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Looking for a replacement capacitor
Hi, the timer on my heating hast stopped running, its a mechanical
driven by a small motor conected to 230Vac, the problem is a capacitor (the only other component) that is in series with the motor. I shorted the cap with a multimeter and the motor started running again. The cap has the following info printed on it: ..1/10 250V ~ MKP1.70 ..1/10 250V ~ What should I use as a replacement? What is the value exactly .1uF/10? Which I assume is 10nF, true? What exectly is the cap for? Cheers Brian |
10 UFD @ 250 VAC is the device specs. It is used as a start capacitor,
function is to lessen the electrical current through the start winding of the motor. Should be able to appropriate capacitor at any industrial motor service or HVAC facility. Even able to be ordered off the web if you google for "start capacitors". "Brian" wrote in message ... Hi, the timer on my heating hast stopped running, its a mechanical driven by a small motor conected to 230Vac, the problem is a capacitor (the only other component) that is in series with the motor. I shorted the cap with a multimeter and the motor started running again. The cap has the following info printed on it: .1/10 250V ~ MKP1.70 .1/10 250V ~ What should I use as a replacement? What is the value exactly .1uF/10? Which I assume is 10nF, true? What exectly is the cap for? Cheers Brian |
Art wrote:
10 UFD @ 250 VAC is the device specs. It is used as a start capacitor, function is to lessen the electrical current through the start winding of the motor. Should be able to appropriate capacitor at any industrial motor service or HVAC facility. Even able to be ordered off the web if you google for "start capacitors". "Brian" wrote in message ... Hi, the timer on my heating hast stopped running, its a mechanical driven by a small motor conected to 230Vac, the problem is a capacitor (the only other component) that is in series with the motor. I shorted the cap with a multimeter and the motor started running again. The cap has the following info printed on it: .1/10 250V ~ MKP1.70 .1/10 250V ~ What should I use as a replacement? What is the value exactly .1uF/10? Which I assume is 10nF, true? What exectly is the cap for? Cheers Brian Hey Al, thats great. I posted few days ago on a german NG but still didn't get any answer. So does the .1/10 mean 100uF / 10 ? I have an electronics catalog, but I wasn't sure what value I needed. Thanks very much. |
Hi, the timer on my heating hast stopped running, its a mechanical driven by a small motor conected to 230Vac, the problem is a capacitor (the only other component) that is in series with the motor. I shorted the cap with a multimeter and the motor started running again. The cap has the following info printed on it: .1/10 250V ~ MKP1.70 .1/10 250V ~ What should I use as a replacement? What is the value exactly .1uF/10? Which I assume is 10nF, true? What exectly is the cap for? Cheers Brian If it's a clock then it will be a synchronous motor, and will have two terminals only (no separate start winding). I would have expected that the motor would be connected directly to the supply, I can only suppose that the capacitor serves as a watt-less voltage dropper. Is there anything on the motor that suggests it runs on less than 230v? 120v maybe? -- Graham. %Profound_observation% |
Graham wrote:
Hi, the timer on my heating hast stopped running, its a mechanical driven by a small motor conected to 230Vac, the problem is a capacitor (the only other component) that is in series with the motor. I shorted the cap with a multimeter and the motor started running again. The cap has the following info printed on it: .1/10 250V ~ MKP1.70 .1/10 250V ~ What should I use as a replacement? What is the value exactly .1uF/10? Which I assume is 10nF, true? What exectly is the cap for? Cheers Brian If it's a clock then it will be a synchronous motor, and will have two terminals only (no separate start winding). I would have expected that the motor would be connected directly to the supply, I can only suppose that the capacitor serves as a watt-less voltage dropper. Is there anything on the motor that suggests it runs on less than 230v? 120v maybe? Graham, looks like you are correct. It says 70V~ 50Hz on the motor. All the start caps I have seen are pretty large things. The Motor here is very small about 3/4 inch diameter and 1/2 inch deep. I assume that the important point here is the frequency controlling the speed, not the voltage. Is that correct? I still haven't found a good replacement part yet. Cheers Brian |
Graham wrote:
Hi, the timer on my heating hast stopped running, its a mechanical driven by a small motor conected to 230Vac, the problem is a capacitor (the only other component) that is in series with the motor. I shorted the cap with a multimeter and the motor started running again. The cap has the following info printed on it: .1/10 250V ~ MKP1.70 .1/10 250V ~ What should I use as a replacement? What is the value exactly .1uF/10? Which I assume is 10nF, true? What exectly is the cap for? Cheers Brian If it's a clock then it will be a synchronous motor, and will have two terminals only (no separate start winding). I would have expected that the motor would be connected directly to the supply, I can only suppose that the capacitor serves as a watt-less voltage dropper. Is there anything on the motor that suggests it runs on less than 230v? 120v maybe? Forgot to say, yes only two wires go to the motor. |
Graham wrote:
