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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Starting cap failure?
I run my machine shop off af a rotary phase converter. It has
starting caps that are switched out of circuit after the motor is started. Lately the device sometimes has a hard time starting. I switch it on and the motor may not come up to speed practically instantly, the way it is supposed to. If this happens I turn off the breaker, wait a minute, and then try again. It always starts fine on the second attempt. Except this morning it took three tries for the thing to start. The motor did actually spin up some this morning on the first try but it was really slow starting so I shut the breaker off. I suspect starting caps but wonder why the second attempt always worked until today. And then today it started fine on the third attempt. The phase converter has been started almost daily for at least fifteen years using the same breaker in the main breaker panel. I thought that maybe the breaker might be making a bad contact on one leg of the single phase 250 volt input. Or maybe a contactor inside the converter is not making good contact. Or maybe, and I think most likely, the starting cap(s) is(are) the problem. I just wonder why, if the thing doesn't start spinning right away on the first try it does on the second or third. This weekend I'll have time to look inside the phase converter and I would like to know if there is a way to diagnose the starting caps. The contactor contacts I know how to check. And I could buy a new breaker. But I would like to not just buy stuff until the thing works properly. Advice? Thanks, Eric |
#2
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Starting cap failure?
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#3
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Starting cap failure?
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#4
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Starting cap failure?
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#5
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Starting cap failure?
wrote:
----------------------------- Or as a quick test clip some additional C across it. ** That reminds me of what was the common practice with suspect electros BEFORE we all got ESR meters. How quick we do forget. ..... Phil |
#6
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Starting cap failure?
On Fri, 25 Aug 2017 09:25:37 +0800, Rheilly Phoull
wrote: On 25/08/2017 6:31 AM, wrote: I run my machine shop off af a rotary phase converter. It has starting caps that are switched out of circuit after the motor is started. Lately the device sometimes has a hard time starting. I switch it on and the motor may not come up to speed practically instantly, the way it is supposed to. If this happens I turn off the breaker, wait a minute, and then try again. It always starts fine on the second attempt. Except this morning it took three tries for the thing to start. The motor did actually spin up some this morning on the first try but it was really slow starting so I shut the breaker off. I suspect starting caps but wonder why the second attempt always worked until today. And then today it started fine on the third attempt. The phase converter has been started almost daily for at least fifteen years using the same breaker in the main breaker panel. I thought that maybe the breaker might be making a bad contact on one leg of the single phase 250 volt input. Or maybe a contactor inside the converter is not making good contact. Or maybe, and I think most likely, the starting cap(s) is(are) the problem. I just wonder why, if the thing doesn't start spinning right away on the first try it does on the second or third. This weekend I'll have time to look inside the phase converter and I would like to know if there is a way to diagnose the starting caps. The contactor contacts I know how to check. And I could buy a new breaker. But I would like to not just buy stuff until the thing works properly. Advice? Thanks, Eric After 15 years I reckon I would just get another cap and see if that fixed it. What sort of device takes out the cap, centifugal ? There is an electronic device that's got its innards potted. It senses the starting current and when the current drops to the set level it drops out the contactor that connects the starting caps. There 10 starting caps connected in parallel so I don't think it's such a good idea to replace them all just in case that's the problem. They are all stuck in place with some pretty good double sided foam tape so removing them would be a hassle too. I cannot see how many mfd the caps are rated for but I can see on one cap that they are made for a phase converter. I just remembered that years ago the device mentioned above failed. When I tried to start the converter it would just hum. There is a button inside that I can press that bypasses the starting device and energizes the contactor coil. When the starting device failed the first time I was told by the phase converter maker to press this button and see if it starts OK. It did which is how I diagnosed the problem. The company that made the converter has gone out of business so I can't call them for advice. But I'm gonna try the button thing again and if it starts fine then I guess I know the problem. What I don't understand is why the converter sometimes starts to spin up slowly and at other times just sits there and hums loudly. And then starts just fine on the next attempt. Could it be that when it starts to spin up slowly that the rotor was in just the right position that the balancing caps in the converter provide enough phase shift to start spinning the rotor, albiet slowly? Thanks, Eric |
#7
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Starting cap failure?
SNIP
After 15 years I reckon I would just get another cap and see if that fixed it. What sort of device takes out the cap, centifugal ? There is an electronic device that's got its innards potted. It senses the starting current and when the current drops to the set level it drops out the contactor that connects the starting caps. SNIP The company that made the converter has gone out of business so I can't call them for advice. But I'm gonna try the button thing again and if it starts fine then I guess I know the problem. What I don't understand is why the converter sometimes starts to spin up slowly and at other times just sits there and hums loudly. And then starts just fine on the next attempt. Could it be that when it starts to spin up slowly that the rotor was in just the right position that the balancing caps in the converter provide enough phase shift to start spinning the rotor, albiet slowly? Thanks, Eric Whoops! I was wrong about the starting device. I just assumed it was some sort of potential relay like I had seen in other motors. It's a bad thing to assume sometimes. In reality the starting device in an adjustable delay solid state relay. The on time, once energized, is from .25 to 5 seconds. It resets when power is removed. Supossedly good for 100,00,000 operations. But the original timer failed after only approximately 600 operations. Eric |
#8
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Starting cap failure?
On Thursday, August 24, 2017 at 6:31:18 PM UTC-4, wrote:
I run my machine shop off af a rotary phase converter. It has starting caps that are switched out of circuit after the motor is started. Lately the device sometimes has a hard time starting. I switch it on and the motor may not come up to speed practically instantly, the way it is supposed to. If this happens I turn off the breaker, wait a minute, and then try again. It always starts fine on the second attempt. Except this morning it took three tries for the thing to start. The motor did actually spin up some this morning on the first try but it was really slow starting so I shut the breaker off. I suspect starting caps but wonder why the second attempt always worked until today. And then today it started fine on the third attempt. The phase converter has been started almost daily for at least fifteen years using the same breaker in the main breaker panel. I thought that maybe the breaker might be making a bad contact on one leg of the single phase 250 volt input. Or maybe a contactor inside the converter is not making good contact. Or maybe, and I think most likely, the starting cap(s) is(are) the problem. I just wonder why, if the thing doesn't start spinning right away on the first try it does on the second or third. This weekend I'll have time to look inside the phase converter and I would like to know if there is a way to diagnose the starting caps. The contactor contacts I know how to check. And I could buy a new breaker. But I would like to not just buy stuff until the thing works properly. Advice? Thanks, Eric Knowing little about converters, it sounds like it could be mechanical? Is it anything like a starter motor with a 'bad' spot? It's hard for me to see how a cap would need two tries to do it's job right. George H. |
#9
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Starting cap failure?
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