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

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!

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

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.

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

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

"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.

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

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

Awesome video! Thanks alot for taking the time to make this! Funny the background behind you, because this is exactly the info i needed to complete my RPC and get my shop back online!! Thanks again! Awesome!

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

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.

Best explanation ive watchd out of 25 vids. Thank u

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

Thank u for the info sir, this is exactly what I need to know for testing a start capacitor.

Excellent demonstration. Good info on the differences.

An educational promotion; don't see that very often in youtube land - well done :)

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

Tip ... never use headphones 🎧 in full volume for this video specially starting.

Thank you for watching! Glad you found it useful.

Great Video. Simple and concise.

Hey thank you for making this video. ;) 100% educational and professional all the way through.

Great work if you have any more heating or air conditioning tips I like to see them very knowledgeable

Good Video! Thanks for Sharing! Happy New Year!!

Looks so good, high quality built

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.

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.

Hey man.. Great video, my motor is humming, I swapped over a capacitor I had in shop, it started motor but cap exploded hahaha after a minute, I will drop a link for my problem, it is a pdf file with all parts listed, I think it is a run capacitor I need, it's the the 66uf 50Hz.. One on the list thanks you my good man

<a href="#" class="seekto" data-time="161">2:41</a> consider this when considering adding a capacitor to my living room bathroom exhaust blower motor to stop it from getting stuck on start up.

thanks for the demo

This is a great video. I have a question about capacitors in parallel, specifically for a well pump. I have not opened my control box yet to see if my well pump controller uses a start capacitor or a run capacitor. Is there any danger in paralleling that capacitor (provided it is the same type) ? I’m in the northeast and we recently had a tornado that left us without power for a week, my generator was struggling with the peak inrush current for our well pump when there were other loads drawing on it at the same time. I wanted to see if I could alleviate some of that stress with an additional capacitor. Any knowledge you have to offer on this would be appreciated. Thanks in advance.

Thang you for that sharing sir.

Great Video. THANKS!

Good Video. Very well done. In your demonstration are you just throwing raw AC power across the caps with out any type of a buffer in the circuit? Thanks.

You are very well spoken, thanks for the vid!

Thank you. Very informative video

Thank you again for your help.

Judging from the capacitance, it appears to be a start capacitor. Start capacitors typically have a range of capacitances, while run capacitors give a single number. The values on start caps also tend to be higher than those on run caps.

Nice job dude,thanks

Thank you! Great video!

Very well done. Thank you

Great video! One question: You mentioned that run capacitors have a 100% duty cycle so they can remain in the circuit. I want to use these capacitors for a pf correction project on an induction motor, but as my pf will be changing, i need to provide nearly constant switching in which the caps are introduced and taken out of the circuit. Is this safe to do for run caps, or should i use a different type of capacitor? Thank you in advance!

Run caps could be use for PF correction. It would be important to be sure that the caps that are out of the circuit at any given time are drained before being reintroduced to the circuit.

Thank you for that sharing sir.

Terima kasih banyak .....

A great tutorial easy to understand and concise. Thank you.

I would like to see the voltage meter readings when you are checking the capacitors in this video. Thank you

Great video! What ohm and power is the discharge resistor you used?

@TEMCo Industrial Power My start up capacitor on my compressor is only 31.5uF at 400v (2 terminal) if i buy a much bigger uF rating ie (400uF) would it make my compressor start easier. Mine at present doesn't always start up every time, sometimes it buzzes upon start up and freezes,if i spin the motor by hand it will start up, is my start up capacitor faulty and would it cause these start up problems??

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.

very professional thanks

Well worth watching.

great Video thanks

Very nice video, thanks!

Useful video !

Is the voltage spec on a Start (or Run) cap an absolute value? In other words, will a 250v rated cap work ok in a 110v circuit, given the µF is correct ?

great video, thanks

This isn't something we specialize in, but you can look up info on power factor correction using capacitors.

