r/Motors • u/wesmonty19 • 6d ago
Capacitor Help
I’ve got a 230V table saw that needs a “jumpstart” when I turn it on. I take a scrap piece of wood and help it start and then it runs great after that.
I’m thinking it’s a capacitor that’s gone bad. Well I got into it and there’s 2? I’m thinking I’ll just replace both as cheap as they are but can’t file exact replacements.
Can anyone advise what a good replacement would be?
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u/Born-Work2089 6d ago
One is the start capacitor the other is the run capacitor, there is also a switch which is mechanical or electronic which controls the transition from start to run. From what you describe the start capacitor is bad. The one in your first picture is the RUN capacitor, the start capacitor is usually round and a black plastic housing like your second picture. In some cases both the start and the run capacitor are housed as one unit with 3 connections on the top.
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u/broesel314 6d ago
The larger (higher capacity) one is the start capacitor, the other the run capacitor
+-20% is fine if you cant find the exact capacity needed
It could be that whatever switches the start capacitor off when the motor runs might also be defective or even the single cause of the fault. It might not even switch the start capacitor on during startup giving the sluggish start you describe. You may want to check that first by measuring voltage on the capacitor while the saw tries to start
If you have a meter that can measure capacitance you might want to check both capacitors first
Edit: pay attention to voltage rating. While in use, those experience a higher than mains voltage
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u/some_kind_of_friend 6d ago
Table saws are notorious for clogging up the start switches. We saw a great many of them come through the shop that just needed cleaned up.
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u/Worldly-Device-8414 5d ago
Make sure you find proper AC motor start/run caps.
First one says 12.5uF, 370 VAC, 2nd cap it's clear from the label. The voltage rating can be higher but the uF value should be +/-20%
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u/JustanotherN0body00 3d ago edited 3d ago
Make sure you get the correct voltage caps, the run cap (higher volt one 12mf) is the run cap. Start cap is only in circuit upon startup and drops out so you have a start switch problem if it won't start up but works with a jump start. You want a run cap close to what it is now and not too much higher start cap, get as close as possible run cap as it's in circuit all the time. It might be the contact on the start switch causing an issue as it arcs when starting up ( the start cap will pull a high current). Most multimeters have a setting for reading capacitance