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Adam Munich

Sun Jul 03 2011, 09:58PM

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

Today I charged the bank to 500V and shorted it via a roofing nail....

...holy shit! 3.1kJ was... wow.

Problem though, I need to make a better charger. My current transformer is just a rewound flyback core, but while it charged that bank to 500V in 3 minutes it was still too slow for me. So, I need a better transformer.

I happen to have a transformer from an x-ray machine, a HF one. It's a nice E core that can be taken apart with ease, so I figured being an E core it'd be able to push morem current. It has 500 turns on it and was designed to be fed 120V at god knows what frequency, so it's not too special when it comes to HV transformers. And considering it was designed to be run under oil I won't be missing much if I take it apart and rewind it.

Image of the slow charger, and the other image is the transformer and the actuator I plan on using for the contactor. I'll get you those drawings soon kludgesmith.

Adam Munich

Mon Jul 04 2011, 07:43PM

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

New transformer done! It's 220 turns of 24ga wire on the secondary, with a 16ga 4+4 turn primary, insulated with only the best masking tape I could find.

There was a huge improvement in charging power: half wave rectified it charges the 24800uF 700V bank from 0 to 160 in 5 seconds. If anyone would like to figure out what the power is be my guest, but there will probably be more juice when I full wave rectify it. Hopefully my diodes will get here tomorrow...

Kludge, I PM'd you those drawings.

vk2fro

Wed Jul 06 2011, 07:59PM

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

Chatting to Grenadier on IRC, he had a spectacular failure of his diodes. This caused the bank to dump all its energy into his lovely new transformer, blowing the core apart!

Second try with a 30A ultrafast diode and a superglued back together ferrite core ended up with similar results.

Hes back to using his original old transformer, but has to gap it 1/4" in order to stop parasitic oscillations...

Forty

Wed Jul 06 2011, 11:13PM

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

i get my drugs at wegman's too.
for banks that big i thought people just used variacs with MOTs. or you could rewind a mot. i mean, for a bank that's obviously not too portable, you might as well have a big-ass charger too. (added the dash so no one asks me what an ass charger is)

Adam Munich

Thu Jul 07 2011, 02:17AM

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

I don't own a large variac. I decided to order some cores those 35v/turn cores from TSC, and the pair should be here by the end of the month. Since they can handle 35v/turn I'm hoping to use a 1 or 2 turn primary, and that will give me a low impedance so I can push many amps through at 12V. Since low voltage fets can handle high currents and have low RDSon heating shouldn't be a big issue. My bigass AGM batteries store 3.2MJ each, so they could charge that bank quite a few times; it's just a matter of charging it very fast...

Put it on wheelse and the entire thing would be portable. Kludgesmith is going to make me the copper parts for the contactor, and if I run my pneumatics at 100psi then I should be able to slam that contactor wedge in with 60lbs of force, and pull it out with the same amount.

Sulaiman

Thu Jul 07 2011, 08:26AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141

Just thought I'd mention a few points;

At 50% efficiency 1.2 kJ requires 2.4 kW for 1 sec. 240W for 10 sec. etc.
with a 12V battery 2.4 kW = 200A average, 240W = 20A average etc.

If possible use your batteries in series
e.g. 4x 12V = 48V which would mean 16x less I2.R heating in wires, transistor Rdson etc. and more primary turns of smaller diameter.

With such large energy discharges do you need a fast charger?
I'd expect quite some time between discharges to reset/repair the load/victim.

Consider thick co-ax cable (e.g. RG8) from your switch to the load,
or tightly twisted wires;
individual spaced wires will loose the low impedance that you've spent money on (good caps and bus bars) and jump around with each discharge.

And of course ear and eye protection are a must.

Adam Munich

Thu Jul 07 2011, 11:27PM

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

That's it; to hell with mosfets. They keep exploding and I'm sick of trying to fix the circuit.

Since my friends apparently want to notify me of anything fun this summer, I'm going to spend this night in the hot tub with a few beers and pile a thousand turns of 24ga wire on this broken 500VA x-ray transformer. That should be indestructible, and if I want to run it off of a 12V battery I'll use one of those 12>120V inverters. Not the best solution, but I'll be damned if it doesn't work.

Nah

Thu Jul 07 2011, 11:55PM

Registered Member #3567 Joined: Mon Jan 03 2011, 10:49PM
Location: USA, 1960s
Posts: 260

I'm just saying...

$50 at a hamfest or less can buy you a 20 amp varaic....

Adam Munich

Fri Jul 08 2011, 03:50AM

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

No hamfests where I reside. Or surplus stores, or parts stores, or kids that are smarter/have better things to say than "that's what she said"

I gave up on the trnasformer after I realized that it gave .5V per turn. Looking upon my MOT i realized though; I can tap into those coils! Well turns out I couldn't since the chinese made the tramnsformer with unsolderable aluminum wire. So I came up with this:

(a pin stuck into the windings). Gives me 508 volts AC, so rectified I'll get 715V; perfect for charging the bank. I wish the transformer had copper windings though :-/

Nah

Fri Jul 08 2011, 05:20PM

Registered Member #3567 Joined: Mon Jan 03 2011, 10:49PM
Location: USA, 1960s
Posts: 260

Adam, can you help me figure out how to create a trigger?

I'm doing a EMP based project using 2 kjoules, and I don't know how to set it off.

I was thinking of using a trigger transformer and a xeon flash tube....

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