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OT: sort of- OK to use a run cap in place of a start cap, right? (home ac blower)

tomjelly

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Aug 26, 2007
Location
GA
Home AC inside unit motor quit, starts fine if I spin it by hand, subbed in a metal cased 10mfd run cap for the 7.5mfd plastic start cap it had and all is well. OK until I get around to getting a replacement 7.5 start or do I need to replace that today? (I'd rather mail order one than make a special trip)

Tom
 
If the value is reasonably close you should be OK. The tolerances on those things are pretty loose most of the time anyway.
 
Using a run cap in place of a plastic start cap is just fine. Bob

Some among us prefer it, make the extra spend to build-up a "bank" of them to hit the MFD's wanted, and with higher ratings as well.

Tends to reduce need of replacement for longer. Done "right", usually VERY MUCH longer.
 
OK I can use a run in place of a start but generally not the other way around. SO- does that mean runs are higher quality & maybe more expensive than starts? Why 2 types and if runs are better why not substitute them for starts whenever a (presumably inferior) start cap fails, if cost is not a significant factor (like my AC when the wife is getting warm or in my 7.5 hp single phase compressor where the motor is big $$ and at risk if the cap bank fails)
 
OK I can use a run in place of a start but generally not the other way around. SO- does that mean runs are higher quality & maybe more expensive than starts? Why 2 types and if runs are better why not substitute them for starts whenever a (presumably inferior) start cap fails, if cost is not a significant factor (like my AC when the wife is getting warm or in my 7.5 hp single phase compressor where the motor is big $$ and at risk if the cap bank fails)

"Starts" use a different technology to get more MFD into smaller and cheaper packages, but are not suited for constant use at high voltage nor ripple.

"Runs" ARE meant for constant use at high ripple, higher voltages, even "spikes", but the technology used wants more space and more money for the same MFD.

That simple from the layman's viewpoint.
 
So if the cost difference is far less than even a small fraction of the cost of a failure it might be beneficial to use all runs instead of starts and runs, correct?
t
 
So if the cost difference is far less than even a small fraction of the cost of a failure it might be beneficial to use all runs instead of starts and runs, correct?
t

Cost diff gets greater the longer you agonize over the obvious. No "upper bound" yet found on indecision, after all.

That does NOT, mean, however, that one should make a crusade out of running about applying that sort of "upgrade" to everything under-roof, 'coz often as not it is simply a needless waste.

Highly-stressed RPC is about the only thing HERE even worth the bother.

The bulk of my stash of run caps are for experimental use, SCR drive for Dee Cee motor quieting.

"Stinky Confetti" is in the BTDTGTTS class of around fifty years ago, already.
 
If you use a start capacitor in place of the run capacitor, it will explode in probably less than 30 seconds.

Run capacitor are 100% duty cycle because they stay in the circuit 100% of the time, a start capacitor is in circuit 1 or 2 seconds.

Jeff
 
If you use a start capacitor in place of the run capacitor, it will explode in probably less than 30 seconds.

Run capacitor are 100% duty cycle because they stay in the circuit 100% of the time, a start capacitor is in circuit 1 or 2 seconds.

Jeff

Jeff

You just added ignorance to an otherwise useful thread.

Yes,, start caps should not be used in place of run caps, but that is NOT the thread topic. Please pay attention!
 
Cost diff gets greater the longer you agonize over the obvious. No "upper bound" yet found on indecision, after all.

That does NOT, mean, however, that one should make a crusade out of running about applying that sort of "upgrade" to everything under-roof, 'coz often as not it is simply a needless waste.

Highly-stressed RPC is about the only thing HERE even worth the bother.

The bulk of my stash of run caps are for experimental use, SCR drive for Dee Cee motor quieting.

"Stinky Confetti" is in the BTDTGTTS class of around fifty years ago, already.


A simple YES would have been perfectly accurate, commonly understood and painless for readers.

WTF is "Stinky Confetti"?
 
What you are doing is fine. It is the other way around that is a problem. Start caps are not built for contiuous use. The bigger cap will give a little more starting torque.

Sent from my SM-G900V using Tapatalk
 








 
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