Comments on: Coil Power Supply

By: SCR Test Fire « Prometheus Fusion Perfection

SCR Test Fire « Prometheus Fusion Perfection — Sun, 18 Apr 2010 05:15:32 +0000

[...] Test Fire 18 04 2010 I successfully fired the coil power supply’s SCR today. Here’s how: I started by grounding the [...]

By: A Day in the Lab « Prometheus Fusion Perfection

A Day in the Lab « Prometheus Fusion Perfection — Sun, 11 Apr 2010 04:12:46 +0000

[...] I rearranged the equipment rack to make room for the coil power supply: [...]

By: Raymond Rogers

Raymond Rogers — Sun, 04 Apr 2010 15:55:05 +0000

“SCR (844-VSKH91/14P). Not sure how to wire this up.”
In case your not joking I downloaded the data sheet; the trigger coil goes between the small pins 4&5. To state the obvious make sure the SCR is mounted on metal with thermal grease or a phase change pad. Make sure the metal heat sink is large. If you sure it’s safe (measure) fire off a couple of realistic shots and check the temperature of the heat sink close to the SCR. I can’t make any more reasonable suggestions without knowing the load characteristics and PRR. Knowing that one can go backwards to the junction temperature. Since they cost a little money you should probably follow the recommendations for mounting torque and checking same on page 3 of the data sheet.

Ray

By: Coil Power Supply « Prometheus Fusion Perfection

Coil Power Supply « Prometheus Fusion Perfection — Sun, 28 Mar 2010 14:03:41 +0000

[...] Power Supply Made some progress on the coil power supply. Soldered an extension cord onto the 600V step up [...]

By: New Arrivals « Prometheus Fusion Perfection

New Arrivals « Prometheus Fusion Perfection — Sat, 27 Mar 2010 23:55:54 +0000

[...] Parts for the coil power supply: [...]

By: Capacitors « Prometheus Fusion Perfection

Capacitors « Prometheus Fusion Perfection — Wed, 17 Mar 2010 20:33:07 +0000

[...] We received 2 of the 10 capacitors for the power supply. I got these cheap on ebay. They were bigger than I [...]

By: M. Simon

M. Simon — Mon, 01 Mar 2010 03:30:15 +0000

Let me reiterate. You need a resistor in series with the relay to limit the current through the relay. The current should be limited to the maximum relay current for rated relay life. If you want to get longer life – nearer the mechanical limit vs contact limit – limit the current to 1/10th the contact rating. The current should be calculated from peak voltage. Although for this application such exactitude is probably not required.

Good on ya for adding the reverse diode. Them SCRs can be expensive. And I must add that I was not thinking clearly. A reverse diode across the coils (with a series resistor to absorb the energy) is also a very good idea. Send me an e-mail and we can discuss values etc.

BTW – nice transformer. It is probably vastly overrated for the application.

Safety: Consider a small (8 or 25A) SCR in Parallel with the capacitors to discharge them. A resistor in series with the SCR to absorb the energy is good. A 20 to 50 ohm wire wound rated at 25 watts (10 watts might do) should be adequate. If you want to get fancy calculate the RC time such that the voltage across the capacitance is reduced to less than 10 volts in 1/10th second. i.e. an RC time constant of 1/100th of a second will work.

By: M. Simon

M. Simon — Wed, 17 Feb 2010 22:46:38 +0000

You need a reverse diode across the SCR. High speed, high current. Probably rated at 600V if you are going up to 450.

You need to build a voltage divider across the coil to watch the transients. A .002 ohm in series with the ground should do nicely for current. Get one of those flat metal jobs rated 2 W or 3 W. You don’t deed the power but it will help with large pulses.

And ramp your variac voltage up slowly. Energy storage goes up as the square of the voltage.

You can replace the relay with a large value resistor of suitable power. The reverse “kick” from the coil will probably turn off your SCR. Two diodes in series would probably guarantee turn off.

And if you are going to use a relay put the capacitor bank next to the diode bridge so the relay is not carrying high current when it closes. And add a little series resistance (50 to 100 ohms of suitable power). To limit the inrush current when you charge the capacitors.

OTOH 5K resistor in series with the bridge might be better from the standpoint of keeping the pulse leads short.

I also have a post up at Power and Control. And soon at CV.

By: Raymond Rogers

Raymond Rogers — Tue, 16 Feb 2010 00:22:54 +0000

Sorry, flows but is tougher than most plastics.

By: Raymond Rogers

Raymond Rogers — Tue, 16 Feb 2010 00:22:06 +0000

If you use a lot of metal be carefull with the higher voltages. Teflon insulation and pads are fairly highly rated,flexible, and common. It’s been ages since I did work over 220 but…
Here is a list:http://www.allaboutcircuits.com/vol_1/chpt_12/8.html

Material* Dielectric strength (kV/inch)
===========================================
Vacuum ——————- 20
Air ———————- 20 to 75
Porcelain —————- 40 to 200
Paraffin Wax ————- 200 to 300
Transformer Oil ———- 400
Bakelite —————– 300 to 550
Rubber ——————- 450 to 700
Shellac —————— 900
Paper ——————– 1250
Teflon ——————- 1500
Glass ——————– 2000 to 3000
Mica ——————— 5000

I am sure all figures are for dry clean materials. I would use Teflon myself for insulation and barriers; but realize it “flows” if consistent pressure is applied. That is tightly wrapped around edges/corners.

Ray