Quote:
Originally Posted by Multibeemer
I'm still very confused about the battery drain test procedure. I've read I need a larger (e.g. 10 amp max) ammeter. Why? Mine only goes up to 250 mA, but I've heard the spec for parasitic current is only about 35 mA. What's this inductive ammeter JCL recommends? Is it expensive? Is it something I could rent? How is it used? How do I get around the need to have all the doors closed when I do the test, and the need to let the car sit for 20 minutes after closing them? Do I have to get in the car, crawl in the back to disconnect the positive cable, sit in the car for 20 minutes, and then crawl back with my ammeter to do the test?
Is it really this complicated? Could somebody please reply with a simple, step-by-step procedure on how to do this? Thanks.
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When you are measuring current draw with an ammeter, using the two probes, you need to have it connected in series with the battery cable and the battery post (or wherever you can disconnect the battery). The trouble is that when you disconnect the battery, you reset various modules, so for this test you have to go from a state of having the battery connected, to having it connected only through the ammeter, without breaking the circuit at any time. To do that, you loosen the cable connection connection, put a jumper wire across the connection, and then remove the cable. The jumper wire completes the circuit, so the vehicle is still powered up (but the jumper wire can't handle much power, so don't try to start it). Now connect the ammeter in parallel with the jumper wire. It won't read anything yet. Now disconnect one end of the jumper wire. The ammeter remains as the only connection, all the current goes through the ammeter, and you can get an accurate current reading. Be careful, because you can damage your ammeter from too much current.
The alternative is an inductive ammeter. It has to be one that can read very low currents. It has a spring clip with a coil in it, which clamps around the battery cable, without disconnecting the cable. It is much easier to use. It costs less than one hour of diagnostic time at your dealer, ie $100 or so. You may be able to rent one, I am not sure.
Yes, you have to determine how you will read the ammeter with the doors all closed. You will be doing this over 20 minutes or so.