Hi, the timer on my heating hast stopped running, its a mechanical driven by a small motor conected to 230Vac, the problem is a capacitor (the only other component) that is in series with the motor. I shorted the cap with a multimeter and the motor started running again. The cap has the following info printed on it: .1/10 250V ~ MKP1.70 .1/10 250V ~ What should I use as a replacement? What is the value exactly .1uF/10? Which I assume is 10nF, true? What exectly is the cap for? Cheers Brian If it's a clock then it will be a synchronous motor, and will have two terminals only (no separate start winding). I would have expected that the motor would be connected directly to the supply, I can only suppose that the capacitor serves as a watt-less voltage dropper. Is there anything on the motor that suggests it runs on less than 230v? 120v maybe? Would the replacement cap need to be 250V Ac? I can find various ones at 250 VDC, 250V AC seems to equate to 630V DC in the specs. Would an electrolytic capacitor be correct? How does that work with polarity (seeings its getting AC)? Cheers |
If you have a selection of capacitors you could find the approximate value
empirically. Most generic capacitors will show their max voltage rating as a DC value, not an AC RMS value. A 250V RMS capacitor should be replaced with at least a 400 volt DC rating. My guess is the value is 0.1uF (same as 100nF) Maybe the "10" just means +/- 10% tolerance -- Graham. %Profound_observation% |
Would an electrolytic capacitor be correct? How does that work with polarity (seeings its getting AC)? Definatly not! see my last post, a 400V DC capacitor is approximatly equivilent to a 250V AC capacitor -- Graham. %Profound_observation% |
Graham wrote:
If you have a selection of capacitors you could find the approximate value empirically. Most generic capacitors will show their max voltage rating as a DC value, not an AC RMS value. A 250V RMS capacitor should be replaced with at least a 400 volt DC rating. My guess is the value is 0.1uF (same as 100nF) Maybe the "10" just means +/- 10% tolerance Great, those are a lot easier to find. Cheers |
Graham wrote:
Would an electrolytic capacitor be correct? How does that work with polarity (seeings its getting AC)? Definatly not! see my last post, a 400V DC capacitor is approximatly equivilent to a 250V AC capacitor -- Graham. He would be better off with an AC rated capacitor designed not to short out, The "X" or "Y" rated AC capacitors would be a good choice. If the capacitor does short the motor will burn up, and could start a fire. -- ? Michael A. Terrell Central Florida |
"Art" wrote in message ... 10 UFD @ 250 VAC is the device specs. It is used as a start capacitor, function is to lessen the electrical current through the start winding of the motor. Should be able to appropriate capacitor at any industrial motor service or HVAC facility. Even able to be ordered off the web if you for "start capacitors". It depends on the type of motor, but it's purpose is to offset the phase of the start winding in order to create a rotating magnetic field. It does limit the current somewhat but that's not it's primary purpose. I usually get motor caps from HVAC surplus dealers, they're a fraction of new cost. |
"Brian" wrote in message ... Graham wrote: Hi, the timer on my heating hast stopped running, its a mechanical driven by a small motor conected to 230Vac, the problem is a capacitor (the only other component) that is in series with the motor. I shorted the cap with a multimeter and the motor started running again. The cap has the following info printed on it: .1/10 250V ~ MKP1.70 .1/10 250V ~ What should I use as a replacement? What is the value exactly .1uF/10? Which I assume is 10nF, true? What exectly is the cap for? Cheers Brian If it's a clock then it will be a synchronous motor, and will have two terminals only (no separate start winding). I would have expected that the motor would be connected directly to the supply, I can only suppose that the capacitor serves as a watt-less voltage dropper. Is there anything on the motor that suggests it runs on less than 230v? 120v maybe? Graham, looks like you are correct. It says 70V~ 50Hz on the motor. All the start caps I have seen are pretty large things. The Motor here is very small about 3/4 inch diameter and 1/2 inch deep. I assume that the important point here is the frequency controlling the speed, not the voltage. Is that correct? I still haven't found a good replacement part yet. Cheers Brian Hmm interesting, yeah it sounds like the cap is just to reduce the voltage then, and yes frequency is the important part. The cap should be non critical, just don't go too big or you'll overheat the motor. |
Would the replacement cap need to be 250V Ac? I can find various ones at 250 VDC, 250V AC seems to equate to 630V DC in the specs. Would an electrolytic capacitor be correct? How does that work with polarity (seeings its getting AC)? Cheers No, you'll want a mylar or other similar capacitor, at least 250vac rated, but personally I'd look for something with a 400vac rating. If you can't find one I probably have one in my junk stash I could send you for the cost of postage. |
i'll put my thoughts in on that. i think it's set up that way as a torque regulator which can effect speed. that would mean that proper size of the cap is required. Not on a syncronous motor, there's no need to regulate the torque on a time clock, and you can't really do it, the motor will either run at the correct speed or it won't run at all. |
On Sun, 2 Oct 2005 15:02:42 +0100, "Graham" put
