Suppression capacitor question

Other Hardware General Electronics
1

Hi: Apologies, this is a bit off the Arduino topic...

I've got an old Bridgeport Interact CNC milling machine, and one of its suppression capacitors has just let go, releasing a large quantity of Lotus-quality magic smoke.

The part number is PMR202MD, and it's so obsolete there's not even a datasheet anywhere on t'interwebs for it.

Markings on the part, however, suggest that P409CP224M275AH221 is similar enough to do the same job (rated 275vac, the old part was 250vac, 0.22uF compared to the old part's 0.25uF - everything else appears to be the same).

Does anyone with greater knowledge than me think the above is a suitable replacement?

Data sheet for the replacement part is here: http://www.farnell.com/datasheets/2755581.pdf

Many thanks in advance. Mods, if this is too far off topic for this board, please feel free to move it somewhere more appropriate.

Thanks,
Ade.

2

Based on the informations supplied I would expect that to be OK.

3

Is is a suppression capacitor? Or is it a motor run capacitor? Motor run capacitors should be replaced with
the exact value.

4

I found this link PMR202 that suggests the component is a combination capacitor + resistor.

This link Kemet

And this data sheet Mouser Kemet P409 shows a replacement as Kemet P409CP224M275(1)H221

If you can't find the replacement part you can get a similar capacitor only and add a 220 Ohm 1 watt resistor in series to do the same function.

0.22 vs 0.25µ is no difference. These parts have a 20% tolerance anyway.

BTY, the application sheet suggests this device is a snubber circuit that will "quench" current spikes of a switching device (transistor etc)

If there are more of these in your CNC device you pickup a few extra and replace them all.

Good luck

5

Thanks chaps - I'll go with these ones then.

Mark - this is, as far as I can tell, a snubber for a 3-phase motor. There IS no exact match for this component, the closest is a PMR209 which is still 0.22uF vs 0.25uF, and is also "not recommended for new designs" - i.e. it's on its way to obsolescence.

There's three of these caps, one's clearly dead, the other two don't look too healthy either. I'll replace all three.

Cheers,
Ade.

6

JohnRob:
0.22 vs 0.25µ is no difference. These parts have a 20% tolerance anyway.

Not for a motor run capacitor, they are film caps and balance the current between windings - imbalance
leads to significant inefficiency in the motor and more heat generation, and uneven running under load:

7

MarkT:
Not for a motor run capacitor, they are film caps and balance the current between windings - imbalance
leads to significant inefficiency in the motor and more heat generation, and uneven running under load:
Motor capacitor - Wikipedia

I believe this is a 400VDC motor, running off a 3-phase supply. This ties in with the thyristor board, which has L1-L3 inputs, but only 2 output wires to the motor.

8

Not for a motor run capacitor

Perhaps but this is not a motor run capacitor and the mfg spec is 20%.