Battery charger question

Back up one step: why do you need a charger?

 

Good planning. If the battery being charged is original equipment, it should have a label on the top that warns against using a charging current > 4A. In that case, I'd suggest that you use the 2A setting on your battery charger.

If you can't select the charging rate, then I would select the maintenance free deep cycle option.

 

If this were my car, I'd hook up an ammeter in series with the 12V battery, with the car IG-OFF. Then I'd remove fuses one at a time, to see which fuse is providing power to the circuit causing the big current drain.

Once I identified the fuse causing the drain, I would refer to the wiring diagram to see which circuits obtain power from that fuse.

I would check any relays downstream from the fuse to see whether any are stuck. If that is not the problem, I would then disconnect the ECUs and any other power consumers downstream from the fuse, one at a time, to see if one of them is causing the problem.

If that doesn't solve the problem, then there must be a further wiring harness issue and that will be hard to figure out if the obvious damage has already been repaired.

Suggest you ask the tech who will be working on your car what his approach will be to solving that problem. Good luck.

 

For this sort of testing I use a clamp on ammeter. It's a lot more convenient than removing and reconnecting wires.

Tom

 

Hi Tom,

What is the minimum current that your clamp-on ammeter can read?

I have a Fluke AC current clamp-on probe which is rated to have a useable range from 0.1A to 600A and a specified range of 1 - 400A. The output is 1 ma per ampere. I've always wondered how linear the probe's response is.

 

Most inexpensive clamp on Amp Meters will not measure DC current. It takes a special expensive $200+ clamp on meter to do that. It uses a Hall Effect to measure the magnetic field.

You can try to measure the tiny voltage loss across the negative cable from the battery clamp to the other end. The more current the more voltage will be across the cable. It will be like a very low resistance shunt. The voltage will be in microvolts or maybe millivolts. So you will need a sensitive DC voltmeter.

I will get to see the cables this week end when I put in an Optima Battery.

Bob

 

My clamp-on is on the boat at the moment, so I can't check for sure. I seem to recall that the lower limit for clamping is around 100 mA, so it sounds like it's about the same as yours.

I only use it for maintenance and high amperage measurements, so linearity isn't terribly important for me. I'll have to test it alongside my Fluke 287 and see how accurate it is.

Tom