Trio

I am a newbie to electronics, but am trying to test for a current drain on the battery using the very helpful write-ups found here on this topic. Anyway, I want to be sure I am reading my multimeter correctly. When placed in circuit with one of the battery cables disconnected, and all lights etc off for more than 20 minutes, and the multimeter set at 10A, I am getting a reading of .03 . I assume this means I have a current draw of 30 milliamps. Correct? This would be a little high but still in the "normal" range, also correct? Thanks for any help.

Sten

Yes, that's a draw of 30mA, which is about the same as my C4 draws.

theiceman

reduce the range of the meter and you will have a much more accurate reading. You should be able to set it to the ma range.

30ma does sound a little high but not unreasonable. PS you don't need 20 mins, should show accurate as soon as any interior lights go out and an alarm has armed.

warmfuzzies

20 mins after a run to allow the CCU fan to switch off.......

Kevin.

chancecasey

Maybe I'm missing something but isn't .03 x 10 = .300 or 300mA? 300 is far too high if that is in fact the current draw.

theiceman

Sorry fuzzies didn't realize you were driving it , I thought you were just going to the car and sticking the meter on. But be aware a bad relay or something that leaves that fan on will kill your battery.

Chance .. he is reading .03 amps which is 30ma

KirkF

The formula is:

.03 Amp * 1000 mA/Amp = 30 mA

Which is typical for a C4. Your car should start fine even if you leave it for a month or so with those readings.

Kirk

chancecasey

I know what a milliamp is - I was multiplying the reading by the scale he selected (10A). I know that sometimes this is correct, sometimes incorrect, depending on the DMM and function in question. For example, when measuring megaohms and using the 1MOhm scale on MY DMM, I get a "1.0" for a 1MOhm resistor, not "1000000.0".

I also have to wonder why he's "testing for current drain" in the first place. 30mA shouldn't cause any problems, but 300mA certainly would.

Trio

Good question. I am testing because I installed a new Optima Redtop last fall. Since that time, I have had intermittent problems with a weak battery after the car sits for 4-7 days. Not every time, but maybe every two out of three times. When it starts after sitting, the battery will read around 12.3V just prior to starting. When weak, it can get all the way down to 7V after a week or so. In checking the alternator output, I consistently get a reading at idle of around 13.5-13.6V.

Over the weekend, I put my trickle charger on for a day after the car left me stranded (had to be jumped to get it started). The trickle charger only got the battery up to 11.7V after 24 hours. I have been checking occasionally for a current draw, but have found nothing other than what I described in the first post. Just wanted to be sure that I wasn't misreading the DMM as 30mA instead of 300mA as Chance suggests.

Methinks I have a suspect battery. Going to get it load tested tomorrow. It is the intermittent occurrence of the problem that has me wondering...

Appreciate all of your ideas.

Sten

Tom,
If your battery is discharged then it will take a trickle charger a few days to fully cherge the battery - it will only be putting mA into the battery. When my C4 is in the garage, I leave it connected to a trickle charger that monitors the battery voltage, and only charges the battery as necessary. If your battery terminal voltage is down to just 7V, then I suspect you have, as you've figured out, an intermittent drain. It's more usual for a cell to go down in the battery completely rather than intermittently, but if you have it load tested then that should prove it one way or the other.

Trio

Had the battery load tested today - strong readings and everything checked out fine. Also had the alternator output tested - I am getting about 85 amps of output at 2000 RPMs, and about 13.6V across the battery terminals at idle. So neither the battery or the alternator were bad (at least today )

This takes me back to testing for a current drain. If I am reading this DMM correctly, then I have a 30mA drain, which is not drastic. This only other item I found was the the driver's side door pin switch was corroded and not grounded, so the interior lights would not turn on when the door opened. I cleaned the switch and now have good contact, and the switch now works as it should. From what I have read from Adrian in the archives, this surely couldn't be related to a phantom current drain (could it?).

I will just watch and wait now for a few days to see if I get a drained battery - I have tried everything else... twice .

DarrylH

I tried to find it but couldn't, but somebody explained the procedure better than I can. I think some current draws will stop after the battery has been disconnected and will not restart when you connect the meter. You need to keep your multimeter probes in contact with the battery terminal and the ring terminal as you disconnect the battery - so the circuit is never broken. I could be wrong...

theiceman

chance the 10 Amp range is just the maximum reading that the meter will read in that range. and it usually just expresses in the larger number .03A vs 30ma. Especially for current you have to be carefull and start at the largest range and move down as the meter is acting as a low impedance device and the current is passing through the meter. That is why the mete is usually fused with a big *** fuse inside if oyu have a decent one. most newer devices are autorangers so this is a dead issue anyway.

I think by nature of your problem ( intermitent ) you are going to have to check it consistently until it happens. If you just check now and again and it only happend now and again ..... well consider buying a lottery ticket. I think you are on the right track and something is intermitently not turning off. What about a light under the hood , do you have deck lid light ?


You could try popping the fuse that runs this stuff for a month ( depending on what else it powers ) if your problem is gone at least you are on the right track. I see you had it tested but a leaky diode in your bridge rectifier on your alternator can also drain your battery.

Good luck.

Trio

I'm not that lucky, so the lottery ticket is out. Good advice on the deck lid light, but I removed the bulb months ago when this first started occurring. Of course I couldn't get by that easily...

Appreciate all the advice. I'll let you know if I have a eureka moment.

theiceman

cool..