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Capacitor and it's testing ?

Started by Magnum, September 14, 2013, 01:26:17 PM

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Sorry, but the following are a hodgepodge of some posts on an electronics forum.

I am fixing a fan. (trying to)

I cleaned and lubed the bearings as the shaft was very difficult to move.

There is an electrical switch and a white rectangular box with these markings

M-16 01


250W 250 V AC

I saw a yellow rectangular cap on ebay that was yellow.

I think it might be a Tantalum Capacitor.

Mine is white.

I can not find that cap based on its markings.

Looking for what to check other than if the switch has continuity.

Take care,



run capacitors are usually poly caps
i think that's a run cap
the "3 FU" marking is probably "3 UF"   :biggrin:

in days of old, these caps (both run and start) were oil-filled electrolytics
now, they have other ways of making non-polarized electrolytic caps

get a cap that is designed for use with a motor
other types rarely fill the bill - this is not a good place for substitutions


Thanks Dave.

A hardware store owner ask me to fix it.

I can't find the same replacement capacitor and if I do I need to consider the price plus my labor charge.

It may be more than an equivalent new fan.

I think the fan is better made than others I have repaired.

It's a Windmere 18 or 19 inch pedestal fan.

The owner runs all his fans non-stop when his store is open.

He threw one away and I was able to get it running by just lubing the bearings.

Take care,



i know that fan - lol
dad had a couple of them at his TV shop

you should be able to find a suitable replacement - well, electrically, at least
it may be a little tricky to find one that will fit in there, mechanically


i see quite a few that might meet the electrical requirements
they are for ceiling fans - but should work - and they are running ~ $5
you might be able to get one at home depot, etc

they don't specify the dissipation wattage
however - the ability for a capacitor to dissipate heat is quite often proportional to it's physical size and mass
what that means is - if it looks like the right part - it will probably work   :P

see if you can find one that is 3 uF, 250 VAC that is about the same size and shape


Quote from: dedndave on September 15, 2013, 01:22:48 AM
what that means is - if it looks like the right part - it will probably work   :P

And if it ain't, what's a little smoke, the fan will quickly dissipate it  :P

Only kidding. dedndave is right, it will probably work.

Magnum, I don't know where you are, but you may want to check these suppliers out:


thanks guys.

I live in El La=go Texas which is also right next to  Seabrook,Texas. (I have two numb fingers that are making it hard to type accurately)

There is plenty of space for different shaped capacitors.

I have a ElectroMate voltmeter with AC and DC voltage, and a 200 ohm continuity checker.

Is it capable of testing the capacitor ?

Take care,



I found this. I could not find one for 250 VAC, would this one work ?
Take care,



Hi Magnum

I'm not familiar with the voltmeter you have but these days one can get digital multimeter very cheaply pretty much anywhere.
They are not the most accurate things but for simple tests like checking a capacitor or even voltages (when accuracy of more then a few % is not important) they are OK.

As regards doing a quick cap test, see here:


Quote from: Magnum on September 15, 2013, 03:50:49 AM
I found this. I could not find one for 250 VAC, would this one work ?

The important things are:

1) Capacitance as close as possible to the original.

2) A cap not having a voltage rating less than the original, so 450Vac is fine.


well - dissipation is an important factor
fortunately - the ones you can find are for ceiling fans, for the most part
ceiling fans probably have larger motors - so that leaves you a lot to choose from

to check a capacitor...
first, short it out and count to 3   :biggrin:

these are no-polarized capacitors - if they were polarized, the test might be a bit different
but - a continuity tester may work....
when you connect the continuity tester across the cap, it should show continuity, briefly
then, it will show no continuity
reverse the leads and do it again - same thing

capacitors hold a charge
the continuity tester is actually charging the cap
when the cap voltage reaches that applied by the tester, continuity will stop
this doesn't take very long, at all - lol
it depends on the tester, but you may not see a response
this is easier with an analog ohm meter - the needle swing is noticable on sizable caps


i re-read the original problems....
if the shaft doesn't turn freely - you have other problems
like a bearing is shot or something

other issues might be the brushes - if you can take it apart, this is something that is visible
and, the windings...
there should be continuity across the windings, otherwise it is "open"
you can also have a "shorted" winding
a shorted winding is a little harder to check for, but something usually gets hot or a fuse blows   :P

if you take a motor or a transformer core, and put a wire around it and connect the ends, that is a shorted winding
if it's tightly coupled to the core, any other windings on that core look like a short circuit in the world of AC
sometimes, the enamel insulation that is used on copper wire breaks down, arcs, and a short occurs
no good way to fix it, really


The cap is still attached to the switch.

I think I can rule out the switch using a continuity check and going thru the various speed settings.

Take care,



Switch is good.

I took apart another fan and salvaged the start capacitor.

It did not light up a light bulb when I dissipated it.

It was the same design except it had a 5 uF cap, it was dead too.

The bearings on that fan had welded and no amount of penetrating oil was gonna get it loose. :-)


P.S. I would not recommend a Windmere box fan, they made it so it's a bee - otch to dissassemble.
        There is a hole in one blade to place a screwdriver thru to loosen 3 bolts.
Take care,



yah - a light bulb type tester might not help
there is a slight time delay between current traveling and visible light   :P
also - light bulbs need some minimum current to be visible

a beeper type tester might be more useful

better yet - if your ElectroMate has an ohms scale - you can watch the charge occur
problem with DVM's is, most of them are autoscaling
it keeps jumping scale, which makes it hard to interpret
i have a fluke 79  and i can turn off the auto-ranging
but, then, i can also measure a capacitor   :P