High voltage high current power source
vasil, Sat Dec 27 2008, 03:47PMI am starting to gather components for my future VTTC. The tube has 2.5 kW dissipation on the plate so I will need some more current. The main problem is that I have not access to a lot of MOTs and they will be probably different size, so they can have some power dissipation because different ratings.
I want to discuss with you two possible settings.
One of them is almost similar with the setup used by Dr Spark for his Quatro Pack. But because my MOTs will not be identical, I will rectify each chain of MOTs separately, as in the pricture:
In this way the voltage will be doubled and I will have some more current. There are some disadvantages: the internal resistence of the seried MOTs adds one to another decreasing the current. Another weak point is that I would use only half of the AC cycle.
The doubler used in the majority of the VTTC setups is the best option in my oppinion. The output voltage ripple above the 0 Volts, so I have always potential on the tube. I can not parallel in direct way the MOTs because they are different (so, a few tens of volts would burn in the weaker MOT), so I was thinking to a setup that allows to feed the tube with paralleled doublers. It uses a lot of diodes to keep the currenty on the correct way, but I feel that it could work:
I would have doubled voltage, doubled current (well almost) even the two MOTs are different...they are not allowed to short each other. The setup is drawn only for two MOTs, but it can use 3, 4, more xfrms, depending by the current capabilities of the diodes. I hope that it will work, because I dont think that I can achieve more than two MOTs :(
So, it would work?
Re: High voltage high current power source
Dr. Dark Current, Sat Dec 27 2008, 04:59PM
Don't mess with complex circuits, the easiest way to extract the most power from a transformer already exists and is called a fullwave bridge rectifier. There are more effective ways but they involve power factor correction (passive or active).
Don't worry if your MOT's don't match, simply connect them in parallel, their reactance is enough to limit the "matching" current to a few tens of mA.
I would probably go with a SMPS, a simple half-bridge and a ferrite transformer, without any feedback etc. If you can get 4 similar cores from monitor or new TV transformers, you can make one "E" core (2x2) out of them which should be good for at least 4kW continuous. Some smaller IGBTs (~60A) should be enough to drive it.
Dr. Dark Current, Sat Dec 27 2008, 04:59PM
vasil wrote ...
One of them is almost similar with the setup used by Dr Spark for his Quatro Pack. But because my MOTs will not be identical, I will rectify each chain of MOTs separately, as in the pricture:
In this way the voltage will be doubled and I will have some more current. There are some disadvantages: the internal resistence of the seried MOTs adds one to another decreasing the current. Another weak point is that I would use only half of the AC cycle.
This is not a good approach. The secondaries will be only conducting one halfwave so they will be able to deliver less power (more resistive heating) and the cores can saturate from the DC bias.One of them is almost similar with the setup used by Dr Spark for his Quatro Pack. But because my MOTs will not be identical, I will rectify each chain of MOTs separately, as in the pricture:
In this way the voltage will be doubled and I will have some more current. There are some disadvantages: the internal resistence of the seried MOTs adds one to another decreasing the current. Another weak point is that I would use only half of the AC cycle.
Don't mess with complex circuits, the easiest way to extract the most power from a transformer already exists and is called a fullwave bridge rectifier. There are more effective ways but they involve power factor correction (passive or active).
Don't worry if your MOT's don't match, simply connect them in parallel, their reactance is enough to limit the "matching" current to a few tens of mA.
I would probably go with a SMPS, a simple half-bridge and a ferrite transformer, without any feedback etc. If you can get 4 similar cores from monitor or new TV transformers, you can make one "E" core (2x2) out of them which should be good for at least 4kW continuous. Some smaller IGBTs (~60A) should be enough to drive it.
Re: High voltage high current power source
vasil, Sat Dec 27 2008, 05:31PM
OK, thanx.
vasil, Sat Dec 27 2008, 05:31PM
OK, thanx.
Re: High voltage high current power source
vasil, Thu Jan 15 2009, 07:34PM
Found two MOTs. They are almost identical.
But with correct primary phasing and secondaries in parallel I have a 11 volts difference bewteen outputs, for 20 volts input from my variac, so it will be more than 100 V at 220 V. I can not simply parallel them.
I will choose another way. I will put the secondaries in serie and full rectify them. On the output of the rectifier I will put a small filter cap (a few hundreds pF), so the voltage wave will swing above 0 V line, almost like in a doubler output. (a staccato is also a possibility). So I will have more power at twice voltage and approx the same current as from one MOT.
Hope that would work.
vasil, Thu Jan 15 2009, 07:34PM
Found two MOTs. They are almost identical.
But with correct primary phasing and secondaries in parallel I have a 11 volts difference bewteen outputs, for 20 volts input from my variac, so it will be more than 100 V at 220 V. I can not simply parallel them.
