Fusor Forums

The over voltage light should come on at the end of the test when voltage set is set to 0V and the output voltage is still decaying(due to it's RC time constant, and no load resistor). This is normal operation if the over voltage light only comes on at the end. Before that the output voltage should be tracking the set voltage on the graph.

Does it make a graph?

A single blank graph with no plot briefly appears. Then two blank graphs appear together. The graphs all disappear and an error message is displayed. "Vectors must be the same length. Error in => Spellman_DXM_control.m at line 137"

I ran the functioning power supply with my fusor today and had some problems. I could turn the voltage up to 27kV, but plasma would not establish at any voltage around 15mtorr. Turning the voltage above 27kV got plasma to establish for a fraction of a second, but the over current light came on immediately and switched off the power. I use a 10-turn potentiometer to control the voltage and have the current set point at the max, but the over current light comes on regardless of how finely I turn the knob. Does anyone have any suggestions? I use a 6-way 2.75 conflat chamber, so Paschen's Law gives different values for my smaller chamber than the standard 6" chamber, but I've heard that other people with smaller chambers have had few problems in establishing plasma.

What value is your series limiting resistor in the HV feed???

It's a 60k resistor, and operating it with vs. without the resistor seems to have very little effect.

It's a 60k resistor, and operating it with vs. without the resistor seems to have very little effect.

OK 60K ballast resisator is a bit on the low side
When your plasma establishes it is better than a dead short so 27kV and 60K ohms means that the plasma is trying to take 0.45amps from your supply

i think that you will find that you will need to increase that resistor to keep from tripping the Spellman internals

try doubling it first if you can 120K
if it still does it double it again 250K
also make sure to limit capacitance from your Ballast resistor to fusor ie no coax (33pf /ft)

This is what I harped on in the limiting value of only 8.56ma on this supply in a posting above in this thread. 60k ohms is fine for a linear supply that has some beef in it. Raising the resistor value might do it, but the working dissapation will go up. The voltage drop would be not important, of course at most any value of ballast, but the dissapation would be.

Lets go figure........ assume you will need virtually all of that 8ma in a running fusor situation. Let's talk 7ma for starters on a working fusor. This will run continuously through, let us say, a 150k ballast.

7ma x 150k = 1050 volts across the resistor...No big deal voltage wise. .007 X1050 = 7-10 watts a good safety margin would demand a 25 watt resistor (would just get warm)
a 300k resistor would double that to about 50 watts. Such resistors are still sold. Just be aware that even at 7ma a large working ballast will dissapate.

This is the terror of a fast safety current trip on a modern switcher that is kissing the current limit for fusor operation to start with. This problem is probably just and operational one. Where there is a will there is a way. If I owned one of these supplies I would shunt the current sense resistor with a chunk of 12 gauge wire and be done with it! You would then become the slower acting human meat-engine trip circuit if something goes horribly wrong at the fusor load end. I have no idea how inherently weak or easily damaged the HV electronics would be to a 1 second half amp gas arc short.

Richard Hull

My supply is now fixed and up and running.
I had to replace:

RV2 - CL70 NTC Thermistor, burned
C149 - 33uf capacitor - visual leak
CR34 - MUR460 diode, shorted
Q10 - Mosfet, shorted, replaced with IPW65R110CFDA
Fuses- Two new 10A since I run it on 220V

I don't have a high voltage divider yet and can't verify it's output, but I can get it to fizzle of corona and arc if I turn it up too high.

I was not able to get HV out of mine even when applying manual control. I disassembled and closely inspected the board again. My board was pretty clean with no apparent over heating or other visible abnormalities except the top of C149 was slightly bulged so I replaced it. I wish I had a video of the power up. The fan and lights started normally but about two seconds later there was a loud pop and a smokey mist poured out of the vent slots. The new C149 had failed. There is no other damage. Any ideas?

Sounds like polarity was reversed, according to my limited experience.

Definitely sounds like installed in reverse. Trolyics don't like that.

Richard Hull

You guys were right. That was reckless. Fortunately I ordered several new caps. I installed a new cap and dialed a low current demand and slowly ramped up a voltage demand of 1 volt or ten percent output. The pin out for voltage out followed along nicely. My next order of business is to build a proper control box, but for now I consider my power supply in working order.

