High Voltage SMPS

[JackStraw]

Hello everyone. I am looking to build a high voltage, high current SMPS for a tube amp project. I am wondering if it is possible and what topology would be best. The specs would need to be 2,700v @ 5 amps continuous. It will be used for a RF power amp and needs to be robust as well as have good protection circuits. Any help here would be great. There is so much information on SMPS I don't know where to start as this is a good bit different then any supply I have seen yet. Thanks for anyone with any ideas!!! Happy holidays!

 

[Nigel Goodwin]

Are you sure about your specs?, you would need an industrial supply to get that much electrical power.

You're not talking about a trivial (or cheap) project, it's going to be complicated and EXPENSIVE - and you're going to destroy a lot of expensive compopnents during development.

What's wrong with a conventional mains transformer?.

 

[JackStraw]

Yeah, I am sure about the specs. The amplifier needs to put out a continuous 7.5KW. The weight of a normal transformer is over 150 lbs with this rating. I am well aware of the complexity and design considerations of this project. If it can be done, I want to try to do it.

 

[Nigel Goodwin]

It could certainly be done, but I wouldn't attempt it - I couldn't afford to attempt it

 

[JackStraw]

well considering a power transformer with ratings like that would have to be custom built. The best price I could find on one here in the states was $2,980. I would rather have the experience and fun of building a SMPS with that money....

 

[tcmtech]

Stack four 240:480 volt 2.5 KVA transformers together with their 480 volt windings in series. Full wave bridge the combined output and you will have 2700 volts DC.

That type of transformer is very common and new old stock sell for around $100 - $300 each.

 

[JackStraw]

Well, if I could find a NOS transformer I would have bought it. I have been looking for over 2 years for something under $1,000. Any place you recommend looking if I decide to go that way?? Stacking the transformers gets me back to where I didn't want to be, over 200 lbs of iron weight. If weight wasn't an issue that might work....

 

[Nigel Goodwin]

well considering a power transformer with ratings like that would have to be custom built. The best price I could find on one here in the states was $2,980. I would rather have the experience and fun of building a SMPS with that money....

You'll also have to have a SMPS transformer specially wound as well, and I imagine a working PSU is going to cost you considerably more than that.

 

[ronsimpson]

You do know this is not going to plug into 110vac.
I think you could get it running from 220 2 phase. This is about all you can get from 220.
Last time I did a 10kw transmitter was years ago. I used 220 3 phase for the little transmitters and 440 3 phase for the big transmitters.
It could be done SMPS. I have some 1200 volt 20 amp transistors that would work fine. You could make 10, 1000 watt power supplies that run in parallel. My BIG transmitters ran that way.

 

[ronsimpson]

I just looked outside. I have a 2.5kv to 220 CT transformer. It could be run backwards. 220 to 2500. If you steal my transformer it will get dark and cold.

 

[tcmtech]

As far as a switching power supply for that capacity your not likely going to find one in that power and voltage range you can build for under $2000 either unless your willing to buy a factory made one that is intended for another application and then modify it.

The closest thing I can think of that pushes that power level in an actual true switching power supply is an inverter welder or a plasma cutter. I work on both and with enough reverse engineering it would be possible to rewind the HF transformers in them for a HV output and change the feedback circuits to work with the HV output.

 

[shortbus=]

Usualy when going into that high off a power rating they go to a "Toroidial" transformer. The weight and performance is much better.

High power amplifiers and transmitters use them. Check out these guys; Antek - Your reliable source of transformers, power supplies, and more.

 

[gary350]

This is not a hard project. Check out the photo of the power supply. All you need to do is connect diodes, resistors and capacitors together as shown in the photo to get the voltage and amp rating you need. 1N4004 diodes are rated 1000 volts 1 amp. You need 2700 volts so 3 diodes in series gives you 3000 volts. 5 diodes in parallel gives you 5 amps. Add a few extra for a safety factor. You can build full wave using a transformer with center tap or no center tap. You can build a voltage doubler too if you like. Beyond the rectifier circuit is the filter so you need some filter capacitors. Not a big deal to build. This is the basic circuit you can add other fancy stuff if you want like current limiting or what every you want. The transformer output will determine the actual voltage of the power supply. Get a 2000 volt 5 amp transformer put a variac on the primary and turn it down to 1909 volts. The filter circuit will make it 1909 x 1.414 = 2700 volts.

**broken link removed**

If you would like to hand wind your own transformer I have a core you can have for free is you pay the $15 postage to get it. I stripped a transformer down and was going to rewind it to get the voltage I needed. That was 15 years ago never did get around to winding it. You will have to do the math but 180 turns of wire on the primary coil, 1909 volts / 120 volt = 15.9 turn ratio. Calculate the core lose. Calculate wire size on secondary and primary coils. Paint each coil with polyurethane varnish let it dry before winding the next layer. I have built many transformers in the past it is easy. I don't happen to remember the power rating on the transformer core that I have but it measures 8" x 8" x 4" thick. You may need to do the math on the core to see if it is rated 7.5KW like you need.

 

[Diver300]

An 8" x 8" x 4" transformer will be nowhere near 7.5 kW. I would guess less 1 kW.

What are you going to power this from? 7.5 kW at 120 V is about 64 amps. That would be down 32 amps on 240 V or 22 amps on 208 V 3 phase.

Figures like that also mean that your switching transistors will need to be quite large.

 

[JackStraw]

Ok, so in the schematic you have VR1 and VR2... What are the values of those two? It will be ran off of 220v split phase, two 120v legs. What kind of core would be recommended for the transformer in that schematic then? What would the rating be? Thanks so much for the help, saying it can't be done, or it's too expensive is self defeating... You don't know what can be done until you try...

 

[Ubergeek63]

220V x 100A = 22KVA service in your house... adjusting for peak current into a power supply capacitor is 220V x 80A or about 17KW... 2700V x 5A x 1.2 (typical good switcher efficiency) = 16200W or about the entire electrical service of your house!

That said there are two other things going on: you need a custom transformer using parts that you are not likely to find, and you are listing class A RF amp properties in your 7.5KW as opposed to the class d or better that RF amps run.

I do have some HF switching cores that can handle 2KW each but you could not afford to wind them as they are planars. I can direct you to suppliers but i do not know if they would give you just the 4 or so cores and bobbins that you would need to make the transformers. I can also send you a copy of the old philips ferrite design software that they supplied to their customers back when they did ferrites.

dan

 

[Nigel Goodwin]

Ok, so in the schematic you have VR1 and VR2... What are the values of those two? It will be ran off of 220v split phase, two 120v legs. What kind of core would be recommended for the transformer in that schematic then? What would the rating be? Thanks so much for the help, saying it can't be done, or it's too expensive is self defeating... You don't know what can be done until you try...

The scematic posted isn't a SMPS, it's just a conventional mains transformer.

 

[Mike - K8LH]

I'm curious about intended use since that's quite a bit more power than allowed for Amateur Radio use...

 

[ke5frf]

I'm curious about intended use since that's quite a bit more power than allowed for Amateur Radio use...

ditto. good question.

 

[Mr RB]

Darn I was going to ask that!

The bit that got me curious was the "light weight" requirement... Like the need for a 13.5kW supply but don't want something that weighs 200 lbs. Well at least he doesn't need to run it from 12v DC.