Current measurement during Battery test

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Current measurement during Battery test

Post by Andrus » Mon Mar 03, 2014 7:55 pm

Hi !

Just one question regarding battery current measurement during Picodiagnostic battery test.

On Picodiagnostic user guide @ battery test connections written:
Connect the 600 A or 2000 A current clamp to Channel B on the PicoScope. Place the amp clamp (600 amp clamp for light vehicle applications or 2000 amp clamp for heavy duty applications), so that it is positioned around the positive cables which are connected to the positive battery terminal. More importantly make sure the amp clamp is positioned around the starter motor feed cable (main positive cable from battery to starter motor).

If I have battery connector with T- type joint ( + supplied directly to starter motor at battery + one side and rest of machine + connected to other side. I can put current clamp to measure only starter motor current or rest of machine.
But I can put clamp around - cable without problem.

As far as I understand, there is no difference, if I measuring current from + or - pole. :roll:

Does anybody knows any theoretical /practical reason, why it is mandatory to use only + terminal for current measurement, or it does not matter ?

Thank You for feedback. :)


Just looked at PICODIAGNOSTIC DVD and on how-to-do video : possible to use both + or - battery terminal for current measurement.

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

Re: Current measurement during Battery test

Post by Steve Smith » Wed Mar 12, 2014 9:24 am

Hi Andrus you are right in what you say at the end of your enquiry

"The current clamp can be installed around the battery negative lead"

Looking at the theory of the current flow in a circuit, all things being equal, the flow should be the same wherever it is measured within the circuit. AMPS=VOLTS X RESISTANCE

There have been numerous times where its has been difficult for me to measure starter/system current at the battery positive terminal and so the negative terminal is a useful alternative returning accurate and relative values.

I hope this helps.....take care......Steve

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