I will choose another way. I will put the secondaries in serie and full rectify them. On the output of the rectifier I will put a small filter cap (a few hundreds pF), so the voltage wave will swing above 0 V line, almost like in a doubler output. (a staccato is also a possibility). So I will have more power at twice voltage and approx the same current as from one MOT.
Hope that would work.
Re: High voltage high current power source
Dr. Dark Current, Thu Jan 15 2009, 07:41PM
Does that sound excessive to you? That's approx. 1/10 the rating of a standard MOT.
EDIT: You can also take out one of the heater windings and wind a few more turns of primary in there to get the voltages ballanced.
Dr. Dark Current, Thu Jan 15 2009, 07:41PM
vasil wrote ...
But with correct primary phasing and secondaries in parallel I have a 11 volts difference bewteen outputs, for 20 volts input from my variac, so it will be more than 100 V at 220 V. I can not simply parallel them.
If it really will be 100V, then each of the transformers will be "dropping" 50V on its reactance. Now, the secondary leakage inductance is around 4H. Xl=2*pi*f*l=~1300 ohms. I=V/R=50/1300= approx. 40mA.But with correct primary phasing and secondaries in parallel I have a 11 volts difference bewteen outputs, for 20 volts input from my variac, so it will be more than 100 V at 220 V. I can not simply parallel them.
Does that sound excessive to you? That's approx. 1/10 the rating of a standard MOT.
EDIT: You can also take out one of the heater windings and wind a few more turns of primary in there to get the voltages ballanced.
Re: High voltage high current power source
vasil, Thu Jan 15 2009, 07:58PM
Ok, thanx, I will try with them in parallel then. If does not work it is simple to re-wire the things. Adding the fillament winding is a good idea.
vasil, Thu Jan 15 2009, 07:58PM
Ok, thanx, I will try with them in parallel then. If does not work it is simple to re-wire the things. Adding the fillament winding is a good idea.
Re: High voltage high current power source
Dr. Dark Current, Thu Jan 15 2009, 08:12PM
If you don't want to mod the MOTs (this should be pretty easy though), you can connect a small transformer between the MOTs like this. The whole winding only needs to be rated for the difference of your voltages e.g. 5% of 220V which is 11V and wire thickness the same as MOT primary, so this should be an easy to make little transformer.
Or you can use any >10VAC >5A centertapped transformer's secondary winding.
Dr. Dark Current, Thu Jan 15 2009, 08:12PM
If you don't want to mod the MOTs (this should be pretty easy though), you can connect a small transformer between the MOTs like this. The whole winding only needs to be rated for the difference of your voltages e.g. 5% of 220V which is 11V and wire thickness the same as MOT primary, so this should be an easy to make little transformer.
Or you can use any >10VAC >5A centertapped transformer's secondary winding.
Re: High voltage high current power source
vasil, Sat Jan 24 2009, 05:59PM
The forum lost the last messages?
vasil, Sat Jan 24 2009, 05:59PM
The forum lost the last messages?
Re: High voltage high current power source
Dr. Dark Current, Sat Jan 24 2009, 06:12PM
Dr. Dark Current, Sat Jan 24 2009, 06:12PM
vasil wrote ...
The forum lost the last messages?
yes, see start pageThe forum lost the last messages?
Re: High voltage high current power source
vasil, Sat Jan 31 2009, 11:36AM
Sorry for the late news but I have so little time to spare with the projects..
I tryied the inductor variant suggested by Dr Kilovolt and achieved a 62 V reduction between the two outputs of the MOTs (from 92 V to 34 V), but it was the biggest core I had in the house and had not another one.
So I folowed my own variant with coupled doublers. The final schema is here:
The cap C is charged to the highest voltage from the two MOts and the currents just add one to another. The diodes allow the correct way for the current, so with a bit of luck I will not have parassite circulating current through the weaker MOT. The schema allow also to add more MOTs in parallel to get more power:
I built the source with the goddies I had in hands, today it was ready to experiment with:
For comparaison I just used my previous built VTTC:
-the output spark using a single MOT:
SINGLE MOT
-the output with the new source: longer and more powerfull sparks:
NEW PSU
Of course the final exam will be the test with the big russian toob:
But I have a feeling that I can hope that will be ok.
vasil, Sat Jan 31 2009, 11:36AM
Sorry for the late news but I have so little time to spare with the projects..
I tryied the inductor variant suggested by Dr Kilovolt and achieved a 62 V reduction between the two outputs of the MOTs (from 92 V to 34 V), but it was the biggest core I had in the house and had not another one.
