LumberJocks

All Replies on Do I need a new start capacitor?

  • Advertise with us
View Ripthorn's profile

Do I need a new start capacitor?

by Ripthorn
posted 11-06-2012 01:28 PM


19 replies so far

View SCOTSMAN's profile

SCOTSMAN

5414 posts in 2272 days


#1 posted 11-06-2012 02:23 PM

TRY this upgrade your breaker a notch to a slightly larger one seems you might be on borderline with the one fitted at present.Alistair

-- excuse my typing as I have a form of parkinsons disease

View MrUnix's profile

MrUnix

555 posts in 885 days


#2 posted 11-06-2012 02:45 PM

Typically, when a cap goes, it goes quick.. but you could pull it and test with a meter pretty easily. I’d be more inclined to think that it might be a bearing problem given the age of the machine.. try turning it by hand to see if you feel resistance or hear noises.. take the belt off if it has one and try that way. Scotsman also brings up a good question.. what size circuit are you running that saw on and how much does it draw and do you have anything else running on it?

Cheers,
Brad

-- Brad in FL - To be old and wise, you must first be young and stupid

View Fred Hargis's profile

Fred Hargis

1885 posts in 1180 days


#3 posted 11-06-2012 02:55 PM

I think upsizing the breaker is asking for problems, it’s probably sized to the wiring and putting a higher capacity one in may lead to problems. But those caps can be easily tested…or if you don’t want to test, simply buy a new one. They are fairly cheap….I think I paid less than $10 for the last one I bought. Or, a motor shop could test it for you. I do think starting it up without the belt(s) on may help with the diagnosis.

-- Our village hasn't lost it's idiot, he was elected to congress.

View muleskinner's profile

muleskinner

678 posts in 1123 days


#4 posted 11-06-2012 02:58 PM

If it was me, I’d suspect either capacitor or bearings. Bearings are easy to check (does it spin easily?). You can check your capacitor with an ohm meter. It should start with a low resistance and ramp up to infinity. (make sure you short it out when you’re done). If it’s questionable, they’re pretty cheap to replace.

-- Visualize whirled peas

View Tennessee's profile

Tennessee

1467 posts in 1201 days


#5 posted 11-06-2012 04:12 PM

You can tell if it is the capacitor if you hear a humming noise in the motor just before the breaker trips, but the motor is not really turning.
Caps are designed to give the magnetic field a push in one direction, and are wired to give a large inrush of one half of an AC sine wave voltage over and over to get the rotor moving. In a lot of capacitor start, induction run motors, the capacitor is used for the first 75% of run-up rotation, and then the switch changes the motor over to standard induction run, taking the cap and it’s start windings out of the circuit.

My guess is either you have a weakening start winding which would raise the inrush amperage, or your breaker is weakening.
Do NOT upgrade the size of the breaker. It is probably sized correctly, after all these years of working well.
Changing the cap may help a little, but I doubt it. Also, if your motor has an internal switch, dirty contacts can raise the amerage, as well as stiff bearings and overall general load bearings. Just do not put in a bigger breaker. Worst case, bad windings, causing you to lose the motor. Best case, weakening breaker. In the middle, bad bearings and machine load.

-- Paul, Tennessee, http://www.tsunamiguitars.com

View Ripthorn's profile

Ripthorn

768 posts in 1671 days


#6 posted 11-06-2012 04:20 PM

The motor is a TEFC motor, 1.5 HP, so running current should be less than 11 amps. The breaker is 15 amp and recently installed (put in a dual breaker in the place of the single that was there). Again, the motor starts fine when it is a little warmer, so it has to do with the cold somehow. As for dirty internal switch contacts, how likely is that on a TEFC motor? It is very likely that no motor maintenance has been performed in the last 25 years, motor is original, etc. The saw has worked quite well except for the cold startup issue. I was able to get it started about midday over the weekend, but in the evenings or early morning, it doesn’t like ot start.

-- Brian T. - Exact science is not an exact science

View JohnChung's profile

JohnChung

265 posts in 761 days


#7 posted 11-06-2012 05:27 PM

When is it cold. Resistance is lower. From what I gather, you need to check the inrush current for the motor.
If the capacitor was bad to start with…. Why after a few attempts it starts up the motor? Each attempt slowly charges the capacitor? It is unlikely. I would suspect that the age of the motor is the issue. Anyway to be sure you would need to check the inrush current first. Use a clamp current meter.

http://en.wikipedia.org/wiki/Inrush_current
http://www.amazon.com/Sinometer-MS2108-True-RMS-Current-Measurement/dp/B0017WRH7O //I have not tried this product before. It is a suggestion

View muleskinner's profile

muleskinner

678 posts in 1123 days


#8 posted 11-06-2012 05:43 PM

A 15 amp circuit is kind of marginal for a 1.5 horse motor. The starting current inrush could be several times full load.

-- Visualize whirled peas

View oldnovice's profile

oldnovice

3790 posts in 2054 days


#9 posted 11-06-2012 05:58 PM

Ditto to what muleskinner said!

-- "I never met a board I didn't like!"

View dhazelton's profile

dhazelton

1213 posts in 983 days


#10 posted 11-06-2012 06:07 PM

If a motor is slow or hums on startup and the motor is fine if you give the pulley a hand (WATCH YOUR FINGERS!) then it is the start capacitor. Before I dug into the motor I’d take the switch apart, maybe just wire in a temporary new one (heavy duty 20 amp switch from hardware store is fine) and see if that is the problem.

