Pressure washer capacitor replacement

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.

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Foo
Reply to
Foo
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I can't offer a technical explanation but parallel odd value caps is not a good idea in many situations besides a few low voltage applications.

I'm sure others will chime in with some mathematical equations that can explain further.

Reply to
Meat Plow

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

Reply to
PlainBill47

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?

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Foo
Reply to
Foo

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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.

Reply to
webpa

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.

Reply to
Sjouke Burry

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...

Reply to
PeterD

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

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Reply to
David Lesher

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.

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Foo
Reply to
Foo

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.

Reply to
Meat Plow

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.

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Foo
Reply to
Foo

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 50µF 440Volt capacitor for $7.00.

PlainBill

Reply to
PlainBill47

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 .............

Reply to
Wild_Bill

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.

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'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.

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Foo
Reply to
Foo

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 .............

Reply to
Wild_Bill

Hey no problem and hope you come up with a safe viable solution.

Reply to
Meat Plow

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

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Reply to
Martin Whybrow

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