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Sjouke Burry[_2_]

wrote:
On Sep 28, 5:29 pm, Foo wrote:
On 2009-09-28, wrote:

On Mon, 28 Sep 2009 15:06:53 +0000 (UTC), Foo wrote:
A few years ago, the motor capacitor from my pressure washer exploded,
it was a large 50uF non-polarized, plastic-cased run capacitor for
a 230V, 2750W motor. Interestingly, it didn't stop the motor right away
but it couldn't restart when shut down.
Its case read ILCEA K 45 5000 50uF +/- 5%b 450V HPFPU.
Because the device was over ten years old, I didn't bother to repair
it but kept it anyway, until a few months ago when someone gave me four
large alumin(i)um-cased caps: 13uF 13uF 14uF and 10uF (non polarized,
450V max or so, all from Bosch).
So I decided to wire them in parallel in place of the old one, and it
worked as before even under maximum load.
After 10 minutes of use, I stopped the motor to make sure the capacitors
were not overheating and found that the two 13uF caps were hotter than
the others (still able to touch them with my bare hand, but the two others
were still at room temperature).
Does it mean that only those two actually work, do you think it's safe
to continue operating the device, or will they keep heating up until they
meet their fate too?
Thanks.
It is likely that only the two that are heating up actually work. If
you wish to use the pressure washer I would suggest buying the correct
part. Cobbling together several capacitors for a piece of equipment
that is handling water at high pressure doesn't seem safe.
I agree that it would be the best solution, and as Meat Plow suggested
above, using capacitors of different values in parallel cannot be good.

However, finding a good replacement part won't be easy (I will have to go
out or something equally complicated) and probably a bit expensive.

In the meantime, I was thinking about an alternate solution to avoid
damaging my capacitors: since the motor seems able to run without them,
what if I disconnect them after it's started?

Alternatively, I'd like to know what would happen if I use less capacitance,
using 2x13uF or 14uF only. Will it be a power/performance problem or will
something get damaged?

--
Foo

It is likely the capacitor does nothing except participate in
generating a pseudo-rotating stator field during starting. Once the
motor is running, it does nothing at all.

The cap produces a pseudo-rotating stator field, and is dragging the
rotor around, even after startup.
If you leave the cap out after starting, the bulk of the torque is lost.
That is,for the motors designed with a permanent cap.