Help with electrical draw/battery problem
09-17-2003, 10:26 AM
#1
Drifting
Thread Starter
Help with electrical draw/battery problem
I am trouble shooting an electrical draw problem on my 96 coupe. I have searched the archives and found some good threads but nothing that gets me the complete answer. So here is the story. Oh, before I start I am not an EE nor do I really have any experience or understanding of circuits, currents, volts, etc., however, I can follow directions well and I like to think I am somewhat intelligent 
I replaced the original Porsche battery in March of this year with a Red Top Optima. It worked well for about 3 months. Then one day the car just clicked. Took the battery back and the store said the battery was bad. Replaced it with a new Red Top in late June. Everything has been fine until two weeks ago. I took the car out on Saturday and went on 2 hour (one way trip) basically driving the car the whole day. On Sunday I pulled it out of the garage and washed it and then pulled it back in. It sat in the garage until Friday. I went out Friday night and it wouldn’t do anything. Not even click
Took the battery out on Saturday and went to the auto store. They test the battery. It needed charging before it would test. After the charge it tested ok. Hmmmm. I am thinking maybe bad Alternator. I bring the car to the store later. They test the Alternator and said it looked fine (putting out 99 amps I think) 
So I do a search and find some threads on electrical draws. I set up a multimeter in series with the battery. My meter does not have the resolution to measure milliamps without rounding. The meter reads .03 with a bounce to .04 occassionally. I activate the immobilizer and get a .03 with a bounce to .04 when the door light flashes. With the immoblizer off I start pulling fuses that have caused problems for others in the past. With fuse #38 (radio booster) out I can drop the current to .02 with a flash .03. With #39 and #29 (interior lights) pulled I get a steady .02.
So here are some questions for everyone. What is the normal draw on a 96 993 at rest? Can someone provide the draw numbers? Does the Porsche battery handle the constant draw better than the Optima? Is the Radio Booster necessary (what does it do – is it just a function of the alarm?) By the way I have the factory CDR-210 with changer. Any suggestions or comments on this? Although it appears to be drain from sitting it scares me to drive because I don’t want to be stranded. It does not seem that a .04 draw should flatten a new battery in 5 days. Does the alternator sound like it is function well. What are my options? I know I can mask the problem by putting hooking up my trickle charger and/or removing the fuses but I want to solve the problem not some half a$$ed patch.
I replaced the original Porsche battery in March of this year with a Red Top Optima. It worked well for about 3 months. Then one day the car just clicked. Took the battery back and the store said the battery was bad. Replaced it with a new Red Top in late June. Everything has been fine until two weeks ago. I took the car out on Saturday and went on 2 hour (one way trip) basically driving the car the whole day. On Sunday I pulled it out of the garage and washed it and then pulled it back in. It sat in the garage until Friday. I went out Friday night and it wouldn’t do anything. Not even click
Took the battery out on Saturday and went to the auto store. They test the battery. It needed charging before it would test. After the charge it tested ok. Hmmmm. I am thinking maybe bad Alternator. I bring the car to the store later. They test the Alternator and said it looked fine (putting out 99 amps I think) So I do a search and find some threads on electrical draws. I set up a multimeter in series with the battery. My meter does not have the resolution to measure milliamps without rounding. The meter reads .03 with a bounce to .04 occassionally. I activate the immobilizer and get a .03 with a bounce to .04 when the door light flashes. With the immoblizer off I start pulling fuses that have caused problems for others in the past. With fuse #38 (radio booster) out I can drop the current to .02 with a flash .03. With #39 and #29 (interior lights) pulled I get a steady .02.
So here are some questions for everyone. What is the normal draw on a 96 993 at rest? Can someone provide the draw numbers? Does the Porsche battery handle the constant draw better than the Optima? Is the Radio Booster necessary (what does it do – is it just a function of the alarm?) By the way I have the factory CDR-210 with changer. Any suggestions or comments on this? Although it appears to be drain from sitting it scares me to drive because I don’t want to be stranded. It does not seem that a .04 draw should flatten a new battery in 5 days. Does the alternator sound like it is function well. What are my options? I know I can mask the problem by putting hooking up my trickle charger and/or removing the fuses but I want to solve the problem not some half a$$ed patch.
