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Bens foray into building a cap bank with uzzors charger

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vk2fro

Fri Jun 17 2011, 02:18PM

Registered Member #3930 Joined: Sun Jun 05 2011, 07:27PM
Location: Sydney, Australia
Posts: 33

I've got a small question regarding uzzors 50W capacitor charger.

I have basically made a modification that allows me to run caps in parrallel (450V) or series (900V) using a switch and second voltage divider. I've also removed the led circuit (mines getting a panel meter - 0-100 V range with a 10:1 voltage divider).

Here is the modified schematic (edited in none other than windows paint. Uzzors2k gets all credit for this schematic - its his work, sorry your copyright is missing mate - I used the left hand bit to do the copy/pasting!)

This should work correctly yes? I've spent a lot of time working out how a comparator works, and really I should know - I am an amateur radio operator after all - had to study this stuff to pass. Also renewed my knowledge of voltage dividers.

As far as I can tell the TL431 (which can be replaced by a LM336-2.5V, I hope), feeds the non inverting input, and when the voltage across either divider becomes greater than 2.5V, at the inverting pin, the comparator switches state, turning on the transistor and stopping charge.

Also I assume that switch is wired as normally closed, and pressing it / toggling it (the charge switch) allows the comparator to take over, charging the caps.

Otherwise the circuit would start charging unless the button is held down / switch is in the wrong position.

For substitution of parts due to what we have here at jaycar:

IRFP250: IRFP540
Bridge (on output) RGP10J : 4 x 1000v fast diodes
Indicator circuit: 100V panel meter (digital) with 1M + 100K resistor + 25k trimpot as voltage divider for the meter.

The trimpot will allow metering to be calibrated against a multimeter from 87V to 105V. So if I am looking at 430v on my meter, I want to adjust my panel meter to read 43.00 volts. (thus turning the 100volt meter into a 1kv one :P)

Any thought? have I made any errors here?

As an aside, I intend to use my bank for launching hard drive platters. I have 10 2400uf 450V capacitors to play with (and yes I know 2.43 kj is lethal, so have a smaller 330uf 450 v cap to experiment with until all my saftey precautions are in place!). Also some fun blowing up soft drink cans and bits of wire wouldn't go astray. Better get some ear defenders, leather gloves and some saftey glasses!

Cheers
Ben

1308320213 3930 FT0 Cap Charger Dual Range

currentkills91

Fri Jun 17 2011, 10:49PM

Registered Member #3831 Joined: Thu Apr 14 2011, 02:54PM
Location:
Posts: 265

I like what you've done, and it should work, but you don't really need the second trimmer. Just add the second resistor to the same pot, and switch between the resistors. :)

vk2fro

Sat Jun 18 2011, 12:22AM

Registered Member #3930 Joined: Sun Jun 05 2011, 07:27PM
Location: Sydney, Australia
Posts: 33

hey thanks for the reply - I thought "duh yeah dont need the second trimmer" then it dawned on me why its there -

We're charging caps, and if a marginal cap is in the bank ready to blow as soon as you go over 450V its better to have a trimmer per voltage range. The setting on the 950 v range may be different to the setting on the 450v range (My system will use logic and 2 big contactors to rearrange the cap bank from parrallel to series). I failed to mention that the range switch is part of a multipole relay, one of the sets changing the range on the charger, the other throwing the contactors.

I may need to include some logic to prevent this contact actioning unless the caps are discharged to a safe level). Or just a big sign on the control cabinet "DO NOT THROW RANGE SWITCH IN CHARGED STATE!" ;)

Am going to try and get some nice industrial saftey switches for the unit, and house the control panel in a seperate cabinet, so the operator can stand well back from exploding wires and flying hard drive platters. Will fit voltmeters to both bank and control box for saftey.

currentkills91

Sat Jun 18 2011, 01:58AM

Registered Member #3831 Joined: Thu Apr 14 2011, 02:54PM
Location:
Posts: 265

Hmm, sounds interesting :D How big you want the switches to be? I might be able to help on those :D

vk2fro

Sat Jun 18 2011, 09:27AM

Registered Member #3930 Joined: Sun Jun 05 2011, 07:27PM
Location: Sydney, Australia
Posts: 33

This is a typical press switch

Ux A11032500ux0173 Ux G

The press button depresses into the shroud around the button, preventing it being pressed accidentally (for example, by a dropped object, or someone leaning on the console). The ones I am after are backlit (and obviously dont need to carry anywhere near as much voltage or current - the contactors and relays will handle that).

currentkills91

Sun Jun 19 2011, 03:22AM

Registered Member #3831 Joined: Thu Apr 14 2011, 02:54PM
Location:
Posts: 265

Well, I don't have anything like that. Radioshack sells some switches with covers over them - These - probably not what your looking for, but they would have the same concept really.

vk2fro

Mon Jun 20 2011, 02:48PM

Registered Member #3930 Joined: Sun Jun 05 2011, 07:27PM
Location: Sydney, Australia
Posts: 33

yep - I have a missile switch for use as the pre firing switch - it'll disconnect the charging circuitry and enable the fire button / remote button.

vk2fro

Thu Jun 23 2011, 09:02AM

Registered Member #3930 Joined: Sun Jun 05 2011, 07:27PM
Location: Sydney, Australia
Posts: 33

Well guys, what do you think of my little fiddle in Eagle cad?

I've designed up a board to accomodate a range of tank cap and inductor sizes, and has plenty of space for heatsinks on the mosfets (I got lazy too with compacting my components LOL).

I'd say keeping it like this gives a reasonable voltage standoff - hence I I didnt pack components in too tightly. Although the switch is located on board, I'd prefer to mount this and the 1 meg resistor off board.

Cheers
Ben

currentkills91

Thu Jun 23 2011, 11:06AM

Registered Member #3831 Joined: Thu Apr 14 2011, 02:54PM
Location:
Posts: 265

Looks like its coming along nicely :D

Forty

Thu Jun 23 2011, 04:16PM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

very nice. i designed a board for just the zvs part, didn't even attempt the regulator bit. make sure you put in some beefy traces for the high current areas, wouldn't want to print that nice board and have parts of it melt. i agree that placing the 1M resistor off board is a good idea, that way you don't have any high voltage on your board. use insulating pads for the fet heatsinks too, i've noticed you can get shocked by touching the sinks if they're not insulated.

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