Author Topic: How to probe and log a small DC current without cutting the wires?  (Read 392 times)

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Offline RoGeorge

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Sometimes, but not always, I find my car battery completely flat, with zero volts after letting the car parked for 2-4 weeks.

The battery seems totally OK after recharging, but since this happened more than a few times now (randomly) I would like to log the current and try to find out why and when it is happening. The battery is 80Ah/12V, and I suspect it to go totally flat in 2 weeks, maybe faster, so a resolution of 10-100mA will be needed. Sometimes the battery is just fine and can start the car after 1-3 months, sometimes is zero volts flat after 2 weeks. I can provide another Pb battery (from a UPS) for the logging device.

Any ideas how to probe and log such a small current (10-100mA) without disconnecting/cutting any wires, please?
« Last Edit: December 08, 2017, 09:21:43 AM by RoGeorge »
 

Offline CopperCone

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Re: How to probe and log a small DC current without cutting the wires?
« Reply #1 on: December 08, 2017, 09:23:12 AM »
thats large enough to use a hall effect sensor. Smaller would require a fluxgate circuit.
 

Online trevwhite

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Re: How to probe and log a small DC current without cutting the wires?
« Reply #2 on: December 08, 2017, 09:25:55 AM »
Sometimes, but not always, I find my car battery completely flat, with zero volts after letting the car parked for 2-4 weeks.

The battery seems totally OK after recharging, but since this happened more than a few times now (randomly) I would like to log the current and try to find out why and when it is happening. The battery is 80Ah/12V, and I suspect it to go totally flat in 2 weeks, maybe faster, so a resolution a 10-100mA will be needed. Sometimes the battery is just fine and can start the car after 1-3 months, sometimes is zero volts flat after 2 weeks. I can provide another Pb battery (from a UPS) for the logging device.

Any ideas how to probe and log such a small current (10-100mA) without disconnecting/cutting any wires, please?
Hall effect current probe will measure dc current. Some can be plugged into a scope or multimeter for logging I think.

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Offline RoGeorge

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Re: How to probe and log a small DC current without cutting the wires?
« Reply #3 on: December 08, 2017, 09:39:21 AM »
thats large enough to use a hall effect sensor. Smaller would require a fluxgate circuit.

I didn't know about the fluxgate circuite, thanks!

Hall effect current probe will measure dc current.

The analog hall sensors I have salvaged from a PC fan doesn't seem sensitive enough, but since both of you are telling a hall sensor should work, I will look for more sensitive ones, thank you!

Offline Benta

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Re: How to probe and log a small DC current without cutting the wires?
« Reply #4 on: December 08, 2017, 09:41:39 AM »
I'd simply buy a clamp meter with USB interface for logging. DC types are available.

 

Offline cdev

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Re: How to probe and log a small DC current without cutting the wires?
« Reply #5 on: December 08, 2017, 09:44:54 AM »
Uni-T UT-210e but doesn't have logging out of the box but so many people are modifying - there is a wealth of info here on the internals, which could be used I'm certain, to let you do that.
"What the large print giveth, the small print taketh away."
 

Offline RoGeorge

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Re: How to probe and log a small DC current without cutting the wires?
« Reply #6 on: December 08, 2017, 10:03:38 AM »
Outch!
Never used a clamp meter, and always assumed they are AC only. Embarrassing, I will go hide under a rock now  :-[

Thank you, will look for clamp-meters, too.
 
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Offline cdev

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Re: How to probe and log a small DC current without cutting the wires?
« Reply #7 on: December 08, 2017, 11:25:41 AM »
I have the UT-210e and its quite useful. People here are investigating turning them into oscilloscope current probes.

Mine can measure down to 1 ma without tapping into a circuit. Also it has a NCV sensor to tell you where the dangerous voltages are.

"What the large print giveth, the small print taketh away."
 

Offline Jeroen3

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Re: How to probe and log a small DC current without cutting the wires?
« Reply #8 on: December 08, 2017, 06:37:48 PM »
100mA is small for clamp meters. You could try a fluke i30s, maybe looping a few times.
« Last Edit: December 08, 2017, 06:39:30 PM by Jeroen3 »
 

Offline RoGeorge

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Re: How to probe and log a small DC current without cutting the wires?
« Reply #9 on: December 08, 2017, 08:52:23 PM »
Ordered a UNI-T210E from Aliexpress, seems like a nice tool to have around. Can hardly wait to hack it, thank you all!
 :)

Online xani

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Re: How to probe and log a small DC current without cutting the wires?
« Reply #10 on: December 08, 2017, 11:35:57 PM »
Just remember that on DC mode clamp will react on any magnetic field which means you should zero it before each measurement
 

Online glarsson

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Re: How to probe and log a small DC current without cutting the wires?
« Reply #11 on: December 09, 2017, 12:07:38 AM »
It is also important not to move the clamp after zeroing. Angle of any magnetic field matters.
 


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