finger to keyboard and composed: If you have a selection of capacitors you could find the approximate value empirically. Most generic capacitors will show their max voltage rating as a DC value, not an AC RMS value. A 250V RMS capacitor should be replaced with at least a 400 volt DC rating. My guess is the value is 0.1uF (same as 100nF) Maybe the "10" just means +/- 10% tolerance The Xc of an 0.1uF cap at 50Hz is 32kohm, whereas for a 10uF cap it is 320 ohm. If the motor is to be driven at 70V from a 240V (?) supply, then the latter option would draw a current of ~0.5A and dissipate 35W in the motor. The first option requires only 5mA and a 350mW motor. -- Franc Zabkar Please remove one 'i' from my address when replying by email. |
James Sweet wrote:
"Brian" wrote in message ... Graham wrote: Hi, the timer on my heating hast stopped running, its a mechanical driven by a small motor conected to 230Vac, the problem is a capacitor (the only other component) that is in series with the motor. I shorted the cap with a multimeter and the motor started running again. The cap has the following info printed on it: .1/10 250V ~ MKP1.70 .1/10 250V ~ What should I use as a replacement? What is the value exactly .1uF/10? Which I assume is 10nF, true? What exectly is the cap for? Cheers Brian If it's a clock then it will be a synchronous motor, and will have two terminals only (no separate start winding). I would have expected that the motor would be connected directly to the supply, I can only suppose that the capacitor serves as a watt-less voltage dropper. Is there anything on the motor that suggests it runs on less than 230v? 120v maybe? Graham, looks like you are correct. It says 70V~ 50Hz on the motor. All the start caps I have seen are pretty large things. The Motor here is very small about 3/4 inch diameter and 1/2 inch deep. I assume that the important point here is the frequency controlling the speed, not the voltage. Is that correct? I still haven't found a good replacement part yet. Cheers Brian Hmm interesting, yeah it sounds like the cap is just to reduce the voltage then, and yes frequency is the important part. The cap should be non critical, just don't go too big or you'll overheat the motor. i'll put my thoughts in on that. i think it's set up that way as a torque regulator which can effect speed. that would mean that proper size of the cap is required. -- Real Programmers Do things like this. http://webpages.charter.net/jamie_5 |
James Sweet wrote:
i'll put my thoughts in on that. i think it's set up that way as a torque regulator which can effect speed. that would mean that proper size of the cap is required. Not on a syncronous motor, there's no need to regulate the torque on a time clock, and you can't really do it, the motor will either run at the correct speed or it won't run at all. your referring to a shaded pole motors ? my education and experience tells me that synchronous motors need the rotor energized with DC to force the rotor to lock with the stator which gives you a good steady speed. in many cases, you have a squirrel cage type rotor that is wound with heavy copper configed so that it acts like a Async type motor on start up getting the rotor to start turning with a very low torque and once the rotor gets near the stator speed using a tach or maybe a centrifugal type switch then applies some DC source via slip rings to the rotor. it is true that synchronous motors do lock their rotors to the stator speed but like i said, there has to be something else to help the rotor to do so. so what ever.. -- Real Programmers Do things like this. http://webpages.charter.net/jamie_5 |
"Jamie" wrote in message ... James Sweet wrote: i'll put my thoughts in on that. i think it's set up that way as a torque regulator which can effect speed. that would mean that proper size of the cap is required. Not on a syncronous motor, there's no need to regulate the torque on a time clock, and you can't really do it, the motor will either run at the correct speed or it won't run at all. your referring to a shaded pole motors ? my education and experience tells me that synchronous motors need the rotor energized with DC to force the rotor to lock with the stator which gives you a good steady speed. in many cases, you have a squirrel cage type rotor that is wound with No, shaded pole motors are different, syncronous motors as used in timeclock drives normally have a permanent magnet rotor and a single field coil with a slotted metal stator, you'll find one in any mechanical lamp or appliance timer. |
Franc Zabkar wrote:
On Sun, 2 Oct 2005 15:02:42 +0100, "Graham" put finger to keyboard and composed: If you have a selection of capacitors you could find the approximate value empirically. Most generic capacitors will show their max voltage rating as a DC value, not an AC RMS value. A 250V RMS capacitor should be replaced with at least a 400 volt DC rating. My guess is the value is 0.1uF (same as 100nF) Maybe the "10" just means +/- 10% tolerance The Xc of an 0.1uF cap at 50Hz is 32kohm, whereas for a 10uF cap it is 320 ohm. If the motor is to be driven at 70V from a 240V (?) supply, then the latter option would draw a current of ~0.5A and dissipate 35W in the motor. The first option requires only 5mA and a 350mW motor. -- Franc Zabkar Please remove one 'i' from my address when replying by email. Frank, very, very, thin wires were used and in use the thing did not get in the slightest warm so IMHO it has to be the first option. All the start caps I have seen in my online searches were obviously for powerful motors, this thing is tiny! Hey thanks to everyone who answered this thread. I have learnt a lot and it should be no problem getting it working again. A normal timer that goes in a socket would not work as this timer controls a three pin microswitch. Socket timers here always switch the mains (230v) on or off, otherwise I would have just bought such a timer. I could have attached a small circuit with a 230V relay to such a timer though! Cheers |
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