Don't leave USB power test meters in line when you are not actually taking measurements, and when you do, make sure no other equipment is hooked up to the power bank - either before or after the measuring device!
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Many of them measure on the ground side by inserting a resistor in line - which causes confusing and sometimes dangerous results if you connect grounds together on both sides of them.
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Also, all of them measure by inserting some sort of resistance inline to produce a voltage drop. At high currents, this will drop the voltage available to the load, and in some cases cause poor regulation.
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They're all great devices, but you need to think about their limitations while using them. They're not great for monitoring - mostly intended for specific measurement setups.
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hope this helps...
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M
