v running, the battery's not getting fully charged.  It's getting a bit of a charge, but not enough to equalize all the cells at a healthy level.

 

There should be no parasitic draw on the starter- it's either drawing 100+ amps, or it's open, completely.

 

The one place that gets people, and it got me 25 years ago, is the alternator itself- it's always connected to the battery directly,

and the diodes in it can get 'leaky' and draw anywhere from 50-500 mA.  Enough to kill your battery in a couple of days.

It's hard to find, since it's a direct, unfused connection.

 

fwiw,

 

t

 

+1 with Toby's idea of the alternator. A diode passing current in the reverse direction can not only flatten your battery but will also impact upon the quality of charging it does. You end up with a spikey DC which your battery won't like. 

 

Change the multimeter to AC and measure between the alternator output and the battery negative. This should be low (mV only) as it should be a very low ripple after rectification. If it's higher (say 1-2 V) then it could be a diode (certainly worth taking off and getting tested somewhere competent).

[josh72ooh2]

Thanks you guys.  Some confessions here...

The car only gets driven either once a week, or sometimes it will sit for 2-3 weeks.  I wish I could drive it more but parking situation makes it difficult to access.

Battery is new-ish (less then a year).

I put the new alternator on, charged the battery and it died in 2-3 weeks of sitting which makes me think I still have an issue.   Before the new alternator, the car was frequently found with a dead battery after charging it (but again, a week or two may have gone by).

i will admit, that i chased the problem down to an alarm i hooked up for door actuators and the alarm was going into some mode in which it was drawing current.  But the alarm has been disconnected for 6 months now. 

 

The car is fuel injected with a '94 chipped ECU.  But that shouldn't have an effect. I have an aftermarket stereo and amp but that shouldn't be an issue. I disconnected the power to the amp and it made no difference.

When car is on, volts are 13+, as expected thanks to the new alternator.

 

While car is off - multimeter set to AMPS - connected between the battery negative and negative cable:

I am showing a .02Amp draw (with amp disconnected).

I disconnect the fuse to the hazard and dome light (Fuse #8) and it drops to .01Amp

If I disconnect the large cable to the starter, it drops to .01Amp.

I disconnect both, and I still see .01amp draw (maybe it is the clock).

 

So if you are saying that  .02Amp draw s nothing to be worried about? 

 

I wish i could run an extension cable out to a battery tender while the car sits but there is too much foot traffic between the car an outlet. As of now, i just disconnect the battery when the car sits for a while.

 

 

 

 

[TobyB]

Hey, there's more going on there than we thought!

What engine's in that car?

 

20 ma is pretty normal.  Your average 50ah battery should hold up to that for at least a month, maybe 2.  And 12.8v resting is a sign of a

charged battery, usually...

 

BUT .02a on the 10A scale might be off by a bit.  Set the multimeter to 200mA, and try again.  If it says 20 mA, you're fine.

If it says 100mA, there's your problem.  I don't think your meter is accurate enough around zero to really tell the whole story.

 

Hmmm....

 

 

t

 

[josh72ooh2]

The engine is a normal M10 block but with a 84 manifold, fuel rail, etc.. it is driven by a 94 ECU that was chipped for the car. 

 

I let the car sit for about a week and a half and it was dead again.  I'll get back out there with the tester and see what else I can come up with. 

 

 

[xferboy]

On 2016-10-10 at 7:31 PM, TobyB said:

BUT .02a on the 10A scale might be off by a bit.  Set the multimeter to 200mA, and try again.  If it says 20 mA, you're fine.

If it says 100mA, there's your problem.  I don't think your meter is accurate enough around zero to really tell the whole story.

 

 

Agreed.  On anything other than a 3 and half digit meter that cost the same as a new car payment, pretty much ignore the last digit.

 

Also, if you hook the meter to the battery so its easy to read, wander past it during the week and see what it reads.  it shouldn't drop more than .1 (starting at > 12.5) with a 20mA draw over multiple weeks.  THe meter will have megaohm or higher input impedance so it won't draw the battery down leaving it hooked up.(12uA or 12nA, I can't math right now).

 

for a later experiment, disconnect a battery terminal, and monitor the voltage.  Internal Resistance could be drawing it down.  COuld have been bad from the factory, but still passed their 'QA/QC'

[TobyB]

Also, it could be something intermittent, as in,

something's kicking in, drawing current, then shutting down.

These things are hard to find...

 

Quote

it is driven by a 94 ECU that was chipped for the car. 

 

This confuses me.  The 84 parts are E30M10, but a 94 ecu is an E36M42?  What wiring harness?

 

t

 

[deanres]

to Quote Rob Siegel  our Electrical Guru:

 

To recap:

• The battery resting voltage (engine off) should be about 12.6 volts.
• The charging voltage (engine running) should be about 13.5 to 14 volts, it should increase slightly when you rev the engine to 2,500 rpm, and it shouldn’t dip egregiously when you turn on a stiff electrical load.
• You can easily measure the voltage with a multimeter at the battery or with a cigarette-lighter-plug-in voltmeter.
• Don’t drive a car far if the alternator isn’t putting out charging voltage. It will strand you.
•  

[josh72ooh2]

21 hours ago, TobyB said:

Also, it could be something intermittent, as in,

something's kicking in, drawing current, then shutting down.

These things are hard to find...

 

 

This confuses me.  The 84 parts are E30M10, but a 94 ecu is an E36M42?  What wiring harness?

 

t

 

Build photos are above.  I'm pretty sure it is the 90 wiring harness.  there are a few odds and ends that aren't connected.  I still want to install an 02 sensor and implement that with the ECU.

Edited October 29, 2016 by josh72ooh2

[JohnH]

The ECUs not permanently powered up is it? It does have a main relay triggered from the ignition switch?

[snowy]

Ok I have just solved a similar problem!  Looking around under the carbs and finding a detached earth strap. Actually stretched then detaching. I think the previous owner had taken the motor out without disconnecting the strap. I have fitted a battery lead to replace the copper branded strap but on the washer bottle side of the engine bay, grinding down to bright metal  on the block and chassis rail and  then repainting. Still good  6 weeks later and not using the battery isolation switch.