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Registered Member #54484
Joined: Sun Feb 15 2015, 06:18PM
Location:
Posts: 46
I just built a high voltage multiplier consisting of 3 stages of 20kv 470pf caps and 15kv 100ma diodes. My question is, when using a type 619 OBT 10kv 23ma do I connect one lead to HV in and the other lead to the ground terminal or am I restricted to using only one lead from the transformer? I got this from instructables website and he was using a 6kv single pole OBT. I'm relatively new to this but this is how I learn. Hands on. Any help would be greatly appreciated and if you can please also include the theory behind your answer to help me learn. Thank you!
Registered Member #11591
Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556
Yes, one goes to the "OBT" the other goes to ground. (the system does not have to be grounded, it just means that you have a common neutral, input to output.)
Be careful: HV isn't the sort of thing you want to actually get "hands on"!
Registered Member #1438
Joined: Sat Apr 12 2008, 12:57AM
Location: Canada
Posts: 218
Are you using these ALLANSON, 2721-619, Oil Burner Ignition?
The output is rated at only 60Hz and with only 470pF, there's going to be some severe ripple in the output of your multiplier.
From the datasheet on the OBT, the RMS voltage is 10kv which means it has a peak of 10,000*1.414 = 14140V. Because the diodes needs to be rated twice the peak voltage, this brings the diode requirement to 10,000*1.414*2 = 28280V meaning that the diode you are using are not sufficient for this multiplier. You could try stringing two of those diodes in series.
Also from the picture it seems like you put the diode in series. You cannot reliably put diodes in parallel for it to handle more current. Here's a good video demonstrating why
Registered Member #54484
Joined: Sun Feb 15 2015, 06:18PM
Location:
Posts: 46
hen918 wrote ...
Yes, one goes to the "OBT" the other goes to ground. (the system does not have to be grounded, it just means that you have a common neutral, input to output.)
Be careful: HV isn't the sort of thing you want to actually get "hands on"!
Thank you! And yes I am very careful. I always check and recheck everything. And always when I'm ready to power something up I have to plug it in then walk out of the room to a switch to turn it on. So I'm never right in front of something I just built when it first powers up.
Dragon64 wrote ...
Are you using these ALLANSON, 2721-619, Oil Burner Ignition?
The output is rated at only 60Hz and with only 470pF, there's going to be some severe ripple in the output of your multiplier.
From the datasheet on the OBT, the RMS voltage is 10kv which means it has a peak of 10,000*1.414 = 14140V. Because the diodes needs to be rated twice the peak voltage, this brings the diode requirement to 10,000*1.414*2 = 28280V meaning that the diode you are using are not sufficient for this multiplier. You could try stringing two of those diodes in series.
Also from the picture it seems like you put the diode in series. You cannot reliably put diodes in parallel for it to handle more current. Here's a good video demonstrating why
Actually the diodes are in parallel to handle the extra voltage. The input current is 23ma, the diodes are all rated 100ma. From what I understand of theory the diodes in parallel will share voltage but not current right? As far the ripple, I'm not concerned, won't be using it for anything sensitive to that. The Caps are rated 470pf but when I tested them them each one was anywhere from 700 to 800pf, which obviosly went down once they heated up a little. Got them from Ukraine on ebay. For a more sensitive project I plan to by American! Now the entire assembly is encased in PVC and filled with paraffin wax. Thank you so much for your reply and video, I'll watch it again for the info to really sink in. If you want to see where I got the plan here's the link from instructables...
[Double post merged together by moderator Mads Barnkob]
Registered Member #1438
Joined: Sat Apr 12 2008, 12:57AM
Location: Canada
Posts: 218
Only stringing the diodes in series will increase the total voltage the diodes can withstand. Diodes in parallel will not share the voltage.
The voltage rating on a diode is it's ability to block the reverse voltage before breaking down (conducting). By connecting say two diodes in series, you will roughly double the reverse blocking voltage of the combined stack.
If you really want to put diode in parallel (especially if they are not well matched), you'll need to balance it with resistors and capacitors.
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
When first powering up these things, put a lamp (incandescent) in series. I have saved some 100 W lamps, that are not made anymore, just for this purpose.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059
Yeah, this is a good tip. IIRC some OBITs are not designed for continuous use so you might want to add a thermal cutout so that if the temperature starts to run away it shuts off the power.
Registered Member #54484
Joined: Sun Feb 15 2015, 06:18PM
Location:
Posts: 46
Thanks for the tips! For now I have been only running up to 30 seconds. When I get to the point of continuous use I already planned on wiring in thermal switches. Especially for the Tesla coil. That will be powered with a 15kv 60ma NST.
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HV Multiplier