09-17-2003, 11:07 AM
#5
Rennlist Member
bet,
I did some experimentation with this last winter when the car was in winter storage. Using a Fluke digital VOM.
Your current draw is insignificant and won't drain the battery. I assume you have the hood, trunk and interior lights shut off, ignition off, ignition key light off, etc. I don't have my notes here at the office, but I remember my numbers being about 50 or 60 milliamps at rest on my car.
You said that the shop checked your alternator. What was the voltage output with a full load on the alternator? It should be 13.75 to 14.25 vdc.
I did some experimentation with this last winter when the car was in winter storage. Using a Fluke digital VOM.
Your current draw is insignificant and won't drain the battery. I assume you have the hood, trunk and interior lights shut off, ignition off, ignition key light off, etc. I don't have my notes here at the office, but I remember my numbers being about 50 or 60 milliamps at rest on my car.
You said that the shop checked your alternator. What was the voltage output with a full load on the alternator? It should be 13.75 to 14.25 vdc.
09-17-2003, 11:14 AM
#6
Drifting
Thread Starter
Mike thanks for the reply I don't know the voltage output on the alternator. The fact that my draw numbers are similar to yours and close to what others were attempting to get in the other post I have read really makes me uncomfortable with the alternator test and am going to go for a second opinion.
09-17-2003, 12:17 PM
#7
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bet,
My TT sat in the garage for about 8 wks (I didn't use it since mid-july). I think it has a Die-Hard (my C4S did as well and no problems there either). Fired up on the first turn of the key.
I've had some problems leaving my first P-car (a 95) for long times but it went away when I changed the P-item for a new P-batt. The Die-hards seem to last a bit better, but they are very chunky and probably weigh a ton.
Rgds
LV
My TT sat in the garage for about 8 wks (I didn't use it since mid-july). I think it has a Die-Hard (my C4S did as well and no problems there either). Fired up on the first turn of the key.
I've had some problems leaving my first P-car (a 95) for long times but it went away when I changed the P-item for a new P-batt. The Die-hards seem to last a bit better, but they are very chunky and probably weigh a ton.
Rgds
LV
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09-17-2003, 01:30 PM
#8
Passed On
Rennlist Member
Rennlist Member
bet, you checked most of the obvious things and I tend to agree that .03-.04 amps isn't enuf to drain a good battery in less than a week. You have a multimeter, so you should be able to check the battery voltage. If it's charged, sitting with engine off and no-load it should be 12.3-12.5 volts. If you start the car and let it idle then check the battery voltage, you should get something like 14.3 volts.
Your report of an Optima going bad in 3 months is scary; was going to get one over the winter, and woul.d prob. have to do a mail-order.
Your report of an Optima going bad in 3 months is scary; was going to get one over the winter, and woul.d prob. have to do a mail-order.
09-17-2003, 01:34 PM
#9
Drifting
Thread Starter
Ray I checked the voltage last night with the car off. It read 12.5 when I started experimenting. After playing with various fuses out it read 12.45 at the end of the night. I have not checked with the car idling.
What does the voltage at idle tell me?
What does the voltage at idle tell me?
09-17-2003, 01:48 PM
#10
Rennlist Member
bet,
The battery vdc static is ok. The alternator output voltage needs to be about 1.5 to 2.0 vdc about the battey voltage in oder to charge the battery.
Check voltage at the battery or cigar lighter with the engine at idle. You should see 13.75 to 14.25 vdc. Rev the engine and see if it changes.
Then load up with a/c on, headlights, fans, etc. The alternator should keep the bus vdc up in the 14.0 vdc range fully loaded. May sink down to 13.5 vdc which is ok.
If alternator voltage to the bus is below, say 13.25 vdc, the battery willl never fully charge. Could be the reason for short battery life while the car is stored.
The battery vdc static is ok. The alternator output voltage needs to be about 1.5 to 2.0 vdc about the battey voltage in oder to charge the battery.
Check voltage at the battery or cigar lighter with the engine at idle. You should see 13.75 to 14.25 vdc. Rev the engine and see if it changes.
