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request for help with parasitic draw test interpretation

dilophosaurus

New Member
Hi,

I would like help from anyone who knows enough about car electronics to help interpret the information from a parasitic draw test. Can you please tell me if my car is acting normally and that it is normal to see a pattern of several Amps on initial multimeter connection that drops to a 0.00 Amp reading on a 10 A multimeter setting within a minute?

I did a parasitic draw test and fuse test in a 2006 Buick Lucerne (without any fancy/aftermarket electrical components) both before and immediately after replacing an old dying battery following guidance from

I used a multimeter with maximum 10 Amp detection and had the leads attached correctly, with the red cable in the 10 Amp socket. My multimeter on the 10 Amp setting is supposed to have a resolution of 10 mA and an accuracy to within +/-5 mA. Theoretically I should neither have to turn the dial to the mA range nor switch the red cable from the 10 A socket the separate mA socket to see what I need to see if I am looking for current in the range of at least 10 mA.

I assumed from watching multiple videos that there should "always" be a detectable current with the car off due to continued power supply to the clock or other electronics. I assumed that I should expect always to see/detect, say, 10 mAmps (multimeter reading 0.01 Amps) and not have the reading go to 0.00 and toward microAmp range, but this is not what I observe.

Test results with both with the old battery and new battery (the results were identical):
The multimeter/ammeter reads (consistently) 2.15 Amps for about 5 seconds upon initial contact with the battery, then drops to 250 mAmps (reads 0.25) and stays right there for a minute, and then drops to 0.00 A. It never (after testing a dozen times) settles to a 0.0X Amp number (in the range of 10-90 mA).

Fuse test results: I used my multimeter to test voltage drop across every fuse in both fuse boxes, and every fuse read 0.00 Volts (normal). I did not test my fuses by pulling each fuse while having the multimeter still attached to the battery and looking for multimeter current drop. I do not think this technique would have worked anyway given the multimeter reading 0.00 Amps within a couple minutes before having the chance to take out individual fuses.

As the speaker in the video suggests, I assume the pattern (2.15 Amps --> 0.25 Amps --> 0 Amps) is due to re-awakening something (like the computer) when the multimeter touches the battery, and that whatever is re-awakened draws 2.15 Amps from the battery then shuts off on its own. I assume that this happens in stepwise fashion or there are two different re-awakenings leading to this pattern of 2.15 Amps --> 0.25 Amps --> 0 Amps. I tentatively conclude that no parasitic draw caused the battery to go bad and that there is no parasitic draw now.

But I cannot explain/do not understand why the multimeter/ammeter never reads in the range of 30-50 mAmps (0.03-0.05 Amps) and just drops to 0.00 Amps, because I assumed that there should "always" be a detectable current above 0.00 Amps such that the range should be detectable at, say, 10 mAmps (multimeter reading 0.01 Amps). Given that the Amps do jump above 50 mAmps (some videos say this should never happen with all components of the car off), there could still be parasitic draw that will kill the new battery if I am interpreting or doing something incorrectly.
 

Diver300

Well-Known Member
If your car is taking less than 10 mA, that's fine and you've probably got nothing to worry about. There is nothing wrong with having no parasitic current. The only reason to want to see a current is to make sure that you are actually reading the current correctly.

Where the car takes 2.15 A then 0.25 A then undetectable current is probably fine. All makes and models will be different, but it is normal for separate things to shut down at separate times.

If you want to measure the current more accurately, one method is to fit a battery isolator, and measure the current when that is disconnected. You fit the isolator, leave it open, and connect the ammeter on a 10 A range across the isolator. When the current has dropped to less than 100 mA. close the isolator, change the ammeter to a 200 mA range, and then open the isolator to read the current.

That allows you to have the ammeter on a low current range, without letting the high currents on turn-on.
 

dilophosaurus

New Member
Hi, Diver300,

I looked up battery isolators on Google and see that there are different devices called battery isolators that are rather dissimilar. Could you please say a little more about the name of a battery isolator or share a website with the type of battery isolator you had in mind?
 

Mickster

Well-Known Member

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
The high kick is likely due to charging of capacitors in the various electronics. The rules are capacitors cannot change voltage instantaneously and an inductor can't change current instantaneously. With an inductor such as a motor it takes a larger current to start. It;s close to the value of the series resistance of the inductor. There is a capacitor parameter called ESR or Effective Seris Resistance and that comes into play when they re initially charged. once they are charged, there is a leakage current.
 

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