User 4221

.21V on the Optima? Wow, that thing is flatter than a pancake.

To discharge that deep and remain there, it must have seen quite a load for the duration of connection.

Most batteries will "bounce" back up a few volts when disconnected. Good luck resurrecting this one.

LlBr

Test amperage as follows: Disconnect positive lead to battery, put ammeter negative to positive on battery, put ammeter positive to the unattached positive cable. Just to be totally clear: we are measuring amps here not volts; set meter for amperes not volts.

You should have a very small draw when the car is parked and shut off with keys out and doors closed. Don't know what it is for your car all I know is it should be much much less than 25 milliamps. Probably should be almost a perfect zero if the car has no alarm or computer stuff; the clock would be the only thing running? I hope that helps.

rusnak

wow, .21v would meant the battery is toast.

We should start a battery thread on deep cycle vs. starter batteries. I was looking at Exide gel batteries, and they look very interesting to me. I was also looking at Optima deep cycle gel batteries.

As for the drain, just keep the ammeter hooked up, and start pulling fuses. One circuit will have a relay or something that is stuck, or have a bad switch. Try the rear heater blower circuit.

LlBr

I thought deep cycle were heavier. Nevertheless I hate it when I'm waiting in the car and that warning comes on the PCM about battery use, "blah blah, only a short time." Who's gonna test it to see how long you can enjoy music or learn the Nav system while parked without getting stranded?

theiceman

PCM ? Nav system ? what year is this ? ... the only music my car ever makes is out the exhaust ..

LlBr

Yeah! I love it! The way it should be. These new "luxury" cars have a written read out warning about using the electrics too much when parked.

RSWiser

Thanks for the info on how to test for drain. I will try this tomorrow.

Rob 1980 911 SC

RSWiser

Before I put my battery back in or a new battery, I need to figure out where the drain is.

Thinking back to last week and what I did differently. The only thing I did different than any other time I go for a drive is that I turned the Rear Defroster on and off. Didn't notice if it worked because it wasn't that fogged up.

Someone mentioned that a relay could be stuck. That is my guess. How do I test for this.

Thanks,
Rob
1980 911 SC

HarryD

Rob:

Find the fuse for your Rear defroster. Remove it. Set your test meter to 10 amps and with your key in the run position, touch both terminals where the fuse used to be. If you read more than 0 amps, go to a lower setting on your meter to verify that there is indeed 0 amps. If more than 0 amps, the relay is stuck.

Again, the way to find a drain is to connect your amp meter to the batery as described above. Note the current draw and start removing/replacing fuses one at a time. when you pull a fuse that is on a circuit drawing power, the ampmeter will reduce it's reading. Verify if that circuit is supposed to be off.

RSWiser

Thanks for the help. I'll get a new battery and give this a go.

Rob

JBrown

I have a red top in my car and I have all kinds of electronics hooked up to it. Amps, stereo, etc.
I can let my car sit for a month and still cranks over and starts with authority.
If the car sits for some time and it barely started and you take it out for a 20 min ride, that is not going to be long enoeph for the battery to charge it self. Do a draw test, if it all looks ok charge up the battery to full capacity and you will have no problems with it.

wwest

But never, NEVER, have the battery disconnected with the engine running, the alternator/regulator will drive the output voltage into "orbit", potentially blowing every electronic, solid state, device in the car.

Also, while this may be obvious, DO NOT attempt to start the car with the ampmeter connected, unless the ampmeter is rated for 300-400 AMPS.

I check for alternator operation by measuring the terminal voltage of the "fully" charged battery(~12.35 volts), starting the engine and turning on EVERY voltage load available and verifying that the battery terminal voltage is now above the non-running no-load voltage(>12.50 volts).

wwest

"...How do I test for this.."

Well, bottom line, you don't....

It would not be at all unusual for a well used/worn relay, especially a fairly high current (window defrost heat), and even moreso a relay used to switch power for an inductive load (fuel pump, blower motors, etc.), to have the contacts so corroded/worn that they stick/"weld" closed once in awhile. The bad news, sorta, is that once the power is switched off even the slightest bump or vibration will often cause the stuck relay contacts to open.

And that "sticking", may only occur one of each 100 cycles, even for a well used/worn relay. The best solution, IMMHO, is that if you suspect a relay to be sticking occassionally then open it up and inspect, up close, the condition of the relay contacts. In days of yore there was always a small file set, relay contact burnishing kit, in my travel, field service case.

Left over from my days in the USAF, keeping B47's and KC97's flying.

LlBr

You sure about the "200" number? Here's the specs for todays electronic-laden cars:

Just checking.

rusnak

We did a drain thread a while back. I believe <40ma was the consensus "normal" range for constant draw. I believe Loren calculated that it would take about a month at that rate to drain a battery. I would probably think something was wrong if there was >50ma draw.