Help with Glassman 40kV, 15mA psu

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Matt_Gibson
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Re: Help with Glassman 40kV, 15mA psu

Post by Matt_Gibson »

Hi John,

I just got done testing the diodes via voltage drop in forward/reverse mode. Didn’t measure current, is that critical? There were 6 that measured 20v in the forward direction and one that had a small burn spot underneath, but read around 14v like the rest. Would you be suspect of these higher forward voltage drop diodes, or leave them be?

As for any bad capacitors, they all measured 2nF or 4nF if paralleled up. Any other way to test?

Before I button it all back up, would there be anything to gain by applying a low AC voltage to the input and probing around with a DMM?

I feel like I’m running out of gas :-(
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Re: Help with Glassman 40kV, 15mA psu

Post by Matt_Gibson »

Looking at the data sheet for the 2CL2FM (Chinese diodes that are essentially the only option out there), these are rated for 20kV, 100mA, and 100nS. They have a max forward voltage of 35v, so it seems that 20v on the 6 outlier diodes may be okay?

If this is the case, and my two shorted diodes were the only diodes that failed, then there must be a capacitor that tests okay (capacitance that is) that is fouling things up? Or, could there be a problem with the board itself? Maybe it’s conducting somewhere?

My last suspicions with the multiplier board is that I upset things by completely removing those two chokes and the two failed spark gaps?

I almost feel like just rebuilding the entire board using those Chinese (ugh) diodes and some new capacitors…It would be $$$ but far less than a new (used) one.

-Matt
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Finn Hammer
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Re: Help with Glassman 40kV, 15mA psu

Post by Finn Hammer »

Matt,

Nothing to (ugh) about. I use the 30kV variety of those same diodes, and they perform flawlessly. Just don't go beyond 50kHz, or they will overheat.
There is a lot of badmouthing, regarding chinese products, but the truth is, even brand name products come off chinese production lines. The lead glass, the quarts glas, the bell jar, the capacitors, the diodes, the pcb, all in my fusion endevour, comes from China. Even my old Tektronix scope had Made in china labelled on it. Just use your sense when buying.

Cheers, Finn Hammer
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Re: Help with Glassman 40kV, 15mA psu

Post by Matt_Gibson »

Hi Finn,

Looking over the PSU PWM chip data sheet, and the r/c values chosen for the PSU, it looks like it runs right at 50kHz, so I may be stressing them a bit. I might need to tune it down some.

-Matt
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Richard Hull
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Re: Help with Glassman 40kV, 15mA psu

Post by Richard Hull »

Assuming some forethought on the part of Glassman in designing the multiplier and the caps used therein, tuning the frequency down could affect the ultimate HV level and the ripple factor. You might not blow anything up but tread carefully.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Matt_Gibson
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Re: Help with Glassman 40kV, 15mA psu

Post by Matt_Gibson »

Yup, I thought of that…I might just risk it seeing as I can’t go for more than 10-15min per run.

This is assuming that I can even get this thing back up to its former glory.
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Richard Hull
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Re: Help with Glassman 40kV, 15mA psu

Post by Richard Hull »

I have said this before. Manufactured supplies, (Spellman, Glassman, etc.), when run to or near their full stated limits, voltage and current wise, with our particular, rare and unusual gas load, are at peril. Our gas load can oscillate at HF frequencies and or bump during operation in a manner that the manufacturers design team might not figure on and why should they. Their mission is to design a ripple free, pure DC supply capable of suppling a resistive load which might have a few rare spikes in it. This is why they have current limit cutoffs in protection circuits in many such supplies. Their output voltage has no real energy backup due to the multiplier capacitive limitations and the high impedance of the original, smallish HF feed transformer. These supplies, due to their work-around over the old 80lb iron core, low frequency transformers of old, are necessarily electronically complex and running their components to a calculated level right at the edge of their engineering capacity with some acceptable margin for safety and longevity.

