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# how to lower the current of a power supply but not the voltage? Answered

ok i built this power supply, DC output.  it puts out about 60volts at a reasonable high amperage(i have been able to do light welding with it) is there a way i can lower the current with minimal voltage drop? if so how?

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the way you reduce amperage is by reducing voltage

Exactly - at a fixed resistance (such as when welding) the current is proportional to the voltage.

but then how in welding do you adjust the current but the voltage stays relatively the same?  i measured my stick welder output on 40 amps(lowest) and 225 amps(highest) it was about 80 volts on both, is this because there is no load?

Yes.

Remember, while you're actually welding you're creating what's nearly a short circuit (that's where the heat comes from). That's one heck of a load -- and for the duration of the welding pass, the voltage is often being dragged down considerably.

so whats the best way to be able to vary the voltage of the power supply? variable resistor?

No, Add an adjustable inductor in series with the secondary, and/or adjust the primary input with a variac.

If your stick welder is an inverter type, the current is limited electronically by using essentially a darn great switch mode power supply. If your welder is a good old fashioned buzz box, the current is limited by the transformer saturating.

A welding arc is not IME an Ohmic resistance - it actually exhibits some negative resistance !

This really pisses me off, it's like everyone will avoid answering this question, I mean everyone. No one wants to touch it with a 60 foot pole.

The guy asked you a simple question, HOW DO YOU REDUCE CURRENT OUTPUT WHILE MAINTAINING VOLTAGE?

And don't tell me it's not possible, because I have seen it time and time again. For example a power supply for electronic devices, 9V 850ma or 9v 1A, so on and so forth. People try to tell you that the device is actually pulling the current from the supply, the supply is not really outputting the amperage. If that were the case we would have infinite amperage to do with as we pleased. Something regulates the maximum current output what is it and how can we do it? Simple.

can u give me a design for a 0~24 v power supply w/ 1 Amp rating

im confuse ~_~

I guess you've got a transformer behind this? Are there any other taps (terminals) you can use on it?

L

Re design the supply so that it is a variable supply instead of a fixed output supply. Or use PWM to control the power.

Resistors are your answer. Remember, Amps = Volts/Resistance, so just increase your resistance by using steel wire or something.

variable resistor or a voltage regulator.

use a lm7805 for 5 volts, lm7812 for 12 volts, lm7818 for 18 volts, and lm7824 for 24 volts. amp max output is 12 volts. you can wire the voltage regulators in parallel to handle more current