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I have a three-phase cable harness (low voltage) for connecting to a motor. I have it connectorized so I can easily plug/unplug the motor.

I would like to insert a short inline cable so I can measure the current on any of the three phases. Here's what I have so far, to measure 1 phase: enter image description here

I've added a pair of banana plugs to connect the white phase to my DMM. I would like to do the same for the red and black phases, but I'm only going to be measuring one at a time, and I was wondering if there is any kind of double-ended banana jack so I could just plug the two halves of each unused phase together so that it conducts current and it doesn't have an exposed conductor. I couldn't find any. Any suggestions?

(The red/white/black connectors are Anderson Power Products connectors, by the way.)

Jason S
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  • There are banana jack bridging links / test points (two male legs with a female socket in between) but I've only ever seen them in telecomms kit - and quite old kit at that. – John U Jul 22 '14 at 21:30
  • If that's a model vehicle brushless motor setup, keep in mind that excessive cabling will introduce losses and may even confuse the rotor position detection circuitry. Also a DMM probably won't like PWM synthesized waveforms to begin with. – Chris Stratton Jul 22 '14 at 22:01
  • @ChrisStratton -- thanks, I'm aware of those issues and I know what I'm doing. (I design hardware + software of DSP-controlled motor drives.) It's measuring current, not voltage, and this is an inductive load so the current doesn't really have much in the way of high-frequency harmonics. This test "fixture" is just for measuring low-frequency waveforms anyway. – Jason S Jul 22 '14 at 22:10
  • Have you considered building fractional ohm shunts into the harness, and measuring across them? That would also let you use a scope as the instrument. – Chris Stratton Jul 22 '14 at 22:36
  • We already have that on our PC board. But neither the shunts nor the oscope are particularly accurate (current shunts are 1%, oscope is 2% for a worst case of 3%). I want to read directly into our DMM. The one on my desk is 1% accurate on current but we have better ones. – Jason S Jul 23 '14 at 19:48
  • I miss my Tek DMM916 I had at my last company. 0.3% accuracy for DC current! But they got out of the handheld DMM business. – Jason S Jul 23 '14 at 19:53

4 Answers4

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Found one from Pomona: they're called banana plug splices.

dim
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Jason S
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You could easily make one from a length of 5/32" ID copper tubing with heat shrink over it or, failing that, http://www.amazonsupply.com/power-probe-pnls029-female-adapter/dp/B002YKIJ8O

EM Fields
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Four pairs of Quick Disconnects (insulated) would work.

enter image description here

Male on one side, Female on the other for each pair. Then a set of Quick Disconnects to Banana Jacks, one with a male and one with the female quick disconnects. Any radioshack or auto store carries them, just make sure you get the right size for your cable gauge/voltage/current capacity.

Passerby
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  • Yeah, that's what I ended up doing, except I used Anderson connectors since those are better and we have them in our lab. – Jason S Jul 23 '14 at 20:47
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For this application I tend to use 4mm stackable shrouded connectors, since they are "stackable" you can easily plug a pair of them together, and since they are shrouded you don't have to worry about the male part touching something.

Of course this relies on your multimeter being able to take proper 4mm shrouded connectors, most will, but some of the bottom of the barrel ones will only take partially shrouded or unshrouded connectors.

Peter Green
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