So I folowed my own variant with coupled doublers. The final schema is here:
The cap C is charged to the highest voltage from the two MOts and the currents just add one to another. The diodes allow the correct way for the current, so with a bit of luck I will not have parassite circulating current through the weaker MOT. The schema allow also to add more MOTs in parallel to get more power:
I built the source with the goddies I had in hands, today it was ready to experiment with:
For comparaison I just used my previous built VTTC:
-the output spark using a single MOT:
SINGLE MOT
-the output with the new source: longer and more powerfull sparks:
NEW PSU
Of course the final exam will be the test with the big russian toob:
But I have a feeling that I can hope that will be ok.
Re: High voltage high current power source
Dr. Dark Current, Sat Jan 31 2009, 11:45AM
Have you actually tried just connecting the MOTs in parallel? I'm pretty sure you wouldn't notice any difference in heating.
As I said, the 100 volt difference is gonna produce around 50mA of current. Standard MOT has 100 ohm secondary resistance, power wasted=IIR=0.25W. That's a lot of power
I'd be more worried about the no-load primary current, and I would focus on reducing it, either by adding a saturable inductor in series with mains, or by removing the shunts and filament winding and wind additional turns here. Note that if you do this, you can wind less turns on the MOT with lower voltage output to make the outputs ballanced (with the shunts removed, the ballancing current would be higher so it would be desirable to match the output voltages).
Dr. Dark Current, Sat Jan 31 2009, 11:45AM
Have you actually tried just connecting the MOTs in parallel? I'm pretty sure you wouldn't notice any difference in heating.
As I said, the 100 volt difference is gonna produce around 50mA of current. Standard MOT has 100 ohm secondary resistance, power wasted=IIR=0.25W. That's a lot of power
I'd be more worried about the no-load primary current, and I would focus on reducing it, either by adding a saturable inductor in series with mains, or by removing the shunts and filament winding and wind additional turns here. Note that if you do this, you can wind less turns on the MOT with lower voltage output to make the outputs ballanced (with the shunts removed, the ballancing current would be higher so it would be desirable to match the output voltages).
Re: High voltage high current power source
vasil, Sat Jan 31 2009, 11:56AM
The shunts seems to be very well glued to the core. I was just too afraid to not damage my MOTs (it is hard to get them, sometime I am waiting mounths for a single xfrm).
I am sure that with an appropriate core I can reduce the output difference as you suggest. I wound in 10 turns increment and measure the difference (the inductor was in serie with the primary from the higher output MOT). For 150 turns the max reduction was 62 V, but adding more turns the difference begin to increase again, so I supposed that it was all I can get from that core. I didnt have another one, but I had all the parts to build the monstruosity seen in my pics.
vasil, Sat Jan 31 2009, 11:56AM
The shunts seems to be very well glued to the core. I was just too afraid to not damage my MOTs (it is hard to get them, sometime I am waiting mounths for a single xfrm).
I am sure that with an appropriate core I can reduce the output difference as you suggest. I wound in 10 turns increment and measure the difference (the inductor was in serie with the primary from the higher output MOT). For 150 turns the max reduction was 62 V, but adding more turns the difference begin to increase again, so I supposed that it was all I can get from that core. I didnt have another one, but I had all the parts to build the monstruosity seen in my pics.
Re: High voltage high current power source
Dr. Dark Current, Sat Jan 31 2009, 12:12PM
Only after you connect the HV leads together, the voltage on the transformer starts being induced and the secondary ballancing current will be very small. Try to measure it.
Dr. Dark Current, Sat Jan 31 2009, 12:12PM
vasil wrote ...
The shunts seems to be very well glued to the core. I was just too afraid to not damage my MOTs (it is hard to get them, sometime I am waiting mounths for a single xfrm).
I am sure that with an appropriate core I can reduce the output difference as you suggest. I wound in 10 turns increment and measure the difference (the inductor was in serie with the primary from the higher output MOT). For 150 turns the max reduction was 62 V, but adding more turns the difference begin to increase again, so I supposed that it was all I can get from that core. I didnt have another one, but I had all the parts to build the monstruosity seen in my pics.
Well, if you used the centertapped autotransformer as I suggested, it will not limit much the no-load difference with "open" secondaries.The shunts seems to be very well glued to the core. I was just too afraid to not damage my MOTs (it is hard to get them, sometime I am waiting mounths for a single xfrm).
I am sure that with an appropriate core I can reduce the output difference as you suggest. I wound in 10 turns increment and measure the difference (the inductor was in serie with the primary from the higher output MOT). For 150 turns the max reduction was 62 V, but adding more turns the difference begin to increase again, so I supposed that it was all I can get from that core. I didnt have another one, but I had all the parts to build the monstruosity seen in my pics.
Only after you connect the HV leads together, the voltage on the transformer starts being induced and the secondary ballancing current will be very small. Try to measure it.
Re: High voltage high current power source
vasil, Sun Feb 15 2009, 04:38PM
Well...I have a guess, that my MOTs are weaker than I thought, so I measured the core section of each transformer. They are identical 3.5 cm x 6.7 cm, so a cross section of the core = 23.45 square centimeters, thats mean 549.9 watts each, so just a merely 1099 watts output with the two paralleled transformers.
