Author Topic: Completed my pulsed power generator  (Read 1302 times)

Offline MRMILSTAR

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Completed my pulsed power generator
« on: July 11, 2019, 05:43:31 AM »
After 6 months of low-level effort I have finally finished my pulsed power generator (coin shrinker, can crusher, disk launcher). I tested it today and it worked perfectly the first time. Currently I am only using it as a coin shrinker. Here are some pictures. The shrunken quarter is a 6000 joule shot according to the voltmeter.

The pink lines are just 10 foot nylon strings (lanyards) used to trigger the following events:

1. Charge capacitor (charging circuit is disconnected from capacitor by pulling this lanyard)
2. Fire (closes the HV spark gap when this lanyard is pulled)
3. Discharge capacitor (dumps capacitor output into 35K ohm power resistors when this lanyard is pulled)

I do not use any electrical parts to trigger events because I don't trust them at these power levels. I use simple mechanical devices which are triggered by the 3 nylon lanyards. I use large Simpson analog microammeters as voltmeters because they do not require external power and are more readable than digital displays from a distance of 10 feet.

The power supply consists of a 15KV, 60 ma neon sign transformer. Rectification is performed by a full wave bridge rectifier consisting of 8 HV diodes (2 diodes per leg).

My HV firing switch was inspired by Bert Hickman's spark gap switch used in his coin shrinker. I can get the brass electrodes to as close as 0.5 mm spacing with excellent parallelism for low voltage firing if needed (future can crusher and disk launcher). It is a simple spring-loaded design which I can cock and then release via a lanyard.

The containment cage is made of steel plates, G10 plates, and HDPE plates. The top, bottom, and two sides are made of 3/8 inch steel. The other 2 sides are made of a sandwich of 3/8 inch G10 and 3/8 inch HDPE. The HDPE facing is intended to be sacrificial and can be easily replaced if it gets too beat up by copper shrapnel. The lid is held in place by 2 inserted stainless steel rods. The volume of the containment box is 0.67 cubic feet.

The mouse trap switch seen in the pictures is the capacitor bleed switch. The discharge resistor bank consists of seven 5K ohm power resistors in series, each of which is rated for 200 watts. The total resistance is 35K ohms.

The capacitor is an Aerovox Aerostor unit with the following specifications:

1. Maximum voltage = 22 KV
2. Capacitance = 100 uF
3. Maximum voltage reversal = 20%
4. Maximum energy = 24 KJ

The maximum voltage that I intend to use is 15 KV so as to not over-stress the capacitor. This corresponds to 11.25 KJ.
« Last Edit: February 22, 2020, 10:44:44 PM by MRMILSTAR »
Steve White
Cedar Rapids, Iowa
Retired electrical engineer

Offline Mads Barnkob

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Re: Completed my pulsed power generator
« Reply #1 on: July 11, 2019, 02:58:13 PM »
Very nice machine you have put together here!

Do you have any links to Bert Hickmanns design for the spark gap?

What is the black cable with a clamp lying on the ground for? Grounded negative rail of the capacitor?

The Discharge voltage meter, is that to get an indication of the voltage reversal? I seem to recall that a way to avoid this is using a thin enough wire for the work coil that it goes open loop before voltage reversal happens.

I only ever tried firing 4 kJ indoor and that was scary, 6kJ is in the same ball park, but at 10+ kJ even the mechanical stiffness of your current path wants to rip itself apart and what is it with that white piece of plastic pipe on the laminated copper bars?

Got any video of it firing?

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Offline MRMILSTAR

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Re: Completed my pulsed power generator
« Reply #2 on: July 11, 2019, 05:48:27 PM »
Here is a link to Bert Hickman's quarter shrinker. I only had pictures of his spark gap to go by. I have also been communicating with him via E-Mail.

http://www.capturedlightning.com/frames/shrinkergallery.html

I have attached a picture of Bert Hickman's spark gap switch and mine. Bert's is electrically actuated while mine is mechanically actuated. You can compare them.

The heavy black cable is the ground (earth) wire. I attach it to a ground rod during operation. It is connected to one terminal (negative) of the capacitor and the case.

The discharge meter is dual polarity to allow for the possibility of the capacitor being left in either polarity after voltage reversal. The charging meter is only connected during charging. Prior to firing, the charging  circuit is disconnected to avoid damaging it. The discharge meter is only connected when the excess capacitor voltage is to be bled off after firing.

The white piece of plastic is just a flash-over precaution because that conductor dips close to the discharge mouse-trap switch. Its just an odd piece of PVC pipe that I had lying around. I may remove it because I don't like the way that it looks. The heavy conductors (laminated copper bars) are oddly shaped because they are salvaged items from a huge 500 KVA distribution transformer. I used them as-is because the fit was close enough and the price was right (free).

The maximum voltage that I intend to use is 15 KV which corresponds to 11.25 KJ. I don't want to run it any higher so as to not over-stress the capacitor with excessive voltage reversals.

The noise isn't that bad because my containment box is very tight. Its not quite as loud as a pistol. I wouldn't operate it indoors. Outdoors only.
I need to make a video. When I do I will post it.
« Last Edit: March 04, 2020, 10:02:43 PM by MRMILSTAR »
Steve White
Cedar Rapids, Iowa
Retired electrical engineer

High Voltage Forum

Re: Completed my pulsed power generator
« Reply #2 on: July 11, 2019, 05:48:27 PM »

 


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