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Miscellaneous => The Orphanage => Topic started by: Magnum on September 14, 2013, 01:26:17 PM

Title: Capacitor and it's testing ?
Post by: Magnum on September 14, 2013, 01:26:17 PM
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

DE 3 FU

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.

Thanks.
Title: Re: Capacitor and it's testing ?
Post by: dedndave on September 14, 2013, 01:35:54 PM
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
Title: Re: Capacitor and it's testing ?
Post by: Magnum on September 14, 2013, 11:24:59 PM
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.




Title: Re: Capacitor and it's testing ?
Post by: dedndave on September 15, 2013, 01:10:18 AM
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
Title: Re: Capacitor and it's testing ?
Post by: dedndave on September 15, 2013, 01:22:48 AM
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
Title: Re: Capacitor and it's testing ?
Post by: Paulo on September 15, 2013, 01:29:53 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.

http://en.wikipedia.org/wiki/Motor_capacitor (http://en.wikipedia.org/wiki/Motor_capacitor)

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

http://www.maplin.co.uk/motor-run-capacitors-250v-569510 (http://www.maplin.co.uk/motor-run-capacitors-250v-569510)

http://www.radioshack.com/search/index.jsp?kwCatId=&kw=starting%20capacitor&origkw=starting+capacitor&sr=1 (http://www.radioshack.com/search/index.jsp?kwCatId=&kw=starting%20capacitor&origkw=starting+capacitor&sr=1)
Title: Re: Capacitor and it's testing ?
Post by: Magnum on September 15, 2013, 03:37:05 AM
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 ?

Andy
Title: Re: Capacitor and it's testing ?
Post by: Magnum on September 15, 2013, 03:50:49 AM
I found this. I could not find one for 250 VAC, would this one work ?

Code: [Select]
http://www.amazon.com/Amico-3000nF-450VAC-Capacitor-CBB61/dp/B005PK62WK/ref=sr_1_5?s=electronics&ie=UTF8&qid=1379180935&sr=1-5&keywords=fan+capacitor+3+uf+250
Title: Re: Capacitor and it's testing ?
Post by: Paulo on September 15, 2013, 03:52:25 AM
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:
http://www.wikihow.com/Check-a-Start-Capacitor (http://www.wikihow.com/Check-a-Start-Capacitor)
Title: Re: Capacitor and it's testing ?
Post by: Paulo on September 15, 2013, 03:56:29 AM
I found this. I could not find one for 250 VAC, would this one work ?

Code: [Select]
http://www.amazon.com/Amico-3000nF-450VAC-Capacitor-CBB61/dp/B005PK62WK/ref=sr_1_5?s=electronics&ie=UTF8&qid=1379180935&sr=1-5&keywords=fan+capacitor+3+uf+250

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.


Title: Re: Capacitor and it's testing ?
Post by: dedndave on September 15, 2013, 04:17:43 AM
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
Title: Re: Capacitor and it's testing ?
Post by: dedndave on September 15, 2013, 04:35:45 AM
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
Title: Re: Capacitor and it's testing ?
Post by: Magnum on September 15, 2013, 04:36:13 AM
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.

Andy
Title: Re: Capacitor and it's testing ?
Post by: Magnum on September 15, 2013, 08:27:38 AM
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. :-)

Andy

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.
Title: Re: Capacitor and it's testing ?
Post by: dedndave on September 15, 2013, 10:26:23 AM
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

(http://www.parts-recycling.com/Commercial-Appliances-/Washer-/Fluke-79-series-ii-multimeter-with-test-probes-photo-1.jpg)
Title: Re: Capacitor and it's testing ?
Post by: Paulo on September 15, 2013, 11:22:05 AM

there is a slight time delay between current traveling and visible light   :P
also - light bulbs need some minimum current to be visible

Interesting point.
Light only travels at the....well...errr speed of light in a vacuum (the often quoted 3X10^8 m/s).
In other mediums, it's considerably lower.

Likewise for electricity, hence the concept of velocity factor in high frequency electronics where the dielectric constant
of the substrate ( the printed circuit board) has a huge influence on the speed and hence wavelength.
At very and ultra high frequency, circuit elements such as capacitors and inductors are made (etched) from pcb traces
and the lengths and/or widths must be compensated for because of the dielectric constant.

This also applies to high speed digital circuits.
Next time you have a PCI card in your hands, look very carefully at some of the traces, they "snake" around instead of just
going directly from point A to point B.
This is so that the correct delay is achieved as required.
In PCI cards, this is normally done to the clock signal where the data lines go straight to a latch and the clock lines snakes around
for a bit to create a delay then feeds the latch enable of the latch.
This is done so that the data is present (and steady) before it is latched.

Sometimes it's also done so as to compensate for the length of travel, i.e. the first connection is physically closer than say the last
thus extra trace length is added so that the arrival of data is at the same time.
It all depends on layout.