So, I upgraded it with two new MOTs (they are completely different kinds):
- one with 3.5 cm x 6 cm core (21 square cm core section ) P = 441 watts
- another with 3.3 cm x 7 cm (23.1 square cm core section) P = 533.61 watts
Adding the two transformer in my setup would rise the max output power to a 2074 watts power capability. Had to add a new stage on the source.
The final result:
Schema is here:
The source with the GU81 vttc together:
The diodes are 22 kV @ 3 A each, doubler cap = 5 microF @ 2.5 kV
Filter cap = 10 nF @ 20 kV - not figured in the schema ( I made it 10 times more than the primary cap as Dr Spark suggested in his posts, now I am runing a primary cap = 714 pF)
...and better spark:
YOUTUBE
I stop here (no more MOTs avalaible), have to work on the new vttc.
I run the same voltage on the doubler, but with higher current capability. The little movie shows very well how important is the power input for the vttc to get out a good spark. So not only the tube is important but the transformer you are using.
vasil, Sun Feb 15 2009, 04:38PM
Well...I have a guess, that my MOTs are weaker than I thought, so I measured the core section of each transformer. They are identical 3.5 cm x 6.7 cm, so a cross section of the core = 23.45 square centimeters, thats mean 549.9 watts each, so just a merely 1099 watts output with the two paralleled transformers.
So, I upgraded it with two new MOTs (they are completely different kinds):
- one with 3.5 cm x 6 cm core (21 square cm core section ) P = 441 watts
- another with 3.3 cm x 7 cm (23.1 square cm core section) P = 533.61 watts
Adding the two transformer in my setup would rise the max output power to a 2074 watts power capability. Had to add a new stage on the source.
The final result:
Schema is here:
The source with the GU81 vttc together:
The diodes are 22 kV @ 3 A each, doubler cap = 5 microF @ 2.5 kV
Filter cap = 10 nF @ 20 kV - not figured in the schema ( I made it 10 times more than the primary cap as Dr Spark suggested in his posts, now I am runing a primary cap = 714 pF)
...and better spark:
YOUTUBE
I stop here (no more MOTs avalaible), have to work on the new vttc.
I run the same voltage on the doubler, but with higher current capability. The little movie shows very well how important is the power input for the vttc to get out a good spark. So not only the tube is important but the transformer you are using.
Re: High voltage high current power source
Dr. Dark Current, Sun Feb 15 2009, 04:44PM
Well this does not apply to MOTs, as they use nearly 2x the magnetic flux in the core so they can put out more power with the same copper heating, what's problem however is the core heating.
I have a standard-size MOT which was used at 1250W even when the core cross-section would suggest ~500W. Of course they must be cooled with a fan to allow continuous operation at 1250W.
Dr. Dark Current, Sun Feb 15 2009, 04:44PM
Well this does not apply to MOTs, as they use nearly 2x the magnetic flux in the core so they can put out more power with the same copper heating, what's problem however is the core heating.
I have a standard-size MOT which was used at 1250W even when the core cross-section would suggest ~500W. Of course they must be cooled with a fan to allow continuous operation at 1250W.
Re: High voltage high current power source
vasil, Sun Feb 15 2009, 04:53PM
Seems that I have no idea about the power I run through it.
If it would be twice the calculated power I would have almost 4 kW....thats would be wonderful for me. Good news Dr Kilovolt!
Another thing is that my 2 kW variac heats a lot, so maibe I have more power in the circuit. Anyway I am using it only for short run times.
vasil, Sun Feb 15 2009, 04:53PM
Seems that I have no idea about the power I run through it.
If it would be twice the calculated power I would have almost 4 kW....thats would be wonderful for me. Good news Dr Kilovolt!
Another thing is that my 2 kW variac heats a lot, so maibe I have more power in the circuit. Anyway I am using it only for short run times.
Re: High voltage high current power source
Dr. Dark Current, Sun Feb 15 2009, 05:22PM
Dr. Dark Current, Sun Feb 15 2009, 05:22PM
vasil wrote ...
Seems that I have no idea about the power I run through it.
If it would be twice the calculated power I would have almost 4 kW....thats would be wonderful for me. Good news Dr Kilovolt!
Another thing is that my 2 kW variac heats a lot, so maibe I have more power in the circuit. Anyway I am using it only for short run times.
If you want them to run continuously @1kVA, consider adding a largish fan such as the one used in microwave oven. (at least one fan for two MOTs)Seems that I have no idea about the power I run through it.
If it would be twice the calculated power I would have almost 4 kW....thats would be wonderful for me. Good news Dr Kilovolt!
Another thing is that my 2 kW variac heats a lot, so maibe I have more power in the circuit. Anyway I am using it only for short run times.
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