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Cordless drill power supply Answered

I am using an EFUEL 30amp 18volt 540watt (model sk-200013)  power supply to power my Ridgid cordless tools. A dead battery was gutted and a power cord was soldered onto the circuit board inside the battery enclosure. My problem is that I encounter an OCP (overcurrent protection) error if I do not slowly power up my tools. I can live with this except for tools that are not variable speed (circular saw). If a Ridgid cordless tool demands full power at start up then the OCP error condition is triggered.
My question is that I have heard that the installation of an external capacitor will eliminate the ripple effect and smooth out the power demand on the power supply so that any tool used at 100% demand at start up  will work without causing the OCP error condition. Is this correct? If so, can anyone tell me the type and value of the capacitor to use?
Any help is appreciated.




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5 years ago

You can also use a PWM controller for a soft start.

For a very basic soft start without the need of big capacitors a circuit like in this post:


works quite well.

Of course something that simple is only useful for a no-load-start, like getting the saw up to speed but not to have full torque right from the start.

The circuit in the link is for a 6V motor but can be easily adjusted to 18V.

You might need more powerful mosfets and heatsinks though.

The charge rate of the capacitor regulates the output to the motor.