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Parasitic Draw Test Interpretation


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dilophosaurus 
Member - Posts: 2
Member spacespace
Joined: May 10, 2019
Location: Florida, United States
Posted: May 10, 2019 at 8:54 AM / IP Logged Link to Post Post Reply Quote dilophosaurus
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 https://www.youtube.com/watch?v=YhC8xj5vHUg
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.
i am an idiot 
Platinum - Posts: 13,674
Platinum spaceThis member consistently provides reliable informationspace
Joined: September 21, 2006
Location: Louisiana, United States
Posted: May 10, 2019 at 4:35 PM / IP Logged Link to Post Post Reply Quote i am an idiot
What is the brand of your multimeter? That is where my guess is. There should always be some kind of current draw.
dilophosaurus 
Member - Posts: 2
Member spacespace
Joined: May 10, 2019
Location: Florida, United States
Posted: May 10, 2019 at 6:32 PM / IP Logged Link to Post Post Reply Quote dilophosaurus
Can you please state a range for how many mAmps should always be showing or where I could find this information? The multimeter should be able to detect +/- 10 mAmps on the setting I am using as described above; it works fine.
mgoetz74 
Silver - Posts: 424
Silver spaceThis member consistently provides reliable informationspace
Joined: February 15, 2012
Location: United States
Posted: May 11, 2019 at 11:04 AM / IP Logged Link to Post Post Reply Quote mgoetz74
60Ma is what is recommended. But if you have a newerish (year or 2 old) battery and the car is a daily driver or even a 3 or 4 times a week driver going over some isn't a problem. Should have a dc10a setting on multi meter, disconnect the negative battery terminal, one side to battery negative terminal and of course the other to the negative cable you unhooked. Give it 5 minutes or so for the car electronics to shut off. You should never show 0. Fuses wont have voltage drop, there ether 12 volts on both sides of the fuse or 12 volts on one side and 0 on the other which is a shorted fuse
33 years as a installer now just a retired old guy. Favorite thing to install/topic are remote starts/car alarms. Stop using test lights!!!
eguru 
Copper - Posts: 340
Copper spacespace
Joined: February 04, 2018
Location: Quebec, Canada
Posted: May 11, 2019 at 6:12 PM / IP Logged Link to Post Post Reply Quote eguru
It is a valid testing method to measure the voltage drop across a fuse. All fuses have some resistance. For example, Littelfuse spec for a 10A ATOF fuse is 7.7milliohms.
That doesn't seem like much, but a decent voltmeter should easily be able to measure the 0.77mV/100mA.
To be honest, I don't understand the OP's statement that no parasitic draw caused the battery to go bad. It is parasitic draw that hastens the degradation of the battery, not that some "ideal" amount of parasitic draw is good for the battery.
Edit:
To the OP:
Get a 100 ohm/5W resistor. Use your meter to measure the resistance. Disconnect all the cables from the battery. Measure the voltage. Connect the resistor in series with your ammeter and measure the current. Let us know if your actual DMM reading is very close to the theoretical value you calculate.

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