How much Idle current draw?

[Brando]

So this weekenend has been pretty productive thus far. Friday I installed a new set of falken ziexes, yesterday I installed new ball joints, set the ride height and installed my new stereo (had been sitting in the box for 6 months now).

But all of that is done and good, now I need to determine if I have something slowly draining my battery. If I let the car sit for more than 4 days, the battery doesn't have enough juice left to crank. I have verified that the system is charging correctly (I see between 12.8V and 13.3V while running, even with the stereo & amps on.

Using my multimeter, I've checked the amp draw while the car is off, alarm disabled, 38-39.8 mA draw. Is that too much? I usually disable the alarm when i park at home, The car goes on a lift that requires a special key to operate so it doesnt have to be locked.

If that is too much, what is ideal?

Thanks.

[86 911 Targa]

Originally Posted by Brando

So this weekenend has been pretty productive thus far. Friday I installed a new set of falken ziexes, yesterday I installed new ball joints, set the ride height and installed my new stereo (had been sitting in the box for 6 months now).

But all of that is done and good, now I need to determine if I have something slowly draining my battery. If I let the car sit for more than 4 days, the battery doesn't have enough juice left to crank. I have verified that the system is charging correctly (I see between 12.8V and 13.3V while running, even with the stereo & amps on.

Using my multimeter, I've checked the amp draw while the car is off, alarm disabled, 38-39.8 mA draw. Is that too much? I usually disable the alarm when i park at home, The car goes on a lift that requires a special key to operate so it doesnt have to be locked.

If that is too much, what is ideal?


Thanks.

38-39.8ma is well within the Bentley spec.

38maX96 hours=4A

How old is your battery?

[Joe Bob]

Might want to have a load test on the battery and invest in a battery tender.

[Brando]

86 911 Targa, the battery is an optima red top, bought it in November 2009 (the sticker says). It holds a charge well enough.

MikeZ, I may have to do that. I don't think my multimeter has a load-testing function, but it does have a clamp attachment... Have to read the manual. Recently I've been pulling the battery and charging it indoors with my small 12v -2A trickle charger and it's like-new.

[Joe Bob]

A quick test.....charge battery, turn lights on, crank engine. If lights dim, you need a battery.

[Lorenfb]

"38maX96 hours=4A"

???

Actually: 38ma X 96 hours = 3.64 ampere-hours (capacity) of loss in 96 hours

or with a draw current of 38ma and assuming a good 70 ampere-hour
battery at 1/2 capacity to allow good cranking to start then:

Time for 1/2 capacity = 70 ampere-hour / 2 / 38ma = 921 hours = 38 days

[86 911 Targa]

Originally Posted by Brando

86 911 Targa, the battery is an optima red top, bought it in November 2009 (the sticker says). It holds a charge well enough.

MikeZ, I may have to do that. I don't think my multimeter has a load-testing function, but it does have a clamp attachment... Have to read the manual. Recently I've been pulling the battery and charging it indoors with my small 12v -2A trickle charger and it's like-new.

I don't think your hand held meter will handle the starter current draw, and, might blow a fuse.

Try a Sears or other battery test station.

The key here is, if your battery is charging, then there might be an internal discharge over the describes time period.

Joe Bob is spot on with a load test.

Good luck,

Gerry

[RoninLB]

Originally Posted by Brando

12.8V and 13.3V while running, even with the stereo & amps on.

while running meaning a high idle of 1,500 rpm with lights etc on

if so that sucks


I'm careful with my Optima as it seems to develop a memory of only accepting a low charge if stressed under abnormal charging. Sometimes I'll whack my Optima with the "start" button for a few minutes on my charger while keeping my hand on the battery feeling for heat. If I start to feel heat "start" charging is turned off but I turn it off before then. Meanwhile that usually brings my running system charge down .2v after it's been running long enough to recharge. In my system I know if the running system is 14v or 14+v I know it needs another whack to bring it down to 13.9v

[RoninLB]

these are cool battery testers to have around and last forever

this Snap-On YA201A is around $100 but other decent mfg are 1/2 that





ps: it's nice to see Loren around

[86 911 Targa]

Originally Posted by RoninLB

while running meaning a high idle of 1,500 rpm with lights etc on

if so that sucks


I'm careful with my Optima as it seems to develop a memory of only accepting a low charge if stressed under abnormal charging. Sometimes I'll whack my Optima with the "start" button for a few minutes on my charger while keeping my hand on the battery feeling for heat. If I start to feel heat "start" charging is turned off but I turn it off before then. Meanwhile that usually brings my running system charge down .2v after it's been running long enough to recharge. In my system I know if the running system is 14v or 14+v I know it needs another whack to bring it down to 13.9v

Here's another thought..........

Good luck,

Gerry

[RoninLB]

when the alternator regulator goes kaput it may overcharge

every 911 should have a volt gauge somewhere or you risk frying electrical parts on an overcharge

the commom alternator failure is when diodes go kaput and amp/volt output fall.

[911pcars]

Originally Posted by Joe Bob

A quick test.....charge battery, turn lights on, crank engine. If lights dim, you need a battery.

When cranking the engine, battery voltage drops normally since it's trying to push much current into the starter motor circuit. In fact, a seat-of-the-pants load test is to crank engine for 10-20 seconds (coil wire grounded) while monitoring battery voltage. If battery is up to snuff, voltage should stay above 9 volts.

And at 9 volts, the headlights, if ON while cranking, will dim, but that's quite normal.

What's the running voltage with all electrical accessories ON (e.g. high beams, A/C/vent. fan motors, rear window defroster, windshield wipers, etc.). If the charging system is okay, the charging voltage should remain higher than the "at-rest" battery voltage. Otherwise, the electrical circuit is running at a deficit under these conditions (i.e. battery is discharging).

Sherwood

[Joe Bob]

My yellow top is going on 8 years....they don't dim.

[T77911S]

have the battery load tested. that is the ONLY sure way to know its condition.

your charging volts is a bit low too.

[Trackrash]

Don't know if this will work on an optima, but this is how I test an old battery.

Make sure battery is fully charged, use a trickle charger over night.

Measure battery voltage. Should be over 12.

Short the coil and crank for 10 seconds. Repeat two times.

Check battery voltage again. If down to say 11 or below the battery is not holding a charge.

[RoninLB]

I used the engine off/lights on starting routine to see if started was kaput. If a good battery/good connections etc and lights just about go out the starter is drawing way to many amps

[T77911S]

if you want to test the battery at home, measure the battery voltage WHILE cranking, you could even check it while cranking with the lights on.