Testing a motor run/start cap. How do -you- do it?

[Ed.Kloonk]

Just interested how everyone does it.

Seen some nasty y/t vids. One thing I don't like is the clumsy shorting out with the screwdriver.

I know it depends on what meters you have on hand and how extensively you want to test. Most of us in the field will know when the cap is dead and replace it. Then the motor works again. Chuck the old one in the garbage.

[floobydust]

I test them like any other capacitor (LCR meter) BUT because they have mechanical failures and the pressure switch inside, they need to get banged around as well. They can go intermittent.

[james_s]

I usually use the capacitance function on my multimeter as a basic test, but the easiest thing to do is usually swap in a known good capacitor of similar value and see if the motor runs.

[floobydust]

Multimeter capacitance test is crap due to timing single-slope. Leakage current misleadingly gives a higher C reading because it's taking longer to charge up. Cheap electrolytics have a weird electrolyte that has high leakage current and gives bizarre readings, almost like dealing with a 1/2 cell.
So the capacitance reading from a multimeter is not much to go on.

[Ed.Kloonk]

I see a lot more of the CBB65 types 40-70uF so they can be unwieldy. As James says you know when they've had it..

I thought it was just me that just test jigs the things.

 

[IanB]

I'm not too bothered about shorting with a screwdriver as the capacitor should already be discharged by the motor windings.

In my case it was a simple run capacitor, and the diagnosis was firstly that the motor did not start well, and secondly the measurement of the capacitance was low.

I don't know much about start capacitors, but I suspect the diagnosis is similar.