Checking capacitor on whirlpool pump

[eveares]

Can I check this with a volt meter ?

Know I am late in here... but Yes to your question.

Take the capacitor out of the circuit and check it using the continuity function of your multi meter. If it is continually in a short circuit state and does not transition to a open circuit state when tested, the Cap is bad and needs replacing. I had the 12uF cap go bad on my spa bath and was just humming until I replaced it.

Providing this replacement cap physically fits, this should sort your problem providing it's the cap: http://uk.rs-online.com/web/p/polypropylene-film-capacitors/3779052/

For how much the replacement Cap costs, I would just try replacing the cap first.

 

[diycooper]

Thanks Ill let you know if it works once changed. Cheers guys

 

[JohnW2]

Take the capacitor out of the circuit and check it using the continuity function of your multi meter.

As you will see, the OP has already done that and reported:

Ok just done this test and mine is staying between 0.6 - 0.7 and not dropping back down. Am I right in saying it faulty ?

Whilst we do not know what the "0.6" and "0.7" mean, this certainly seems to suggest that the capacitor is faulty.

Kind Regards, John

 

[Mikefromlondon]

Guys those who asked question why capacitors are rated at 400v and not 230v,

In Britain our nominal mains supply voltage is 230v AC, but power companies are obliged to keep it within a certain limits i.e. it can rise upto 10% or go lower by 6% of this.
So that means we can often get as much as 253v AC, or as little as 216V AC. But what is important is that this voltage is equivalent of providing a same amount of power or energy as if it were a steady DC voltage. So we refer to our mains voltage as an RMS voltage, and not a peak voltage.

So in other words, if you were to wire up 20 car batteries in series each at exact 12v Dc, such that your total DC voltage was 20x 12 = 240V DC, then our 240v DC would provide exact same amount of power as our 240V AC, However AC voltage is a lot different, because it is not a steady as a DC voltage , but AC voltage has series of peaks and troughs, or valleys, and so its peak has to be much higher in order for it to be rated as equal to a steady DC volts,

This means our 240V AC must peak at up to 330 - 340volts in order to qualify as equivalent to a DC voltage.

So we are never told this unless you were studying in electrical engineering that as an actual fact, our voltage is much higher than it is labelled, so maximum voltage that power companies are allowed to supply us is 230V AC plus 10% that means 253V AC, (RMS) but this really means it is in fact 253 x 1.414 = 357Volts peak voltage.

So in reality when we do get electrical shocks from mains we are actually being subjected to not just 230v but 1.414 times more, so that comes to 325V !
1.414 is a conversion factor for converting any ac RMS voltage to as peak voltage.

Therefore capacitors will only store what is being applied to them, so when you apply RMS 230V they will store the true Peak voltage and not the actual labelled 230V RMS.

So capacitors must be rated to stand true peak voltage and not labelled RMS voltage.
Any capacitors used on mains appliances, they must be rated at peak voltage rather than RMS voltage or equaivalent DC voltage which is also called Root Means Square or RMS.

So if you must select a capacitor it should be rated to handle peak mains voltage, so for 230v that can rise to 253v you must use a minimum 400V capacitor.
If you were to use a capacitor rated at 230V, it will fail very quickly as it is actually being subjected to by a voltage that is 1.414 times higher or true peak voltage.

 

[Mikefromlondon]

One other way to test a capacitor is to charge it up with a known source of DC voltage such as two 9v batteries in series, or even a 12v battery, then get your multimeter, it should show 12v for a fair amount of time and voltage starts to go down slowly, if it was shorted out it will store no charge and may short your battery, capacitors can go both shorted out or become open circuit or lose their capacity. capacity is measured in micro farads.

A 1000uf 16V capacitor can be much smaller than a 6uf capacitor rated at 400v, capacitors increase in size as they get bigger in capacity and even bigger when going up in voltage.

 

[JohnW2]

..................... So if you must select a capacitor it should be rated to handle peak mains voltage, so for 230v that can rise to 253v you must use a minimum 400V capacitor.

Indeed. This point was made, succinctly, by endecotp back on page 2.

Kind Regards, John

 

[JohnW2]

One other way to test a capacitor is to charge it up with a known source of DC voltage such as two 9v batteries in series, or even a 12v battery, then get your multimeter, it should show 12v for a fair amount of time and voltage starts to go down slowly ...

Indeed, provided one uses a DVM or other high input impedance meter. With a moving-coil analogue meter (as in videos presented earlier in this thread) the voltage would go down pretty quickly unless one was testing a very high capacitance component.

For example, with a 6μF capacitor and a 10kΩ/V meter on its 20V range, the voltage would (with a perfect capacitor) halve every 0.83 seconds or thereabouts.

Kind Regards, John

 

[diycooper]

Just thought I let your guys know. I changed capacitor and the pump fired up. Thanks alot everyone. Much appreciated.