Are inexpensive Chinese shunts and hall effect sensor accurate and/or precise?

Inkidu · 2019-02-20T19:45:20.000Z

Amateur hour with parts I’ve bought years ago. I got my eye on some high amp builds. Put this together because I don’t have a clamp meter. Wondering about the % tolerance of this inexpensive Drok shunt. Thinking about getting a more appropriate 20 or 30amp shunt. Obviously 0.5% (tolerence) of a 100 amp shunt will be less accurate than 0.5% of 30 amp shunt. There are more accurate shunts out there, but I wasn’t sure spending the money was worth it. As you can see from the one picture, it is already 0.1 amp off. I used 0.5% as an example because that is what I came across in some spec sheets. So, is the amp reading on my older Convoy L6 on high accurate? (Fully charged cells) The precision is good since it does repeatable measure the same reading. Are the $3 shunts out there wildly in accurate and/or precise? Are the markings on the meter just to for packing purposes or is there a difference between meters which have a particular shunt? I’m using a 13v wall wart to power meter. Some of this might be splitting hairs, but if I’m spending the time to measure these things I would like to be correct.
Thanks for any help.

EasyB · 2019-02-20T20:31:03.000Z

I would guess they are pretty accurate. I’m using one with a 50A analog gauge and I would say it’s within +/-5% of the real value. The shunts are designed with a resistance such that the voltage across it will be 75mV at the current it’s designed for. Then the meter is just a millivolt meter that displays the full-scale current number at 75mV.

But in general for measuring current in a flashlight you have to consider the shunt resistance because it can affect how much current flows. In your case the 100A shunt has a resistance of .75 mOhms which is very small. But you have to consider the resistance of all the wire you have also.

Inkidu · 2019-02-20T21:31:34.000Z

EasyB:

…But in general for measuring current in a flashlight you have to consider the shunt resistance because it can affect how much current flows. In your case the 100A shunt has a resistance of .75 mOhms which is very small. But you have to consider the resistance of all the wire you have also.

Thanks for the reply. Good point.
I’m really brushing the dust off this stuff. I forgot that I even bought this. Usually waited till their flash sales. I was getting far more different readings (precision) with this setup. (4.6-5.0) Might just be user error. Funny I’m still getting a unconnected 0.1amp reading. I didn’t connect the voltage meter. This actually might work and be useful for my DD Ledil Seanna xhp70.2 build. (much less size and weight) This does have pots, that I assume are used to dial it in.

BlueSwordM · 2019-02-21T02:22:18.000Z

@Inkidu, what you want to do is find the resistance of the shunt first.

1. What you do is take a power supply, adjust it to 1A, measure the voltage drop across it, and do this operation: V/A.

You’ll find the resistance of the shunt. Say it’s a 5mOhm shunt. At 5A, you’ll get a 0,025V drop across it.

You get the idea.

2. Compare what you calculated to what the LCD display says.
If it’s accurate, it should say 5A.