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aboard_epsilon
12-01-2005, 10:04 AM
The motor on my tool and cutter grinder I have .I think is buggered.
The original was three phase.
I have another motor that is around the same size but is single phase.
it is 2850 rpm just like the other and says "fan motor" on it.
SAYS ON THE PLATE
250 watts
12 uf
2.0 amp
220 volt
0.88 cos
Problem is there is no capacitor with it .
The question is...
Do all single phase induction motors have caps...........or do I need to get one ..............and how do I wire it in.
and what size of one do I need.
I can get caps no problem.....does it matter if the cap is more powerful than what it needs to be.
The motor drives a belt and pulley and spins a spindle at 5000 rpm plus.

This is a wiring diagram found inside the box for the wiring on the motor.

http://img.photobucket.com/albums/v190/aboard_epsilon/diagram1.jpg

all the best.............mark


[This message has been edited by aboard_epsilon (edited 12-01-2005).]

malbenbut
12-01-2005, 11:22 AM
motor is capacitor start and run.If motor does not start but hums pull pulley or belt. if it starts and runs rough either cap or starting winding down, cap size is approx 20 mfd for half hp on 240 volts 40 mfd for 1 hp pro ratio
do not exceed these values or motor will overheat and may burn out' cap start has switch to turn of cap

John Stevenson
12-01-2005, 11:29 AM
Cap size is 12 mfd, it says so on the plate.

Sir John.

aboard_epsilon
12-01-2005, 11:29 AM
where's the switch Mal ....I thought that switch on the diagram was the overheat switch
all the best.....mark

John Stevenson
12-01-2005, 11:31 AM
No switch that funny thing with two black boxes is the cap.

Sir John.

aboard_epsilon
12-01-2005, 11:45 AM
OK thanks John........all is clear .....off to the tip in the next few days to grab a cap off a washing machine.

all the best..........mark

Evan
12-01-2005, 11:54 AM
Also, the cap doesn't have to be EXACTLY 12uf. Anything from about 8 to 16 should work ok. If it is lower expect a little less torque. If higher a bit more torque but will run hotter.

[added]

You can also parallel caps to get the right value, two 6s in parallel gives a 12. You can also put them is series and it will reduce the value. Two 20s in series gives a ten.

[This message has been edited by Evan (edited 12-01-2005).]

aboard_epsilon
12-01-2005, 12:29 PM
Thanks Evan that's good news.
because I was thinking .the last caps I had off washing machines were for 1000 watt motors.
These would not do .....
The other motors on washing machines are the pump motors these are about 125 watts....so maybe two caps off these will do the job.
all the best.mark

Jim Hubbell
12-01-2005, 02:54 PM
As stated above, but be sure to use RUN cap. and not start cap. There is no cent. sw. to disconnect start winding so cap. is connected at all times.

aboard_epsilon
12-01-2005, 03:41 PM
HI JIM
how do you tell one from the other
does it have run and start printed on them.
all the best.mark

sauer38h
12-01-2005, 03:59 PM
Uhhh .... sure it's not a reversible split-phase motor? In which case, there would be no capacitor, and the mystery marks would be motor contacts indicating a centrifugal switch. The "fan motor" label is a clue, as fans are the classic low-starting-torque load, which is about all a split-phase motor is good for.

aboard_epsilon
12-01-2005, 04:13 PM
I've just dug a cap out of my archives
it says 10 uf on it .
it also has a circle with a plus and an S in it.
it has only two terminals.
what's this.. a start cap or run cap
.it also has many other numbers and letters on it...
shrugs shoulders

sauer38h said
"Uhhh .... sure it's not a reversible split-phase motor?"

The mystery marks aghhhh.
I assumed that the all knowing ,very wise Sir John had diagnosed them as well known electrical symbols meaning it has a cap there .

So who's right and who's wrong
all the best.mark



[This message has been edited by aboard_epsilon (edited 12-01-2005).]

aboard_epsilon
12-01-2005, 04:37 PM
http://library.thinkquest.org/10784/circuit_symbols.html

here
http://www.kpsec.freeuk.com/symbol.htm

here about half way down the page it is described as .....Unpolarised capacitors (small values, up to 1µF)

http://www.kpsec.freeuk.com/components/capac.htm


and here aboput half way down is a general symbol i supose for any capacitor

http://www.bcae1.com/capacitr.htm


all the best.mark

Evan
12-01-2005, 05:00 PM
John is correct, the diagram shows a capacitor. On the one you have is the circle with the plus and S near one of the terminals? What shape is the capacitor and what material is the case of the capacitor?

sauer38h
12-01-2005, 05:01 PM
You can't tell from the schematic alone if the mystery marks indicate a capacitor, open switch contacts, or open relay contacts.

