Pressure washer capacitor replacement

[Foo]

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.

--
Foo

[Plain...@yahoo.com]

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.

PlainBill

[Foo]

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

[we...@aol.com]

On Sep 28, 5:29 pm, Foo <m...@not.here> wrote:

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.

[Sjouke Burry]

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.

[PeterD]

On Mon, 28 Sep 2009 22:29:28 +0000 (UTC), Foo <m...@not.here> wrote:

>
>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?

Disconnecting might work, they are for starting probably. But if it is
capacitor run then it may be a bad idea.

You may find that 2x13 works OK...

[David Lesher]

PeterD <pet...@hipson.net> writes:

>Disconnecting might work, they are for starting probably. But if it is
>capacitor run then it may be a bad idea.

If they were starting-only, they'd not be getting hot while running.

--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

[Foo]

I'll try disconnecting them or using a single, smaller cap. If the
resulting torque is not enough, I'll buy something equivalent to the
original.

Thanks everyone.

--
Foo

[Foo]

On 2009-09-29, Meat Plow <me...@petitmorte.net> wrote:

> On Mon, 28 Sep 2009 22:29:28 +0000 (UTC), Foo <m...@not.here>wrote:
>
>>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?
>
>

> Do yourself a favor and try to find a replacement of value within the
> rated specs. The motor needs that cap to start and run if it is not
> designed to disconnect after startup.
>
> You have to weigh the cost of a replacement cap against:
>
> 1. Risk of electrocution (priority)
> 2. Risk of motor damage
> 3. Do I really need a pressure washer
> 4. What would it cost to replace the whole thing.
>
> Caps are generally available as either exact factory replacement
> (recommended) or OEM if you do a little homework.

Yes, of course. I seldom use this pressure washer and don't have the right
capacitor at hand. To be honest, it was more a "what if?" question to try
to use what I have here and understand what could go wrong.

Thanks.

--
Foo

[Plain...@yahoo.com]

I'm not sure how run capacitors are wired into a motor like this. A
few years back my 'high efficiency' pool pump started overheating. The
thermal protector would shut it down. Investigation showed the run
capacitor had failed. Replacing it solved the problem. IF that is
the only function of a run capacitor you could probably use the
pressure washer for short periods without the capacitor. Inevitably
it will lead to other problems.

As far as being expensive, a quick search on eBay finds a store
selling a 50�F 440Volt capacitor for $7.00.

PlainBill

[Wild_Bill]

One reason for electrolytic capacitors to get warm or hot, is internal
leakage.
Internal leakage develops when the insulating layer(s) between the elements
starts to break down.

I don't know if this is the reason why some of your capacitors were warm,
and excessive leakage is not easily detected with a common VOM or DMM,
instead, leakage is measured while the capacitor is subjected to the working
voltage (or rated voltage).

I'm not certain that the NP non-polarized caps you have are the same as AC
motor caps. The two types are basically the same construction, but if the
caps aren't specifically labeled xxxV AC, then they may not be suitable for
use with AC induction motors.
Although if the caps weren't intended for AC, they would likely have
self-destructed during your test.
I just don't recall seeing AC motor caps that are marked NP.. maybe it' a
european habit.

You don't mention the horsepower rating of the motor, or state that the
motor is an induction type (no brushes), but the 50uF value of the cap would
indicate that it's a Run cap (not a Start cap, as I think you already
understand).

I looked at the ILCEA website, and didn't see any special characteristics
shown for the K45 series caps, but I didn't download any of their catalogs
or literature.
The 5% value tolerance is a little uncommon, since many motor caps are rated
as loosely as 30% value tolerance.

As the other replies have suggested, the best approach for restoring
operation would be to get a new, fresh stock replacement cap with the
original rating and value.

--
Cheers,
WB
.............

"Foo" <m...@not.here> wrote in message news:h9qjed$2tkd$1...@saria.nerim.net...