I'm glad you got it up and running.

Richard Hull

I finally gave up trying to make my DXM work and returned it. Although I was not happy that the vendor had listed these as working on eBay, Jon at NTC has been very cooperative. He even sent me another unit (marked "scrap") for spare parts to try to get one working. On my first unit, I was able to communicate via the web interface and could control the voltage up to 1400 volts. For any higher setting it failed. The spare parts unit had a blown fuse, which suggested problems on the PC board, so I tried the high voltage potted section with the PC from my original unit. I got the same results. I'm inclined to believe that both units have a failure in the potted HV section. Cliff had indicated that the ceramic capacitors in the potted section tended to fail when the units were operated in excessive ambient temperature. Although I have no way to know if the PC in my original unit was fully functional, I was definitely able to communicate with it. So if anyone is interested in a board that does communicate, the serial number on the communicating unit is 100785082-A00323. My guess is that Jon would be very amenable to an offer, since it is likely destined to be labeled "scrap" also.

I suspect the failure mode of my non working unit went something like this.

1. High ripple current causes C149 to overheat, rupture, vent electrolyte, finally shorting internally becoming a resistor
2. Diode CR34 feeds C149 and with the fault current overheats and also becomes a resistor
3. The internal 24VDC supply that runs the DSP and other low voltage circuitry starts to drop
4. R218 a 0.05ohm 5W current sensing resistor overheats and cracks in half
5. The 24VDC supply collapses and K3 relay contacts open inserting inrush current limiter RV2 in series with the rectified 120VAC mains. This temporarily reduces the fault current
6. The fault current finally exceeds RV2 max continuous current. It heats up and cracks in half partially melting adjacent relay K3
7. The input full wave rectifier CR35 survives the fault current and the fuse finally opens
8. FET Q10 is destroyed (three leads get shorted together) while parallel component Q6 survives. An interesting failure transient. (FYI at lower output energy the DXM is fully operational on just Q6)

The two units I have are not identical. My older unit that arrived working was manufactured 23rd week 2013 and has a factory mod, see pic. My newer not working unit was manufactured 5th week 2014 and does not have the mod. The factory mod (and current design) puts a small restive load on C160 which reduces the ripple voltage/current on C149 (the issue is two separate 400VDC rails share one switching regulator). The two extra diodes in the picture are a belt suspenders plus rope kind of thing. Without the factory mod the ripple was about 100V every 0.75 seconds. BTW you need a 120V line isolation transformer if you want to connect an oscilloscope and probe the power factor correction circuitry looking for problems.

Not having the parts for the factory mod I put a 1N4007 from C160 to C149. My mod seems to work fine and reduces the ripple to 0.5V at 120Hz when the HV output is off and disappears with any HV output energy. To be honest I prefer my mod but I will continue to keep an eye on it because “Only the paranoid survive”.

I replaced C149 with a higher ripple current capacitor (on both my supplies) that has over twice the original capacitor rating, Digikey 450BXW100MEFR18X35, it is physically taller and a tight fit for the available space. Electrical tape above the capacitor on the lid inside reduces any shorting possibility if the capacitor top should ever bulge. I also replaced 4 questionably functioning parts K3 and CR35 and Q6 plus its driver IC in addition to the obviously failed parts. The total repair cost is about $40.

The two internal fuses will be replaced with one slow blow 5A and one fast blow 6 or 7A (lower values provide better component protection).

Lastly the service guy with not great eyesight (me) caused the problem in pic 3 requiring a scope to locate. The fix was simple just shove the wires into the connector…Doh Have fun
-Peter

Andrew,

Are you willing to make and sell a C11 replacement connector to single conductor? I contacted claymount and they want $190 for p/n 12096 (recommended by spellman)

That sounds way too expensive, can you send me the cad file of the cable they were quoting?

I don't have time right now to manufacture more connectors, though here is some ordering information

Ask for a quote on:
PN 14896, a 2m cable version should be $69.21
PN 10008 ring nut w/ r16 cutout should be $10 ea

I have ordered parts from claymount, it's generally straightforward to order with a credit card, they will want you to submit a purchase order to them, I have attached a template I used, It probably helps to have a fedex account number to give them to simplify shipping.

