Start Capacitors & Run Capacitors for Electric Motors - Differences Explained by TEMCo

What's the difference between a start capacitor and a run capacitor? Can you use them interchangeably? See why these two types of capacitors cannot always be substituted for one another.

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TEMCo offers many related products including: Soft Starters, Motor
Starters, Electric Motors, Phase Converters, and more.

If you'd like to speak with an application engineer or a sales associate, please call 510-490-2187, and we will be able to assist you.

[ledbetterjack]

This is one of the best UTube videos I've seen. You explained the capacitors & their uses very well PLUS you blew one up for everybody to see how they fail. Yeah

[melendr]

Very well done! All tutorials should be this easy to understand. I have absolutely no doubt now how to identify a running or start capacitor or how they shouldn't be used. Thank you!

[nomercadies]

"IF" the clock on the back wall was accurate, you did this in one take. Until you started blowing stuff up, you just kept rolling without a bleep or hiccup. Sometimes people aren't just watching what you do, but how you get it done as well. Very good on both counts. Congratulations.

[TEMCoIndustrial]

Thanks for the feedback - we'll definitely keep the audio quality in mind for future videos.

[butchp]

I can’t tell you how many capacitor videos I’ve watched. This video gave it to you in layman‘s terms it shows you a start capacitor had to run capacitor and how they work. Very good.

[VerifyVeracity]

Great video but one thing to note....   When recording the video I think you had the sound levels volume to high for your microphone., that is why the volume is kind of popping up on a lot of you words.   thanks.  

[TEMCoIndustrial]

Some capacitors are 1000+ mfd, though many have low capacitance ranges as well. In your case, you could easily use a run cap in place of a start cap.

Some capacitors are built with a "Pressure Sensitive Interrupter" design that causes them to fail before internal pressures can cause serious injury. The one we showed is designed so that the top of the capacitor expands and breaks internal wiring.

[JoeSmith-isfo]

Excellent! Just what I needed to keep from blowing myself up. Got the new "start" cap installed and motor running.

[stuartsjalund]

Your video on differences between run and start capacitors is very good. What you did not mention is the larger capacitance will deliver a certain current for a LONGER (time) as required. One can obtain the same current level with a small capacitance but the time constant is much shorter, and this will not work! In reality, current delivered by a capacitor is determined by I=V/R. Remember there is a time constant! For example a voltage of 100 volts across a capacitor with a 1 ohm resistor across capacitor will deliver 100 amperes (time constant not taken into account, ) Capacitors can more or less be inspected on performance by using an ohm meter on the megohm scale, across a discharged capacitor. Reading should be in the megohm or higher, Basically an open circuit. For quality, apply the operating DC voltage across the cap. to charge. Then install a DC Ma meter to view current flow into the capacitor. This determines the number of DC ohms of this capacitor, ( ohms =V/I ) and shows the power factor. The higher the Ma flow into this capacitor, the worse this capacitor is or is rising to 1, power factor. Power factor is PF = R/Z. It should be 0, or almost no current flow indicates a good capacitor! (R is extremely high.). FYI, there should be no heat detected at any time. To increase capacitor life, add parallel capacitors at the same voltage but adding to required capacitance only, not over. For example a 100 uf cap. can be split twice of 2 x 50 uf or more. Splitting the current demanded by the motor capacitor is always easier on a cap. when multi units are in parallel, and this results in added capacitor life! You might need hundreds of amperes for starting and the small R of the capacitor adds up when delivering lots of amperes, resulting in heat in the capacitor, a no, no.

[TEMCoIndustrial]

Thank you for watching! Glad you found it useful.

[takethetotarzana]

Excellent demonstration. Good info on the differences.

[MrGarcon]

i took hvac class about 8 years ago, ,,thanks for your video, interesting . love to learn

[PDS]

These videos need to be re-recorded with a better mic. Amazing information, but physically painful mic quality. These peaks actually hurt to hear.

[jonnymiskatonic]

I have an older AC motor that is 240v and runs two capacitors. I went to fire it up and one of the capacitors smoked up. The other one was entirely cool and I noticed it doesn't seem to have any juice in it. The smokey one was spraying heck all over the place.

My suspicion was that one capacitor went bad and it wasn't able to get up to speed and thus the centrifugal switches weren't able to kick in and it smoked the other one. Does that make sense or am I completely off the mark.

Also for replacing these would I need 120v capacitors since it's one capacitor on each 120v circuit or would I need two 240v capacitors? Mine also don't have the bleed down resistor on them, not sure if that's necessary for the newer ones or not. It's an old saw from the 20s but the motor is definitely newer.

Stumbled across these videos from your ebay auctions. Figured I'd see what you guys have to say on it.

[jayhiz]

Best explanation ive watchd out of 25 vids. Thank u

[exoticillusions]

Great Video!!! thanks for explaining the two different types. I know nothing about them. Installed a start capacitor in a run setup by mistake and it blew up right away hahaha. Now I know that it needs a run capacitor to work. Thanks again, saved me from buying a new motor for the bandsaw

[dtinman]

you have provided me knowledge and one day I will reciprocate by buyimg parts from you. that is how the world should be.

[rolfvanderbijl]

Compact and clear yet propper information to get going with, great video which helped me forward

[yachtwork]

Just what I needed at this moment. Thanks for taking the time to share.

[MattsShop]

You are very well spoken, thanks for the vid!