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Hazmatt_(The Underdog)

Sun Feb 12 2006, 02:16AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Here is something I worked on today and finished. It's a common mode and differential mode voltage divider! It's really neat! It's 2 dividers in one package case grounded, but with a twist. You get a differential divider that's ground lifted from the case, summing both divided hots for easy measurement!
I aligned it today with my HT probe and couldn't help but laugh in joy as it actually works!
Measured ~7KV on each leg, and ~13KV through the differential output. A must have for voltage and current measurements for any coiler!

Part Scavenger

Sun Feb 12 2006, 02:24AM

Registered Member #79 Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673

That's pretty cool! I need to build one of those...

HV Enthusiast

Sun Feb 12 2006, 03:54AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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Posts: 3068

Looks good.

From the photos, it appears to be a capactive divider only. Is this correct? If so, you should put resistors in parallel as well with each capacitor so that you get a more flat response from DC up to your AC end.

Here is one of the high bandwidth dividers i built a few years ago. This divider is good for 60kV and works extremely well - frequency response almost completely flat across the band out to about 50Mhz.

Hazmatt_(The Underdog)

Sun Feb 12 2006, 07:10AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

The very last stage has an adj. pot so I can calibrate better. Otherwise the output on the bottom with the caps I chose was way too high, like 90VAC. So with the pot I got it down which works for me for now.

I want to do what you have on your page because that's a really sweet divider. At this time I'm not really sure what R value to use because I'm pretty new to the dividers. This one is just a capacitive divider. I have the right value for my calculations, but they were removed from boards so their leads are too short, and this is just a bodge-job to get me on my feet.
I'll look into getting some really high value resistors eventually.

The goal though is that with the two dividers I can get terminal voltage at the one AND measure the voltage drop through the protective load (1500R 50W) so I know the current, that's the key! Voltage and Current at the same time!

HV Enthusiast

Sun Feb 12 2006, 04:03PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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What are your goals for your divider design (i.e. bandwidth you wish to measure?) Also, i'm not sure i follow you on how you are measuring current - do you have a diagram or something that can explain this better?

Hazmatt_(The Underdog)

Sun Feb 12 2006, 10:29PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Current measurment is just the proportional drop across the two terminals through the 1500 ohm load resistor. This should be 90*root2 / 1500 = 60mA AC
and 90 Volts being the meter reading.

HV Enthusiast

Sun Feb 12 2006, 10:41PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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Ok, so you basically have a very low frequency divider for DC and 60Hz. Can you post some of your waveforms that you've taken already?

Hazmatt_(The Underdog)

Sun Feb 12 2006, 11:16PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

wave...forms.......aaaahhhh...... scratches head I'll work on it. It's not like I don't have a scope, or a good scope, its just that getting a capture of the waveform isn't a simple task for me. The last time I tried with the digital camera i only got part of the sweep.
I dunno about a DSO. I might be able to find one at the swapmeet sometime soon, but the money is kinda an issure at this time.

Ill see what I can do.

Steve Conner

Sun Feb 12 2006, 11:37PM

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

To capture the whole sweep, you need to use a slower shutter speed, which is kind of difficult if your camera hasn't got a manual mode.

HV Enthusiast

Sun Feb 12 2006, 11:52PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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Wow, i've never had that problem before. You must have a pretty old oscilloscope. Of course, now that i remember, i took shots of my oscilloscope after the waveform was captured in storage (digital scope) so i honestly never tried taking a shot with it continuously sweeping . . .

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