Andrew,

They quoted $160 each and a 40 day lead time. (Also "Please note that the 14896 does already include 1 of the 10008 ring nuts in the hardware kit that accompanies the cable assembly. ") I've asked them to match the $70 price.

Garrett,

that does sound weird, there was some variation between quotes on certain parts (one quote to me was $10ea for the ring nut, the other was $4) so they don't seem to have fixed prices, but such a large jump in price sounds unusual.

Andrew

I am waiting for a quote from Claymount for both the part numbers you mentioned.

The web page product inquiry email address for North America is:
Philippines.Claymount.CS@vareximaging.com

Do you have a different contact address?

-Peter

My sale's contact was:
Karen Albright
email: Karen.Albright <at> varian.com

If you were being quoted through a different division, particularly an international one, they might quote a different price.
The 40 days lead time on the cable sounds correct, they quoted the same lead time to me.

Thanks. Just sent an email with fingers crossed.
-Peter

Andrew,

The price you were quoted was given as a "one-time, educational institution courtesy".

What contacts are you using in your replacement connector?

I bought two of these units from the same eBay seller [ntc_tech]. The main difference was the fact they were listed as [For parts or not working] and it was true; both broken as expected..

I have both up and running and bench tested to 5k volts. I have been unable to get a response on the HV cable so I can't test them at full throttle.

Thanks to Cliff S. and his generous contribution in time and sharing partial schematics the repairs went like this.

Unit Serial Number 411: (showing 13.8 hrs)
Replaced Q11 and Q8 [IXFH26N50] Symptoms: showing shorts on all 3 pins.
Replaced Q10 [65F6110] Symptoms: showing shorts on all 3 pins.
Replaced C149 (working and tested OK, but slight bulldog in top, you know how sensitive CAPs are to heat and they will fail eventually)

Unit Serial Number 341:
Replaced Q6 and Q10 [IXFH26N50] Symptoms: showing shorts on all 3 pins.
Replaced C160 and C161 (preventative maintenance, they tested fine)

Time:
Learning schematics and finding physical PCB part locations: 1 hour
Tracking down faulty components with Fluke meter: 1hr on first unit, 30minutes on second due to learning the layout.
Desoldering and verifying parts were defective: 30minutes (20 of which was switching to leaded solder so i could actually get them desoldered)
Ordering components: 30min all Mouser
Replacing faulty components: 30min.
=========
Total: 3 hrs for 2 units, or 1.5hrs / unit.

Cost ~$57 for two units. I actually used one MOSFET from unit 341 in 411 that I switched out both so they would match, but then found the same component bad in the other unit that I missed at initial debug. Thus I had one extra part, and needed it.

Shopping List:
C160 and C161
Mouser #: 5985-450V150
Mfr. #: 381LX151M450K022
Desc.: Aluminum Electrolytic Capacitors - Snap In Aluminum Electrolytic Capacitors - Snap In 450V 150uF 30X30
2 $3.80 $7.60

C149
Mouser #: 667-EEU-EE2W560
Mfr. #: EEU-EE2W560
Desc.: Aluminum Electrolytic Capacitors - Leaded Aluminum Electrolytic Capacitors - Leaded 56uF 450volts AEC-Q200
2 $3.26 $6.52

QQ8 and Q11
Mouser #: 747-IXFH26N50P
Mfr. #: IXFH26N50P
Desc.: MOSFET MOSFET HiPERFET Id26 BVdass500
2 $5.91 $11.82

OEM Fuses - Ceramic + extras
Mouser #: 576-0314015.HXP
Mfr. #: 0314015.HXP
Desc.: Cartridge Fuses Cartridge Fuses 250V 15A Fast Acting
10 $0.744 $7.44

Q6 and Q10
Mouser #: 726-IPW65R110CFDA
Mfr. #: IPW65R110CFDA
Desc.: MOSFET MOSFET N-Ch 650V 31.2A TO247-3
2 $8.22 $16.44