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When being charged by the alternator you can expect to see roughly 14.1 volts at a reasonably charged battery assuming there is no heavy load and the alternator is good.
When not being charged the battery voltage will gradually drop to roughly 12V. How quickly depends on the health of the battery and any residual load.
If the battery voltage gets down to about 10.5V there will be insufficient power to drive the starter motor.
The parasitic drain does not have to completely discharge the battery to render it inoperative for starting. (See above.)
If you let the battery discharge completely the plates can sulphate which reduces the capacity of the battery significantly, often rendering it totally inoperative if left discharged.
100mA is way too large a discharge unless the car is used almost everyday.
I gave up trying to find the sources of the parasitic drain but the items mentioned in the thread all apply. i.e clock, radio, alarm etc. My solution was a trickle charger as I am lucky enough to have a garage with power.
I plug it into the cigar lighter as this is live on my model all the time and quick to fit and remove.
If anyone does get the drain down to near zero I would love to know what items are problematic.
('96 951 (944 Turbo))
My brutalized early 85 944. A very pretty car which I have been casually fettling to keep on the road. The window lifter relay was always ON but the windows would not work without the Ignition ON.
I disconnected the Brown/Yellow wire from the lifter relay. This appears to be connected to the door and boot lid switches ?. The window lifters now only work from the ignition key and the lifter switches
as they should until I can figure out the wiring.The result was a drop in drain current.
The key operated electric Pax/Driver unlocking system was very unreliable so I disabled the relay for that system. The car unlocks manually from the key without the extra electrics. More work on that system needed.
The result has been a large drop from 97+ mA to less than 1mA..The very small current can now be attributed to the Radio memory and clock.
Beware of the wireless as I was fooled by it for a bit.
I gave the battery an equalizer charge with my external charger and a week later the battery is still sitting at 12.65 V.
My car once had an alarm but I suspect it is long gone.
Each door switch has two circuits: one for the interior lights and one for the window relay. This allows the windows to go up/down if the door is open, even if the key isn't in the ignition.
Each circuit is a single wire grounding to the bodywork. If the insulation has worn off or it's gunked up with something conductive then it might always be signalling that the door is open.
I've tried re-building the door switches, but their design is pretty cheesy. It's easy to get one circuit or the other working, but they don't want to balance once they've got a few decades on them. I ended up getting new ones.
Thanks for the extra info, Jeyjey,
The door switch turns on the interior light so that lot is probably ok. However as I am always working on the interior I have been leaving the drivers door open. This would explain
the window relay being on.
The only way I know of how to deduce which circuit it is with the drain on it, is to ! disconnect the positive (or negative) battery terminal. connect a 12 v DC bulb to the cable and the other side to the battery. with the switch off, the light should glow. then you go to the fuse panel. Pull the #1 fuse..and check the light...did it stay on or go out? If it stayed on, then replace the fuse in the panel and pull #2. Keep going until you get to the point when, you pull the fuse, the light goes out. You have just found the faulty circuit. The only circuit that might remain connected would be the DME circuit.... but not very much. All doors closed and the hood illumination bulb removed. As long as there is a draw on the system, it will remain until fixed. THAT we know. GOOD LUCK!
Each door switch has two circuits: one for the interior lights and one for the window relay. This allows the windows to go up/down if the door is open, even if the key isn't in the ignition.
Each circuit is a single wire grounding to the bodywork. If the insulation has worn off or it's gunked up with something conductive then it might always be signalling that the door is open.
I've tried re-building the door switches, but their design is pretty cheesy. It's easy to get one circuit or the other working, but they don't want to balance once they've got a few decades on them. I ended up getting new ones.
You know I don't get the way the window motor relay is wired. When the relay is in a de-energized state, I get a dead short to ground with the door open because of that door switch ground circuit wire tied into pin 87a when the ignition is off. That's the only way it can work: pin 30 is hot at all times, and when the relay is de-energized pin 87a has power as well. Turn on the ignition switch, which energizes the relay, and now pin 87 has power, allowing you to move your windows. The first time I connected a battery to my '84 something started smoldering, and that was the reason why. I pulled the five terminal relay and installed a four and all is well. I also tagged that wire on 87a to remind myself what it is and why it doesn't go to anything.
On later cars (at least) there's some logic in the relay.
The door-open circuit energises the relay based on +12V (KL.30) on pin 30 and GND (door switch) on pin 85b.
The key-on circuit energises the relay based on +12V (KL.X) on pin 86 and GND (KL.31) on pin 85.
I just experienced a similar problem. I spent many hours chasing a drain that would empty a battery in under 24 hours. Ultimately it was the driver's passenger window switch. I'll note that about two weeks before the drain appeared, the switch ceased working. So, if you encounter this problem, you may want to focus on the doors first.
On later cars (at least) there's some logic in the relay.
The door-open circuit energises the relay based on +12V (KL.30) on pin 30 and GND (door switch) on pin 85b.
The key-on circuit energises the relay based on +12V (KL.X) on pin 86 and GND (KL.31) on pin 85.
That schematic is interesting. That's not the garden variety 5-pin Bosch relay my early cars use. I'll have to look up the part number and see what it looks like in the flesh..
Having a parasitic drain on my 2006 Boxster S. Seems to have started all of the sudden after I washed and waxed my baby. Drain is 1.2 Amps with Key off, doors shut, hood open (for access to battery terminals) and light in front trunk removed). Pulled every fuse last night, no change. I lifted the Positive terminal on my alternator and got the draw to drop to 0.9 amps.
Anyone see this before.
Are there any other fuse panels besides under the dash drivers side? Where are the relays? How hard is it to get the alternator out?
My solution to a parasitic drain was to install this historic style battery cut-off switch as used on historic Porsche 911 RSR, 917 and 356 models. Yes, I know -- it's sacrilege -- but kids dig it.
since apparently the drain reared it's ugly head, disconnect the battery, let the car dry out for a day or two, then reconnect the battery and check for more drain. It could? be a situation where water has pooled and is shorting out a wire or two. If you pulled all the fuses and there wasn't an indication, it could also be bad diodes in the alternator..apparently from earlier posts, the DME drain would be very low. There is a very remote possibility that it could be the starter grounding out internally, but it is unlikely, and if it werre it would be probably smoking hot to the touch. Also the battery would go flat in a VERY short time. Pull the alternator and get it tested at your local FLAPS. If the diodes are bad, it'l show up on the quick test. HTHsome.
04-18-2020, 07:19 AM
Voltages
