DC power supply for CNC?

Which brings up another function of the caps, which is to absorb energy returned from the motor when it's decelerating a load. It's possible to fault the amp by exceeding its input voltage limit if the caps aren't large enough. A case like lowering a suspended load is worse than decelerating a mill axis, but it's something to keep in mind.

I never was stung by a charged cap. However, once I did short a cap with a screwdriver, just in case, as I was sure it was discharged. It was very LOUD!

i

I may get the caps tomorrow, in which case I will give the device a try. I have some caps (not exactly suitable, 50v) that I can try today for experimenting.

i

Too large a filter cap -- excessive surge current -- blown rectifier, or worse. Iggy, these things are well covered in Eng. design handbooks.

After a bit of thinking, I began to realize that the whole setup is limited by the transformer, and so, putting lathe caps on output would not be likely to ruin the existing diodes. I will try turning it off and on a few times. If the diodes fail I will oversize them.

worse. Iggy, these things

Bob, would not the transformer limit current?

i

50/1.414 = 35.36 RMS at the transformer plus the diode drops. Start at a lower voltage, if you're not trying to turn those capacitors into confetti and the cans into projectiles.

worse. Iggy, these things

Not for a single motor. A transformer's ability to limit current is based on the DC resistance of the windings.

worse. Iggy, these things

OK, what motor?

i

worse. Iggy, these things

Or leakage inductance.

worse. Iggy, these things

The motor you are trying to test? Its current loading is below what the transformer can supply, so the transformer can not limit current. That's why the circuit breakers in your home are rated for 10,000 A interrupting capacity.

Mike sez:

" . . .if you're not trying to turn those capacitors into confetti and the cans into projectiles."

Caps can be dangerous alright. I remember an incident from a military class on HV (radar) power supplies. The class clown got knocked on his ass by touching the wrong part of the (experiment) power supply. As he was picking himself up off the floor and when he cleared the edge of the workbench, a cap blew and he got slapped between the eyes with part of the cap's aluminum case. Down he went, again.

Bob Swinney

On Tue, 08 Jun 2010 10:26:12 -0500, Ignoramus8975 wrote the following:

Well, if you touch the leads to your tongue... . . . . CAUTION: KIDS, DON'T TRY THIS AT HOME!

-- Never tell people how to do things. Tell them what to do and they will surprise you with their ingenuity. -- George S. Patton

Look, if you're using digital encoders and controllers, the DC input does not have to be regulated, and a gutsy toroid plus fullwave bridge and a modest capacitance is fine. The digital servo controller is itself a regulator by nature. The input DC can sag and ripple as long as you have enough volts there to meet the speed demand and current for the torque demand. The controller's digital feedback loop responds much faster than any sag or hum frequencies.

on HV (radar) power

of the (experiment)

the edge of the

cap's aluminum case.

Some of those large computer grade electrolytics could cause a concussion, or even kill you if you're careless enough. I had a hell of a time teaching some people to test low voltage linear power supplies with a variac. They insisted on setting it at 120 VAc, then flipping the power switch. If one of the nine electrolytics was installed backwards, you didn't have time to turn it off before they vented. Luckily, they had a 1/8" plate bolted down to keep them in place.