Capacitor Size

i have a friend .. who has a very old motor ...lkooks a strange one ...with either a big bearing on the front or epicyclic gearbox.

the caps buggered on it ...keeps popping the earth leakage

says its 60 mfd

this is a huge one ...

squarish about 2x3x4 inches .

the 60 mfd ones i find on ebay are cylindrical and very much smaller.

will they do

BTW ... oddly.....the motor does starts on its own without being pushed in one direction and gets up to speed quickly when the cap is taken out of circuit...but don't know if it will do the same when connected up and running something.

there is no label on the motor ...so dont know how many hp it is or the speed ... will measure tommorrow.

all the best.mark

Reply to
mark
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Hi, If they are of a sufficiently low value of ESR (equivalent series resistance) which will dictate how hot it gets when being run. This is also probably a Power Factor capacitor. Do you know if it really is a starting cap, or is there a starting winding?

Cheers,

Rob.

Reply to
Robert Wilson

says on it electrolytic condenser 60 mfd

the only one i can find on ebay says ... 60 +100 mfd and has three poles ..

btw

measured the motor

and it runs at 1450 ish rpm

and it uses 340 watts to tick over

Reply to
mark

That will be a special sort of electrolytic capacitor that is designed to tolerate AC for short periods during starting. An ordinary electrolytic capacitor designed for DC will NOT do. It is very highly likely indeed that the twin capacitor you have found is a DC type often found in valve equipment power supplies.

The choices are to find a motor start electroltyic capacitor - which will be specifically marked as such with an AC rating and often with a max number of starts per hour or to buy a motor run capacitor which will continually tolerate AC. These are more common but will be physically bigger than the eltrolytic type for the same capacitance value. Typical suppliers will be Farnell or their cheaper associated company CPC or RS. All will deal with the public but may charge handling. Otherwise go to a motor rewinder who will almost certainly have something suitable and in my experience are very helpful.

typical parts

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part no CA02790

or

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partno 117-192

HTH

BOb

Reply to
Bob Minchin

hi in regards of the 60mf start cap the reason why its blowing the earth leakage is that the cap is a metal cased one and its tracking,just to prove it will work put the cap in plastic bag then run the motor hope this helps regards kevin

Reply to
lecmotors

thanks for that ... he's giving it a go tomorrow with a double layer of insulation tape.

will let you know if it works ...

cap surrounded by cardboard ...that is probably damp ....and he's told me its not coming out without a struggle ...thinking the stuffs swollen with moisture myself.

if it don't work

I've told him to go to a TV engineer around the corner and order the RS one from above post....as they all have accounts with RS

thanks chaps for the help so far ..

all the best..mark

Reply to
mark

The small capacitors you have found on ebay are almost certainly radio type electrolytic capacitors and only work if polarised by a DC supply. They are NOT suitable for motor start duty.

You need either an AC rated paper/plastic dielectric capacitor or the special type of AC rated electrolytic capacitor made for motor starting duty.

RS (used to be called Radio Spares) stock suitable items.:- Capacitor,electrolytic,aluminium,motor start,220/275Vac,60uF RS Stock no. 117-108

Jim

Reply to
pentagrid

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