capacitor for plasma cutter

[jpier]

I have a HYPERTHERM MAX20 PLASMA CUTTER. Bought at a Tech school auction for parts, since someone "borrowed" the capacitor out of the chopper assembly. Does anyone own this model and can give me the specs for a replacement. Hypertherm will only sell a replacement in a module assembly,BIG BUCKS.

[Hobart Expert Rock]

JPIER........SORRY MAN DON'T THINK WE HAVE ONE SETTING AROUND ANYMORE....................ROCK
SSCOTT@MILLERWELDS.COM

[jpier]

Well, I know a bit about what I need. A capacitor of 2.5" diameter, 4" or 4.5" long, screw-post connector on top. Transformer feeds 173 Volts AC to the diodes, so it should be rated at 250VDC. The figuring the mfd. is what's giving me trouble.

[Hobart Expert Rock]

JPIER.......WELL GOOD LUCK ON FINDING THE DIAMETERS....... AND I DON'T HAVE A SPARE PARTS MANUAL IN FRONT OF ME HERE, I'M JUST GETTING THIS OFFICE SET UP.........CALL MILLER ELECTRIC AND ASK THEM IF THEY HAVE A REPLACEMENT CAPACITOR OF THE VALUES YOUR NEEDING. I DOUBT YOU WILL GET THE DIMENSIONS UNLESS YOU KNOW WHO THE MANUFACTURER IS THEN YOU COULD GO BACK WARDS..........AND DO A SEARCH FOR THE MFG.........YOUR CALL.......................ROCK
SSCOTT@MILLERWELDS.COM

[Phil]

Originally posted by jpier
Well, I know a bit about what I need. A capacitor of 2.5" diameter, 4" or 4.5" long, screw-post connector on top. Transformer feeds 173 Volts AC to the diodes, so it should be rated at 250VDC. The figuring the mfd. is what's giving me trouble.

2 questions:

1- Is this transformer line fed (60Hz), or fed by the chopper (then you need to know what the chopper frequency is).

2- How much current is drawn from the 250VDC side.

With this info you can calculate the value of the filter cap.

Phil

[jpier]

I have my manual now. And a wiring diagram 120V 60Hz going in on side of the transformer and out 24V to the controls, 173V to a bridge diode on the chopper assembly, next the missing capacitor
crossing the - and +. Not much help, except for replacement numbers on parts like relays and switches.

These are the electrical SPEC's
Chopper SA, 20A 240 OCV
Max OCV... 240 VDC at 120 VAC input power
Output Current...10 Amps Min to 20 Amps Max
Output Voltage....90 VDC
Duty Cycle Rating...@ 90 OCV...35% @ 20amps....50% @ 17 amps....80% @ 13 amps...100% @ 11 amps

[Phil]

Well, the exact value is not that important. I suggest you pick the value based on the type of capacitor and physical dimension. You can buy regular, computer grade, inverter grade, etc. For the same size, the inverter grade will have a lower capacitance because of internal construction to handle hi-freq ripple. In this instance, I would suggest a computer grade type.

Here is a part number that should work for you (Cornell-Dubilier):

Their web site

CGS722T250X4C, 7200uF 250 VDC 300VDC surge size 2.5" x 4.125"

Hope this helps.

Phil

[jpier]

OK I will get a replacement capacitor, then post how it works out.