If it's a start cap with centrifugal switch it should be ok but if it's a run cap it can overspeed and heat the motor. Pumps usually don't need the extra torque of a start winding so it may be in the circuit all the time like some of the pumps I've seen.
try playing around with the cap values on a cap run motor the speed will vary and the motor runs much hotter at higher speeds.
I have replaced a 12 uf +/-10% start capacitor in a pump motor with a 15 uf
+/- 5% cap. The supplier did not have a 12 uf in stock Should I order a 12uf or leave the 15uf in place ? I have read elsewhere that it will just slightly increase the strarting torque and should not be a problem. The motor is working ok now. Would there be any adverse effects? ....Opinions ?
Shouldn't be a problem.
15 uf
elsewhere
be
Overspeed??
All the best Ian Macmillan
bristan Inscribed thus:
It will be just fine. Leave it be...
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Best Regards:
Baron.
It is a davey xp900h and looking up the specs says it is P.S.C. start. ie permanent split capacitor which according to Wiki , is in the circuit all the time . and is a start and run capacitor.no centrifugal switch other specs... 2 pole, 0.8kw, 2850 rpm I haven't noticed it running any hotter. It may be a bit faster. The cap I pulled out of it was measuring only 6.7uf tho marked 12uf. Pump is not new and gets a lot of work stopping and starting as a household water supply. Pump was failing to start sometimes even tho the pressure switch was on. now ok with new cap. I might try and pick up a 12 uf as it is no trouble to change and only $12. regards
In that case you might want to pop in the right value before summer, just so the motor is run to spec., especially if the pump runs for long periods.
The 15uF is letting through more current to the start winding, gonna come out as heat, perhaps a little more work done. Cost you a little more in power. I doubt it will kill the motor unless there's already a heat problem.
Grant.
bristan Inscribed thus:
I wouldn't waste my money ! Look at it this way. Assume that the original cap was at the top of its spec, ie 12uf + 10% = 13.5uf and assume that the 15uf is at the bottom of its spec, ie 15uf - 10% = 13.5uf. It ain't worth messing.
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Best Regards:
Baron.
It's just as valid to consider the pessimal worst case too, if the pump's start winding cooks this summer, OP is out of pocket a fair bit more than a $12 cap.
Grant.
Grant Inscribed thus:
I agree, I would bet that its low rather than high, but only by measuring the caps actual value would confirm that.
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Best Regards:
Baron.
measured it at 15.13uf there has been a very noticeable increase in water pressure since replacing the old cap which had deteriorated to only 6.7uf. Pump seems to run more quietly also. Slighly warm to touch after running for a while in winter temps.
bristan Inscribed thus:
Mmm. I'm slightly surprised its high.
That is the behavior I would expect with the new cap. There is more current flowing through the windings and therefore more torque to drive the impellor, so the motor isn't slowing down under load like it did with the duff (old) cap. There may be an over temperature cutout in the motor windings to protect it from stall conditions.
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Best Regards:
Baron.
For a brand new 5% cap? I'm not ;) Is there an industry norm of supplying caps at bottom of error range?
One would expect so. But constant higher temp operation may shorten life... Then again, it might keep the pump warmer and drier for less corrosion?
Grant.
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