Hello My new/used Xrt came and its time to build my power control system. Because I would like to continue working on this project a little longer then 1 ms. after I fire it up or be dragged off to jail for wanton destruction of property, perhaps you could advise me on a few points. Its a 220 60hz-125kv 300ma oil filed
center tapped + + - with metering points for MA and KV.
I have read all the other post and have a good general idea what needs to be done but specifics in this case would aleviate my irational fears and replace them with real fears:) scematics would be a big plus. Thanks to all, Doug
safety/current limiting,ect?
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guest
Re: safety/current limiting,ect?
hi douglas
im no expert on fusors but have used a lot of transformer on tesla coils so i might be able to help a bit
the first thing i would do is ballast the supply primary side as 300ma is not going to be required i would ballast to 50ma to begin with using inductive ballast
although the vacuum and grid design primarily control grid amp draw it would be a good safety margin
obviously the voltage you are going to run at would also affect the ballasting
cheers
colin
im no expert on fusors but have used a lot of transformer on tesla coils so i might be able to help a bit
the first thing i would do is ballast the supply primary side as 300ma is not going to be required i would ballast to 50ma to begin with using inductive ballast
although the vacuum and grid design primarily control grid amp draw it would be a good safety margin
obviously the voltage you are going to run at would also affect the ballasting
cheers
colin
Re: safety/current limiting,ect?
Douglas -
I would recommend use of a variac set to quite low voltage to check out your new transformer. I am presuming from your description, that this is just the transformer portion of the HV unit - 220 VAC input, and 125 kVAC RMS output, center tapped. That would mean at full output 62.5kV RMS potential to ground at each end of the transformer. The peak voltage will be 1.414X VRMS or about 85KV peak.
The effective AC turns ratio is 125,000/220 or 568 and something to one..So... be careful.. each volt of input becomes 568 plus volts of output.
Also the input current is 568 times the output... so if you did get 300 mA of output... the input current would be huge... around 170 amps... at 220 v. This is right up there with the rated current for a typical whole house power input panel (at the meter).
You could clearly dim a few neighbor's lights in this case.
Use of a ballast as suggested by Colin is one approach, but will make your voltage control difficult since each new current level will lower the output voltage. (It does work great for helping to keep a constant output) I would suggest you decide what output current and voltage you wish to have as absolute maxima, then get a circuit breaker of the next highest rating to protecting the input from over-current. For voltage control, again use a husky variac, if you can. An awkward substitute would be a switchable bank of heavy duty resistors.
I am not sure how the current and voltage monitor signals are being obtained. For the secondary side, current, it could be simply a low resistance shunt in the HV RTN (high voltage return) lead. For a current measured in mA, a 10 to 100 ohm, non-inductive resistor could be what was used. It could also be a small current transformer ( CT) a toroid with the RTN lead threaded through it. The HV on the other hand, could be a tap of a few turns of the secondary. down at the ground end of the secondary winding. The transformer will operate at some volts per turn value.. and the secondary tap gives a very accurate measure of the total voltage. You can probably check out both current and voltage by measuring the resistance to ground at each terminal.
A current shunt should show a few ohms resistance. A current transfomer will show very low resistance.. possibly milliohms. If the output is obtained by using a secondary voltage tap, it will have a resistance ratio to the total winding resistance of the same value as the monitor voltage ratio is to the total output. For example, if the HV monitor reads 1v per 1000v output, then the resistance for the HV monitor to Center Tap (the gnd point here) will be in the same ratio 1/1000 of the total secondary resistance.
With high turns ratio transformers like yours, be careful you don't get bitten, when making resistance measurements. The inductive "kick" can be substantial when you dis-connect your meter..
I would be extremely hesistant about using this transformer at anything near its full voltage rating of nearly 170 kV DCon a fusor... since Xrays of this energy level can penetrate nearly a 1/2 inch of solid lead!! For a steel or stainless steel enclosure, you are looking at well over 1.0 inches thickness. This is serious business.
Also,,, as the current level increases, whatever voltage you are using, the level of shielding provided by any material, goes down. It still attenuates the same ratio, but now as the absolute number of Xray photons increases with current, the residual number emerging from the shielding increases proportionately. So .. what is safe at 1.0 mA at say 40 kV, may not be safe at 10 mA at the same voltage.
Be very careful... You have a large high voltage Canon there. Treat it with respect.
Dave Cooper
I would recommend use of a variac set to quite low voltage to check out your new transformer. I am presuming from your description, that this is just the transformer portion of the HV unit - 220 VAC input, and 125 kVAC RMS output, center tapped. That would mean at full output 62.5kV RMS potential to ground at each end of the transformer. The peak voltage will be 1.414X VRMS or about 85KV peak.
The effective AC turns ratio is 125,000/220 or 568 and something to one..So... be careful.. each volt of input becomes 568 plus volts of output.
Also the input current is 568 times the output... so if you did get 300 mA of output... the input current would be huge... around 170 amps... at 220 v. This is right up there with the rated current for a typical whole house power input panel (at the meter).
You could clearly dim a few neighbor's lights in this case.
Use of a ballast as suggested by Colin is one approach, but will make your voltage control difficult since each new current level will lower the output voltage. (It does work great for helping to keep a constant output) I would suggest you decide what output current and voltage you wish to have as absolute maxima, then get a circuit breaker of the next highest rating to protecting the input from over-current. For voltage control, again use a husky variac, if you can. An awkward substitute would be a switchable bank of heavy duty resistors.
