capacitor or MOV?

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rebeltaz
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capacitor or MOV?

Post by rebeltaz » Mon Oct 19, 2009 5:05 pm

I have a bag full of components that I find regularly in television and DVD/VCR power supply circuits. They are small, circular, blue components with two leads and the following numbers printed on them:

KX472M
X1Y1
BS415

From their position in the power supply circuits on the AC power line, I was under the impression that they were MOVs. In building a surge suppressor for a water bed, I was going to use three of these (one across the line and the other two from either side to ground), I figured I had better make sure of their ratings before finalizing the project. Doing a search on the BS415 number, I found datatsheets describing the components as ceramic capacitors.

With that being the case, I have to guess that they won't help much in surge suppression, so my question is: What is their purpose in power supply circuits if not surge suppression?

Thanks...
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Re: capacitor or MOV?

Post by haklesup » Mon Oct 19, 2009 6:08 pm

If they are in circuit across the AC input then they are probably an MOV. A cap across an AC line would be more like a short. If they are in series with an AC signal or across the caps at the DC output then I would believe they were caps.

GO ahead and put one on the end of an extension cord and plug it in. If nothing happens it's an MOV. If it explodes, it's a cap. Just keep your distance and probably a good idea to wear goggles.

You'll probably find than in almost any commercial power supply if you look close enough.

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Re: capacitor or MOV?

Post by Janitor Tzap » Mon Oct 19, 2009 8:05 pm

That KX472M part of the ID number looks to be a capacitor value.
.0047uF at 20%.
It would be helpful if there was a picture.

I've seen VAC capacitors used with choke transformers on the front end of TV/VCR's and Stereo's.
It acts as a RFI/EMI line noise suppressor.


Signed: Janitor Tzap

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rebeltaz
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Re: capacitor or MOV?

Post by rebeltaz » Mon Oct 19, 2009 8:37 pm

Tzap, I have attached a photo of it... this one is KX222M instead of KX472M, but the component is identical.

Hakelsup, I like your suggestion! I'm always up for a good explosion. :cool: I will give that a try tomorrow.

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Re: capacitor or MOV?

Post by Robert Reed » Mon Oct 19, 2009 8:58 pm

Its a 2200 pf 250v probably ceramic capacitor with prebent leads for automatic insertion. I beleive the X1Y1 stuff relates to a safety designation. I have seen these on line entry filters. Across the line is one designation. Line to grd is another and neutral to ground yet another .

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Re: capacitor or MOV?

Post by rebeltaz » Mon Oct 19, 2009 9:00 pm

Robert Reed wrote:Its a 2200 pf 250v probably ceramic capacitor with prebent leads for automatic insertion. I beleive the X1Y1 stuff relates to a safety designation. I have seen these on line entry filters. Across the line is one designation. Line to grd is another and neutral to ground yet another .
And it's purpose would be....?
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Re: capacitor or MOV?

Post by reloadron » Tue Oct 20, 2009 2:25 am

The purpose would likely be input filtering of the AC mains power. In the below cutaway circuit of an ATX power supply C1, R1, T1, C4, AND T5 are all part of the AC line filtering. I would bet your capacitor figures into there:

Image

Ron

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Re: capacitor or MOV?

Post by Robert Reed » Tue Oct 20, 2009 5:22 pm

Not only input filtering but also PS noise reduction on the powerline itself.

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Re: capacitor or MOV?

Post by rebeltaz » Tue Oct 20, 2009 9:27 pm

Ok.. Thanks... I appreciate the info. I guess I need to find some MOVs then...
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Re: capacitor or MOV?

Post by Dean Huster » Tue Aug 03, 2010 6:02 pm

There's nothing at all uncommon about capacitors directly across the AC line. They used to do that all the time, putting a cap between hot and chassis, neutral and chassis and sometimes between hot and neutral. It was a really common practice befor the advent of 3-wire grounded line cords. Those caps didn't explode. If you want an explosion, put a 100µF, 16v e-cap across the line. It all depends upon the cap value and voltage.
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Re: capacitor or MOV?

Post by Robert Reed » Tue Aug 03, 2010 8:49 pm

They used to do that all the time, putting a cap between hot and chassis, neutral and chassis and sometimes between hot and neutral.
And they still do,maybe even more common now than before. Almost every line filter configuration I have seen uses the connections of C2,3,4 & T5 with common of C3,4 going to ground rather than a shield. Not only filters line noise, but more importantly reduces PS noise from switchers feeding back into the line. The X & Y ratings are applied to those capacitors depending on their position in the circuit. At the moment it escapes me as to which ones are which.

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Re: capacitor or MOV?

Post by Edd » Thu Aug 12, 2010 9:28 pm

.


Ahhhhh yes, those two different types, and if you are not using them frequently, leaving you always wondering . . . . which is which ? . . . for that next time you run across one of them.

Ye olde Safety Capacitors:

Class X capacitors are used in “across-the-line” applications where their failure would not lead to electric shock. Class X safety caps are used between the “live” wires carrying the incoming AC current. In this position, a capacitor failure should not cause any electrical shock hazards, rather, a capacitor failure “between-the-lines” would usually cause a fuse or circuit breaker to open.

Class Y capacitors are used in “line-to-ground” (line bypass) applications where their failure could lead to electric shock if a proper ground connection were lost. The failure of a “line-to-ground” capacitor would not open any safety fuse. In other words, the failure of a line bypass capacitor could create a 120 volt “hot” chassis that could give you a potentially fatal shock.

Because the terms X and Y are pretty non-descript, it can be hard to remember which type go where.

To associate the situation firmly in your main and be able to remember it, just think of the X as being A CROSS such as you see on a railroad crossing sign, and there you have it ….X is for “A CROSS the line” applications.

Most safety capacitors have voltage ratings of 250 VAC and can be used in circuits up to 250 VAC. With a 250V voltage rating the capacitors can used in the USA and Canada where typical household voltage is 110-120 VAC.

The different classes of Safety Capacitors:

Safety capacitors are grouped into a number of different classes. For X Type capacitors there are class X1, X2 and X3. For Y Type capacitors there is class Y1, Y2, Y3 and Y4.

The only types you will probably see for sale are X1 (impulse tested to 4000 Volts), X2 (tested to 2500 V), Y1 (tested to 8000 V) and Y2 (tested to 5000 V).

Of the above capacitors, type X2 and Y2 are the most popular and the type that you will probably want to use. X2 and Y2 safety capacitors are used in appliances that plug into ordinary household wall outlets, while type X1 and Y1 are for heavy duty industrial use.
For example, a type X1 capacitor would be used in an industrial computer or industrial lighting ballast that is connected to a 3-phase line (the main power trunk lines within a building).

Thassit . . . .


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Re: capacitor or MOV?

Post by Robert Reed » Fri Aug 13, 2010 8:17 am

Glad to see you back Edd. As usual your comments are very informative and to the letter. Also the added humor always gives me a chuckle.

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