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Current Shunts

I wanted to do some work with battery charging and powering a 100 W load. So I bought a couple of combination panel meters that will measure voltage, current and power as well as an energy running total. One came with a 50 amp shunt the other a 100 amp shunt. It has been a while since I got them and I seem to have mixed up the shunts and panel meters.

The strange part is the meters seem to be the same! They have the same part number PZEM-051. The shunts are 50 amp at 75 mV and 100 amp at 75 mV. So clearly the resistances are different and so the meters need to be different to account for the different voltage they will see for the same current in the shunt.

What am I missing? Am I misinterpreting the spec? 100 amp 75 mV means it will drop 75 mV at the rated current, right?

I thought there might be a setup in the meter as it does have a button, but that seems to only be for clearing the energy reading, toggling the back light and setting a voltage range which I believe makes the display flash to alert you to a problem. Nothing to set the current range.

I'm using the 50 amp shunt at the moment and I suspect my current readings are doubled. I guess I'll have to try the other shunt and then the other meter to see what the heck is going on. Lots of wires to mess with.

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Rick C
Reply to
rickman
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I think I found it. I switched the shunt and the current is right. But I also found a video (in Russian) which indicates there *is* a setting in the meter for the two different shunts. None of the eBay listings bother to give any info on the button and what it does. Lots of options based on how long you hold the button. So one meter, two shunt options.

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Rick C
Reply to
rickman

tiny little trim-pot on the back?

connect both meters in series. swap shunts until meters aggree about current.

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Reply to
Jasen Betts

Why? If the meters have over 1000 times the resistance of the shunts, they will both read full-scale at 75 mV applied. The meter face numbers, those will be the only difference. Or, are these digital readouts?

Reply to
whit3rd

Digital and as I said in my last post, there is a fourth setup mode which selects between a 50 amp shunt and a 100 amp shunt. They seem to have a different unit for measuring 20 amps with no shunt.

It seems to work ok. The whole setup is pretty annoying though. I have the LED bolted and heat sink greased to an aluminum frying pan as a passive heat sink and the LED is really bright even at 50 watts! I need to get one working at the full 100 watts! But only after I find a shield of some sort.

The LEDs run really hot though. The base plate is thin steel and runs

LEDs have to be even hotter! That's one crappy package!!! I guess this is not an LED made for commercial work, likely just for eBay.

I wonder what they use in real lighting?

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Rick C
Reply to
rickman

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