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I have bought a replacement Run Capacitor for a forced action mixer (special cement mixer), as the run cap on the mixer blew. The mixer has a single phase motor, and although we are in the UK, it runs from a 110V power supply (standard on UK construction sites).

Possible reason it blew is that we used a power supply that didn't provide enough continuous power. Manufacturer recommends 5KVA continuous but we used 3KVA. Or we left the mixer on too long. Either way we have purchased a new 10KVA power converter and the electrician connected up to a 32A type C RCBO.

The motor is labelled with run cap and start cap values (130uF and 1200uF respectively) and I have researched a replacement capacitor and purchased this: https://www.mouser.co.uk/ProductDetail/80-C9TS6MD6137AARX. Unfortunately the manufacturer was unable to send a like-for-like replacement as the mixer is an old model.

I researched the subject and bought a polypropylene / film capacitor of 137uF, slightly more than the old one.

However my new replacement capacitor has three terminal blocks on the top, not two, and came with a tag on the connectors. I have looked at the data sheet but still don't know how to hook this up, or what the tag does. Behind the label of the tag appears to be PCB traces. The tab may be there to keep it discharged?

I am aware of the dangers of handling capacitors and how to discharge them.

1/ Have I bought the right capacitor? It is much larger in physical size than the original.

2/ Should this tab be removed? What is it for?

3/ Please see photo, showing three connections on the new cap. Which terminals do I hook up to the brown and blue wires (i.e. + and -) on the capacitor connection box on the back of the motor?

Photo of replacement cap - three terminal blocks

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    \$\begingroup\$ The blue 'tag' appears to be a discharge resistor; I think you can keep that in place. \$\endgroup\$ – Richard the Spacecat Aug 28 '18 at 13:28
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It looks like you bought a 3 phase PFC cap for a single phase motor.

There must be a neutral connection (lower terminals) to 3 separate caps with 1 for each phase (upper terminals).

Datasheet says "aluminum can capacitors are three-phase capacitors for power factor correction (PFC). KEMET C9T 415 / 440VAC rated voltage capacitors feature polypropylene metallized film and include an overpressure safety device. C9T PFC capacitors are also available with delta connections"

enter image description here The Run cap is chosen to shift the phase of the coil to maximize torque and minimize conduction heat losses from excess current during operation.

schematic

simulate this circuit – Schematic created using CircuitLab

Unfortunately between any 2 pins of a 3 phase delta cap is the equivalent circuit of 3 caps = 1.5x C. If two pins were shorted then it would be 2xC.

You really want a single cap equivalent to ~ 130uF within 20% or so, but perhaps the 3 phase 92.2uF cap (138uF) is close enough and is Amp rated to exceed your needs. KEMET C9TS5MD5920AARX

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  • \$\begingroup\$ Thanks. I didn't mention in original post that the top three are connected in line to the bottom three, which you can see when removing the black plastic. I googled "Delta connections", they are three caps in a triangular arrangement (i.e. 1 cap between A-B, 1 between B-C and one between A-C). Can I simply hook up between A-B, as long as I determine the polarity? EDIT TO ADD: also I bought the 450V cap because original cap had 400Vac written on the side. Perhaps a 250V would be sufficient? \$\endgroup\$ – hazymat Aug 28 '18 at 13:59
  • \$\begingroup\$ I cannot tell if this cap is Star or Delta, but your DMM can test each connection for resistance and voltage from the resistance test to see how it connected or contact KEMET. They assume alot in their datasheet. .. perhaps but depends on X rating \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Aug 28 '18 at 14:04
  • \$\begingroup\$ If C measures 1.5C between any 2 terminals then you need 2/3 of 130uF or 87uF and 92uF 3ph is closest C9TS5MD5920AARX \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Aug 28 '18 at 15:07
  • \$\begingroup\$ Strange, when connecting up my DMM in cap mode (it's an Extech EX330), it starts at 0pF then the display changes after a few seconds to 0uF, but I leave it on for minutes and it still says 0uF. Does this for the old blown cap and the new cap as well. Does it sound like my DMM is broken?! It still measures resistance fine. p.s. given there are three terminal blocks I think it's Delta not star \$\endgroup\$ – hazymat Aug 28 '18 at 15:16
  • \$\begingroup\$ What does Resistance indicate? then voltage? then C? Does it charge up with a 9V battery? Short out Vdc prior to measure C for your meter....maybe \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Aug 28 '18 at 15:32

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