It says 4 microfarads on mine.

Hmm, the capacitance is important for the motor to run properly but the voltage rating just needs to be sufficiently above the square root of 2 x the mains supply voltage or it will likely go pop quite soon. Too high is not so important – but will cost far more than a capacitor with a reasonable ‘head space’ voltage rating.🙂

Just need an allowance for the maximum allowed mains voltage range plus 10%, so 400V working range should do – although cheap capacitors may fail early at that rating (they may not like any spikes on the supply or are particularly temperature ‘fussy’.

+1 for NDIY – so long as the working voltage is high enough, it should be OK – assuming it is running on 230 VAC mains.

Capacitor value is a little more sticky – I took a quick look at some of my motors, and the capacitors seem to vary from 4uF up to 25uF, with no relation to motor size. I had to change a 1/2 HP pump motor capacitor that was unmarked, and simply fitted a 12.5uF one that I had available – the pump motor has been running for months now with no problems, so I would take the plunge and simply fit something like 5 or 10uF, and see what happens. If the motor runs smoothly and doesn't overheat – problem solved. These capacitors are by no means 'precise' in value.

Nigel has 4uF – as good a guess as any.

Edited By An Other on 18/09/2020 10:31:42

Way ahead looks clear to me: Nigel says the capacitor on his Burgess is marked 4µF, and John Haine provided a link to suitable 4µF motor run capacitor on RS, cost £4.51. No need for guess work in Laurence's case!

Assuming Nigel hadn't been able to confirm 4µF, how could the size of a run capacitor be found? Replacement run capacitors available between 2 and 40µF and what's needed doesn't seem to be related to anything obvious like HP. My guess, inductance of the winding, which is a consequence of the amp/turns needed to produce a suitable magnetic field.

There is so much I don't know! What is it about a motor that decides start and run capacity, and is it possible to establish the size with a measurement? (In my youth Inductance meters were expensive Lab tools, today ebay is your friend!)

Dave

Here is a link to photo of the capacitor I've tried.

https://drive.google.com/file/d/1YBbjwj5RXAd5hH2j6JL_qMFCMIXu-SBI/view?usp=drivesdk

Edited By Russell McGuinness on 22/10/2020 11:48:43

Hello Emgee

Thanks for the speedy reply. I had a feeling about that. For the sake of a few quid I will order one like in the previous post on this thread and try it and keep you posted.

Thanks

Russell

Hello Not done it yet

Many thanks for your reply. The mains input is 230v. Can you clarify which type of capacitor I need as I am still a bit stumped!

Thank you

Get the one from RS that I linked to above! It is rated 440vac and clearly designed for this application.

The one in the link will be fine.

Steve.

Hi All

Replaced on/off switch as wasn't switching neutral. Seems to be working OK and cutting fine with the capacitor I have shown in my previous post. Hopefully this will be everything.

Anymore advice welcomed and thanks for all your input.