View EEngineer's profile

EEngineer

895 posts in 2300 days


#11 posted 11-06-2012 06:56 PM

so I am thinking maybe the capacitor is not holding a charge
are wired to give a large inrush of one half of an AC sine wave voltage over and over to get the rotor moving
Each attempt slowly charges the capacitor?

No, no, no! I refer you to wikipedia for an accurate but brief description of what the cap is for.

Troubleshooting: you can disconnect the belt, turn on the power and if the motor starts with a quick twist of the motor pulley in the right direction, bet on a bad cap.

If the motor is having problems when it is cold, I would be more inclined to look at the bearings. Interfernces all get tighter when cold. However, I wouldn’t rule out a bad cap.

-- "Find out what you cannot do and then go do it!"

View Tennessee's profile

Tennessee

1467 posts in 1201 days


#12 posted 11-06-2012 07:17 PM

Ok, I phrased it slightly wrong. The capacitor is there to give an inrush in direction, which it does over and over as it charges and discharges. It also keeps the magnetic field slightly ahead of the rotor, causing it to “chase the magnetic field”, so the motor comes up to speed. If the rotor cannot keep up due to faulty bearings, excessive load, etc, the current rises, and the breaker trips. That is why when the cap is bad, you can still make the motor go one way or another by giving it a spin. (In some cases) You are advancing the magnetic field in a particular direction and the rotor will follow the magnetic field, since we’re dealing with AC.
But it is responsible for the first directional current inrush to make the motor go one way or another, depending on how the cap is wired in the circuit.
Also in my experience, caps don’t go bad slowly. Once they short across their any of their plates internally, the party is pretty much over at those amperages.

-- Paul, Tennessee, http://www.tsunamiguitars.com

View Ripthorn's profile

Ripthorn

768 posts in 1671 days


#13 posted 11-06-2012 09:46 PM

So it is possibly the bearings that are going? I am curious as to why this would happen only in the cold. Also, I took the belt off and it is still tripping the breaker even with no blade to spin. I suppose that if the caps are not bad, then what is my path forward? I am supposing I can’t replace the bearings myself. Would this mean that the motor is starting to die a slow death?

-- Brian T. - Exact science is not an exact science

View Ripthorn's profile

Ripthorn

768 posts in 1671 days


#14 posted 11-07-2012 12:23 AM

Okay, so some more info. I had the belt off of it, gave the pulley a spin and hit the power button and it spun up just fine. Put the belt back on, hit the power button (no spinning help, I’m not that dumb) and it tripped the breaker. Does the extra info shed any extra light on the situation?

-- Brian T. - Exact science is not an exact science

View dhazelton's profile

dhazelton

1213 posts in 983 days


#15 posted 11-07-2012 12:27 AM

Start capacitor.

View exelectrician's profile (online now)

exelectrician

1661 posts in 1114 days


#16 posted 11-07-2012 08:17 AM

Wow (comment deleted)

The fault IS IN THE STARTING SWITCH this is a centrifugal switch which is usually located inside the motor on the opposite side to where the shaft sticks out.

Take off the fan cover, the fan, the end cover on the motor, and there is the switch. it has a spring which keeps the switch on, when the motor is not running. Put an ohmmeter accross the contacts – the ohms should be 1/2 ohm or less, (the start windings are controlled by this switch) when the motor gets to half to 2/3rds full speed the centrifugal action kicks in and the switch switches the start windings off.
If this contact in not switched on when you test it, you can buy a new one. I would just tweak the contacts with a pair of needle nose pliers. Note; silver contacts always look black and burned, do NOT sand or clean them excessively, try and preserve what silver is left after 15 years of use you have had out of them.
If you have one of the newer digital electrical testers you will be able to check the capacitance of the cap. Should be in the range of 100 – 200 microFarads.

There should be NO loose wires that can get caught up in the action of the switch when you reassemble the end cover of the motor.
Let me know if this works for you.

-- Love thy neighbour as thyself

View Ripthorn's profile

Ripthorn

768 posts in 1671 days


#17 posted 11-08-2012 01:22 PM

So I pulled of the fan cover and fan and the centrifugal switch was right there. I pulled it off, got rid of all the dust there (this was on the outside of the motor cover, not inside). After getting it put back together (and learning how it works, which is genius by the way), I fired up the saw and away it went with no problems. I went back out this morning just to make sure it wasn’t some other factor and it started up no problems again.

Short and long is that exelectrician was dead on and now it’s working as well as it ever has. Thanks for all the help and suggestions, everyone.

-- Brian T. - Exact science is not an exact science

View exelectrician's profile (online now)

exelectrician

1661 posts in 1114 days


#18 posted 11-09-2012 06:26 AM

You are welcome, and I was glad to be of help.

-- Love thy neighbour as thyself

View MedicKen's profile

MedicKen

1599 posts in 2149 days


#19 posted 11-09-2012 10:56 AM

You said you replaced the breaker. Is it a GFCI breaker by any chance?

Teh grease in the bearings is probably getting pretty gelled up and hard after almost 30 years. Its time to replace them. They only have a 25 yr or so life span.

-- My job is to give my kids things to discuss with their therapist....medic20447@gmail.com

Have your say...

You must be signed in to reply.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics

HomeRefurbers.com

Latest Projects | Latest Blog Entries | Latest Forum Topics

GardenTenders.com :: gardening showcase