Then load up with a/c on, headlights, fans, etc. The alternator should keep the bus vdc up in the 14.0 vdc range fully loaded. May sink down to 13.5 vdc which is ok.
If alternator voltage to the bus is below, say 13.25 vdc, the battery willl never fully charge. Could be the reason for short battery life while the car is stored.
09-17-2003, 03:25 PM
#11
Drifting
Thread Starter
Mike to clarify. After I check at idle (I assume I check by using the meter on the terminals of the battery) I should then check with the engine rev'd (any certain RPM?). Then load up the system with lights, ac, radio, etc. When I do this test should it be at idle or with the engine rev'd?
09-17-2003, 03:44 PM
#12
Rennlist Member
bet,
Sorry if I confused you.
1) Check at the + and - of the battery, as long as you can see or hold the meter from the driver's seat. Readings will be the same if you can grab the + and - inside the cig lighter. Bus voltage is the same.
2) Check the alternator (bus) voltage at idle and then revved a little, maybe 2,000 rpm. No load on the bus. You should see the 13.75 to 14.25 vdc. Could be as low as 13.6. No sweat.
3) Turn everything on to load the bus. A/C, HVAC fans, rear window defog, headlights. etc. Bus voltage should stay at 13.5 vdc (ish) or higher at idle and maybe go up a little when revved.
4) If your voltage is low (below, say 13.0 vdc) when the bus is fully loaded and the engine revved, you may have an alternator problem, like a shorted rotor or diode.
Basically this is a load test of your alternator. See if it will carry the load or if the voltage collapses.
I'll be around later if you check this, call me on my cell at 315-246-2173.
Sorry if I confused you.
1) Check at the + and - of the battery, as long as you can see or hold the meter from the driver's seat. Readings will be the same if you can grab the + and - inside the cig lighter. Bus voltage is the same.
2) Check the alternator (bus) voltage at idle and then revved a little, maybe 2,000 rpm. No load on the bus. You should see the 13.75 to 14.25 vdc. Could be as low as 13.6. No sweat.
3) Turn everything on to load the bus. A/C, HVAC fans, rear window defog, headlights. etc. Bus voltage should stay at 13.5 vdc (ish) or higher at idle and maybe go up a little when revved.
4) If your voltage is low (below, say 13.0 vdc) when the bus is fully loaded and the engine revved, you may have an alternator problem, like a shorted rotor or diode.
Basically this is a load test of your alternator. See if it will carry the load or if the voltage collapses.
I'll be around later if you check this, call me on my cell at 315-246-2173.
09-18-2003, 11:56 AM
#14
Drifting
Thread Starter
The volt readings were as they were suppose to be. I stopped at my independent p-car mechanic this morning to run some quick test. Regarding the alternator in his words..."you could weld with that thing, nothing wrong." However, his current readings at rest now show 140 miliamps....which would explain the problem. I tested again last night and only had 40. hmmm? But, I bet the climate control was buzzing when he took his. I will have to call him about that. I just left it to let him investigate a little.
09-18-2003, 12:04 PM
#15
Rennlist Member
bet,
You're exactly right. The 140 ma is with that little HVAC fan motor running. Ignore that reading. The 40 ma to 60 ma or so if repeatable is correct.
Last thing to do is pull the battery out, bring it to a battery shop (one that just sells batteries) and have them charge and load test the battery.
You could have another bad battery (shorted cell).
I've been very happy with my DieHard from Sears if you need to go that way. Perfect fit. Nice quality. I moved the vent to go through the trunk floor using one of the nipples and grommets already there. Much better than venting into the LH fender well.
Feel free to call me if you have any questions.
You're exactly right. The 140 ma is with that little HVAC fan motor running. Ignore that reading. The 40 ma to 60 ma or so if repeatable is correct.
Last thing to do is pull the battery out, bring it to a battery shop (one that just sells batteries) and have them charge and load test the battery.
You could have another bad battery (shorted cell).
I've been very happy with my DieHard from Sears if you need to go that way. Perfect fit. Nice quality. I moved the vent to go through the trunk floor using one of the nipples and grommets already there. Much better than venting into the LH fender well.
Feel free to call me if you have any questions.