I am not saying they are weak or relatively worthless, but most of them are found to be pushed right up to their limit with non-designed for loads by those using them here at fusor.net. Now, if you buy or obtain a Glassman 60kv supply that is rated for 50ma, that is another matter. 50kv at 20ma into a fusor would not peck at the lobes of its extreme limit. It is operated well within its design parameters.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Matt_Gibson
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Re: Help with Glassman 40kV, 15mA psu

Post by Matt_Gibson »

I hear you, Richard. Unfortunately, outside of building something, it’s my only option. There aren’t any suitable transformers anywhere anymore. I may wind up having to just replace diodes and capacitors with higher rated components as they fail…
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Richard Hull
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Re: Help with Glassman 40kV, 15mA psu

Post by Richard Hull »

It is rather sad that the fusor's power requirements to do good fusion strain at the limits of modern technology and more importantly at the purse strings of those who would do amateur fusion to a largely successful degree. This for those who are not well funded or well versed in high voltage, high power systems, is a big issue. Those who persist are the real winners here.

I would focus on the diodes. Ceramic capacitors do not like HF filtering at real power levels. We learned this the hard way in tesla coiling at oscillation energies of 400 watts and above. The silver plating on the ceramic knob body sides gets blown away internally. The capacitance drops and often the main contact to the coating is often blown clear of the flat contact and internal arcing occurs at a level not easily detected. In a string of capacitors this starts a down hill run and stress on the rest. Ceramics are best used for filtering at lower frequencies to DC. If rather large oscillatory power is expected at high voltages, polypropylene is preferred, but commands large volumes at required high voltages per unit capacitance. Paper is also good with some loss. Mylar is very high loss at HF and high power.

Good luck

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Help with Glassman 40kV, 15mA psu

Post by John Futter »

Check with a resistive load
does it provide full current??
if not
Suspect caps
these have to be tested at elevated voltage close to their max rating

As I said previously the diodes should work with 3 or more pp9s in series with suitable resistor to get say 50mA
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Re: Help with Glassman 40kV, 15mA psu

Post by Matt_Gibson »

I don’t have a resistive load that can handle 500w…I probably need to cobble one together if I’m going to get the other psu running though…

I played around with things a bit more. Still can’t get beyond 4mA with the voltage set to -40kV. I decided to check voltage, before the ballast, with my 40kV probe, while running at max. I’m seeing -35kV. It would seem that an entire stage has been omitted (-40kV, 8 stages, -5kV per stage)?

At this point, it’s not really a matter of finances (I can’t be going to Glassman for brand new though), but a matter of finding stuff.

Even in this crippled mode, Im hitting 8mR/hr on my Ludlum, so maybe I can activate silver and then fully shift gears towards getting my other psu online.

Edit: Some progress!

I decided to throw caution to the wind and played with the voltage and current follower trimpots. The voltage follower let me adjust the voltage such that the meter showed what my 40kV probe was showing. The current follower let me bump up the current to 5mA before it cut out. I then adjusted pressure until I was seeing 39kV on both meter and 40kV probe. At this point, I’m hitting 16.5mR/hr (up from 8mR/hr) on my Ludlum!

I ran out of gas before I could try out my watt meter to see if I was in the neighborhood of 500w.
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Re: Help with Glassman 40kV, 15mA psu

Post by Matt_Gibson »

I’m noticing (been noticing from long ago actually) that the mA meter will swing in the negative direction before the plasma strikes as I increase voltage…

What is causing this and is it a clue as to what could be plaguing this current trip issue?
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Richard Hull
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Re: Help with Glassman 40kV, 15mA psu

Post by Richard Hull »

Plasma strike is a killer! A rough time for any supply. Only the big boys need apply. This is the sole reason for a ballast resistor! The strike! Realistically with an infinitely low power supply impedance, thousands of amps would be fed to the strike. The ballast will temper this. Weak supplies will just buckle to some lower voltage at their max current. We rely on backing off the voltage or gas to end this brief excursion to gain control of the system.

As for why your current meter goes negative, I have not a clue, unless it is some reverse current just before strike sensed by the current circuit electronics in the supply. I do not see this in my brawny system.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Rex Allers
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Re: Help with Glassman 40kV, 15mA psu

Post by Rex Allers »

Issues with components in the multiplier certainly could cause you the problems you are seeing. Worth trying to rule it out.

If I remember right, your low current issue at max voltage began after you did some adjustment to tweak the current meter. Many adjustments could affect that. A few could also change the feedback signals used by the circuits to regulate. Only one pot would be the one you should have adjusted to change the panel current meter reading.

I don't know if it will help but I looked at the schematic and board layout in the manuals for the EW and made a guess on what the pots do. I'm providing here an anotated board image with the pots highlighted, and then a text of my guess of approximately what they do.

If you didn't adjust R78 to tweak the I-meter reading you probably changed the I feedback signal in the circuits. Hope something in this might help.

