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doubler for DRSSTC

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LAN_403

lightlinked

Mon Oct 11 2010, 11:40AM

Registered Member #2087 Joined: Tue Apr 21 2009, 08:32AM
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- My current DRSSTC setup has a full bridge with 10 x 820uf 200 volt snap caps and I would like to convert it to a voltage doubler by splitting it into two banks of 5 x 820uf caps. I am concerned about what would happen if they see AC if it starts pulling too much current. I am also concerned about the way I am going about this with the bridge capacitors, using multiple little caps instead of one or two giant caps. It looks like most people use two gigantic caps for their bridges. Right now I like having the input current limited by a big light bulb since it helps save it from people killing it during demonstrations but that might also create an issue if I make a doubler.
- Another Idea I have would be making the doubler in an external box with SCRs for variable voltage and running a HVDC line to the bottom of the coil where the main electronics are with Neutrik powercon connectors. It would be along the lines of one of the soild state variac replacement concepts, simpler than a boost converter but without the PFC advantage. Either way I still would have to make the bank of caps 2 series of 5 x 820uf. I would be up for getting more of these caps but getting two giant ones might be too expensive or require watching ebay. Pic of what the bridge and caps looks like...

HV Enthusiast

Mon Oct 11 2010, 05:51PM

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

What do you mean by "see AC?"

Your capacitor bank, whether its a conventional rectifier arrangement or a voltage doubler will always see some AC component.

lightlinked

Mon Oct 11 2010, 11:53PM

Registered Member #2087 Joined: Tue Apr 21 2009, 08:32AM
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I dont mean ripple, i mean the possibility of reverse voltage in an overload condition, if the load wants more power than is coming in and so the electrolytics might get reverse voltage? i guess the question would be how much power i can pull out of the doubler before such a situation occurs. or if such a situation can occur in a DRSSTC where it wants the energy in many short pulses. it seems like it definitely would be an issue if the bridge fails and shorts. Are diodes parallel with each cap proper protection for this?

ScotchTapeLord

Tue Oct 12 2010, 01:13AM

Registered Member #1875 Joined: Sun Dec 21 2008, 06:36PM
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If the doubler you are talking about is the "charge pump" circuit then, from what I read on the hvwiki, it will see harmful AC when the doubler limits the current too much. You should monitor the output voltage to make sure it doesn't drop. Antiparallel diodes will just short out the supply when the output voltage swings negative, I would think.

I would also watch the ripple current ratings on this little capacitors...

lightlinked

Wed Oct 13 2010, 09:21PM

Registered Member #2087 Joined: Tue Apr 21 2009, 08:32AM
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they are elna LP5 caps rated for 2.6 amps ripple each which looks to be similar to the gigantic caps. I was thinking of a config such as this...

in which case it should just be a full bridge when the caps get drained.

ScotchTapeLord

Wed Oct 13 2010, 09:58PM

Registered Member #1875 Joined: Sun Dec 21 2008, 06:36PM
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That's no good. Look hard enough and you'll see why.

dingo27

Thu Oct 14 2010, 04:37PM

Registered Member #890 Joined: Tue Jul 10 2007, 10:06PM
Location: Slovakia
Posts: 180

1ohm resistor?

really there is nothing bad.

ScotchTapeLord

Thu Oct 14 2010, 05:29PM

Registered Member #1875 Joined: Sun Dec 21 2008, 06:36PM
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**I was mistaken... this will work.

Steve Conner

Fri Oct 15 2010, 09:49AM

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

Yep, two of the diodes are redundant (unless you intended them to stop the capacitor voltage reversing under extreme loads) but the circuit will work.

lightlinked

Sat Oct 16 2010, 04:15AM

Registered Member #2087 Joined: Tue Apr 21 2009, 08:32AM
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Posts: 115

Steve McConner wrote ...

Yep, two of the diodes are redundant (unless you intended them to stop the capacitor voltage reversing under extreme loads) but the circuit will work.

protection against reverse voltage is exactly what i want. I got a new "big" soldering iron and re-configured the deallie with the planned doubler. It works but half the bridge mysteriously died. I think it was because I accidentally had the on time all the way up on the first full power test or I might have a bad TVS on that board. As a half bridge at 300 vdc it does make longer sparks than when it was a full bridge at 170 vdc. I need to get the relay wired that bypasses the charging light bulb.

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