capacitors

[howie209]

Hi guys, first time poster here. I have an electric cement mixer which has decided to do no more mixing. It seems dead although checking contacts with a screwdriver, the neon light lights up, so electricity is getting around. Opening it up there is really nothing inside. A motor, a switch and a capacitor. The switch contacts seem clean. I was wondering if it could be the capacitor. Would that be likely ( do they blow often)? and if so do my symptoms sound like a capacitor has expired?
Thanks for all help forth coming.

 

[dknguyen]

If it's just a cement mixer and is that simple, it's not the capacitor probably. THe capacitor is just there to absorb voltage spikes and smooth voltage ripples from the motor as well as react to quick changes in power demand when the battery can't react fast enough.

Is the capacitor in parallel with the motor? If it is, that is what the capacitor is for and a failed capacitor would not cut current off from the motor and stop everything from running. If the capacitor blew...you wouldn know, hehe. Is it swollen? Even if it is, it wouldn't stop current from getting to the motor.

It's probably a burnt motor winding or something. (How big is this system anyways?)

 

[bioborg]

I agree with the motor being at fault. What kind of motor is it ?

 

[Roff]

I've never heard of a battery-powered cement mixer. Do they exist?
If the motor is AC-powered, the capacitor is what allows the motor to start. If it fails, guess what?
Do a Google search on "capacitor start motor".

 

[dknguyen]

I've never heard of a battery-powered cement mixer. Do they exist?.

Get with the times! Haven't you ever heard of the saying "Mix cement in the comfort of your very own car?"\

Anyways, you are saying that some motors require so much starting current that the battery cannot provide enough? Not even enough for the motor to very slowly start? And that a capacitor has to be charged up to supply this current before the motor will start?

 

[Roff]

Dknguyen, how is it that you joke (presumably) about battery-powered cement mixers, then proceed to ask questions about DC motors? Not all motors run on batteries (believe it or not). I repeat - Google "capacitor start motor".

 

[HarveyH42]

Usually when the start capacitor on a AC motor (batteries are DC), it's pretty obvious. They are also pretty cheap (under $20). Motors, one with enough horsepower to mix cement (mixed 11 X 80 lb bags by hand last week), I'm guessing $200- $300....

Anyway, if the start capacitor looks damaged... Swollen, top popped off, terminal missing, leaking fluids... might be a cheap repair.

Now, the motor... Well, if not overworked, its most likely fine. Don't know how old, or how much work its seen. If you use it professionally, 8-10 hours a day, 5-7 days a week, and only service it when there is trouble... yeah, maybe.

 

[dknguyen]

Dknguyen, how is it that you joke (presumably) about battery-powered cement mixers, then proceed to ask questions about DC motors? Not all motors run on batteries (believe it or not). I repeat - Google "capacitor start motor".

I dunno, when I read that, I pictured a cheesy salesman saying that on TV and I just had to get it out. I also guess it never occured to me that the cement mixer might not be using a battery. A whole bunch of things make sense now. (When I thought that the capacitor might be there to assist the battery in fast current changes in current demand, I was thinking that running something as large as a cement mixer on a battery was a bit strange. Never occured to me that it might be plugged in a wall. WHen I think cement mixer I think a cement truck which moves around rather than being plugged into a wall.)

Case in point, yeah, makes more sense now when you say the capacitor is a starting capacitor considering something as large as a cement mixer probably would be plugged into the generator or something rather than a battery. I see your train of thought now.

PS. I googled an article about capacitor start motors and it makes a lot of sense now. Ive seen starting capacitors advertised but always thought that meant they were used to absorb the voltage and current spikes of a motor starting up, rather than providing a delay that is absolutely necessary to the motor starting.

