82sc Parasitic electrical draw

[Kerschbaumer]

Hello All,

Bear with me - I admittedly have a blindspot for all things electrical. Last fall I replaced battery and since then the new one dies too. I have been advised I may have some parasitic drain on the battery so hooked up my multimeter (ammeter) and seem to be losing 0.5 Amps. I started pulling fuses and have determined I am losing about 0.2 Amps from the fuse #16 (Fuel pump) and 0.2 Amps from fuse #17 (Emerg flahser, wipers, defog). The other 0.1 amp I have no idea as of yet.

Other thing of note - the charging system seems to output 13.1 volts which a friend said is ok but low - I had alternator replaced about 3 years ago so assumed it is good but not sure.

I have the Bentley manual but have never read a wiring diagram before so before I start trying to figure things out I was hoping some folks in the group may help focus my efforts.

In case it may be partially a result of the last work I did on the car - over last winter I did a major tune up (new plugs, cap rotor wires) and heater back date (removed blower motor). Also had took apart power rear view mirrors to fix broken bushing and when I put back together I must have gotten some wires crossed as but have yet to dive back in there.

I am hoping to have battery replaced under warranty - maybe a bit cheeky as it was me who likely killed it but worth a shot.

Thanks in advance

[proporsche]

the alternator should give you up to 14,2 V..any lower is not really good.If you have internal regulator i`d start replacing the regulator only and in the same time look at the rotos where it meets the brushes ,how it looks...
Ivan

[mysocal911]

Originally Posted by Kerschbaumer

Hello All,

Bear with me - I admittedly have a blindspot for all things electrical. Last fall I replaced battery and since then the new one dies too. I have been advised I may have some parasitic drain on the battery so hooked up my multimeter (ammeter) and seem to be losing 0.5 Amps. I started pulling fuses and have determined I am losing about 0.2 Amps from the fuse #16 (Fuel pump) and 0.2 Amps from fuse #17 (Emerg flahser, wipers, defog). The other 0.1 amp I have no idea as of yet.

Other thing of note - the charging system seems to output 13.1 volts which a friend said is ok but low - I had alternator replaced about 3 years ago so assumed it is good but not sure.

I have the Bentley manual but have never read a wiring diagram before so before I start trying to figure things out I was hoping some folks in the group may help focus my efforts.

In case it may be partially a result of the last work I did on the car - over last winter I did a major tune up (new plugs, cap rotor wires) and heater back date (removed blower motor). Also had took apart power rear view mirrors to fix broken bushing and when I put back together I must have gotten some wires crossed as but have yet to dive back in there.

I am hoping to have battery replaced under warranty - maybe a bit cheeky as it was me who likely killed it but worth a shot.

Thanks in advance

Focus on eliminating the current draw first, i.e. it should be less .10 amps (typically about .030 amps).

[Kerschbaumer]

Ok, thanks all - I think I have my decimal places mixed up - I seem to have between 0.04 and 0.05 amp loss per attached pic

[Kerschbaumer]

Sorry - no pic - cant seem to upload a photo

[Kerschbaumer]

Should the fan belt not slip when turning fan using the fan belt tool?

Just checked charging system and getting 13.25V. When troubleshooting the 101 book says to check alternator belt tension first. I replaced the belt this winter (size 10x710) and have correct tension (10-15mm) according to the book but when I use the fan belt tool to turn the fan - the belt slips.

Wondering if that is why I am not getting correct charging

[proporsche]

if the belt would be way too loose i could understand it might affect the charging but not really.Are you using 6 shims when you did the belt re?if you want to turn the fan blade with the tool use one hand to push od the side of the belt and the other on the tool to turn..

the 13,2 is not good at all...

[Kerschbaumer]

Ok, thanks - so it sounds like belt tension should not be the problem. What is my next move - buy a VR and if that doesnt solve it then I have to buy a new alternator (which includes the VR)?

Should I be looking at anything else?

