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I have this little drill battery charger and I was testing the contacts for output voltage with a Fluke 87V, and the result was "-0L" and was showing the hazardous voltage lightning bolt symbol. Then I tried testing it with my old UEI multimeter and at first the voltage goes up to 15V or 16V for a split second, then jumps around to random voltages for example from 0V to 8V to 2V to 4V in a random pattern. The charger requires a 24V 400mA AC adapter and my AC adapter is not the original but the output is 24V 500mA and the AC adapter is right on 24 volts when tested with the voltmeter. I get that maybe something isn't working right in the charger but I can't figure out why it would be showing a hazardous voltage symbol on the multimeter. Is there a chance that the charger is working as intended but this type of behavior could be shown when tested on a multimeter due to something in the circuitry? I haven't tested the charger before or with any other AC adapter. enter image description here enter image description here

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I assume you set your Fluke87V to autorange. This means the 87V internally switches between ranges to find the correct range for your measured voltage. The switching process isn't very fast. DC ranges on the Fluke are 6, 60, 600, 1000 V afaik. When your measured voltage fluctuates, the 87V will at one point switch to 6 V range and then indicate overload, the second your measured voltage jumps up.

The "Hazardous" symbol just means overload on your Fluke.

Push the range button until you reach a range (60 V) that your DUT doesn't exceed and the symbol will be gone.

For the measured output on the charger, I assume it is sort of a "battery present" probing pulse. It doesn't output the charging voltage you expect until it senses there is a battery present.

It is also possible your charger just probes with low voltage if there is a current between it's terminals and then ramps up the voltage to charging voltage. In that case the ramp will cause the 87V to go into overload for the smallest measurement-window, which causes it to cut the current and switch to the next voltage range. The cut, however, is sensed by the charger, which makes it reset. So "bad oscillation" I'd call that :)

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  • \$\begingroup\$ Yep thanks that all sounds good and I switched the range and that got rid of the hazardous voltage symbol. \$\endgroup\$
    – wdbwdb1
    Commented Nov 9, 2023 at 7:06

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