Here is a pic of my multimeter.
With the selector on 250 mA, the needle is where the “100” is written in black (with 20 and 4 written below it) when I performed a parasitic drain test on my car.
Does that mean I have a reading of 100 mA?
I am getting different maximum allowable readings on different websites, but 100 mA is too high according to all of the sites I’ve looked at.
Yes, 100mA
That’s the way I read it.
Yeah, that’s 100mA.
Yep, 100 mA. (Did anyone say that already?)
And yes, that’s too high. That will kill your battery fairly quickly, a few days to maybe a week depending on the size of your battery.
Thanks guys. I’m going to go out and re-check and make sure that’s the reading.
Did you zero the meter before you started?
What made you decide to check this in the first place? Are you having issues or did you just read about parasitic drain and thought you’d check out your own vehicle?
Zeroed out first.
I decided to check because my battery has been going dead on my second car when I leave it for a week or even under without running it. The battery is only a few months old, but it’s a very cheap battery I got from Walmart for under $50. I’m going to get a much better one regardless if anything is wrong with the car or not.
I just re-checked. I might have been remembering a reading from a different test.
I’m getting a reading that is steadily fluctuating between 25 and 40 mA.
I wonder why it fluctuates like that? It’s an older car ('99) and doesn’t even have an alarm system.
Besides zeroing, wipe the face so as to remove any static charge on it.
Most cars I test have parasitic drain of less than 20 mA. I’d say anything over 40 is a concern.
HOWEVER…
Many modern-era cars have various control modules that draw extra power until they “go to sleep,” which can take from 20 minutes to a few hours. Drain testing needs to wait until that stage is reached, and it’s important to construct the test so that battery power is not disconnected/reconnected (don’t turn the key on either) or else the modules “wake up” and you’ll have to wait again.
The fluctuation you describe is from a module that’s not yet asleep.
Thanks Gary. I’ll do the test again next week when I get a chance after disconnecting the negative cable and waiting at least half an hour. If it still fluctuates, I’ll wait a couple hours.
This is pure speculation, since I don’t know exactly how you have connected your leads to measure the current, but it’s not at all unusual to get a fluctuation in such a low reading due simply to variation in the pressure of the leads on the conductors/terminals/clamps. The terminals and clamps could have an oxidation layer and this could cause a variation of a hundred ohms or so, which is enough to account for the changes you see. Again, it’s just speculation.
once you’ve determined you have a draw worth pursuing, put the meter down and
grab a test light.
hook it up between your disconnected positive battery cable and the positive battery terminal (having a spare temp battery cable end to put on the positive post works well when doing this).
it should illuminate. how brightly depends on the amount of current flowing thru it.
next, start pulling fuses one by one until the light goes out. that’s the circuit you’re having problems with. some circuits are powered thru fusible links so you may need to unplug those.
diagnose that circuit by unplugging it’s loads first, then check wiring if needed.
if the door is open to access a fuse compartment, the interior lights will make the light glow. same with the hood light. either pull those fuses or do what you have to do to make the vehicle lights not illuminate.
don’t turn the key on during this test. it could blow the test lamp bulb. if you tried starting it, it for sure would.
Better to not put the meter down. A test light isn’t accurate enough to measure a draw on modern vehicle, not even a '99. I’ll use the multimeter if it gets to that, but since I’m getting a fluctuating reading with the high being 40 mA, I’m most likely okay.
Safer to work with the negative cable.
Better to close the latch on the door. Open doors can put a drain on things other than those lights.
you trying to school me is adorable.
I think this is the best practical test even though it doesn’t give you an actual reading. I have found that most excessive parasitic drains are due to stuck relays. Sometimes just feeling the relay boxes after it has been setting for a few hours will quickly expose this as the relay will be warm. Older cars had a lot of problems with bad diodes in alternators.
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mr horsepower, this is an official warning for being a jerk. Since you already have previous recent warnings for the same offense, with another you will find your posting privileges under discussion. If you can’t be civil to other posters, there’s no need for you to post.
Colibri
General Questions Moderator
this is to officially tell you to ban my account. it’s going to happen, let’s get it done.
If you’re talking about disconnecting without the ammeter in place, that’s not going to work. As soon as the meter is placed in the circuit, power will be restored to the vehicle and the modules will wake up.
The thing to do is hook up the meter so it shows the power draw, then leave it in place and wait. (For those using a meter with an automatic shut-off [battery saver], disable this feature or it will thwart you.) Check the reading periodically. It may go to nothing but parasitic drain in a number of minutes, or at worst it may take a few hours.
I’m confused. Yes, I was going to disconnect the negative cable from the battery, wait, and then connect the ammeter.
You’re saying disconnect the cable from the battery, waste no time and connect the ammeter and then wait, correct?
If disconnecting the negative cable from the battery and waiting before connecting the ammeter will wake up modules, why wouldn’t connecting the ammeter immediately just keep the modules awake? Or did I misunderstand you?
