Need a BOOST? A slick way to get another HV supply tap

[K1JJ]

How do you justify running 315V on a 240V winding? Have you measured the primary current in idle and full load?

Carl
KM1H

Carl,
Nope, it's 315V on a 480V rated  primary. (two 240's in series)

I'm using TWO HV transformers, each with a 240V primary - in series giving 480 V.  The secondaries are in parallel. The sag is negligible under heavy load- about the same as when the booster is out of circuit.  100uf as the filter cap helps...

Yes, Frank, you're right -  I'd estimate the primary of that booster(Variac) IS 30A.  But that's perfect, cuz it's only drawing the power it needs from the source 240V line and that's less than  1/3 the total overall power... way conservative.

T

[Gito]

Hi

I admit ,first I'm a little confused  How the circuit work.
Maybe it's like this ,the primary winding  two transformer is series connected and has  a total "240 AC" volt and series connected with a "75 Ac" volt booster Transformer so it looks like a "315 Ac" volt input.

The secret is how we connect the 75 VAC booster , in phase or out of phase,when connected in phase we got a 315 VAC output( boosting the AC output) and that's to high for the load 220 VAC

If we connected out of phase than we got 165 VAC output (bucking the AC output) About 77% of 240 VAC .
That means the HV VAC is reduced to 77% of it value.
Look at the picture I attached before ,in the picture the load "resistance" is the 240 AC of the series of two 120V transformer

Gito

[K1JJ]

Hi

I admit ,first I'm a little confused  How the circuit work.
Maybe it's like this ,the primary winding  two transformer is series connected and has  a total "240 AC" volt and series connected with a "75 Ac" volt booster Transformer so it looks like a "315 Ac" volt input.

The secret is how we connect the 75 VAC booster , in phase or out of phase,when connected in phase we got a 315 VAC output( boosting the AC output) and that's to high for the load 220 VAC

If we connected out of phase than we got 165 VAC output (bucking the AC output) About 77% of 240 VAC .
That means the HV VAC is reduced to 77% of it value.
Look at the picture I attached before ,in the picture the load "resistance" is the 240 AC of the series of two 120V transformer

Gito

Gito:   The two transformers each have 240v primaries (not 120v primaries) and are connected in series giving the equivalent of a 480V transformer primary.

The Booster IS in phase and adding 68 V to the 240 line.  So we have 308 volts on a 480V primary.  

It works FB.



T

[Gito]

Hi Tom

Sorry I didn't read Your last Comment to Carl, but actually
like Carl I had a conclusion that You series feed the 120 VAC input,giving an input of 240VAC

But using Boosting or Bucking ,the " booster "transformer ,You got nearly the same result,when You used 240 VAC connection or the 480 VAC connection ,depends on the secondary voltage of the "booster transformer" and the power handling of it.
Right Tom?


Gito

[K1JJ]

Gito,

Yes, the booster was used as a "fine tuning" to dial in the HV to exactly where I need it.  I had 2KV and 3KV - and the booster gave me 4KV.   Any other configurations without the booster made too much voltage, higher than I could use.

T

[KE6DF]

I have a nice condition old Thordarson power transformer. 1500 v CT 200ma with some filament windings.

One of the filament windings is 7.5V at 5 amps. There is also a 5v and a 2.5v winding. There is a 150v bias tap on the HV secondary and I think the intention is to use the 2.5v secondary for a half wave rectifier like an 866jr or 2x2.

Anyway, what to do with a 7.5V winding? I could use it for 6.3 with a series resistor, but that wastes a lot of energy as heat.

Then I got the idea that the 7.5V winding was perfect as a bucking winding.

I have 123Vac at my shack and the tranny was designed for 115. So are all my other old transformers. So I will have a problem with filament over-voltages with all of them.

But using the 7.5 V winding for bucking brings me down almost exactly to 115. Plus at 5 amps, I can use it to "buck" for another smaller power transformer used for the low level audio and RF circuits.

