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I trust this hasn't been answered already. I have read some of the posts and I understand that the basic answer to the question is 'yes', but, before I damage something valuable, I'd like to clarify....

I have a concrete mixer which operates on 110V ( site voltage ). In fact, we salvaged this from a skip. It isn't very old and cost 400 UKP when new. It has been brutally mistreated, is dented and covered with concrete, BUT most of the damage is cosmetic IMO.

The motor is a 750W induction type and it all looks in very good nick. They binned it because the motor wouldn't turn, but that's just a dodgy capacitor. However, this particular start capacitor ( 100uF @110V ) costs 15-20 UKP.

I have plenty of very big electrolytics from big SMPSs: two of these rated at 250uF in series ( the voltage is plenty big enough ) should work, but this is lots of volts and lots of uF and I wonder if anyone has ever done this or can confirm the scale-up from low voltage work will fly? I don't want a shower of sparks.

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Motor Caps must be rated for 3kV transients and so must be made of polyurethane plastic or similar and in fact be rated for attachment to the grid to certain X1 or X2 cap standards. SMPS use dc electrolytic caps for a different purpose cannot and must not be used. 15UKP is a reasonable price. THe plastic is extremely pure and free of contaminants, and more turns with the lower k dielectric constant found in plastic, is offset by increase in size and cost of a tightly controlled process for quality reasons.

http://ca.mouser.com/ProductDetail/KEMET/C870CG36100AA0J/?qs=sGAEpiMZZMv1cc3ydrPrF0%2fKYujtVgoKqm92MwSkRkI%3d

THe suitable cap will be;

  • Self-healing
  • VDE, CQC and UL810 approved
  • Rated frequency of 50 Hz and 60 Hz
  • High capacitance density
  • Safety device protection (pressure release valve)

THere are other AC options that may be cheaper in Ceramic and paper but less reliable. ( ceramic limited to 1uF at 600V) http://www.kemet.com/Lists/Filestore/EvoxRifaRFIandSMD.pdf

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  • \$\begingroup\$ Tony, thanks for the clarification. I'll spend the money on a new one. However, a local dealer told me that this brand of mixer has a reputation for capacitor failure, but we don't know if this is a particular manufacturer or a function of the motor design. \$\endgroup\$
    – bruce
    Jul 12, 2017 at 22:29
  • \$\begingroup\$ You're correct when it comes to motor run caps -- NP 'lytics are used routinely for motor start service though \$\endgroup\$
    – ThreePhaseEel
    Jul 12, 2017 at 22:46
  • \$\begingroup\$ I didn't know that. I guess the short operation, reduces the risk of coincidence with PLT transients. otherwise they just go bang and spew nasties.. But ATX PSU's would not use Non Polar caps except for XY line filters < 0.047uF \$\endgroup\$
    – Tony Stewart EE75
    Jul 12, 2017 at 23:39
  • \$\begingroup\$ Digikey had nothing in stock nor cheaper in bipolar alum e-caps near this range \$\endgroup\$
    – Tony Stewart EE75
    Jul 12, 2017 at 23:44
  • \$\begingroup\$ @bruce the (mouser) Kemet link I posted would be very good quality \$\endgroup\$
    – Tony Stewart EE75
    Jul 12, 2017 at 23:46

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