Burgess BK3 MK2 capacitor

My Burgess BK3 MK2 will not run when plugged in to the mains. Motor turns easily and someone suggested that the capacitor (capacitator) was at fault. I need to find the mu factor as there was a sticky label covering this data which was erased on removing the label. Can anyone help?

Bit confused - I guess I will be shot down in flames by one of the many experts in this forum, but I don't understand what you mean by mu factor. Do you mean the value of the capacitor in microFarads? The symbol commonly used for micro is the Greek mu.

It says 4 microfarads on mine.

Do we know the required capacitor voltage? This is almost more important than the uf rating.

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’.

Something like this...

**LINK**

https://uk.rs-online.com/web/p/polypropylene-film-capacitors/1964539/

+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

I’ve got a Record BK3 bandsaw ,appears to be same as Burgess ,it has a 4uF 450Volt capacitor.Roughly 2.5 in long and 1.25 dia with fixing stud on end. Hope this helps.

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

Hi Laurence, not directly relevant but connected to the BK3.

I have just completed the blade guide modification on my BK3 based on the details in ME Vol 170 Issue 3944. If you haven't seen this I would recommend it. It has made mine a completely different machine to use.

Alan

Thank you all for your help. I had given the bandsaw to a local Men's Shed only to be told it did not work so thanks.

Hello All

Following this topic I've got a Burgess BK3 bandsaw someone's asked me to look at. He was told by someone else it could be the capacitor but the original capacitor is not attached to the motor.

I've asked another Electrician who's given me a new capacitor but it is not the same rating as the one discussed in this post.

The bandsaw powers on as the light emits but when you press the switch on it doesn't do anything.

I have attached a photo of the capacitor he has given me and this one is 230v the bandsaw is 230v but would it need to be a 400v rated capacitor. This is beyond my scope of electrical knowledge.

Many thanks in advance.

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

Russell

That says 40uf so 10 times what is called for and the voltage is too low for motor working.

As said you need 4uf and 400v AC working.

Emgee

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

The UK mains voltage fluctuation/delivery can be up to 253V, so that voltage tolerance is only just adequate, but would work (at least for a short while🙂 ). As above the capacitance value is far too high.

A 400V capacitor would be good for 280V a/c (400/1.414) - see my earlier post

400V a/c is a different matter altogether. You require a non-polarity conscious capacitor of 400V d/c working voltage which would allow about a 40V margin over the minimum rating required.

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

As above. Seems like four microfarads is the value required. 400V working voltage (DC) is a reasonable rating, but higher is better - but increasingly expensive, to the point of uneconomic and unnecessary.

I would not recommend a ‘bargain’ from ebay/china. RS Components generally supply very good quality (but sometimes at slightly elevated prices).

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

Hello yes I've seen your link but then Not Done It Yet has mentioned about 400V DC which is confusing me.