Pressure washer capacitor replacement
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From: Wild_Bill on 29 Sep 2009 16:44 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" <moo(a)not.here> wrote in message news:h9qjed$2tkd$1(a)saria.nerim.net... >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
From: Foo on 29 Sep 2009 19:37 On 2009-09-29, Wild_Bill <wb_wildbill(a)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
From: Wild_Bill on 30 Sep 2009 09:02 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" <moo(a)not.here> wrote in message news:h9u5nn$1011$1(a)saria.nerim.net... > > 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
From: Martin Whybrow on 30 Sep 2009 14:35
"Foo" <moo(a)not.here> wrote in message news:h9qjed$2tkd$1(a)saria.nerim.net... >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 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 |