Single Phase with 3 Phase Transformer

[N4HZ]

Hi Everyone:

Before I discard the idea I thought I'd ask.  Has anyone successfully used a three phase power transformer fed with single phase as the xformer in a HV power supply?  I have a large three phase xformer removed from a TV transmitter.  Weighs probably 75 lbs or more.  All winding points come to an external barrier strip.  Only rating info I can find is " 1110 V, 1.5 A  line to neutral" written on the transformer.   Wire in the windings looks pretty hefty.  I put 5.4V from a wall wart  on one of the primary windings and got 60V on a secondary winding.  Built a little full wave bridge and filter ( forget what value of load resistor I used) but anyway measured about 79 V loaded DC at the filter and with no ripple noted on the scope.  I realize a wall wart is not the way to check this and my DC voltage doesn't quite compute.  I can use a variac to check more but before doing so I thought I'd see if I get an " absolutely not" before wasting a lot of time.  It's just that I have the transformer and wanting to see if I could use it in a HV power supply.  If I build a supply I'll want about 2500V DC for a couple of 8122's.

Thanks
Roger, N4HZ

[W7TFO]

I've done that with success, so there is no reason why not.

You cannot pull anywhere near the full boat on it, but using two coils will make power and just make sure it doesn't run too hot.

It is also a good way to get 'tune-up' power on a 3-ph PS, opening up one leg.

73DG

[KL7OF]

This is something that interests me...I have been running a couple of 3 phase transmitters on single phase with some success....But the supply sags so much under single phase that it is impossible to get full scrote ...I have been reading posts on a welder site about running 3 phase transformer welders on single phase  and being able to get full snot out of them...this guy uses a couple motor start capacitors to cause a 270 degree delay in the three phase transformer  and cause it to act  to act like it has real 3 phase feeding the primary..Google "Haas-Kemp practical machinist" and check it out...I've only taken a cursory look but it seems like if it will work for welding machines, it will work for transmitter transformers as well....If any of you guys well versed in AC supplies would take a look at it and be able to explain it to the rest of us...I for one would appreciate it..Heavy metal is coming up you know...Thanks guys and good luck to you Roger...Keep us posted please....Steve KL7OF
 t

[W7TFO]

The "fake 3-phase" tends to make dangerous harmonics in a rectifier power supply.

Caps & chokes suffer, so does the RF.

That i wouldn't do.

73DG

[KL7OF]

Dennis...Are you referring to the Haas-Kemp as "fake three phase"??  It is highly touted by the welder guys...and is supposed to work well on DC welding machines...I'd like to know more about the harmonics etc....
 I have been using 3 core 3 phase transformers and feeding 2 cores with each leg of the single phase and applying voltage to the third core from one of the 2 single phase legs...It sags badly when you apply the load....I have a rotary phase converter that I built from a 3 phase motor to generate the missing third leg...It works well running 3 phase motors but I haven't tried it on any transformers yet....Is there any reason why the rotary converter won't work on a transformer??
  I saw somewhere on the net where a guy took a 3 core 3 phase transformer and literally sawed one core off the primary to make it into a single phase transformer...I have lost the details of how well it worked...

[KI4M]

Maybe you were thinking about this guy:

http://www.qsl.net/kf8od/transformer.html

[W7TFO]

The broadcast companies even said not to use an open delta feed on their transmitters.  That is closer to true 3-phase, and the cap vs. phase things work OK for things with inertia, like a motor.

On transformers from Basler or Electro or Dahl, usually you can pull them apart and reassemble the laminations for just two cores.  I've done that on a 37.5 kVA plate job for a single-phase site that didn't need that much oomph.

73DG