Get Your Motor Running: Testing A Start Capacitor
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- Опубліковано 17 гру 2020
- Many large electrical motors found on shop tools or in the AC and heating systems of your home use a start capacitor to assist the motor on start-up. Table saws, jointers, band saws, dust collectors and other tools all typically have start capacitors. Your central air conditioning condenser pump uses a start capacitor. In this video I'll use my dust collector as an example of how to troubleshoot motor starting issues and how to test start capacitors safely using a meter.
In this case my start capacitor tested good, but at the end of the video I'll show what proved to be the real issue why my dust collector motor would sometimes snap a breaker when switched on in colder ambient temperatures. Problem solved!
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amzn.to/37gIe5y (meter with capacitance/farad scale used in video)
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best video i've seen tells me what i need to know without all of the technical mumbo jumbo THANK YOU
The capacitor is connected by a centrifugal switch on the rotor shaft. It that isn't closed when you apply power, the motor won't start and will probably trip the power . If there is a wiring diagram in the motor terminal block, look for a direct short across the terminals to the centrifugal switch. in my experience, these contacts cause more start failures than failed capacitors particularly if the machine has only intermittent use. The most common reason capacitors fail is prolonged exposure to high temperatures. This rarely happens in workshop machinery which isn't running continuously. Use a resistor to discharge not a screwdriver. That prevents a very high current discharge which could damage the component.
for my vacuum it was the centrifugal switch , i tested the capacitors the old fashioned way by loading and discharging
Very informative video. Now I know what’s wrong with my wood lathe. Thank you very much for the video.
Best explanation on capacitors I've ever watched 👏
Great job. Thanks for taking the time to share this info.
Excellent tutorial video !!!!! Thanks
best video regarding capacitor testing , god bless u
Hi I really like your videos especially tiles and bathrooms this is a good vid well presented and accurate I should have been a electrician your doing well thankyou
Glad you like them!
Great information 🖖. Thank you very much for this great info video.
another problem with trying to start fans in cold air is just that...cold air....cold air is denser and needs more energy to move it, try placing a damper (if only temporary for start up) on the fan inlet for cold starts. Also if the motor drops out (after starting) on overload in cold weather you may need to restrict the flow rate with an inlet damper, probably not much.
Great useful video - i have that dust collector as well and i’m guessing i’ll need that cap replacement someday.
The big one is so cute tho ❤❤❤ The motor hums but will not start.
My sears craftsman grinder hums when turn it on. It sat for close to 18yrs but I needed to use it and it worked fine but the next day when i turned it on it smoked and now just hums. I wonder if the cap is the problem. Dont know if my electircal testor has capedence testing or not. I dont want to buy a new cap for $15-$20 and find out its not the problem. Guess I'll see if there is any deformation in the cap
Thank you for a great vid. Just a question though, at 6:37 you said that you can switch polaritys without a problem. But i've learned that switching polaritys on a capacitor can make the capacitor explode, is that only on DC-powered ones and since this one is AC it doesnt really matter?
That's correct--start capacitors for alternating current have no polarity but capacitors used in DC applications such as circuit boards or bigger DC devices may.
@@enduringcharm thank you very much, I bet this video will save me a lot of time and/or money in the future ☺️
There is a fourth way that will allow to determine capacitance but I can’t recall how to do it
I have a hot tub. House power to it is borderline low. This is a power company failing and not the house wiring.
Anyway, sometimes when I turn the tub on the pump motor will just buzz.
This motor is fed by one red wire from a mother board and has no capacitor.
Can I add a start up cap. to this set up?
