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Checks Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Tue, 5 Mar 2002 11:15:24
In Reply to: Parasitic Battery Drain-Chapter 2-Electric Door Locks?, KevinD, Mon, 4 Mar 2002 16:34:29 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The typical current drain for the door lock fuse is about 10-12 ma. If you pull the fuse then reinsert it, you get a big current jump for about 30 seconds - this is the time for the dome light to time out. Assume another 10 ma or so for the clock and radio.
I usually see about 20-25 ma quiescent drain. Remember, if you have the hood open, it may be higher, because in some cars there is a hood open switch for alarms and/or a hood light. 20-25 ma won't drain down a battery in days - more like months.
Basic method for checking quiescent current draw - Remove the ground clamp from the battery. Connect up the current meter between the ground clamp and the post. Now hold the ground clamp to the negative battery post for a minute. Why all this? When you disconnect the battery then reconnect it, a bunch of timers restart. You hold the clamp to the post to give this higher current a nice path. After a minute most everything will have charged back up or timed out. Make sure all doors are closed. Since the hood's open, make sure if there is a hood switch that you put something heavy on it to keep it closed.
If you see only about 20 -30 milliamps at this point, it isn't current draw from the car that's causing the problem. Reconnect everything. With your voltmeter set to VOLTS, put the negative lead on the negative post of the battery, and move the positive lead of the meter over the case of the battery. If you see more than 0.1 volts or so, you have parasitic leakage on the CASE of the battery. Batteries outgas when they charge. Some of this acidic mixture condenses on the case of the battery, mixes with moisture from the air and plain old dirt and dust to produce a current-carrying mixture on the case of the battery. This can cause the battery to discharge just by sitting there. If you see a voltage on the case then that's the problem. Wash the case of the battery with water with some baking soda dissolved in.
Lastly, it can be a battery problem. Batteries lose life over time. Car batteries aren't designed to be totally discharged - if they do, they build up sulfates from the acid on the plates that never comes off. These sulfates block the surface of the plates, reducing the current carrying capability of the battery and speeding up self-discharge (a good battery loses about 1% of its charge a day - faster for a sulfated battery). Every time the battery goes dead, it sulfates some more, making it more likely that it will go dead again - an accelerating process.
If the battery has been fully discharged a bunch of times, chances are it's never coming back. There can also be a defect in the battery - I bought a new battery last October, and after about a month, it wouldn't hold a charge for more than a couple of days. I measured voltage on the case, and it turned out to be a crack in the case weeping acid. Not pretty. I returned the battery under warrantee. The replacement battery has no trouble starting the car even after a couple of weeks of not driving it. In fact, it did so today, after a week plus of no driving, and a 19 degree F morning.
Good luck!
posted by 140.157....
, Tue, 5 Mar 2002 11:15:24 <-- Viewing This Message
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