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Old 3rd May 2013, 08:53 PM   #161
nhuwar is offline nhuwar  United States
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I recall you posting your supply specs but I didn't go digging through the thread to find them.

I'm sure you could find a thryratron that would work at that voltgage dorm pretty cheap. But it would take a bit of space. If I were you id look for some high voltage gto's and use them as the crow bar. There basically silicon control rectifiers. You don't need a hockey puck though. The trigger circuit could be a basic current sensing resistor or the right size the switches on a transistor. That intern sends clamping voltage to the scr. They don't usually take more then a few volts. You could probably use a 9 volt to make hv isolation easier.

Just to let you know what I meant by hockey puck. Big high voltage and current gto' are the same size and shape as a hockey puck. Hence there nick name.

I'm sure there are other semiconductor options. Just not thinking of them at the moment. But scr's are the #1 device for this low voltage.

But just to let you know, the resistor online can be just as effective in protecting things from a filter discharge.

Nick

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Old 4th May 2013, 12:00 PM   #162
Funker is offline Funker  Germany
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Quote:
Originally Posted by nhuwar View Post
I recall you posting your supply specs but I didn't go digging through the thread to find them.

I'm sure you could find a thryratron that would work at that voltgage dorm pretty cheap. But it would take a bit of space. If I were you id look for some high voltage gto's and use them as the crow bar. There basically silicon control rectifiers. You don't need a hockey puck though. The trigger circuit could be a basic current sensing resistor or the right size the switches on a transistor. That intern sends clamping voltage to the scr. They don't usually take more then a few volts. You could probably use a 9 volt to make hv isolation easier.

Just to let you know what I meant by hockey puck. Big high voltage and current gto' are the same size and shape as a hockey puck. Hence there nick name.

I'm sure there are other semiconductor options. Just not thinking of them at the moment. But scr's are the #1 device for this low voltage.

But just to let you know, the resistor online can be just as effective in protecting things from a filter discharge.

Nick

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Hi ,

I would use one or two photo transistors as arc sensor in combination with an overcurrent detector. A lock relay establish a safety circuit. In event of a shorted capacitor or an arc over, the relay becomes dead and drop out. Another option is a primary circuit breaker with an voltage release coil. Both of these measures are common practise in commercial equipment.

In my homebrew 400W amp I use the latter. A combined circuit consist of an overvoltage detector for Vg2, a Vg1 undervoltage detector , and a plate overcurrent detector trigger the main circiut breaker and a SCR. This device dicharge the main capacitors via a dumping resistor.

Ok, the SCR solution is not an option for 2500V, but my amp runs only with 500V.

73
Wolfgang
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Old 4th May 2013, 03:06 PM   #163
nhuwar is offline nhuwar  United States
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Originally Posted by Funker View Post
Hi ,

I would use one or two photo transistors as arc sensor in combination with an overcurrent detector. A lock relay establish a safety circuit. In event of a shorted capacitor or an arc over, the relay becomes dead and drop out. Another option is a primary circuit breaker with an voltage release coil. Both of these measures are common practise in commercial equipment.

In my homebrew 400W amp I use the latter. A combined circuit consist of an overvoltage detector for Vg2, a Vg1 undervoltage detector , and a plate overcurrent detector trigger the main circiut breaker and a SCR. This device dicharge the main capacitors via a dumping resistor.

Ok, the SCR solution is not an option for 2500V, but my amp runs only with 500V.

73
Wolfgang

You wrong. Relays are never used in crowbars. You don't know what your talking about. And I said use a gto which is a type of scr. They go up to 6000 volts.

Do some homework before ya speak Wolfgang.

And learn about crowbars before you try and give some advice.


the reason relay are not used is there switch time. From the time a relays coil is energised to when it switches is in the milliseconds. More then enough time for a discharge event to happen completely. A gto's turn on time is in the microseconds.

And how would you use a photo transistor to detect arcs on a bright filament tube?

I've used them in waveguide. But they are void of light. Photo diodes or transistors would be useless.

Nick
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Old 4th May 2013, 05:09 PM   #164
Magz is offline Magz  United States
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I completed the C1 capacitor banks, with (7) 150uF, 450V TSHA caps and (7) 47K 5W resistors in each. Everything measures fine at 21uF and 329K for each bank. The caps are spaced apart for air circulation and cooling and I may also put some hot melt glue between them for further mechanical strength. The resistors are lifted about 1/8" off the board for the same reason. I can bend them further off the board when I install in the amps if space permits.
As with the rectifier stack, I removed all the solder pads near the HV connections and coated the connections and the board with high dielectric acrylic conformal coating (1500V/mil thickness) to help prevent arcing or surface discharges. I prefer the acrylic to urethane or silicone varieties of conformal coating because it is quick drying, easily removed with solvent and can even be soldered through without removing if you're in a hurry. I think coatings are an often neglected area in DIY - they can offer a lot of benefits for not much cost or effort.
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File Type: jpg 833 C1 Cap Stack.jpg (349.9 KB, 650 views)

Last edited by Magz; 4th May 2013 at 05:34 PM. Reason: Clarification
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Old 4th May 2013, 05:20 PM   #165
nhuwar is offline nhuwar  United States
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Originally Posted by Magz View Post
I completed the C1 capacitor banks, with (7) 150uF, 450V TSHA caps and (7) 47K 5W resistors in each. Everything measures fine at 21uF and 329K for each bank. The caps are spaced apart for air circulation and cooling, and the resistors are lifted about 1/8" off the board for the same reason. I can bend them further off the board when I install in the amps if space permits. I may also put some hot melt glue between them for further mechanical strength.

