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Battery POWER DRAIN Question

 
Old 03-10-2011, 10:49 PM
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Default Battery POWER DRAIN Question

I've had a batt drain in my 90 for a while now and just been unhookin the batt at night but it's getting beyond annoying so I recently got out the multi and tested the draw at the negative terminal with my own wire rig and a 1 ohm resistor. I first got a .50 Volt reading (500 mV) and the sparks were flyin the minute I touched the negative terminal to the post. Enough to drain the batt over night if left hooked up essentially. So with the rig out and connected, I start pulling the fuses one by one. Pulled all of them that I'm aware of and watched the multi for changes(both on the side instrument fuse panel and the 4 under the passenger side). I found only a slight drop from the radio fuse and a couple others that are normal, but none making that dramatic of a drain. Until of course I pulled the fuse plug from the alternator, I noticed the drain immediately drop to .16 Volts (160 mV) which is still a big drain but not nearly as big obviously. The norm that should be allowed from what I understand is 35 mV which is .035 Volts when the car is off for the radio/stereo clock settings etc. Anyhow, I stupidly figured it was a bad diode thinking it was the alternator that was causing a continuous draw when the car was off so I replaced the alternator(one that's been in there for almost ten years). So now I had a new ac delco alternator in there. It ran great and runs great so it seems. Immediately after I put it in though, we tested it on the multi and we got the exact same readings of draw in total .50 V(500 mV). SO now I thought wasn't the alternator afterall and was something with the wiring. Next thing I did was bring it to a reputable electric shop here in town earlier today and have them do a diagnostic for the wiring and see where the draw's coming from. So they look it over after I leave it there all day and finally call me up and say I have multiple draws and one of them is a bad alternator. They tell me the draw's 500 mV total and the alternator is the problem that's drawing most of it with 160 mV owed to something else. Obviously the same numbers I got with the multi, old news. I told them its highly unlikely that its the alternator since it's pullin the same exact readings of draw as I had gotten with the first one which I tested and replaced myself. For a 10 year old alternator to pull the EXACT SAME energy draw as a brand new AC Delco unit even if the new unit was malfunctioning would seem extremely unlikely I would think. I asked them if they were sure its the alternator 3 times and they said yes, which I now know to be bu11sh1t. What I did tonight is took the old alternator I myself took out the first time when I tested it in the car down to an auto zone to have them do a multi layer diode test. That old one passed every test thus showing that there couldnt be a jacked diode nor a continuous two way current draw when the car's off from the alternator. This logic also shows that the new one I put in that they just tested can't possibly be bad all the same because if it was bad then the draw would be 1 Volt (1000 mV) instead of .50 V which was the reading they got and the reading I got for both alternators when I tested them in the car. Where the remaining .16 V (160 mV) draw is coming from remains the mystery that apparently they needed to keep my car overnight for them to diagnose. So I know the alternator most likely isn't bad at all, but a question I have is about the fuse plug that goes into the alternator. Is it possible that the plug is bad and some switch in it is stuck thereby causing the continuous current draw we see when the car's off? Also what else do you think I should look for? I noticed that when I reconnect or disconnect the negative batt terminal, there are two sounds; one that makes a brief kick sounds like its coming from the dual fan area(fans work and this alone does not turn them on just makes a kick sound when I connect the terminal), and the other of course is a low pitch whine type sound from the alternator when the fuse plug is connected(even though we just determined that it would be next to impossible to be the alternator itself). Also just fyi, I have a modded "auto fan" switch rigged that I keep the switch in the on position so the fans kick on at first turn of the key before the engine's on which I was thinking could possibly be some of the draw that I haven't diagnosed yet(they have my car tonight at the shop as I mentioned), but I wouldn't think it would be draining much. Any other ideas or suggestions?
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Old 03-10-2011, 11:10 PM
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Doesn't your multimeter measure current? Measuring the voltage across a one ohm resistor in series with the removed neg battery cable, the voltage you measure is also the current draw. That is, both alternators draw 500 milliamps (1/2 volt) which I do not believe. GM says leakage current should not exceed 50 milliamps, my 87 draws 28 ma. and I have no battery problems.
Every wire that comes off the positive battery cable to power every circuit needs to have the current measured through each wire to find where the leakage current is and this is a time consuming job. You also need the electrical diagnosis manual which has the entire car electrical circuit diagram which is a tremendous help for locating leakage current. Good luck.
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Old 03-11-2011, 10:04 AM
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Originally Posted by jfb View Post
Doesn't your multimeter measure current? Measuring the voltage across a one ohm resistor in series with the removed neg battery cable, the voltage you measure is also the current draw. That is, both alternators draw 500 milliamps (1/2 volt) which I do not believe. GM says leakage current should not exceed 50 milliamps, my 87 draws 28 ma. and I have no battery problems.
Every wire that comes off the positive battery cable to power every circuit needs to have the current measured through each wire to find where the leakage current is and this is a time consuming job. You also need the electrical diagnosis manual which has the entire car electrical circuit diagram which is a tremendous help for locating leakage current. Good luck.

