I just got one of these from ebay:I am trying to read V and Amps while charging a battery on the bench. I have the shunt attached to the negative battery post, and the charger clamped to the other end of the shunt. I've tried both shunt positions for the yellow and black wires, and all I get is a 0 reading for amps, even with 7 amps flowing as measured by my clamp meter. The volts read fine.There are calibration pots on the back side. The voltage one works. The amps one doesn't move the reading from 0. The shunt is passing current. The wire pigtails have continuity back to the plug.Before I attempt to contact China Tech Support, based on the wiring diagram, how should I wire the yellow and black to measure battery charging? Any suggestions on how to troubleshoot?

Shunts are fairly simple but. First you have to know the actual full scale of the meter you want to shunt. If you don't have that info you are guessing at shunt values. I suppose you could calculat that by putting a reistor in series apply enough voltage to get a full scale reading. You would then know resistance of meter.

Google says:here is same diagram but maybe wired slightly different. Maybe the AMMETER side needs a supply voltage?I know nothing about how this works just noticed your same drawing when I was looking for schematic for shunt meters...Looks like you need a source to power up the ammeter. For a test I would add a ouple of D-CELLS to the RED and BLACK cable coming out of the meter. If that makes it work then I would use the RED wire and connect to 12VDC and leave the black wire open ...Roy Ken

Roy, the way I understand it, it gets Positive from the red wire, and it must be less than 30v. The one you found can read up to 100v, but then it needs a <30v power source. here is the listing

Help with shunt ammeter | Good Sam Community

31 Replies

Big_Katuna
Explorer II
Aug 21, 2013
I see Weston shunts on EBay for not too much. Quality units, very accurate.
Snowman9000
Explorer
Aug 21, 2013
I tried it with my Morningstar SunSaver PWM solar controller. It worked. I checked the reading against two multitesters, and it appears the shunt meter is 0.7A low. I'm not sure if it will change when I add wire length to install it. I'm re-thinking the application anyway.
Snowman9000
Explorer
Aug 21, 2013
Sea'scape wrote:
Off low, or off high? A difficulty in calibration is knowing exactly the value that you are trying to set. It is possible that your reference meter is off slightly, and the digital meter is off slightly. If you have a good multimeter, measure the output voltage of the shunt, 75 mV is 30 A and you will have a better sense.

Remember the stated accuracy of clip on meters and off the shunt with its meter. Digital meters are also +/- one count, so if you are measuring XX.X, the last digit could differ by 0.2 without even considering the stated accuracy.

Glad you are making progress.

It was off low. But it's close enough for my purposes. I definitely have learned a lot here.
Sea_scape
Explorer
Aug 21, 2013
I just looked at the specification for dc clamp on meters. The accuracy varies but is typically 1.5 to 2%, and +/- 2 to 5 digits. You may be getting the same readings on the two meters after considering accuracy.

Comes down to how do you know what is right.

The hall effect meter measures electric field, but on a noisy waves have it is hard to know what the displayed value means. Sensing and digital measuring of distorted waves hopes is very difficult. A lot comes down to sample rate and input filtering.
Sea_scape
Explorer
Aug 21, 2013
Off low, or off high? A difficulty in calibration is knowing exactly the value that you are trying to set. It is possible that your reference meter is off slightly, and the digital meter is off slightly. If you have a good multimeter, measure the output voltage of the shunt, 75 mV is 30 A and you will have a better sense.

Remember the stated accuracy of clip on meters and off the shunt with its meter. Digital meters are also +/- one count, so if you are measuring XX.X, the last digit could differ by 0.2 without even considering the stated accuracy.

Glad you are making progress.
Old___Slow
Explorer
Aug 21, 2013
I assume the shunt was wired into the negative circuit and the yellow wire was attached to the shunt as shown in the diagram. What I understand from others is the shunt negative circuit on this meter is a little different?
Big_Katuna
Explorer II
Aug 21, 2013
If the shunt is reading low, you can calibrate it by removing metal at full load until it is accurate OR. Move the measuring points.
Snowman9000
Explorer
Aug 21, 2013
OK, it works with loads. It's a little off, even with the calibration pot adjusted all the way. Like a half amp off.

It also works with a better charger, my B&D 40a charger.

It didn't work with the Harbor Freight Mexicowanderer charger, or with a little transformer trickle charger. So those who said the chargers could have been the problem, were correct.

It looks like a hall effect (donut) ammeter would work in all cases? At least my clamp meter works in all of them.
Snowman9000
Explorer
Aug 21, 2013
Thanks for the interpretation of the diagram.
I'm heading to the garage to test some more. I can put a load on the battery and test it that way too.
MrWizard
Moderator
Aug 21, 2013
looking at the picture
substitute the battery for the fan motor

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Help with shunt ammeter

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