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Xfmr identification

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HM_Murdock

Tue Oct 05 2010, 01:52AM

Registered Member #3075 Joined: Fri Aug 06 2010, 02:44PM
Location: Athens, GA
Posts: 148

Scavenged this Xfmr from a fairly big bug zapper...can't dig up any relevant info online, and am hoping someone here can tell me more based on experience...

Mainly:

1 - any idea about what V and mA this thing might be?
2 - would this type of xfmr be current limited like an NST, or not?

The arcs from it are high pitched in sound (like a flyback, but a lot louder), and VERY bright...like "lens flare/don't look at it" sort of bright. It's considerably louder than any of my big NST's when arcing.

No ratings info on it, only the following:

XFMR400-32NB
0850
B-10
made in Vietnam W

Here's a couple of pics and a short video of the arcs:

]bug_zapper_xfmr.wmv[/file]

GhostNull

Tue Oct 05 2010, 02:20AM

Registered Member #2648 Joined: Sun Jan 24 2010, 12:45PM
Location: Australia
Posts: 291

In the last picture picture I can see what looks like a HV capacitor. This is probably what is causing such a big bang. It probably works by changing up this cap and when the unfortunate insect flys between the two grids, it completes the circuit and gets discharge of the capacitor, killing it. I think it isn't very powerful. Probably around the low KV, 1-3KV and not that much current since it would only need to charge the capacitor but it does looks reasonably sized so I might be wrong.

Adam Munich

Tue Oct 05 2010, 03:09AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

It is likely not more than 3kV, and not more than 10mA. A rough way to measure voltage is by spark (not arc) length. Using 2 marble sized steel balls as electrodes, bring them closer and closer together until it sparks over. Do this over a plastic ruler so you can measure the distance. On an average day it'll be about 10kV/cm.

I'm not sure if it's current limited, but judging by how far the primary is from the secondary it may be.

Also, old thread discussing the same transformer.

Patrick

Tue Oct 05 2010, 03:30AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

just on a related note... when you say marble size grenadier... doesnt the diameter of the ball relate to how uniform the e-field between the balls is?

ive always seen tables that seem to go no smaller than 1 inch and go up to like 2 inches

Adam Munich

Tue Oct 05 2010, 03:35AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Smaller balls cause larger sparks, but I've always had good accuracy with marble sized balls.

Also HM Murdock, remember your peak voltage will be the rated voltage / .707. This means a 15,000V transformer will have a peak voltage of 21206 volts, which explains why the sparks tend to be longer on an AC source. I'm not sure what effect that unknown cap could have though.

It's still likely not over 3kV RMS though.

Wolfram

Tue Oct 05 2010, 08:46AM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

Grenadier wrote ...

A rough way to measure voltage is by spark (not arc) length. Using 2 marble sized steel balls as electrodes, bring them closer and closer together until it sparks over. Do this over a plastic ruler so you can measure the distance. On an average day it'll be about 10kV/cm.

This doesn't sound right. 10kV/cm is the usual quoted figure between sharp points, for balls it would be much lower. According to the graph on the bottom of this

page it's more like 30kV/cm between balls of larger diameter than the gap between them.

Steve Conner

Tue Oct 05 2010, 09:42AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Anders M. wrote ...

This doesn't sound right. 10kV/cm is the usual quoted figure between sharp points, for balls it would be much lower. According to the graph on the bottom of this

page it's more like 30kV/cm between balls of larger diameter than the gap between them.

+1, it's nearer 30kV/cm for balls. But the value depends on the surface condition, if the balls aren't smooth, clean and shiny it could be less.

GhostNull

Tue Oct 05 2010, 10:46AM

Registered Member #2648 Joined: Sun Jan 24 2010, 12:45PM
Location: Australia
Posts: 291

Edit: Scrap this, You would need a decent DMM with RMS AC.

If you got a cheap DMM you don't mind lossing. You can put two resistors with known value across the output and measure the voltage drop. From this you will also me able to get the current output, depending on what resistors you decide to use.

ScotchTapeLord

Tue Oct 05 2010, 01:14PM

Registered Member #1875 Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635

If you charged a capacitor through a HV diode, then you could use a resistive divider to measure the DC voltage, which should be equal to the peak voltage of the ac, then divide by 1.41 to find the VAC. Easily done with maybe a couple MO diodes and a MO cap. and a string of megohm resistors. Just remember to factor in your device's internal resistance.

Luca

Tue Oct 05 2010, 03:41PM

Registered Member #2481 Joined: Mon Nov 23 2009, 03:07PM
Location: ITALY
Posts: 134

If I see correctly, there is a sort of magnetic shunt between the primary and sec. So, it should be current limited as standard NST.

Regards,

Luca

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