I was told the amps reading(milliamps) is a totally different measurement not equivalent to volts, but if for some reason the voltage I'm measuring off the neg batt terminal is also the current draw then I'm reading .50 V in total drain which equivalates to 500 millivolts. Yes I know the vid on youtube explains that this should be no more than .035 V when measuring in volts which is 35 millivolts. The numbers are correct even though I personally have no idea about the amp measurement equivalency. These idiots should just explain it in one friggin measurement. I have a draw that I know is most likely NOT from either alternator even though it appears to be drawing from them. I had one of them tested through the diode test as I explained and it passed with flying colors so logically it has to be something in the wire or the connection from the wire, maybe a bad switch somewhere, I have no idea other than that. That's why I took it to an electrician, but these monkeys are telling me its the alternator. It is a time consuming job I'm sure. From what I understand they have to measure the wires for continuity. This is why I took it to a professional electrician as I'm none of the sort. It's just common sense that it isn't the alternators considering I measured both and got the same reading in the car and then had the one I removed later pass the diode test.
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Old 03-11-2011, 11:36 AM
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Is it possible the fuse plug connector connecting to the alternator itself is the culprit? This plug's probably as old as the car. The guy in the parts dept didn't know if it was a fuseable link but by reason of deduction it seems this is one of the only remaining culprits since a wire itself couldn't draw power and the power draw is definitely lowered when that fuse plug is removed from the alternator. When I had issues with the fan relays burning out, no one ever suggested the connector plug to the relays should be changed. I changed it and havent had problems since.
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Old 03-11-2011, 12:40 PM
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First, you should not post the same subject in both C4 tech AND c4 Gen. C4 tech is for technical questions.
You measure current out of the battery by setting up your mulitmeter to measure current and it should be connected in series with the removed negative battery cable. One test lead goes to the battery terminal and the other test lead goes to the disconnected negative battery cable. DON'T MEASURE VOLTS! Leakage current should not exceed 50 milliamps and if it does, watch your ammeter while you pull each fuse one at a time. This should identify the circuit that has the excessive leakage current. Some circuits use a circuit breaker and some breakers plug in. You need an electrical diagnosis manual to see where to insert your multimeter set up to measure amps ( or milliamps).
While your alternator appears not to have leakage current flowing into the output wire, by your description it appears that there is current flowing into the alternator voltage regulator when you plug the alternator in. With the ignition off, no wire in the wiring harness plug for the alternator should have 12v on it and if one does, you need to find out why and this requires the electrical service manual which shows were each wire in the plug goes to.
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Old 03-11-2011, 12:53 PM
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Originally Posted by jfb View Post
First, you should not post the same subject in both C4 tech AND c4 Gen. C4 tech is for technical questions.
You measure current out of the battery by setting up your mulitmeter to measure current and it should be connected in series with the removed negative battery cable. One test lead goes to the battery terminal and the other test lead goes to the disconnected negative battery cable. DON'T MEASURE VOLTS! Leakage current should not exceed 50 milliamps and if it does, watch your ammeter while you pull each fuse one at a time. This should identify the circuit that has the excessive leakage current. Some circuits use a circuit breaker and some breakers plug in. You need an electrical diagnosis manual to see where to insert your multimeter set up to measure amps ( or milliamps).
While your alternator appears not to have leakage current flowing into the output wire, by your description it appears that there is current flowing into the alternator voltage regulator when you plug the alternator in. With the ignition off, no wire in the wiring harness plug for the alternator should have 12v on it and if one does, you need to find out why and this requires the electrical service manual which shows were each wire in the plug goes to.