[proporsche]

start with removing the alternator ..don`t forget to disconnect the battery...once it is out remove the regulator and see how the brushes look also - i have mentioned -check the rotor ..
Ivan

[dhanl82]

Hello,
I thought that I would share a few thoughts since I had a similar issue with my 1982 SC.
I did not have parasitic draw problems but alternator was only charging at a little over 13 volts. After checking some thinks it turned out to be a problem with transmission ground strap, replaced that and it solved problem. The other issue I had was that the cars "switched" power was always one volt less than what I measured at battery - turned out this was caused by a weak compromised contact in the ignition switch. Changed the electrical part of ignition switch to solve problem. I would also share that my car charge rate is usually between 13.7 - 13.9 depending upon what accessories are in use. I have absolutely no problem with maintaining battery full charge at this rate.
Hope this helps.
Dave

[pampadori]

Had the same issue with the transmission ground strap.

Easy to test- use a jumper cable and connect one end to fan housing and other end to chassis, essentially making the jumper cable into another ground strap. Confirm what voltage is now with supplemental ground strap.

[porsche930dude]

Somebody correct me if im wrong but the only things that should be drawing power are the clock and the stereo. Unplug them and retest. They shouldnt kill the battery for atleast a few months

[Kerschbaumer]

All great advice - will try and get to it tomorrow!

[gomezoneill]

If it's not the ground strap pull the alternator and have it tested at a local parts store. My money is on the ground strap though.

[scotricker]

I have watched this with my 78SC, too. It has been mentioned before, clock, and maybe the over the doors light switches. Whatever. I just keep a battery tender on the car always when it's home in the garage. Probably not fixed, but it starts every time.
Sometimes it is a few weeks between drives. It might be different if used daily.

[porsche930dude]

Originally Posted by scotricker

I have watched this with my 78SC, too. It has been mentioned before, clock, and maybe the over the doors light switches. Whatever. I just keep a battery tender on the car always when it's home in the garage. Probably not fixed, but it starts every time.
Sometimes it is a few weeks between drives. It might be different if used daily.

yes good thinking! make sure the overhead lights arnt on they do get bumped sometimes

[aoncurly]

If you're like me, I park in my garage and cover my car and leave my frunk hood closed but unlatched. I've found out that when the hood is unlatched, it is open just enough to turn on the frunk light but I couldn't tell it was on. My new battery would drain in a week this way. I've since disconnected the light and hooked up a Battery Tender and all is fine. But if you leave your frunk hood unlatched, it's something to be aware of.

[Lyle O]

With the hood open, but within the safety latch, the trunk light should not be on. You can adjust it (the light switch) so it only comes on when opened beyond the safety latch (at least my '87 has a threaded switch).

[TwoBluPorsches]

The 1982 ought to have alternator mounted regulator.
Regulator could be bad or the brushes that connect regulator to the rotor could be worn out. (unlikely you have worn brushes if your alternator is only a few years old)
However you should have it checked and consider a new regulator if it won't deliver correct voltage on a tester.
A new regulator gets you new brushes.

The alternator regulator supplies a voltage to the rotor (through brushes) that ought to result in the alternator providing 14 volts. If the alternator and regulator aren't properly grounded (compared the battery or car chassis) the voltage won't be right and the alternator can't provide it's full current rating.

As been mentioned by several people, check the transmission ground strap.
Also, check the battery ground strap.

More difficult, but very important, check the ground strap between the alternator and engine case.

Checking the ground strap means looking at it to see if it has corrosion, broken wires and if the surfaces where it is attached at each end allow for good conduction.
You are likely to need to take it off for inspection.

Make sure you're getting 13.5 to 14.2 at the battery with the engine running 1,500 RPM and accessories off. (per Bentley manual)

Braided ground straps are preferred over wire for grounding equipment in many electronic and electrical systems because it does a better job of grounding noise and it is more flexible. (a cable with a very high count of fine conductors has the same result)

However, a problem with ground strap or cable that is not using fully tinned wire is that it corrodes more easily. I can't recall if the 911 has tinned copper or if it is bare.
I think you may find both depending where you're looking and the year of the car.

If you suspect anything with the ground straps, you can buy tinned copper braid and make your own.


A bit off topic, but while your looking at things and doing stuff.
If you want best performance from your CDI, make sure the CDI case is grounded with the appropriate straps and consider beefing up the grounding between the coil and the electrical panel/CDI. Besides having a good path to the positive side of the coil it's important to have a good return path to assure the best operation of the CDI and coil.

[Kerschbaumer]

Just tried the jumper cable thing and still getting 13.3v charging. Trunk light has been disconnected, and interior lights etc seem ok - heading out now for long weekend but will get back at it next week.

Perhaps next step is pull alternator and get it tested. Thanks everyone - talk soon!