Battery cable identification for power drain

MuffinMan · 05-22-2004, 02:59 PM

I recently had a 3.6 conversion performed on my car, and since then I've had a battery drain issue. In the below picture, I hooked up a test light, removed every fuse, and disconnected everything from the positive terminal except for the large cable. You can see that the test light is very bright, indicating a large drain. Does the big mother cable hooked up to the positive terminal go to the starter? Does it go anywhere else? I have an aftermarket high torque starter, why would it be drawing enough power to drain my battery in less than two hours?

I can disconnect the starter to confirm that it is the problem, but I'm not sure what to do to alleviate the issue if it is the culprit. Thoughts?

RoninLB · 07:02 AM

Quote:

Originally posted by MuffinMan
Does the big mother cable hooked up to the positive terminal go to the starter? Does it go anywhere else?

the big mother goes to the starter, obviously.. but the stock wiring should have another cable going to the alternator attached. I would eyeball the starter and see what's happening.

I would use a millamp meter. Try not to have not more than 50ma - 60ma total battery drain.

raceman · 05-23-2004, 12:37 PM

l just posted with the exact same problem on my 84 3.2! l`m right where you are right now but l`ve been checking my battery voltage daily(ground removed) and l`m losing a volt every 24 hours for the last three days.l did the test with test light/voltmeter like you and with the same results.l`ll keep you "posted" on what l find out

Bill Verburg · Bill Verburg's Garage

Do you have a good current diagram? If not these might help.

rick-l · 05-23-2004, 04:39 PM

could be a shorted diode in the alternator. Unfortunatly it isn't easy to disconect the alternator.

Early_S_Man · 05-24-2004, 06:40 AM

One bad diode wouldn't cause a drain ... it takes a shorted one in the positive array/trio and another shorted one in the negative array/trio!!!

MuffinMan · 05-24-2004, 07:02 AM

I'm still sorting this out. When I started to turn the nut to disconnect the wires to the starter, the test light bulb went out. I initially thought something was loose, but later realized the bulb blew in the test light. There must have been a surge or something, but I've confirmed that the starter is the culprit...

rick-l · 05-24-2004, 07:02 AM

Quote:

Originally posted by Early_S_Man
One bad diode wouldn't cause a drain ... it takes a shorted one in the positive array/trio and another shorted one in the negative array/trio!!!

See
http://www.buchanan1.net/charge.shtml
If one of the three or four diodes that go to the battery short out it will keep the regulator energized and it will supply current to the field winding resulting in a moderatly fast discharge. If the right two (maybe wrong two) diodes in the output and ground return short out you will see smoke and fire.

911pcars · 05-24-2004, 08:44 AM

Rob,
It isn't clear where you're connecting the lead for the test lamp, but a test light is not the best diagnostic tool to locate parasitic current drain.

I recommend a VOM, preferably a digital type (more accurate). You can purchase an inexpensive one at Radio Shack or many other places. The meter should be setup to measure current and connected in series between the negative battery post and the battery cable.

Isolate the malfunctioning circuit by disconnecting fuses until the ammeter reads "normal" (<30-50 mA). Then further isolate. You should have the factory circuit diagram to know what you're looking at/for.

Hope this helps a little.

Sherwood

MuffinMan · 05-24-2004, 09:46 AM

The reason I'm using the test light is the drain is too large to measure on a multimeter. In fact, I think I fried my multimeter by trying to measure the drain

. The draw is somewhere between 20-30 amps, I'm guessing.

I currently have the test light setup in series between the negative ground cable and the negative post on the battery, as you recommended.

vash · vash's Garage

man, i hope your figure this out fast. your poor battery is hating life. good luck. can you put your stock starter back on, just for kicks? i dont know crap about electrical problems, but if you are losing so much juice that fast, something has to be getting hot right? newton's first law, is that you cannot make energy disappear, it has to be transfered to another form. good luck rob fusi!

MuffinMan · 05-24-2004, 10:48 AM

I don't drive this car daily, and I have been disconnecting the battery whenever the car is not actually running. I agree that it's not a pleasant thought to have all of that juice running through the system, though. I can't use my old starter, as it's not powerful enough to crank the 3.6. Believe me, nobody wants this sorted out more than I do

Early_S_Man · 05-24-2004, 11:22 AM

Rob,

Most likely your alternator ... pull it and have it tested.

Rick-I

That diagram you linked to is NOT CORRECT for pre-1990/964 911 models with Bosch, or Marchal/Motorola alternators...

... your response is incorrect on both counts!

1. A shorted exciter diode could NEVER cause a drain that would run a battery down in two hours or less ... the maximum current through the field winding would only be an Amp or two. Please consider ... whether your response is reasonable and whether the possible fault could actually cause the symptom described by Ron!