So you're saying that the plug itself, if it IS in fact drawing power (if this is what you're referring to as the alternator voltage regulator), is drawing it because something else is drawing power that this plug is somehow wired to in the system?
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Old 03-11-2011, 02:49 PM
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Originally Posted by MaSTeRofDZaSTeR View Post
I was told the amps reading(milliamps) is a totally different measurement not equivalent to volts, but if for some reason the voltage I'm measuring off the neg batt terminal is also the current draw then I'm reading .50 V in total drain which equivalates to 500 millivolts. Yes I know the vid on youtube explains that this should be no more than .035 V when measuring in volts which is 35 millivolts. The numbers are correct even though I personally have no idea about the amp measurement equivalency.
Measuring small currents across a 1-Ohm resistor is an easy method of determining current draw, if you don't have an ammeter handy. Here's what's going on:


From Ohm's law:

I = E/R
I (amperes - units of electrical current) = E (voltage) / R (resistance)

So, any voltage reading mesured across 1 Ohm is I = voltage / 1. Thus the voltage reading translated directly into current reading.

However, most DVMs have the ability to measure current directly - usually having two different current ranges; 100 mA perhaps, and 10A scales. (Note: The 10A scale often requires you to plug the red lead into a special connection on the meter labeled 10A (or the like).

For what it's worth, the addition of the 1-ohm resistor to the circuit, obstensibly to measure the current, will reduce the total current that would flow in the circuit had the resistor not been there. However, in this application where the current draw is very small - the effect of the additional 1-ohm of resistance is negligable.

P.

Last edited by Paul Workman; 03-11-2011 at 02:57 PM.
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Old 03-11-2011, 03:24 PM
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Originally Posted by MaSTeRofDZaSTeR View Post
So you're saying that the plug itself, if it IS in fact drawing power (if this is what you're referring to as the alternator voltage regulator), is drawing it because something else is drawing power that this plug is somehow wired to in the system?
How I understand your recent explanation, current higher than normal leakage current is drawn from your battery when you plug in the alternator (ignition must be off in this measurement). Inside the alternator is the voltage regulator and it normally draws current when the ignition is on. IF I understand your explanation, current is drawn when you plug in the alternator with the ignition off. If so, then something is wrong with your ignition switch because power to the alternator plug occurs only when the ignition sw is on.
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Old 03-11-2011, 03:42 PM
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Originally Posted by jfb View Post
How I understand your recent explanation, current higher than normal leakage current is drawn from your battery when you plug in the alternator (ignition must be off in this measurement). Inside the alternator is the voltage regulator and it normally draws current when the ignition is on. IF I understand your explanation, current is drawn when you plug in the alternator with the ignition off. If so, then something is wrong with your ignition switch because power to the alternator plug occurs only when the ignition sw is on.


That sounds about right. And yes current is drawing when I plug in to the alt when ignition is off but stops when I unplug that plug to the volktage regulator in the alt apparently.(Thus nothing's necessarily wrong with the alt) And I posted something on the tech forum indicating a recent prob with the vats which usually has to do with the ignition switch also from what I understand. Ignition switch is lookin more and more like the main culprit here then.
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Old 03-11-2011, 06:11 PM
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VATS doesn't involve the ignition switch except that the start enable relay coil which is controlled by VATS gets 12v from the ign sw.
One thing to check for is the rod from the ign lock which activates the ign sw. If it is out of place it could be that the ign sw is left on when you remove your key.
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Old 03-11-2011, 06:44 PM
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I had a battery drain overnight that was intermittent.

What I discovered was the Blower Motor Control module was slightly draining the battery until it dropped below 11 volts. At that point, the blower motor would turn on and drain the battery completely.

I replaced the control and the battery stays charged fine now.

BTW. The Blower Motor Control is directly connected to the battery on my 87 but I'm not sure if your 90 is the same.
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