I'm impressed and I don't know anything. I am experimenting with running an AC 230volt washing machine motor on DC 12volts and upwards. I am pleased with the results. However I need more start torque. Can I achieve this with capacitors and if so how do I go about it. Many thanks for the video. I learnt something I did not know today.

great video I never knew a capacitor could store DC voltage

Thanks for the info! Do you sell high voltage pulse capacitors?????

I was looking at Baldor 6" Bench Grinders. They have approx. 14 different models! One of the descriptions says: Built for heavy duty grinding, powered by 1/3 hp Baldor PSC type motor (except 612E & 662E which are split phase) What would be better for that type of bench grinder, a (PSC) Permanent Split Capacitor or a Split Phase motor? Is one harder or take longer to start? Do you have to spin the wheels to get it going?

We don't have specific instructions on repairing this, as they can vary depending on motor manufacturers. You might want to just try getting a capacitor of matching values, as they're fairly inexpensive.

To sum this up when you connect caps in series you add the voltages but you divide the mfd by the number of caps in series. Caps in parallel you add the MFD and the voltage remains the same

Good. Helpful.

Whoops! Hope your house smells normal again soon. Definitely something good to know for anyone else out there.

Yes, from what you stated, it sounds like a run capacitor.

If this is the wrong place/channel for this question, I apologize upfront for not being technical in this area. I have a situation I need help with involving Start-Up and/or Run Capacitor(s). I think..... Situation: When my 6,500 Watt (peak) house back up generator is used to power my home in power outages, my A/C will start slowly and run as the generator slows way down, but the generator recovers after the A/C fully starts up (pump and fans). The A/C will run powered by the generator for whatever time is required for the thermostat setting. The rest of the house circuits can be turned on (Frig, lights, .....) while the A/C is running and all is well and the generator does not sound overloaded or toggle its breaker off. However, once the A/C turns off when the set temperature is achieved, it will not cycle back on without the generator throwing its main 220VAC breaker which shuts everything down. Then, with ALL circuits to the house off (except A/C), and the generator breaker reset, the generator will struggle to restart the A/C and most of the time will throw the 220VAC generator breaker. While during this condition, I can turn on everything/every circuit in the house and the generator will power everything without issue until I try to start the A/C and the cycle repeats. (I know to give the A/C n Generator the best chance to restart is to turn off all the other circuits, my point is to show there is nothing else out of the ordinary while in this condition) I think I need a larger Startup Capacitor for my A/C Condenser (pump and fan). How would I figure out what type/size/capacitance, ......Capacitor to purchase and how would I identify the terminals such that I can swap it out with the existing correctly? Please note: I do not need a lesson in the generator peak/run and house demand (load). I am that technical (for a mechanical guy, but this is Magic Smoke Stuff and so I am in the deep end and barely treading water). For review: 1.) The generator runs the house with no issues with the A/C off. 2.) The generator runs the house with the A/C starting first and the rest of the house load added after the A/C starts the First Time. 3.) The A/C will seldom start the Second Time even if all the house loads are turned off and only the A/C is connected to the generator. 4.) Other than this Second Start (or anything after) failure of the A/C running on the generator, the A/C works flawlessly on-grid power as does the rest of the house. Thank you in advance for any help.

Very informative, kind of a shame the audio is bad quality. Gotta watch those clip levels.

Thanks for the video =)

Hi and thank you for your help. I was going to take the motor apart but thought an easier test. I snipped off one of the cap wires then turned on the small band saw. The motor just hummed so I quickly turned the motor but it would not start. I then reconnected the cap, turned the motor on and it ran. While it was running, I removed the jumper from the cap and the motor slowed down a bit. So I think this is a run cap. Have I diagnosed this correctly? Thank you.

would one for a celin fan that has the same UF and voltage work cause i can find those but not the round ones

Great video

can u help me find these videos on how to test a DC motor, slipring motor and a single phase motor..its for my trade test that am writing monday..Or explain to me how to do these test

They make a great filter capacitors on the cheap for tube amplifiers and last a long time

Thank you for commenting, and we're glad that the video helped you out. If you have any other questions or ideas on future videos, let us know!

really do like your videos. I have a compressor and need to use a generator to run it. Vendor says don't use a generator. Is there a percentage increase on the size of the start capacitor that would make the combination of motor/generator a little more friendly and work together a little better? This is what I have now, Microfarad Rating: 324-389 165 volts. Thanks!

