Battery drain - need Auto electrician

Gurmot · 6 Jan 2017

Captain Lockheed said:
http://www.maplin.co.uk/p/400mm-automotive-current-standard-blade-type-tester-n48cy

A blade fuse ammeter is useful for these sorts of jobs.
You can get cheaper and more expensive ones (and ones for micro fuses), ir just a lead set for a multimeter _ I am sure you get the idea...

Thank you! I had not seen these before and I can see how this would help with this sort of job :thumb:

deMort · 6 Jan 2017

I use something called an amp hound ..

https://www.amazon.co.uk/Amp-Hound-Voltage-Drain-Tester/dp/B00M7S28MQ

Not the cheapest tool around but it saves haveing to pull fuses .

Do a discharge check and post the values you get .. on a 996 you will have to wait at least 30 mins and probably 60 mins to get an accurate reading ..

996 do a lambda sensor burn off for approx 30 mins so the readings will be high untill it stops .

A pulsed discharge of approx 1 amp could indicate a tracker has been fitted and the battery has failed.

Very high discharge of say 4-6 amps and its seat adjustment motors.

I expect you will have 1 - 1.5 amp discharge and i would start with the PCM , amp etc ..

Remove and unplug the PCM to see if it drops .

Alternator .. hmm .. ive seen it once on a Cayenne , discharge of 1 amp .. very rare if its that .

Have a quick check under the passenger seat .. make sure its not damp or water bottles stuck there that might be leaking .

If you pull fuses then DONT pull any alarm ones .. dead meter and painfull ears at that point !

To test i open the drivers door and drop the catch so its locked , ignition on and connect your meter , then lock with a double press of the key to turn off interior monitoring .

Or just drop the door lock and as above but dont lock and wait till it goes to sleep .

I prefer the locked way as thats how the drain would normally be but either way will work and less chance of an alarm trigger if you dont lock it .

Alarm trigger tends to blow a standard meter as its 10 amp rated .. ok if you have a higher or surge protected meter though.

Gurmot · 6 Jan 2017

Can you please explain what "drop the door lock" and "drop the catch" mean?

Thanks

deMort · 7 Jan 2017

The lock in the door which closes and holds the door shut ..

with the door open you use a screwdriver to push the lock closed.

The car will now think the door is shut so can be locked ot left and it will go into sleep mode .

Gurmot · 9 Jan 2017

Gurmot said:
Mine doesn't have heated seats so this can be ruled out.

I have ordered a DC clamp on ammeter and will have a go at the fuse pulling trick.

I have read some accounts of the voltage regulator (part of the alternator) can develop a fault whereby current can flow back from the battery - diode failure? I'm thinking about order a regulator pack to change as a precautionary measure as I believe these are around £40 or so for a genuine Bosch item - although not sure how easy it is to change and if the alternator needs to come out for this........

Update after a little investigation at the weekend:

I measured the voltage difference with the engine running (cold):

Alternator body to airbox ground stud = 0v
Battery voltage vs alternator (at airbox and jump start stud) = 0.3v

I also bought a voltmeter which plugs into the aux socket and I've left it in as I can easily read the voltage without unlocking the car. This reads about 13.7 - 13.8v at start up and slowly drops to around 12.8v once the car is warmed up (say 20 minutes).

After switching off the engine the voltmeter immediately drops to 12.4v and then decays to 12.2v within 5 minutes (key still in and dashboard illuminated).

I checked about 4 hours after driving and it had dropped to 12v and was the same this morning.

Latest thinking is that it may not be parasitic drain and more likely to be a charging issue (battery has been discharge load checked by a specialist).

Questions:

What should the output voltage of the alternator be and should this be stable or is it normal for it to drop whilst driving?

Assuming the voltage is too low for an effective charge, is this more likely to be caused by a duff alternator, a duff regulator, high resistance connections, slipping alternator drive (is there a clutch on the pulley?)?

