Battery discharge check : dumb questions

Bukowski · 12:27 PM

I'm following the Clark's Garage how-to for excessive battery discharge check.

I followed instructions on the HF multimeter for current. I touched the red lead to the + battery post (car cable disconnected), black lead to - battery post (car cable attached). I saw about 100 mA on the meter. The cables get hot fast, so I touch for two seconds. Tried removing a couple fuses, not much change.

Is that right?

FYI : HF alternator tester says bad alternator. Battery ~ 1 year old.

Also dumb : the 944 is a negative-ground vehicle, yes?

Bradical · 02:05 PM

If you are checking amperes and going across the battery posts, you are shorting the battery out through your meter, which would explain why the leads get really hot. You want to check for VDC with that. The idea with the mA is to check from the positive post to the positive LEAD, ie the wire that connects to the post, check the mA and then remove fuses to try to track down what is draining your battery.

Bukowski · 09-05-2016, 03:56 PM

So

take the + car battery cable off the battery post

Touch red multimeter lead to the + battery post

Touch black multimeter lead to the + car battery cable

...?

Bradical · 04:44 PM

Yep. The ampere function sets the meter up to be in series with the load, and read the amp draw of the load going through the meter, so essentially you are putting the meter between the car's electronic system and the battery to see how much current the car is consuming when the ignition is off, then narrowing down the power-consuming component by pulling fuses and waiting for the amps to drop. Normally the current draw with the car off should be 35mA.

When you go post-to-post you are shorting the battery with the meter, hence the hot wires! The meters usually have a fuse that pops to prevent the meter from burning up if you accidently put too much current through it. With it reading 100ma across the posts, I assume your meter has some internal function in it that limits the current draw through it to keep it from exploding- because from post to post with no load it should draw as much current as possible before your leads caught on fire, hehe. That, or the battery is almost dead.

Bradical · 09-05-2016, 04:46 PM

Reading your post again, check it but I am sure your troubles are with your bad alternator. Charge your battery and then run the amp draw test as described if you want, but it sounds like you already know the problem.

djnolan · djnolan's Garage

If you put a 2 amp rated multimeter across the battery as you describe, there could be something in the circuit that has a high initial charge current that's going to show in a major draw and then it will settle back down to a reasonable number like .05 amps. Things that could show a high initial draw as described could be a aftermarket radio Kama an alarm system, or the window relay switch stay energized if your door switch dome light switch is not working properly.

djnolan · djnolan's Garage

If you want to do a quick check of the alternator, hook up the battery and check the battery voltage while engine off, nominally should be about 12.5 volts. IF it is low trickle charge the battery. With the engine idling and accessories off, the batt voltage should increase to about 13.5. Turn on the lights and a/c and the voltage should still stay around 13.5 at idle... IF it drops significantly with an electrical load then your alternator isn't handling the load. This assumes your battery is charged up.

Bukowski · 09-12-2016, 03:07 AM

quick update:

thanks to all - makes sense now. yes, the battery wasn't fully charged, but now the alternator is new. tried the tests again. my multimeter has a "200m" setting, I figure means "200 milliamps". I tried a number of tests - removing fuse, connecting battery through multimeter - and got "00.5" each time. not sure why this meter has leading "00" digits, but hey, it was free. the number didn't shift, so I interpret that as no problem. the absolute value of the 0.5 according to the scale would be 0.5 mA, but that's way to low so it must mean 50mA. Clark's says its supposed to be 65 mA...

to be continued...

Bukowski · 03-27-2017, 07:48 AM

update:

completely detached the radio including detaching the now working powered antenna.
result : [ 00.0 amps ]
needle on cluster approx 11.7 V, so, just below 12 V.
will check again to verify I set this up correctly.

btw I think it doesn't make sense to turn the key on (engine not running) to test this, but...