441Views7Replies

Author Options:

Does Increased resistor wattage effect peak amperage output? Answered

Hello, I am in the process of building a 900W+ (60v  ~14a)  RC EDM generator. I am using a heavily modified hairdryer heating coil at  4 Ohms resistance at about 1200 watts. According to my calculations (derate transformer output wattage 20% in order to obtain minimum wattage required), I needed a minimum of 720 watts of dissipation on the resistor. Would it be okay to use a higher wattage resistor without any amperage drop on the circuit while it is operating?

7 Replies

user
steveastrouk (author)2013-01-16

RC-EDM machines need a low inductance resistor

Select as Best AnswerUndo Best Answer

user
abadon (author)steveastrouk2013-01-19

Not sure if 3.2 microhenries (I remeasured it) would be enough to not cause any disturbance or decrease in performance in the circuit. Just curious why this would need to be low inductance...

Select as Best AnswerUndo Best Answer

user
steveastrouk (author)abadon2013-01-20

It acts as a current limit, more than you might accept.

Select as Best AnswerUndo Best Answer

user
iceng (author)steveastrouk2013-01-17

Plain wire wound resistors are also coils of resistive material on a ceramic tube.
And coils become an inductor when current flows through them.
That is why resistors can be inductive.

IF you wind the resistive material in such a way so that current flow in one direction is matched by current flow in the opposite there is almost no inductance.

The picture below demonstrates one way to make a non-inductive resistor.

Select as Best AnswerUndo Best Answer

user
abadon (author)iceng2013-01-17

Thats what I was thinking, a bifiliar-style layout for the resistive element to cancel out the inductance. Not sure if 6.5 microhenries on the resistive element would be enough to interfere with the generator's operation. Thanks for the constructive input though!

Select as Best AnswerUndo Best Answer

user
iceng (author)abadon2013-01-17

You know more about electronics then your question reveals :-)

Select as Best AnswerUndo Best Answer

user
iceng (author)2013-01-16

Yes  ....  as long as the resistor is the Same Ohms.

You can increase the wattage ( a bigger sized component )
as much as you want to.

The beneficial affect is a bigger wattage runs cooler because of
the surface area and also you won't burn your hand.

A

Select as Best AnswerUndo Best Answer