TA018 Amp Clamp Negative mA reading?

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owense1
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Posts: 5
Joined: Sun Jul 10, 2016 12:06 am

TA018 Amp Clamp Negative mA reading?

Post by owense1 » Tue May 12, 2020 4:38 pm

Good day to all.

I am doing a parasitic drain test with a TA018. The Amp Clamp is new, I have Zero Offset performed along with Analog Options at 20HZ. Everything is golden and we fixed a couple of issues so far. I am having a little struggle with readings of NEGATIVE Amperage reading when reading off a good battery of 12.79 vdc. The Amp Clamp is pointing where it should be as it pertains to flow.
Again everything is straight but why am I getting a negative Amperage and then it will just about Zero then bounce back to negative. I open a door and amperage spikes as it should in positive numbers and again the number will fall back down to almost -20mA.
I keep seeing if the battery is fully charged and at a calm steady shut down state it might show this but just wanting to go over that with the big brains in here thanks!

Steve Smith
Pico Staff Member
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Joined: Sun Aug 25, 2013 7:22 am

Re: TA018 Amp Clamp Negative mA reading?

Post by Steve Smith » Wed May 13, 2020 11:04 am

Hello and thank you for the post

Could you confirm the vehicle under test uses a single 12 V battery and not 2 x 12 V batteries connected in parallel as here we could see reverse current flow due to battery charge equalization?

It sounds like you have followed all the rules surrounding parasitic drain measurements which are covered here & here

Having used a number of current clamps for parasitic drain measurements it remains one of the most challenging techniques to capture over prolonged time periods without the clamp (or other clamps) “drifting”

The low current resolution required, combined with atmospheric noise conditions and thermal drift adds to the complexity.

Could you confirm if removing the clamp from the battery lead, the value displayed on the scope returns to zero amps?

If not, the value displayed is your current zero point and should be used to add or subtract from your parasitic drain measurement to find the true value

You will discover that the TA018 is vulnerable to atmospheric conditions during very low current measurements and often I find zeroing the clamp adjacent to the cable you are about to measure improves this concern.

I.e. try not to zero the clamp away from the vehicle and then place the clamp around the cable to be tested. Zero the clamp adjacent to the cable being tested and no not change the clamp orientation post zero.

When all is said and done, the volt drop method here will remove all the variables above during with such a challenging measurement

I hope this helps, take care……Steve

owense1
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Posts: 5
Joined: Sun Jul 10, 2016 12:06 am

Re: TA018 Amp Clamp Negative mA reading?

Post by owense1 » Thu May 14, 2020 11:02 pm

Steve,

Yes, when removed the Amp Clamp does return to normal and when turning on a dome light, amperage will spike then slowly drift to zero. We were using it on a 2020 Camry that has an Enhanced Flooded Battery. We did surmise that the negative could have been slight discharge from the battery. It was so minimal that we dismissed it but knowing a real explanation is out there for these readings I though Id ask while it was still fresh. We just have never seen it. To add the clamp we were using at first was almost 10 years old and wasn't accurate then we used a new one just purchased by the tech.
We will be using TA189 next time as I just purchased this amp clamp for the precision. Thank you for the tip on the adjacent Zeroing. That will be added to the printout and notes we have for making our parasitic draw tests faster and better.

matt07181986
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Joined: Wed Mar 07, 2018 4:31 am

Re: TA018 Amp Clamp Negative mA reading?

Post by matt07181986 » Tue May 19, 2020 5:27 pm

You will like the TA189 much better for parasitic draw. A tip I have found helpful is to zero the current probe right next to where you will place it on the vehicle. I hold the current probe next to the battery cable, hit the zero button and then clamp it. This may be overkill for current ramping an ignition coil, but necessary for something sensitive as parasitic draw.

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