I am not sure how the current and voltage monitor signals are being obtained. For the secondary side, current, it could be simply a low resistance shunt in the HV RTN (high voltage return) lead. For a current measured in mA, a 10 to 100 ohm, non-inductive resistor could be what was used. It could also be a small current transformer ( CT) a toroid with the RTN lead threaded through it. The HV on the other hand, could be a tap of a few turns of the secondary. down at the ground end of the secondary winding. The transformer will operate at some volts per turn value.. and the secondary tap gives a very accurate measure of the total voltage. You can probably check out both current and voltage by measuring the resistance to ground at each terminal.
A current shunt should show a few ohms resistance. A current transfomer will show very low resistance.. possibly milliohms. If the output is obtained by using a secondary voltage tap, it will have a resistance ratio to the total winding resistance of the same value as the monitor voltage ratio is to the total output. For example, if the HV monitor reads 1v per 1000v output, then the resistance for the HV monitor to Center Tap (the gnd point here) will be in the same ratio 1/1000 of the total secondary resistance.
With high turns ratio transformers like yours, be careful you don't get bitten, when making resistance measurements. The inductive "kick" can be substantial when you dis-connect your meter..
I would be extremely hesistant about using this transformer at anything near its full voltage rating of nearly 170 kV DCon a fusor... since Xrays of this energy level can penetrate nearly a 1/2 inch of solid lead!! For a steel or stainless steel enclosure, you are looking at well over 1.0 inches thickness. This is serious business.
Also,,, as the current level increases, whatever voltage you are using, the level of shielding provided by any material, goes down. It still attenuates the same ratio, but now as the absolute number of Xray photons increases with current, the residual number emerging from the shielding increases proportionately. So .. what is safe at 1.0 mA at say 40 kV, may not be safe at 10 mA at the same voltage.
Be very careful... You have a large high voltage Canon there. Treat it with respect.
Dave Cooper
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guest
Re: safety/current limiting,ect?
hi doug
what dave says about the inductive limiting is true its ok for constant voltage but i would advise a fuse as well as a breaker as i have heard of breakers welding shut in high overcurrent so belt and braces would be good
cheers
colin
what dave says about the inductive limiting is true its ok for constant voltage but i would advise a fuse as well as a breaker as i have heard of breakers welding shut in high overcurrent so belt and braces would be good
cheers
colin
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Jon Rosenstiel
- Posts: 1494
- Joined: Thu Jun 28, 2001 1:30 am
- Real name: Jon Rosenstiel
- Location: Southern California
Re: safety/current limiting,ect?
I'm using a 15/30 NST, (with secondaries shorted), to limit the current on my GE, 100kVp, tube type, (Kenotron), X-ray power supply. I also use a 62k wirewound resistor just before the fusor cathode to further limit any current surges.
To date the maximum fusor input I’ve run with the above configuration is 40kV at 10mA. At that power level, (400W), the input was 180Vac. (With a max input of 240Vac I still have plenty in reserve)!
To get a handle on how to connect/construct the power controller I pulled the power supply out of the oil tank and did the "reverse engineering" thing.
Jon Rosenstiel
To date the maximum fusor input I’ve run with the above configuration is 40kV at 10mA. At that power level, (400W), the input was 180Vac. (With a max input of 240Vac I still have plenty in reserve)!
To get a handle on how to connect/construct the power controller I pulled the power supply out of the oil tank and did the "reverse engineering" thing.
Jon Rosenstiel
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guest
Re: safety/current limiting,ect?
This is a + + - DC output trani. From what I understand from the other post im going to have to pull the guts out of the can to change the polarity of the internal rectifiers although I would like to move them outside completly in case of burnout, in any case Ill get a good look inside,
Thank you once more for all your help
Thank you once more for all your help
Re: safety/current limiting,ect?
Adding a fuse ahead of the circuit breaker is an excellent safety measure.
One way you can control the output voltage of a Kenotron rectifier set, is to control the filament voltage. While filament control of an electron tube is quite non- linear, it is a practical way to reduce the output DC voltage without handling the the full HV transformer's load. Xray tube beam current is controlled by filament drive.
As to the (+ + - ) outputs, check whether these are DC.
They could be the designation of connections to the Rectifiers - for either a Full wave or half wave doubler connection.
If it is DC, one set of + and - should be at full DC potentials for the anode and cathode ends of the Xray tube. The extra + may be for bias to a triode type xray tube. If so, it will be a few hundred volts away from the Cathode potential, but probably can't supply much current.
The best all around approach is "reverse engineering" as Jon suggests.
Also... check that your transformer oil is NON-PCB BEFORE you open the case. While PCB oils are nowhere near as hazardous as they are made out to be, (just don't drink them!!), disposal could be a problem, and.....if you contaminate your shop with PCB oil spills, you could be in for expensive cleanup if you were ever to move.
Dave Cooper
One way you can control the output voltage of a Kenotron rectifier set, is to control the filament voltage. While filament control of an electron tube is quite non- linear, it is a practical way to reduce the output DC voltage without handling the the full HV transformer's load. Xray tube beam current is controlled by filament drive.
As to the (+ + - ) outputs, check whether these are DC.
They could be the designation of connections to the Rectifiers - for either a Full wave or half wave doubler connection.
If it is DC, one set of + and - should be at full DC potentials for the anode and cathode ends of the Xray tube. The extra + may be for bias to a triode type xray tube. If so, it will be a few hundred volts away from the Cathode potential, but probably can't supply much current.
The best all around approach is "reverse engineering" as Jon suggests.
Also... check that your transformer oil is NON-PCB BEFORE you open the case. While PCB oils are nowhere near as hazardous as they are made out to be, (just don't drink them!!), disposal could be a problem, and.....if you contaminate your shop with PCB oil spills, you could be in for expensive cleanup if you were ever to move.
Dave Cooper