There is another schematic symbol for a capacitor which removes the ambiguity, but it's not used as often as it should be. Here she is -
http://www.electronics-tutorials.com/basics/capacitance.htm

If the motor has a centrifugal switch, that would resolve the mystery.

Evan
12-01-2005, 05:05 PM
"You can't tell from the schematic alone if the mystery marks indicate a capacitor"

In this case it's pretty clear. Since the namplate states 12uf it must be a cap to phase shift the AC to the Z2 winding

John Stevenson
12-01-2005, 05:13 PM
Yup,
These motors are as common as dog muck over here.
Remember we only have 240v so we don't get these dual wound motors seen in the US.

Sir John.

aboard_epsilon
12-01-2005, 05:24 PM
it's aluminium Evan

http://img.photobucket.com/albums/v190/aboard_epsilon/cap1.jpg

the terminals show no markings

http://img.photobucket.com/albums/v190/aboard_epsilon/cap2.jpg


all the best..mark

sauer38h
12-01-2005, 05:40 PM
Sure enough, 12 microfarads. I was looking at the schematic, which is consistent with either a split-phase motor or a permanent split capacitor motor.

A permanent split capacitor motor is not, of course, the same thing as a capacitor start/capacitor run motor, there being the little difference of another capacitor and a switch.

Evan
12-01-2005, 05:48 PM
That's an AC cap for sure. I can't be sure if it's a start or run cap though. I have a sneaky feeling the S means "start". Also, start caps are usually round.

darryl
12-01-2005, 08:41 PM
sauer, the symbols you were looking at for capacitor shows them as polarized, though it doesn't show + and -. A capacitor symbol with two parallel lines denotes a non-polarized one, and with one line arced away from the other is a polarized one.
I would agree the value for the cap is not too critical, but if it's the right value for the motor, 12 uf in this case, it will tend to run the quietest and smoothest, as well as the coolest.

aboard_epsilon
12-01-2005, 08:47 PM
May as get a new one ..
you guys sure its a "run" one I need
they are quite cheap here
http://tinyurl.com/a8j3d
I have an account with this comnpany.

All the best..mark

J Tiers
12-01-2005, 11:07 PM
No polarity mark on teh cap. The "S+" is a safety approval.

This one says volts AC, and does not appear to be electrolytic, no visible vent or rubber seal.

10uF, -2% +8%, ratings vary with what seems to be duty type, from 400 to 450VAC.

I am virtually certain its an OK run cap, based on the pics of what's marked on it.

Pic lightened and rotated to see the specs

http://img.photobucket.com/albums/0803/jstanley/cap1.jpg



[This message has been edited by J Tiers (edited 12-01-2005).]

sauer38h
12-01-2005, 11:55 PM
<font face="Verdana, Arial" size="2">Originally posted by darryl:
sauer, the symbols you were looking at for capacitor shows them as polarized, though it doesn't show + and -. A capacitor symbol with two parallel lines denotes a non-polarized one, and with one line arced away from the other is a polarized one.
I would agree the value for the cap is not too critical, but if it's the right value for the motor, 12 uf in this case, it will tend to run the quietest and smoothest, as well as the coolest.</font>


I didn't look that closely at it, I just grabbed the first schematic which came up in a search, having no idea how I would describe that little arc. I'm afraid none of that stuff is standardized. The only standard is that if the comnponent is drawn in a vertical orientation, the curved line is toward the bottom of the schematic. I commonly see either symbol for both polarized and non-polarized caps. The only standard way to indicate polarity is with an explicit "+" adjacent to the symbol.


Since in this application the capacitor provides a phase shift whenever the motor is running, the time constant is moderately important. Vibration is likely to creep in if the cap departs too far from 12 uf. Nothing fatal, but maybe annoying. On the other hand, the everyday capacitor isn't a precision device. Tolerances are on the order of 20%.