(http://s22.postimg.org/sewrwwgwh/Clock_Trace.jpg)
Title: Re: Capacitor and it's testing ?
Post by: dedndave on September 15, 2013, 11:46:33 AM
that's how you make an inductor on a PCB   :P
i doubt the propogation delay alone would be signifigant
at least - at the frequencies that are present on that board
Title: Re: Capacitor and it's testing ?
Post by: Paulo on September 15, 2013, 11:52:08 AM
that's how you make an inductor on a PCB   :P
i doubt the propogation delay, alone would have meaning
at least - at the frequencies that are present on that board

Well yes and no.
To create inductance, it must have a given length and width for a certain dielectric constant.
So when one creates a thin trace like that, it will be mostly inductive (except for the small amount of capacitance due to the ground plane)
so creating a trace of the same length but wider will decrease the inductance but increase the capacitance.
Which ever is the dominant reactance, it's the length we are interested in here as both capacitance and inductance create delay but one also has to watch the phase
so simply creating a long line is not going to work, it must have the right combination of XL and XC.

The propagation delay is very much a factor considering that the dielectric constant of FR4 PCB is 0.5 and at PCI 66MHz with bit times in the region of 15nS, it's enough to cause very weird errors.
Remember that PCI is a parallel bus so if one of the bits is delayed by evena few nS relative to the others, it could mean the bit is interpreted as a high instead of a low or vice versa.
Of course the situation gets even more critical with PCI @100MHz and above.
This is also the reason why one cannot use "normal" logic gates with PCI (and other high speed digital circuits) as the propagation delay thru these gates and logic chips is simply too great
not to mention their input capacitance which would cause unacceptable bit error rates.
Have a look at the PCI specs and you will see why many PCI cards make use of ASIC technology and highly optimized pcb layouts.
Title: Re: Capacitor and it's testing ?
Post by: Paulo on September 15, 2013, 12:00:41 PM
Keep in mind that propagation delay is directly proportional to velocity factor for a given substrate which is unfortunately not constant with frequency.
That is why good PCB manufactures always publish VF versus frequency charts of their products.
BTW, you will also see that these traces always have mitered corners, this is done so that there isn't an abrupt change in the magnetic field which
cause impedance disturbances (or bumps).

The fun really starts when one is designing at 1GHz and above.  :biggrin:
Title: Re: Capacitor and it's testing ?
Post by: Magnum on September 15, 2013, 01:01:45 PM
Meter with ohms is high on my list.

Considering what to charge. (I have a steady income, so I don't need to get rich or whatever)

$6 for part + 1 hr. of actual labor (other time spent was educational)

Andy

Since I moved, I no longer have access to a computer repair shop waste container.  :icon13:

But I have been accumulating furniture, bookcases, etc.

My 2 daughters and hubbies, 2 of my 4 step kids and 3 grand kids live close by.




Title: Re: Capacitor and it's testing ?
Post by: dedndave on September 15, 2013, 01:08:19 PM
i think you can get an analog meter for about $10
it doesn't have to be digital
sometimes, an analog meter is actually preferable
i still have an old Simpson 260 that i like to use for monitoring supply current, etc
i also have several Weston meters, but those are more as collectors items   :P
they do work, though
Title: Re: Capacitor and it's testing ?
Post by: Magnum on September 18, 2013, 07:01:28 AM
I received the new cap. It has a white and red wire.

I remember the can style caps as having a + and - terminal but no markings indicating polarity.

I don't want to miswire that puppy.

Andy

Title: Re: Capacitor and it's testing ?
Post by: dedndave on September 18, 2013, 08:28:18 AM
i am thinking....
it's a non-polarized capacitor
they provide a red and a white wire so the directions will jive - lol
these things are put together by trained monkeys
if you gave them 2 black wires, it would never get assembled   :biggrin:
Title: Re: Capacitor and it's testing ?
Post by: Magnum on September 18, 2013, 11:53:35 AM
When I hooked up the cap and tried the fan, nothing happened.

I looked at the armature and it's a silver color unlike the copper color that I have seen in others.

I replaced the armature and rotated it, and it sort of wobbled instead of being a fixed distance away from the windings.

The owner of the fan ran it about 12 hrs. a day for 7 days a week, so I think he got his money's worth.  :t

The bearings were frozen before using PB Penetrating Catalyst to loosen it up.

If it had oil lube holes for the bearings, the fan would last for a long time :-)

I'll just keep the starting capacitor for something else.

Adios,
         Andy
Title: Re: Capacitor and it's testing ?
Post by: dedndave on September 18, 2013, 06:04:42 PM
you may be able to see that one of the windings is "open" with the continuity tester
give the whole thing back to him and tell him to save it for parts - lol
that way, you don't have to store someone else's junk   :biggrin:
Title: Re: Capacitor and it's testing ?
Post by: Magnum on September 18, 2013, 10:57:09 PM
I will tell him I could not fix it and ask if he wants it back.

He probably won't want it back and I can salvage the cord to use for a short extension cord.

Andy

I may keep the blade too.

I repaired a fan for my daughter that had a small piece of one blade missing,
so I used Gorilla glue and glued a dime to the blade to balance it.