Christmas Comes Early!

This forum is for specialized infomation important to the construction and safe operation of the high voltage electrical supplies and related circuitry needed for fusor operation.
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Garrett Young
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Re: Christmas Comes Early!

Post by Garrett Young » Wed Jun 14, 2017 9:40 pm

Actually, the V/mA feedback from the multiplier must be different between the 200W and 350W version.

Either R23 or R24 needs to be changed as well to adjust the gain of the opamp (currently a gain of 2, this would need to be reduced in order to increase output current).
- Garrett

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Garrett Young
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Re: Christmas Comes Early!

Post by Garrett Young » Thu Jun 15, 2017 3:12 am

Please ignore all my previous posts regarding modification.

Here is my tested to 504W (42kV @ 12mA, 1M++ n/sec) configuration:

1. JP2 Moved to Jumper Pins 2 and 3 on the enable header (this will enable the supply by default - Note: besides the additional danger this modification requires the input EMI filter to be spaced away from the housing several millimeters to accommodate the jumper in the 2-3 position)

2. R23 changed to 294kohm 1/4W 1% which decreases the current feedback op amp gain from 2 to 2/3 and increases the regulated current from 4mA to 12mA.

3. Removed CR11 (added for the X2947 version) which I believe provided OL (over load) protection.

4. Changed C39 to 0.022u/100V (i.e. KEMET R82EC2220DQ50J) and R50 to 4.7k 5% 1/4W (these are part of the current error integrator circuit and are the slower response values for the 350W version. Generally, additional tuning of the feedback and compensation loop is probably required since the supply is operating at a power greater than 350W. Some audible noise/instability can be heard and it passes through the transition from constant voltage to current. Ultimately, once in constant current mode it seemed stable.)

5. Changed the input fuse to 6A (was 4A).

6. Refer to Spellman's PTV model documentation for the 9-Pin control/monitor header. I used the reference voltage from pin 1 to set the current to the max (pin 2) and bias a 50kohm potentiometer to control the voltage (pin 4).

--Warning---
These changes are my own and not recommended. Power supply failure is very possible. A fan will only cool the un-potted components and this will place stress on the multiplier diodes. Proceed at your own risk.
- Garrett

ian_krase
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Re: Christmas Comes Early!

Post by ian_krase » Thu Jun 15, 2017 4:56 am

Huh. Nice job.

Do you have a suggestion as to what to do for just the 330W mod? Go by the schematic?

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Garrett Young
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Re: Christmas Comes Early!

Post by Garrett Young » Fri Jun 16, 2017 3:20 am

Another note:

7. Remove several turns (3-4) from the inductor (L1) in series with the primary of the high voltage ferrite transformer (T2). This will allow higher peak current through the primary. (Careful removing too many turns will cause problems).

Previous warning still applies.

For 350W operation - my suggestion is to follow the schematic but either R23 or R24 needs to be changed as well in order to adjust the gain of the opamp (currently a gain of 2, this would need to be reduced in order to increase output current). The fact that the table at the end of the schematic doesn't indicate this is slightly concerning and either the current feedback (V/mA) is different between 200 and 350W models or I'm missing something.
- Garrett

ian_krase
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Re: Christmas Comes Early!

Post by ian_krase » Fri Jun 16, 2017 8:59 am

I got mine today but wasn't able to get it operating. (Also, I don't yet have ballast parts or a working vacuum chamber to test it with, just a high voltage probe...)

The interior looks fairly different from that thread about the 40kv unit.

Am I correct that just leaving pin 7 of the connector floating should turn the unit on?

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Garrett Young
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Re: Christmas Comes Early!

Post by Garrett Young » Fri Jun 16, 2017 1:33 pm

This version requires a jumper change to be enabled by default (see note 1 from my previous post)
- Garrett

ian_krase
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Re: Christmas Comes Early!

Post by ian_krase » Fri Jun 16, 2017 7:20 pm

And without that it won't turn on at all?

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Garrett Young
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Re: Christmas Comes Early!

Post by Garrett Young » Fri Jun 16, 2017 7:47 pm

I assume by driving JB3-7 high or low will enable it as well (but moving the jumper is easy) ... take a look at the schematic
- Garrett

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Garrett Young
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Re: Christmas Comes Early!

Post by Garrett Young » Sat Jun 17, 2017 1:44 am

I've now optimized the control loop components and the supply operates smoothly at 600W. I'm still operating at a low duty cycle, but it's very usable for fusion.

If anyone is interested I could purchase supplies and modify and test them to 350 - 600W (depending on what you want) for $250 including the cost of the supply. I'll make all the necessary component changes (including an upgrade of a couple of key parts in the half bridge), tune the supply's control and power stages, add a fan, and test to the desired wattage. Message me if you are interested.
- Garrett

ian_krase
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Re: Christmas Comes Early!

Post by ian_krase » Sat Jun 17, 2017 3:47 am

i managed to get it working.

Unfortunately I think something is wrong with either the voltage feedback or my cable. At about 2/3rds of the voltage dial I start getting corona type noise.

Also I think it is interlocked to the cablebeing plugged in.

Does your voltage output work? What are you using for the cable? I have rg-213u.


(please excuse my typing, I am out of desk space.)

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