Strong Electrical drain problem! 1999 Porsche Boxster

[JFP in PA]

Originally Posted by radiodjkev

I have tried test's with a cheap Sears mulitimeter..
(so it says, but I think it is far short of a multimeter) and I have tried all the settings. The meter has on it: dcv, acv, dcma, dcua, temp, and there are 5 different dials to read from..

I just can't get anywhere with this problem. I have to disconnect my battery anytime I leave the car sit for more than 3 hours. It is a strong drain.
And it will also drain like this with all fuses removed from fuse box.

No lights on, no Ignition drain, key out always. No aftermarket completely stock.


Kevin

What you need to do is disconnect the + cable at the battery, set your multi meter to "milli amps" (mA) and connect it between the + cable and the battery. It will then read the current draw on the battery. You can then pull fuses and relays out, one at a time while watching the meter for a drop in the current draw. Replace each fuse/relay after each test, and by a process of elimination, you will eventually indentfy the circuit or circuits that are causing your problem............................

[Paul]

A drain measured in milliamps (less than an amp) would not drain a good battery in 3 hours.

The drain in this case is high enough to possibly damage a multi meter set to milliamps.

Since the drain exists with all the fuses out, one must limit troubleshooting to those parts that are not fused.

[litteng]

i have seen you posts regarding the problem over at pelican too. to say the least it is baffling...
so lets start with the basics.

cables on battery post stif and hard or flexible, and signs of corrosion? if so replace ends and clean cable and coat with protective slime (nonconductive grease etc)

test battery voltage disconnected should be around 13.xx+ volts, let it sit for a day and recheck; still 13.xxv? if not the battery is junk get it replaced on warranty. swap it into some other vehicle and see if it goes flat there, this would indicate the battery is bad, and lastly you can take it back to the supplier and have them do a load test to confirm the battery.

charging system check with alternator running, what does porsche say? id expect 14+ v at say 3500 rpm

if as you say you cannot see any milliamp or amp draw between the ground cable and the battery or the positive cable and the battery

what recent modifications have you made to the car or what service work has been done. i remember you claim no mods, but even service work if not done correctly can screw something up... so double check this and ensure you haven't got something a foul

the biggest draw item on a car is the starter, so now with the advanced age of your "B" its time to check the cable from the alternator to the battery and the starter. check the place were they go thru the "firewall" to the front of the car, is the rubber grommet still there? any chaffing on the plastic sleeve?

thats all i can think off

i had the battery in my r1100 die over winter, if the bike sat for anymore than 1 day, the battery didn't have enough juice to start the bike, and had the same with a 2 yr old battery in a 2 yr old car, sometime you get a lemon, i know it s hard to believe but it can happen.

best of hunting and hope this is of some help


ps

ground straps, can come loose and the battery may have the juice to light the bulbs, but not to spin the starter, ive also seen the grounds straps totally corroded away, and with no ground strap no ground path no go, so this would mean checking the ground strap at the battery and down under the engine and also by the starter if there is one...

[JFP in PA]

Originally Posted by Paul

A drain measured in milliamps (less than an amp) would not drain a good battery in 3 hours.

Actually, yes it can. We have seen several cars with this type of issue in our shop that had current draws less than one amp that killed a battery in an hour or two.....


The drain in this case is high enough to possibly damage a multi meter set to milliamps.

Not necessarilly as most meters are fused to protect themselves if excessive current flow takes place, and nearly all digital meters "autorange" and will switch to a suitable range by themselves.

.................................................. ...

[Paul]

A new, fully charged, and warm battery in our cars should be able to provide at least 60 amp hours. To drain such a battery in 3 hours would take a 20 amp load.

A one amp load would take 60 hours.

A 20 amp load could even damage the leads of a multimeter.

[Paul]

Also a 20 amp load at 12v will generate 816 BTUs of heat

[Jaxonalden]

Amen Paul, I'd love to hear what the "We have seen several cars with this type of issue in our shop that had current draws less than one amp that killed a battery in an hour or two..." fix was. Less that an amp and killing a 800+ amp hour battery? Are they kidding? The math simply doesn't support that statement... and they run a shop?

[JFP in PA]

Originally Posted by Jaxonalden

Amen Paul, I'd love to hear what the "We have seen several cars with this type of issue in our shop that had current draws less than one amp that killed a battery in an hour or two..." fix was. Less that an amp and killing a 800+ amp hour battery? Are they kidding? The math simply doesn't support that statement... and they run a shop?

Yes, we do run a very successful shop; and in the Northeast, where weather often goes into negative numbers, a battery with a couple of years of service on it can be pulled down enough by a low amperage drain to not be able to turn over a cold engine after a couple of hours in the cold.

While you are "checking your math", go to the BCI (Battery Council International) and check on how amp hour ratings tests are done and their actual relationship to and real-world problems effecting cold cranking performance. I would also suggest you consult Vinal's fourth edition of Storage Batteries which has an excellent discussion on issues that impact the amp hour output efficiency in lead-acid storage batteries, paying particular attention to effects of aging and temperature...............

As for the fix, we isolated the problems circuit(s) using a digital multi meter and either repaired the problem, or if requested by the owner, disconnected the problem circuit, usually by leaving out the fuse.

Have a nice day………………….