On 20/09/2020 11:46, ARW wrote:
On 20/09/2020 11:13, Martin Brown wrote:
On 20/09/2020 09:20, jeff Layman wrote:
On 20/09/2020 01:57, John Rumm wrote:
On 19/09/2020 21:03, ss wrote:

Mini lathe 50 odd years old, the motor not original.
I would like to reduce the size of the electric box.
It contains an on off switch, an indicator lamp, and a reverse switch.
Inside is a large capacitor which takes up the space if I can replace
the capacitor with a smaller dimension then I can reduce the elec
box size.
Is a more modern one smaller and if so what sort of ratings am I
looking
for on eBay?

Image:
https://imgur.com/igFcKqj

It looks like a 4 uF motor run cap.

Something like:

https://cpc.farnell.com/ducati/4-16-...un%20capacitor


claims to be 55mm tall, and 28mm diameter - so probably a bit smaller
than the one you have.

Why is a 440v AC capacitor being used with a 230/250V motor?The OP
did say the motor had been replaced, so maybe it was a 440V (3
phase?) motor previously, although that seems a bit strange for a
mini-lathe. Anyway, that capacitor is well past its sell-by date if
the "1966" on it is accurate. I haven't checked, but a 240V capacitor
should be even smaller.

The capacitor has to survive being attached to 240 rms ac mains
voltage which has peaks 1.4x higher and with a margin for the odd glitch.

This site labours the point a bit but shows the difference.

https://www.electronics-tutorials.ws...s-voltage.html


What if the cap is charged up one cycle and power is applied with the
other cycle. That wound mean you need a 750V cap

Its not much different from normal operation - just the alternate
polarity cycle will come a bit quicker.

(note many are setup with a bleed resistor to drain off any charge after
power down anyway)


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/