2. I have seen several cases of pairs of shorted main rectifier diodes ... never any smoke or fire, just a battery that would run down in 2 - 6 hours! Shorted rectifier diodes don't exhibit the characteristics of copper wire, i.e., a dead short ... they have finite, small resistance values, sometimes varying with load.

rick-l · 05-24-2004, 12:36 PM

Quote:

Originally posted by Early_S_Man
Rob,

Most likely your alternator ... pull it and have it tested.

Rick-I

That diagram you linked to is NOT CORRECT for pre-1990/964 911 models with Bosch, or Marchal/Motorola alternators...

... your response is incorrect on both counts!

1. A shorted exciter diode could NEVER cause a drain that would run a battery down in two hours or less ... the maximum current through the field winding would only be an Amp or two. Please consider ... whether your response is reasonable and whether the possible fault could actually cause the symptom described by Ron!

2. I have seen several cases of pairs of shorted main rectifier diodes ... never any smoke or fire, just a battery that would run down in 2 - 6 hours! Shorted rectifier diodes don't exhibit the characteristics of copper wire, i.e., a dead short ... they have finite, small resistance values, sometimes varying with load.

It is not the exact diagram but should be typical. It is pretty much what is in my 88.

I didn't notice the drained in two hours statement in the original post, all I saw was the bright test light. If one of the rectifier diodes are shorted it would be difficult to say the battery was fully charged at the start of the two hours. Two hours would mean at least a 75 amp draw. 75 * 12 = 900 watts That little semi shorted diode should be glowing pretty red.

I didn't say exciter diode, the four diodes I refer to in the picture are rectifier diodes. If one of those are shorted the current flows back through the forward biased exciter diodes to the field winding. A sure sign of this is the alternator light is always lit. Where did you get the two amp value?

Just trying to share some of the research/testing due to my alternator fiasco. It's a moot point anyhow since he has isolated the problem to the starter.

MuffinMan · 05-24-2004, 01:09 PM

If the alternator is associated with the starter, that could also be my issue. I just know that when I moved the nut on the started, it had an effect on the test light/drain. I need to get more bulbs to further investigate the problem.

Ahh...the joy of electrical gremlins. Gotta love 'em!

Early_S_Man · 01:54 PM

Rob,

On most 911 engines [all I have seen] ... the alternator 'hot' output lead is attached directly to the same stud on the starter solenoid as large cable from the battery positive post. I have no reason to believe it would be any different for a 3.6 conversion ...

Sears sells a couple of AC/DC clamp-on multimeters in the $50 - $100 range. I prefer to use a clamp-on meter or probe when tracing mysterious drain problems because of the ease of moving the probe without having to disturb connections.

The Fluke Y8100 AC/DC current probe I use is good to 200 Amps and can be used with any common digital multimeter ... and the HP 428B Clip-on DC Milliammeter is good to 10 Amps, and the probe is more compact. Both were found on eBay for under $60.

MuffinMan · 05-29-2004, 09:09 AM

As a review, I had everything disconnected from the battery except for the main lead going to the starter. I had the test light hooked up, and it was lit very brightly. With someone watching the light, I began to disconnect the leads on the starter. As soon as I began to turn the nut on the starter, the bulb in the test light blew (obviously there was a spike).

I got a new bulb, and disconnected everything from the battery, except for the lead going to the starter. I disconnected the leads at the starter. The light didn't come on (just a sanity check). I connected the cable going to the battery. No light. I connected the other lead on the starter that goes to the wiring harness. Still no light. I left everything hooked up for a few days, and the battery didn't die. In the meantime, I soldered the wires together that went into the bundle from the wiring harness, to ensure a good connection.

Today I went out to start the car, and made sure everything was connected, and I fully charged the battery. I turned the key, and got a loud "click" from the starter. I tried a few more times and got the same thing. I then put the charger on the battery in "start" mode, and got the same click. I then swapped in my new and fully charged odyssey battery, and got the same click.

The starter is a brand new high torque unit. I believe starters can develop flat spots that give you the "click" and won't turn, but this thing is brand new! Thoughts??

MuffinMan · 05-29-2004, 09:37 AM

I just played with this thing for a little while. I turned the nut on the starter just a hair, then the starter would turn & the car would start. Then I tightened it a bit and I got the click again.

Do you think it's the starter itself?

RoninLB · 05-29-2004, 10:05 AM

Quote:

Originally posted by MuffinMan

Do you think it's the starter itself?

I'm with Warren on buying a amp/current probe. If the sol wasn't drawing current then#$%^&*.

maybe in the mean time try jumping the starter sol from the big starter feed either with a screwdriver or jumper.
Key in run position, netural, etc.. please be safe on this one.

rick-l · 05-29-2004, 10:53 AM

Not sure about your partiicular starter but some have two coils on the solenoid that pulls in the gear and makes contact to the windings. One is draws huge current to start everythin moving (the pull in coil) and the other is smaller (hold coil) and just holds everything in position. The motion of the plunger of the solenoid opens the pull in coil. It sounds like these contact could be open.