WARNING - residual high voltage from LIFEPO4 68V battery charger when turned off

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GreenBiker
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Joined: Monday, August 30, 2010 - 10:27
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WARNING - residual high voltage from LIFEPO4 68V battery charger when turned off

We got a noisy spark from the EMS 68V charger while the charger was off.

This charger shows 1.5V when plugged in an AC wall outlet but "off" switch position.

Also, after turning the charger to "off", the voltage goes down gradually. There must be a capacitor retaining power.

marylandbob
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Joined: Monday, June 22, 2009 - 12:24
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Re: WARNING - residual high voltage from LIFEPO4 68V battery ...

What you experienced is not that unusual, many good power supplies/chargers use large capacitors to filter the output, and such capacitors will retain a charge for considerable time, unless a relatively low value resistor is connected in parallel with the capacitor, but such a resistor wastes power and generates heat. (other alternatives, such as a RELAY to disconnect/discharge the capacitors, increase cost and size, and add reliability problems.--Best advice? Be CAREFUL, especially with devices/circuits operating at voltages greater than 28 volts, or utilizing high amperage! (Thecapacitors in some motor controllers, such as the one on the VECTRIX scooter, can retain over 125 volts with the battery and charger both disconnected!)-Bob

Robert M. Curry

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