As with the rectifier stack, I removed all the solder pads near the HV connections and coated the connections and the board with high dielectric acrylic conformal coating (1500V/mil thickness) to help prevent arcing or surface discharges. I prefer the acrylic to urethane or silicone varieties of conformal coating because it is quick drying, easily removed with solvent and can even be soldered through without removing if you're in a hurry. I think coatings are an often neglected area in DIY - they can offer a lot of benefits for not much cost or effort.
1/8 is a little close. I would almost have them perpendicular to the board. I would not use hot glue on anything in the high voltage circuit. In high voltage heat is a double whammy. It causes air to ionizing and flash over. The more space between components the better.
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Old 4th May 2013, 05:30 PM   #166
Magz is offline Magz  United States
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Originally Posted by nhuwar View Post
1/8 is a little close. I would almost have them perpendicular to the board. I would not use hot glue on anything in the high voltage circuit. In high voltage heat is a double whammy. It causes air to ionizing and flash over. The more space between components the better.
Like I said, when I get ready to install them in the amps I'll know better how much room I have and how best to orient them. I do envision bending them further away from the board, but it doesn't make sense to do that before I know the ultimate layout.

The amps will have forced air cooling with a fan mounted under the 833 sucking pre-heated air from the chassis and directing it up around the 833. I'll orient the air intake slots to ensure that cool air is directed over the resistors and rectifier diodes.

Oh, and the hot melt glue would go between the bases of the caps on top of the board, not on the resistors - I re-read the post above and realized it might be misinterpreted that way so I edited it...

Last edited by Magz; 4th May 2013 at 05:37 PM.
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Old 4th May 2013, 08:22 PM   #167
nhuwar is offline nhuwar  United States
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Originally Posted by Magz View Post
Like I said, when I get ready to install them in the amps I'll know better how much room I have and how best to orient them. I do envision bending them further away from the board, but it doesn't make sense to do that before I know the ultimate layout.

The amps will have forced air cooling with a fan mounted under the 833 sucking pre-heated air from the chassis and directing it up around the 833. I'll orient the air intake slots to ensure that cool air is directed over the resistors and rectifier diodes.

Oh, and the hot melt glue would go between the bases of the caps on top of the board, not on the resistors - I re-read the post above and realized it might be misinterpreted that way so I edited it...

Ok I see. Ya those big caps could use more support. Are you going to have a filter on the fans? The only reason I ask is high voltage attracts dust. And dust can make a good discharge path.

I've got more experience with big high voltage equipment then any other area of electronics. Just trying to pass on anything that I think might help you is all.

Nick
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Old 4th May 2013, 08:33 PM   #168
Magz is offline Magz  United States
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Originally Posted by nhuwar View Post
Ok I see. Ya those big caps could use more support. Are you going to have a filter on the fans? The only reason I ask is high voltage attracts dust. And dust can make a good discharge path.

I've got more experience with big high voltage equipment then any other area of electronics. Just trying to pass on anything that I think might help you is all.

Nick
Thanks, I appreciate your input. I'll have some type of low resistance filters on the air intake slots, to minimize the amount of dust that gets in. That's another reason I'm applying the conformal coating as well - dust can't form a discharge path if the circuit is coated with a barrier.
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Old 4th May 2013, 09:01 PM   #169
nhuwar is offline nhuwar  United States
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That's good. The more dust you keep out. The less headaches you get, lol.

As for coating, you can us some corona dope.its made by gc electronics. Its a thicker then regular paint. Has a little brush in the bottle with it. Kind of like fingernail polish. Its made exactly for this purpose.
Just don't put a lime in it and drink it what ever you do. Not that kind of corona,lol.


Ya I know, corny. Just can't help myself sometimes.

here's a link to a place that sells it.
GC Electronics 10-4702: Corona Dope, 2-oz. Bottle

There is also red varnish that work pretty good for this application but the corona dope is by far the best.

Nick
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Old 5th May 2013, 12:16 PM   #170
Magz is offline Magz  United States
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I went ahead and hot glued the bases of the caps in the C1 bank for added mechanical strength, and I glued a strip of Lexan polycarbonate between the first and last caps in the bank for added electrical insulation, since the metal cans of those caps have 2000V potential difference between them. See Pic.

Now onto the big C2 bank!
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