Thanks
:thumbs:

Windy101 · 9 Jan 2017

jimC2 said:
I'm experiencing a drain on my battery which occurs when the car is left for 2-3 days without use and proving difficult to identify what's causing it. Local garage has checked major components/likely culprits but can't seem to get to the core problem and was wondering if anyone could recommend a good Auto electrician in Central Scotland. Thanks.

Brian Miller Motors on Lanark Rd in Edinburgh may be worth a call. He is a well established Porsche specialist who works in conjunction with an Auto Electrician for tricky electical problems.

Harv · 9 Jan 2017

Doesn't the ign switch kill the power at the accessory socket/cig lighter? I thought that was fairly normal.

As far as I'm aware the alternator should kick out a constant voltage, say 13.8v-14.5v (on 900rpm idling) regardless and that should be easily measurable with the engine running (make sure there's no other loads turned on/lights/stereo etc).

There is a clutch on the alternator pulley and I have heard of these failing, remove the aux drive belt and it should be apparent when spun by hand if this is duff (slipping in normal drive direction) or not.

deMort · 9 Jan 2017

Turn on all loads .. lights , heated screen etc etc and test at battery .. should be 13 volts if much less than this or just battery voltage and the alternator is failing ..

Alternator faults show up more if under a load .

Gurmot · 9 Jan 2017

Harv said:
Doesn't the ign switch kill the power at the accessory socket/cig lighter? I thought that was fairly normal.
.

Mine is definitely on all the time. I'm curious to learn if this is not right...

deMort · 9 Jan 2017

Gurmot said:
Harv said:

Doesn't the ign switch kill the power at the accessory socket/cig lighter? I thought that was fairly normal.
.

Click to expand...

Mine is definitely on all the time. I'm curious to learn if this is not right...

I think it was the case that early 996 had an ignition based cig lighter and later ones was permanent .. think we used to rewire them to be permanent .. but going back a lot of years now so not 100% on this .

Gurmot · 13 Jan 2017

Update. I made a J shaped pipe from a bit of small bore central heating copper pipe and used it to blow out the back of the alternator (having seen various posts about brush wear on voltage regulators and wondering if there could be current leaking across the alternator/regulator). I'm not saying this was the issue but the voltage has been much more stable for the last few days and not dropped below 13.4v even on a long run.

The other suspect is corrosion in the positive cable running from the alternator/starter/jump start post but I will keep monitoring things and see how it goes.

Voltage sits at 12 / 12.2 in the morning before I start the car. Even afte standing for a couple days. Ok for now.

Gurmot · 15 Jun 2017

Another update with the solution.

I bought a replacement "Y" cable, the one that runs from the alternator to the starter and positive charging post. I also replaced the voltage regulator whilst the alternator was out.

The car now runs at just under 14 volts according to the dash voltmeter, and drops a bit on a long run. Importantly, it now holds a good charge after sitting for a few days and the starter is noticeably faster at cranking.

I did notice that one of the connections on the regulator was not very tight so this could have been the problem but the Y cable crimps were showing signs of corrosion so this was probably the main factor.

Anyway, if you have low voltage, slow cranking and/or apparent battery drain I would look hard at the above.

Cheers - Simon :thumbs:

Gurmot · 21 Aug 2018

Hmm. The slightly dodgy reply above has prompted me to post an update to say that the replacement Y cable is still doing its job and the car is charging properly. I have noticed a slight drop in charging voltage so I guess they all degrade over time but this one should have a few years left in it.

pzero · 21 Aug 2018

Spam advert above Gurmot's last entry has been removed.

cvega · 21 Aug 2018

Gurmot said:
Another update with the solution.

I bought a replacement "Y" cable, the one that runs from the alternator to the starter and positive charging post. I also replaced the voltage regulator whilst the alternator was out.
:thumbs:

Care to share cable part no ?

I had the same issue, battery dead in 2-3 days. This started happening after voltage regulator was replaced. Ended up replacing the whole alternator and now it seems better but still a drain of 0.14amp. At the moment i've given up and the car is on a charger all the time when not driven but would like to sort it out eventually..maybe the cable is the one to go.
Can it be replaced with alternator in situ ?

Battery drain - need Auto electrician

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