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Measuring flyback output

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ZakWolf

Sun Dec 26 2010, 03:47AM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
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I am going to make a new sgtc with me new wire i just got in. I am going to power it with a flyback transformer. How can i measure the voltage? i read that you can lower it with 1 million ohm resistors. If so how many do i have to use?

Thanks

Adam Munich

Sun Dec 26 2010, 04:05AM

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

Well what's the impedance of your voltmeter?

Ash Small

Sun Dec 26 2010, 06:57AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Ithink this is a bit more complicated than it might first seem, but I'm no expert on this subject.

I think the voltage will depend partly on the load, ie open circuit voltage will be higher than short circuited voltage (I hope I'm using the right terminology here)

If you place a 1 million ohm resistor in series with a 1 ohm resistor, and measure the voltage across the 1 ohm resistor, the voltage displayed on your voltmeter will be one millionth of the total voltage (approximately)

But this will not be the same voltage that you will obtain under normal running conditions of the sgtc, as you will be drawing more current under normal running conditions (at least, I think that is the case)

If you also draw an arc while using the two resistors and meter the voltage will be different again, but will probably give a figure closer to the answer you are after.(EDIT: I don't think this bit is correct)

I think what I'm trying to say is that this is not a straightforward procedure.

Also, depending on which method you use, you'll have to consider the wattage of the resistors as well

I do know that DMMs don't like to be used for this and tend to die. You are better off using an analogue (moving coil/needle) meter.

Best to get some more advice or do some research before you attempt this (especially if you only have one DMM)

EDIT: read this:

And this:

radhoo

Sun Dec 26 2010, 10:31AM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 699

There are some ongoing discussions on how to measure HV, see:

Erlend^SE

Sun Dec 26 2010, 04:46PM

Registered Member #1565 Joined: Wed Jun 25 2008, 09:08PM
Location: Norway
Posts: 159

Depending on the driver, you may actually be able to do it on the primary side.

If you know the resistance of the windings, you could possibly messure the ABL(HV return) to figure out voltage drop, and use some of the other windings to find the voltage.

Given it's a TV LOPT/flyback, maybe the focus resistor is possible to access? Since then you already have the upper resistor in place and you only need to figure out a factor.

On the other hand: I have good experience with a resistor string connected in series with a analog meter with a modified scale.
a multimeter in the mA / ÂµA range can give you the voltage, just make sure it's actually set for current and NOT voltage e.t.c.

Adam Munich

Sun Dec 26 2010, 05:26PM

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

Just figured I'd put this here.

radhoo

Mon Dec 27 2010, 11:25PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 699

Grenadier wrote ...

Just figured I'd put this here.

Things get a little more complicated, but after all a hv probe is a simple device to build.

First, One should use an analogue voltmeter, instead of a DVM. The HV may create a lot of interference with the sensitive electronics found in a DVM. This will give you a lot of false/random readings or it might damage the DVM. I found out 1 GOhm resistor for the divider and an analogue microampmeter are perfect for this job.

Then there is the insulation problem, the divider must be carefully insulated, and from my tests it seems WAX or HOT GLUE are not good for 50KV and above, but instead mineral oil seems to do a decent job.

I also do not recommend using a probe-like design since it is not practical. Instead a well insulated case with HV cables and crocodile connectors will better serve its use, and avoid possible accidents, because everything will be well connected together when doingthe measurements.

Adam Munich

Tue Dec 28 2010, 12:07AM

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

You could always just buy a probe, it's not exactly an expensive item.

Patrick

Wed Dec 29 2010, 02:14AM

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

I got the tek 6015A, from ebay. Now I can check my own resistive divider, with an already known probe type.

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