hans57

All,

I need to tap all the experts out there with the experience of what I have heard as a known issue with these cars. Battery drain while sitting in the garage. It is not a daily driver and when I go to start it there is not enough juice to crank it. Dead battery. I performed the milliamp draw test and consistently come up wit around 90MA. I removed one fuse and one relay at a time and got no more than 2 -4 MA reduction from only a couple fuse or relay pulls.
What else is there? The car is box stock, including the radio and under seat amp.

What are your thoughts? I was planning on just getting a battery disconnect if all else fails, but that seems to be just side stepping an issue.

Thanks in advance.

Rocket Rob

Can you tell us what circuits/fuses were the source of the power draw? I had a very high current draw on my new C-2, I was seeing 440ma. I isolated the problem to Fuse #1. I then used the factory wiring diagrams to isolate the problem within the circuit. In my case, it was the climate control unit. Once I remove it, the power draw went down to 20ma. I had it rebuilt and have been happy since.

The bottom line, is these power draws can be tracked down, you just need to approach it methodically.

Edit: Meanwhile, I recommend you invest in a battery maintainer. I have one for each of my cars. They do a great job of keeping the battery fresh without risk of over charging. I purchased mine from here No affiliation.

darth

Hans57

How long does it take for the battery to go dead?
The 90ma is likely going to the alarm which is hardwired to the battery and has an internal fuse not easily accessed. I have a 90ma draw and I can start it after weeks of sitting in an unheated Canadian garage. Maybe your battery is weak or something is turning on after you leave it which is taking more than the 90ma's you measured. You can calculate how long the battery will last if you know it's Amp-Hour rating. T(time)=AH/a where a = amps taken, in your case 0.090Amps. For example a 20AH battery will supply 1Amp for 20 hours before it goes dead.

Hope this helps
Bill
90C2

1991 porsche carrera 2

I have the same problem with my 91 cab. I just plug the battery maintainer in the cig lighter if I know I am not going to drive it for more than a week. I am not good at tracing shorts and it is not bad enough for me to pay the labor to let a shop track it down. I do hear a light hum from somewhere on the passenger side from the dash up when I shut her off. I do also have a jump station just in case.

hans57

Darth,

This last time it took only one week to bring it down. The battery is less than two years old, it has a 115 reserve capicity rating. 115ah X 0.90ma = 103.5.hours. Three weeks at that rate of draw. The only thing I do not know is the usage history of the battery before August of last year when I got the car. I am going to have the battery tested.
So, it seems like the consensus is that around 90ma is what these cars pull as the norm, most of which is the alarm. Where is the alarm fuse?

hans57

Rob,

I am nowhere close to that draw, thankfully. I have a battery maintainer that came with the car but now I wonder if it really is working, or my less than two year old battery is bad.
Did you look around at other maintainers before you got the Porsche one? It looks very nicely constructed, but it is about double the price on others that do not have the Porsche logo on it. Do you just plug it in the lighter socket?

hans57

'91 PC2,

Where did you purchase your maintainer?

darth

hans57

A bone stock 964 should draw 30ma ideally. Mine has an aftermarket radio which contributes to the 90ma draw. On MY91 the alarm is located under the front right seat and the fuse is between two connectors. On earlier models it is in the trunk below the hood hinge and the fuse is inside the unit. Some causes of excessive current are the light switches in the doors (i.e hood, passenger, glovebox, engine lid doors). The radio rack alarm system switch.

Hope this helps
Bill
90C2

hans57

Bill,

I also used a test light for my test and when I opened up a door/lid or anything with a light, that made my test light light up. I imagine the MA is huge at that point. I think I may try the alarm fuse just to see what it does. I have also read that an fauley alternator diode can cause high readings, have you heard that?

darth

Hans57

Yes, a leaky diode will cause a drain as it is connected directly to the battery and at the same time would probably create a less than perfect charge condition. The voltage across the battery when the engine is idling should be between 13.8 and 14.4 Vdc. Above 14.4 Vdc at idle indicates a shorted diode and if it's below 13.8Vdc above 1200rpm you have a charging problem.

Bill
90C2

hans57

Bill,

Are the two red wires attached to the positive clamp the alternator wires?

darth

Hans57

Yes, atleast one of the red wires goes to the alternator but I'm not sure about the other - it could go to the alarm or the starter relay or fuse box or something else? You can also check if the alternator diodes are OK by the detection of AC voltage at the battery while the engine is running and charging the battery - there should be almost zero AC voltage at the battery.

Bill
90C2

hans57

Bill,

I'll give that a shot. Thanks.
I am also placing a order for a CTEK battery maintainer to make sure I am good in that area.

Tinwan

I replaced the original braided earth strap, that was the main culprit. Then installed the following equipment below
1- Yellow Top Optima Deep Discharge Battery
2- Priority Start Pro 12v (buy in the US) direct
3) C-Tek Trickle Battery Charge (leave in the compatment) so you can charge it anywhere anytime when AC outlet is close by
When the car is parked in the garage, I open the hood and leave the battery on Trickle charge as its not driven everyday. Even if the battery gets low the Priority Start will sense the voltage fall off & auto cutt off the battery electronically so you will always be able to start the car.

hans57

Tinwan,

You found the braided earth strap to be a main culprit in drawing the battery down? How so? I have a Ctek on the way, and I may do some research on the Priority Start. I also have a new battery, they replaced mine for free.