Hi All
I have an acquaintance who is trying to repair a Bosch pressure washer.
The faulty component appears to be a capacitor rated at 25uF. Not sure if it's a start or run capacitor. Maplins stock the same make but only in 20uF or 30uF.
Can either of these be used instead - and which one?
TIA
Probably - yes as all these devices have a wide tolerance. To be on the safe side I'd use 20uF in parallel with a 5 or 4.7uF.
Do make sure you use the correct type!
and voltage rating.
Thanks Fred. How would I identify the correct type? What am I looking for?
It's probably a motor run capacitor and so is designed for the specific motor windings of the motor. If you go for a lower value, the motor may not even run. If you go too big, it may run unevenly due to an unbalanced rotational field or result in a lower motor life, due to the higher current = heat. If you look in CPC or RS components, etc, you should find the correct value.
I'd experiment with other values if you have them available, to check the fault is the capacitor, but if you are buying one, get the right one. The voltage rating can be higher but the capacitance should be as close as possible.
AFAIR, If it is a motor start capacitor, there will be a second run capacitor, often in the same case (look for 4 terminals), and some form of contact that opens when the motor is up-to-speed. Given the application, I don't think it is a dedicated start capacitor, even in a Bosch :-) Start capacitors are less critical and you can normally use one of higher capacitance without a problem.
Have a look at the old one and use that as a basis for comparison. I presume the ones you saw in Maplin are:
Either. Needs to be 400v AC rated
Is it yellow and squarish in shape? if so my guess is its a spark suppressor cap and 30uF will suffice.
That sounds unlikely with the size of capacitance given. Spark suppression capacitors require a low ESR to absorb the RF and a capacitor of 25uF is not going to have that typically. Spark suppressors are normally in the 0.1uF range - further I doubt that pressure washers use universal motors so there are no sparks to suppress.
I converted a 2kw motor from a broken pressure washer to run my circular saw some time back. In doing so I had to replace the timer capacitor and the start/run capacitors. The timer capacitor in my case was in an electronic circuit and was small - the start/run capacitors were like the ones shown in the Maplin advert and were of that physical size, voltage and tolerance. If it is a timer capacitor it is most likely to be electrolytic and have a tolerance in the order of 50% or more, so any of the values given will do.
The Maplin site has a website
Rob
Sounds a bit big to me for RF suppression. The range of these tends to be about 0.01 - 1µF.
well its always nice to see complete and utter ignorance displayed on the forum isn't it?
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