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resistor value for power supply precharge? leaving resistor connected all the time

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Circuit Learner

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I have a basic cheap china DC 72 volt to 12 volt 10 amp power supply. When I connect the 72 volts I get a large spark.

I want to use an On/OFF switch on the power supply.

I heard someone say if you use a very large value resistor, like a 10K resistor, you can keep that permanently connected to the positive input.

This 10K resistor will keep the caps and power supply powered so when you connect the main positive connection it will not spark.

I was thinking about using a on/off switch on the main positive input, and keeping a connected 10K resistor connected also to the input.

Will something like this work? What value resistor would I need? I would like a highest value so that it drains the battery the least in case of a short.

Thank you

In the picture, lets just say the connector is a switch on the positive side. The negative has no connector or switch on it.


 
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When you connect the 72 DC output to the battery (as shown in the figure), you get a spark? If the battery is fully discharged, the spark will be more because the voltage difference will be larger. But I do not see how the 10K resistor is going to help. You can connect the battery terminals to the power supply first and then turn on the power switch on the power supply or on the mains. The sparking will be still there but hidden inside the switch.
 

That resistor will only help if you connect the switch after the power supply input capacitors.

You have to isolate those capacitors from any kind of load to have them permanently charged by that small resistor.

If you don't want to (or can't) make connections inside your power supply, you may use a NTC thermistor in series with your power supply to limit the start-up inrush current thus to avoid that spark.
 

Try delay circuit to avoid surje current of the DC DC converter. Use soft switch to the relay with time delay of 1 to 2 seconds.

Delay ckt.png
 

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