I think you are barking up the wrong tree. Rather than looking to modify the set up it would be wiser to fix the existing issues. When you say the power is borderline, what does that mean? Is the voltage supplied from the street low? That could be monitored by the motherboard controller you mentioned and it may be trying to save the motor from damage. Better to find the low voltage problem. Similarly, the motherboard controller itself could be the issue. Have you examined it closely for burned up capacitors or other damage? This video is on a different subject, but the control board damage is similar to what you should look for: ua-cam.com/video/bR6jjTOd5e8/v-deo.html
My workshop isn't very warm and I can usually get the temperature around 50, my dust collector struggles getting started and I don't want to keep throwing the breaker to warm up the Cap so I thought about hooking up a hair dryer near it. Do you think that would help?
If you want to try keeping the collector warm, I would instead use a utility style space heater near it. Also, take a look to see if the circuit feeding the dust collector is especially long or undersized. In the long run it might be cheaper just to run a new, more appropriately sized circuit than run a heater.
on a 80 uf, I test 77.2 uf but doing ohm test only shows 7 m ohm and slowly reaches to 9 in 60seconds with my Fluke 116 multiple times tested. Is my cap bad?
So the ohm test sounds a little wonky and the capacitance test shows you are not quite reaching the stated spec. You could try a different meter to be sure, but it appears your cap is marginal. These are not expensive items, so I would go ahead and replace it.
Sir, if I may ask.
What is the value of your capacitor if you have 5hp induction motor with dual capacitors respectively?
Some say you need to use 50 to 100mfd in every horse power on your starting capacitor and 12 to 16mfd per horse power for the corresponding running capacitor.
I wonder if someone like you have a certain table chart 📊 for that effect.
Just curious here. 👍
Sorry, I don't have a chart for you. I typically just use the manufacturer's recommendation and I haven't got into motor design.
I mean, the markings of the old busted caps are pretty unreadable already.
Thanks for your time replying by.
More power on your tutorials.
👍
What are the comanley tools you have in your trailer
You can see my trailer organization here:
ua-cam.com/video/AnRKxBCj8og/v-deo.html
@@enduringcharm you have intagram
No, sorry. You can reach me here in the comments or on my website shown at the end of each video.
What tools of dewalt you have 20v mam not the 18v
I currently use the 20Volt system, so all my battery tools are that. I've reviewed many of them here on this playlist:
ua-cam.com/play/PLD4oAOZqK9mDRnc-GiaRH8YjZu-ndUnHV.html
What if the meter reads OL and no number? I read one capacitor and the meter reads nF, but checking my other capacitor I get a meter reading OL.
Were you using the farad scale both times? Sometimes meters have a shared setting and there may be a button or switch to pick which one is being used. Also, did you check the capacitors with the ohmmeter?
@@enduringcharm yes I was. No worries. I think it stands for Open Loop but not sure. I assumed it meant it was bad and replaced the capacitor. And now my bandsaw is back up and running.
My air compressor (single phase motor) starts and runs fine, but..... I have multimeter with capacitance reading and run capacitor is in the tolerance (nominally 40uF +-5% and i measured 40,2uF) . My start capacitor dont have tolerance labeled and is 100uF nominally but i measure 186uF. Is it something to be concerned about? It looks like new, no swelling, discoloration, smell etc.
Sounds like you don't actually have a problem! If the unit is starting and running normally and the capacitor looks fine, you should be good to go.
@@enduringcharm thanks, yes, no problem (so far), but worried if capacitor is failing and if it could damage the motor somehow.
No, if the capacitor fails it will be limited to that component.
@@enduringcharm thanks
@@enduringcharm Just learned that my start capacitor have internal resistor and thats why im getting higher capacitance value - seen video on youtube measuring with and without resistor and the same happened.
I just replace them if I think there bad if if not I have them if I need them
💯
When you test the capacitor with the first test using the 20k Ohm setting, it does what it's supposed to. What would be a failed reading using this test?
Good question--I could have been clearer on that. If the meter did not gradually rise to infinity but displayed a fairly constant low value, then the capacitor has a short. If it displays a constant very high value then the capacitor has an open fault. So either way if you don't get a rising pattern toward infinity then the capacitor is trash.
Shocked more like roasted