[Foo]

On 2009-09-29, Wild_Bill <wb_wi...@XSPAMyahoo.com> wrote:
> One reason for electrolytic capacitors to get warm or hot, is internal
> leakage.
> Internal leakage develops when the insulating layer(s) between the elements
> starts to break down.
>
> I don't know if this is the reason why some of your capacitors were warm,
> and excessive leakage is not easily detected with a common VOM or DMM,
> instead, leakage is measured while the capacitor is subjected to the working
> voltage (or rated voltage).
>
> I'm not certain that the NP non-polarized caps you have are the same as AC
> motor caps. The two types are basically the same construction, but if the
> caps aren't specifically labeled xxxV AC, then they may not be suitable for
> use with AC induction motors.
> Although if the caps weren't intended for AC, they would likely have
> self-destructed during your test.
> I just don't recall seeing AC motor caps that are marked NP.. maybe it' a
> european habit.

I'm pretty sure they are AC caps for motors. I should have provided their
refs. What I could read on the 13µF caps is:

BOSCH MP 0 670 312 455
13µF +- 10%a
360V ~ DB / HSPM
400V ~ DB / HSPM
430V ~ AB 20% ED
SD 24h / HSFH
-25° b/a +70°C

Followed by a small diagram that looks like this:

___||___
| || |
| 1 2 |
_|_ || _|_
_____||_____
------------
3

They have 3 pins, none of which are connected to the case, which should be
grounded (guessed from the screw at the top). I'm not sure what the third
one is for.

The 14µF capacitor looks the same, only slightly larger. The 10µF only has
two pins and is as large as the 14µF but only half its length.

> You don't mention the horsepower rating of the motor, or state that the
> motor is an induction type (no brushes), but the 50uF value of the cap would
> indicate that it's a Run cap (not a Start cap, as I think you already
> understand).

Yes, I can't disassemble the motor but it's likely an induction type. It
cannot start without a capacitor but won't buzz either. As for the run
capacitor, it's directly wired to the motor without anything else between.

The motor is rated at 2750W.

> I looked at the ILCEA website, and didn't see any special characteristics
> shown for the K45 series caps, but I didn't download any of their catalogs
> or literature.
> The 5% value tolerance is a little uncommon, since many motor caps are rated
> as loosely as 30% value tolerance.
>
> As the other replies have suggested, the best approach for restoring
> operation would be to get a new, fresh stock replacement cap with the
> original rating and value.

I'll do that, which brings a new question. I found a shop that sells
capacitors adequately rated, but they list those as 'start' capacitors.
Are they somehow different? I thought that it was only how they were wired
to the motor.

--
Foo

[Wild_Bill]

I should've just calculated the HP of the motor (approx 750W per HP), which
indicates the HP at about 3.6.

A lot of people confuse the purpose of capacitors for motors. Generally, any
value under 100uF will be a Run cap, while those over 100 being Start caps
(130uF start cap for a 1/4 HP split-phase induction motor, for example).
My local motor shop informed me that the appropriate values for Start
capacitors is based upon 500uF per HP.

So, your 50uF value cap appears to be a Run cap, as you initially stated,
and also appears to be a normal value for a motor that size, based upon
similar values of Run caps used on motors with high loads, such as larger
air compressor-duty rated motors.

--
Cheers,
WB
.............

"Foo" <m...@not.here> wrote in message news:h9u5nn$1011$1...@saria.nerim.net...

[Martin Whybrow]

"Foo" <m...@not.here> wrote in message news:h9qjed$2tkd$1...@saria.nerim.net...

One thing that I haven't seen anyone else mention is that start caps are
often non-polarised electrolytics, identifiable by an aluminium case with a
rubber plug, but run caps are always low loss types, typically film; an
electrolytic cap used as a run cap will overheat and will probably explode
sooner rather than later. Given that your caps are running hot, I would
think it is a cap-run motor.
Farnell do sell 50uF 450V working film capacitors for motor run use, I have
several of them in my rotary phase converter; the price was not
unreasonable.
Martin
--
martin<dot here>whybrow<at here>ntlworld<dot here>com