 

[howie209]

thanks for replies guys. The info is great. The cement mixer is mains electricity. I am in Scotland UK so its 240volts. There is no battery. The mains runs into the off/on switch from there onto capacitor and the to the motor. Is it possible to post u guys pics of my Scottish 'Mickey Mouse' mixer to let you see it. It would let you see the components.It was actually a great we mixer when it was going.Isposting pics possible? Thanks from Howie

 

[dknguyen]

On the posting screen, look a bit below to find the button "Manage Attachments" to post a picture

 

[howie209]

Cheers dknguyen I shall post some pics tomorrow as it 10.30 at night in UK here at the moment. Thanks again. Howie

 

[howie209]

All your guys debate about my mixers fault is very educational for me. I have learned a lot just since yeaterday. Your knowledge has fascinated me and I thank you for that.Ok ive tried to upload pics of my mixer (not sure if ive done the right thing but will try again if they have no appeared). I appreciate that u cant sort a problem with pics alone. You can see the switch, motor and the capacitor on its side. Do you guys think it may be the capacitor after all now you know its mains powered?
Thanks from Howie in Scotland

 

[howie209]

I hope this is my mixer pics!

https://i54.photobucket.com/albums/g105/howie209/STA60005.jpg
https://i54.photobucket.com/albums/g105/howie209/STA60003.jpg
https://i54.photobucket.com/albums/g105/howie209/STA60002.jpg
https://i54.photobucket.com/albums/g105/howie209/STA60001.jpg

 

[Nigel Goodwin]

It could be the capacitor, there are essentially two types - start capacitors (which are only used to start the motor spinning), and run capacitors (which are used all the time, and provide the required phase shift to make it run).

I would imagine your's is probably a run capacitor?, they seem more common.

Do you have the facility to check a capacitor?.

 

[howie209]

Thanks Nigel. I would not know how to check capacitor unfortunately. Would a close up pic of the capacitor and the writing on it identify it as either a 'run' or a 'start'. If it was start capacitor would it be most likely that the capacitor is where the fault lies as motor does not start at all?
Thanks again Howie

 

[Nigel Goodwin]

Thanks Nigel. I would not know how to check capacitor unfortunately. Would a close up pic of the capacitor and the writing on it identify it as either a 'run' or a 'start'. If it was start capacitor would it be most likely that the capacitor is where the fault lies as motor does not start at all?

If it's just a start capacitor there should be a centrifugal switch that disconnects it once the motor is running - a run capacitor is permanently connected.

 

[howie209]

Would this help identify type of capacitor?

https://i54.photobucket.com/albums/g105/howie209/capacitor.jpg
I guess im trying to establish if its capacitor or motor at fault. If capacitor I will just go buy another.If its motor then the mixer is for the dump i presume and its time to get the shovel and mixing board back out lol

 

[howie209]

Capacitor pic

Hey. I just noticed capacitor is called 'StaCap'. That wouldnt be short for 'Start Capacitor' by any chance? If it was my problem may be solved and my mixer could be back going again! Any thoughts?
Thnaks always

 

[HarveyH42]

Here's a picture of a bad start capacitor I took out of my AC outside unit. Notice how the top is swollen, and the terminals pushed up? This is what I've seen with bad start capacitors. Don't know how you would check one with a meter, if even posible.

Have you put a meter on the power cord, the switch? You can test for coil resistance, might be able catch a short or open that way.

 

[Hero999]

Hey. I just noticed capacitor is called 'StaCap'. That wouldnt be short for 'Start Capacitor' by any chance? If it was my problem may be solved and my mixer could be back going again! Any thoughts?
Thnaks always

I don't think that means anything, it could be a trade mark or something.

Is there a switch connected to the motor shaft?

My guess it's a run capacitor, especially as the motor is quite small, start capacitors are normally only used on larger motors.

The capacitor should read open circuit on a multimeter, disconnect one of the terminals and connect a multimeter across it, it should ideally read open circuit but don't be suprised if it reads about 1Mohm, this is perfectly normal as it's probably a bleader resistor to discharge it when you disconnect the power.