EW adjustment Pots
EW adjustment Pots
------------------------------------------------------

Code: Select all

Glassman EW HV Supply Adjustment Pots

These are probable functions deduced from the schematic.
In the diagram the numbers on the highlighted pots are the resistor code number.
(eg., 78 = R78 on the schematic)

  R#        Function
--------  ------------------
    5         10 V Ref adj
   78         I meter
   80         V meter
   82         Duty cycle clamp (dead time)
   84         Switch Frequency adj
   89         I Feedback Gain
   90         I Amp Balance
   93         I Positive adj
  103        P Compare level
  113        V Feedback Gain
  117        V Positive adj
  125         ? -- (Couldn't find in schematic)
Rex Allers
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Re: Help with Glassman 40kV, 15mA psu

Post by Matt_Gibson »

Hi Rex, thanks for taking the time to look that deeply into this! Before I started adjusting the other trimpots, I had only adjusted the one for the current meter.

Later down the road, I found the one for the voltage follower and adjusted it because I saw, via my 40kV probe that the meter AND voltage monitor output both showed “40kV” yet the probe showed 33kV. Adjusting the voltage follower trimpot brought up the probed voltage to 40kV and now everything matches. Neutron count also went up quite a bit.

Current, on the other hand, hasn’t been so much improvement. I tried adjusting one of the trimpots around the “I follower” circuit and gained 1mA before the psu kicks it down.

Seems that the psu is thinking that 5mA is actually 12.5mA when I’m running near 40kV. I don’t know which circuit does this (P comp?). My next idea is to swap out the current sense resistors on the multiplier board such that it’s only seeing half the voltage as it sees now. Maybe that will trick it into behaving?
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Re: Help with Glassman 40kV, 15mA psu

Post by Rex Allers »

I never worked out all the complicated circuit interactions of the feedback signals to control the output on the supply. Today I looked at the P-COMP device and it does seem to be the clamp that limits the output as both the KV and mA outputs approach their max (would be 40 KV and 15 mA for this supply).

So maybe you can check some voltages and see if you can see this tripping too early, and why.

Here's what I worked out today.
------------------------------------------------
Some EW circuit notes

The gain of the I-Follower amp, U8/A, produces the I-monitor signal. This should be +10 V when current feedback from the multiplier indicates 15 mA output. So gain adjusted for,
Imon voltage = I (in mA) / 1.5

The gain of the V-Follower amp, U9/A, produces the V-monitor signal. This should be +10 V when voltage feedback from the multiplier indicates 40 KV output. So gain adjusted for,
Vmon voltage = V (in KV) / 4

These monitor voltages can be seen on the backpanel TB1 strip.
TB1-4 is V-monitor, TB1-7 is I-monitor.

The P-COMP device, U6/B, appears to be the clamp that limits power output as the I and V both approach their max (would be 10 V on both monitor levels). I'm guessing P-COMP means Power Compare or Power Compression.

The device is an op-amp but it is being used as a comparitor. The (+) input is a DC level that is set by R103 pot. Doing the math, the level can be set between 8.5 and 9.5 volts.

The (-) input to the comparitor is the average of Vmon and Imon as,
(Vmon + Imon) / 2

When that (-) input level goes above the DC level on the (+) input, the comparitor will trip, clamping the output.

From the supply specs, we know that with V maxed at 40 KV the I output should be clamped to 12.5 mA. At these levels the comparitor input would be,
(Vmon + Imon) / 2 = (10 + 8.33) / 2 = 9.165 V

That's around the middle of the R103 setable range for the DC level, which makes sense.

If this P-COMP comparitor is tripping too soon for some reason it could be why your output current isn't getting up to 12.5 mA.

As mentioned, the Vmon and Imon signals are availble to be measured on TB1.
The output of the P-COMP comparitor can be measured on the main board circular test pad E31. This can be found on the circuit board about 1 inch below the pot R5, and can be seen on the diagram I sent earlier.
Rex Allers
Matt_Gibson
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Re: Help with Glassman 40kV, 15mA psu

Post by Matt_Gibson »

Rex,

I owe you a beer for all that (scotch actually).

I took some measurements and got the following:

V mon: 9.6
I mon: 3.8

Raising either beyond these levels knocks current down and I have to adjust it back up.

Looks like I’m running around 70% of what I should be doing?