I'll probably make the 7.5 V bucking winding switchable so I can switch it out if I ever run the power supply on a 115v service -- if there are any of those still around.

[Opcom]

same topic, may as well continue it.

The supply made 2100V before and now makes 3100V. like the OP 4KV was too much so a bridge was ruled out. Its a 500mA max load.

The plate transformer has to be well insulated to do this. There is no problem so far with a pole pig core but that's well insulated and designed for series or parallel connection. It works really well with the same regulation and has 5-6 hours on it so far in each of two identical plate supplies. Not many hours but if it were going to blow up it would have.

[WD5JKO]

Patrick,

  That circuit is interesting. I wonder what KVA rating that pole pig is, and how big is that sucker? I suppose you could reverse the primary on T3 to drop to about 1KV for a low power or 'tune' position. Thanks for posting that idea.

Do you ever get on 75m? Maybe we can make a sched? PM me.

Jim
WD5JKO

PS: Stay away from licking the pig!

[AA4HA]

Looks like that is no bigger than a 7.5 KVA

Tisha, AA4HA

[KM1H]

Tom, were you at Nearfest a few years ago when I grabbed the pair of 7.5KVA Powerstats?
With them ganged there aint no excessive sag even on a YC-156 but it sure takes up a lot of room. I like your idea mo betta. Then you can also configure for buck or boost and with several taps get any voltage needed.

Rummaging thru the trailer out back I came across the 11000-0-11000 V iron that fed some industrial rig was surplused when the shoe factory closed. Never did have the nerve to fire that up!

The one that fed a Amperex water cooled triode industrial amp is bad enough, thats 7500VDC at 2.5A (with 53uF at 10KV in a 100+ Lb Sangamo) and the Powerstats are on that for now until I ship this YC-156 amp.

[Opcom]

Jim,

The pole pigs I use are the cores, they have no can of oil. I used to worry about that but these seem to have never been in oil because they have no evidence of it, I don't know what is the deal on that. I think they are at good for least 2KVA each

Have you ever operated one out of the can or opened a can maybe to change the oil?

I didn't think about a tune position in the power supply because the TX has a variac for every voltage and I can just turn the screen voltage down on the 4-1000. That is what I have been doing. I have temporarily removed those small center transformers because they need to be mounted. Before they sat on the floor behind the TX because there was no room yet. I want to mount them to the inside of the cabinet on the walls as close to the large transformers as possible, just a matter of space. I use 15KV outdoor luminous transformer wire for all that stuff.

They look a lot like the one shown in the following article, which is seen on its side in the lower compartment rear view at the right on page 9:
http://bunkerofdoom.com/lit/deluxeam/deluxe_amateur_transmitter.pdf

Sometimes 0730 CST Saturday on 3885 for the Texoma traders net. I just check in, the rest is listening. Weekends are my only time.  I'll PM before the weekend.

OOPS! - Jim, I forgot I have an early Saturday morning appt. I PM'd, if you can suggest a time and place..

[KA2DZT]

Patrick was able to run the two xfmrs in series because the one xfmr had a split secondary instead of just a CT.

The same scheme can be done with xfmrs that don't have split secondaries.

Example,  using a plate xfmr with a CT able to run above ground, you can connect the DC output from a second xfmr directly to the CT of the plate xfmr.  Both xfmrs will need their own set of rectifiers.  The rectified DC pulse from the boost xfmr is connected directly to the CT of the plate xfmr.  Do not use any chokes or caps on the boost xfmr, just the diodes.

You can do the same thing even if the xfmrs are using FWB rectifiers.  Connect the DC pulse from the boost xfmr to the negative (ungrounded) terminal on the FWB diodes of the plate xfmr.

This is a good way to bring up the DC voltage of any supply by whatever added voltage you need.  Both xfmrs will need to handle the same current load.  You can lower the voltage, for whatever reason, by simply shutting off either xfmr without having to disconnect anything.  The one xfmr will need to be well insulated to handle the added boost voltage on its secondary.

Fred