No problem. Yes, if there's a centrifugal switch, you would definitely know for sure whether or not it is a start capacitor.

There are replacement caps that match that spec out there, but we don't carry them. eBay might be a good source for them.

Thank you for the reply. Perhaps I should open the motor and look for an centrifugal switch.

16 uf is generally not enough to start a motor, but CBB60 SH seems to be a part number for an Amico brand start capacitor.

Love your video!

Me gustan los vidéos son totalmente intersantes lastimosamente no entiendo le ingles

At what temperature do standard motor windings melt?

I like your idea

Some of the speed controllers can't be used with a motor with a capacitor. I was wondering if this refers to the start capacitor only?

I have a 3/4 hp bench grinder with a PTC relay for the start winding. The PTC relay is bad but I can't find any for a 3/4" hp motor. Any suggestions?

I’m confused about you usage of “duty cycle”. I’ve only been exposed to the term regarding a DC square wave signal at a fixed frequency and duty cycle refers to how much of the wave is “high” vs “low”. Never heard it used discussing AC signals. I would appreciate any feedback.

My AC went out. My intent was to do the electrical checks, but it started out with a dead mouse on top of the capacitor. I cleaned all the debris, then did the checks for the compressor which was fine as was the relay and controller voltage, leaving the capacitor. I couldn't find any shorts on the capacitor but it is the last item to prove out. It did have a bulge on the top. So I ordered it. I get it tomorrow. Question: was it the mouse that may have cause the capacitor to fail?

thank u sir

Well done

Thanks for the information and demonstration. I have one question about start capacitors. I assume they are parallel to the load … ie., across the 240 vac power. What makes it “drop out” of the circuit once it does its work?

I have a 220 VAC sanding machine motor, replaced Now starts slow and take time to gradually get to proper speed (around 5-8 sec). Is it the wrong replacement mtor or starting capacitor? Should I increase the capacitance? Appreciate your help.

So just to clarify, you can replace a start capacitor with a run capacitor if it has sufficient micro-Farads? For example I have a 8uF start capacitor, I can replace it with a 8uF run capacitor?

I have a 2002 Fleetwood Bounder 32' rv. One of the rooftop (Coleman Mach) air conditioners stopped throwing cold air because after getting up there to check it, there was oil everywhere on the wires and it smelled from the wire casing melting. Is it safe to just replace the hard start capacitor, or should I replace all 3. (There is a bundle of 3 there). Thank you for any thoughts and/or responses. (Roger)

Okay tell me a bote the run capacitor. How you know the size of capacitor to use on your 3phase motor?

AC capacitors are non-polarity specific, so it doesn't matter which side you connect the wires.

Hi I have a air compressor used for painting cars, when its very cold weather the compressor sometimes won't start up. When i pull the red switch up to start it, it buzzes loudly tries to start but doesn't have enough power. If the weather is hot, then most of the time it starts. It has gotten progressively worse at starting now it's about a 50/50 if it's going to fire up or not, when it does start it runs perfect and generates lots of pressure. If i helped the motor along with my hand by spinning the fan blades it does start, sometimes it starts slowly whilst buzzing then gradually build up speed then runs okay after about 10 seconds. Does it sound like the start capacitor at fault? , I do not have a run capacitor on this compressor. Could the start capacitor (faulty) CAUSE ALL THESE ISSUES?

If replacing a capacitor, if not 1.5x the line rated voltage, what voltage can it be or does it need to be exactly the same?

Good Stuff

Can you explain how you are running an AC motor on DC power? This will help us understand more about your set up.