I’ve already maxed out the P comp trimpot to get current to this level. I don’t know what would need adjusting at this point.

Any harm in popping the P comp op-amp out and trying?

Edit: Forgot to add that e31 shows 12.98v no matter what I adjust (I/V).

-Matt
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Re: Help with Glassman 40kV, 15mA psu

Post by Rex Allers »

Matt,
Not sure what to make of that info. I believe the output of P-COMP (E31) should be high when not clamping and go low to clamp. You say E31 is always high ~13V so it doesn't seem to be clamping. I would expect it to go close to 0V. But you say that adjusting the DC level on the (+) of the op-amp comparitor does have an effect on the supply current. I can't understand that.

I don't think you can pull the U6 chip. First, not sure about the result of floating the E31 level. Second, its a two op-amp chip. The other half seems to be one way to shutdown the switcher chip. Can't figure out what it is doing, though.

Without understanding all those control circuits I can't suggest what else to look at.

-Rex
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Matt_Gibson
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Re: Help with Glassman 40kV, 15mA psu

Post by Matt_Gibson »

Rex,

I’ll watch E31 while operating to see what happens when the supply knocks the current down…I’ll also check the value on the input pin to see if it’s somehow getting more than 9.5v (I jacked the trimpot all the way up).

I’m having trouble tracing out where this signal goes and how current is actually adjusted down. It seems that it touches many of the circuits before making its way to the PWM chip.

I reached out to Glassman, but never heard back. I think they really want me to spend big money on a refurbishment…

-Matt
Rex Allers
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Re: Help with Glassman 40kV, 15mA psu

Post by Rex Allers »

I just took another look at the schematic and I got the function of the P-COMP device wrong. It's not a comparitor, it's an integrator. So the output won't be bang bang as I was thinking. It will be a level.

With this new point of view I think I now understand basically how the control circuits work.

-----------------
The signal line that goes to pin 2 of the 3524 switcher is what controls the PWM of the switcher outputs.

The I-AMP, V-AMP and P-COMP are all integrators. The DC bias on the (+) input sets the desired control level. For the V-AMP and I-AMP these levels come from front panel V and I pots.

The V-AMP sets the main operating control going to the PWM line through R100. This will strive to set the output so the V feedback matches the V set pot.

The I-AMP output connects to the PWM line through a diode. If the I feedback starts to exceed the I pot set point, the output will go negative, being able to pull down on the PWM level through diode D66, overriding the level from V-AMP.

The P-COMP works basically the same as the I-AMP. Its output connects to the PWM line through D68. If the combined average of the V and I feedback signals exceed the set point from R103, then P-COMP will pull down to limit the output.

There are a lot more circuits, but I now feel comfortable that this describes the main feedback signals and how they control the output.

I think most of my earlier description is ok, except for the part where I though P-COMP was a comparitor.

------------
How to debug your situation is another matter. If the output of either I-AMP or P-COMP is lower than the output of V-AMP then that is what is limiting your output. Unfortunately, only P-COMP seems to have a test point. You would have to measure at the amp chip output pin, I guess.
Rex Allers
Matt_Gibson
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Re: Help with Glassman 40kV, 15mA psu

Post by Matt_Gibson »

I poked around and everything looks like it should. Nothing is exceeding the 9.5v input…

While poking around, I saw that the trimpot for the PWM frequency was turned down. I turned it up such that the red glue/marker looked like it had originally been set. This went from 29khz to 40khz. This wound up getting me up to 7.5mA, up from 5mA!

Looking over at my power meter (I know they aren’t all that accurate) I was now pushing 550w, up from 430w or so. So, a “100w” improvement. I let it run like this for a few minutes…

Unfortunately, I could hear some popping noises (much like corona discharge) from near the multiplier and then a sudden loss of current and the dreaded “smell”. I shut down and waited a minute before turning back on. I was able to bring it back up, used my probe to see I was near 38kV, and then the noises started up before loss of current and the smell.

I pulled the multiplier and took a look. No signs of damage or anything, nothing tested as shorted (like before). Trying it again does the same as before. Not sure what’s going on, but I’m guessing the Glassman isn’t happy at all.

An interesting note: The other identical Glassman on eBay (5x what I paid for this one) had the seller telling me that these are custom designs from a flight simulator. There have been tweaks and mods made to them for whatever reason.

No telling what the hell has been done (turning down the frequency) to these that could be causing these problems.

Ugh!$!$!
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