The AM Forum

There are several ways to run a 3 phase transformer on single phase.....Most are a compromise of some sort...The conversion linked to here is for a welding machine but the result should be the same for a transmitter plate transformer.   http://pounceatron.dreamhosters.com/docs/misc/CP-200_Single-Phase_Step-By-Step.pdf    Using motor run capacitors to achieve the proper circulation of currents in the iron core seems like it should be effective for a transmitter.  I'm not just sure how the capacitors "delay" the current to achieve proper phasing.. They don't say how the capacitance value was calculated but I presume it depends on the total current drawn.  Any comments about the "Haas-Kamp" method would be appreciated....  Steve KL7OF


addition:  Found this capacitance formula..https://www.practicalmachinist.com/vb/transformers-phase-converters-and-vfd/miller-cp-250ts-converted-single-phase-206509/
is this correct?

Hi!

Usually I keep my mouth shout if I'm not sure of what I'm saying...
But, I curious about this, so let me share my thoughts.

The main problem I see is the (usually) varying load that the transformer will see.
As a result of this, the phase shift will vary.
I suspect that this will result in ripple in the DC voltage.

Remember that a 3-phase rectifier usually calls for a fairly small capacitor bank.
(Specially if the secondary is a combination of D/Y windings.)

IF the transformer is affected in any detrimental way, I do not know, have to ask my wife.

Here is another approach...https://www.qsl.net/kf8od/transformer.html   I may try this one.  I am wondering about how much the current ratings will change.

I looked at the band saw conversion of 3-phase to single-phase transformers.  I have a big honking one out in the garage that would be a nice candidate.  My concern is the the band saw would leave burrs that would short circuit most of the laminations to each other.  Perhaps a belt sander with progressively finer grit would solve this, followed by a varnish treatment.

By the way, that same KF8OD site has a good article on winding your own plate transformer on C-cores.  Now that Peter W. Dahl company is out of business, you have to do your own if you want good transformers. 

Burrs, shorted laminations, wont make a difference. Laminations should all be "shorted" anyway. I have done this trick with a few 3 phase beautys and found out that you have to experiment with the connections to make sure they are not out of phase. Just use a variable supply at 20vac, monitor the current draw which should be pretty close to nothing at 20 vac, on the primary. If its drawing a fair amount of current then try another connection. While your doing this to the primary, be sure that all the secondary windings are not connected. If they are, your just chasing your tail.
Regards,
Gary

I've successfully disassembled several of them and set them up as single-phase jobs for clients. 

So far, the alternating nature of the lams allowed it to go together fine without any cutting. 

Look to get a little less than 2/3 the power out of it, or basically the difference between CCS and ICAS service.

73DG

I vouch for the high quality of the above work.

The plate iron from TMC GPT 10-K.  Spec book says 1.6 Amp.   Has 3 ea. multi-tap primaries and 3 ea. 3400V secondaries. It is set up as Delta primary, Wye secondary. weighs over 200 lbs.  I'm going to town to buy some new band saw blades...

I find it easier (and cheaper) to restack them.

73DG

Dennis...Thanks for the information..Especially useful is your comment from your personal experience that one can expect a little less than 2/3 power out...I have been looking at the interleave pattern on the transformer I want to modify and it looks like I would have to take all the coils off and disassemble the entire 3 pillar core in order to restack them as a 2 pillar core....Is that how it works for you?  How long does it take to restack one of these things?  Any tricks for keeping the leaves aligned as you do it....?  I have several 3 phase transformers...I am going to try the Haas-Kamp method at some point as well....

I have been separating the horizontal lams from those vertical thru the core, leaving them in the core(s).

Then I sort out those that will bridge the two cores with necessary clearance, and reinsert them.

Cut and redrill the angle irons and terminal plate, done.

This leaves a lot of silicon steel left over.  You can, if you have enuf steel from several rebuilds, make an "O" core with the single leftover core for a decent HV trans as well.

Around here, I'm lucky enuf to have real 3-phase power: 277/480 200A.

73DG

I sawed one core off my 3 phase transformer and hooked it up to the transmitter and it is working very well ...No hum....no buzz... no sparks...I did have to swap the leads around on the 240V primary to get everything in phase as recommended by Gary.  It  did nothing with the phase incorrect...This transmitter idles at 1/2 amp and that is all the load I've put on it so far..It was quick and easy to cut the core off and trim the mounting hardware down to fit..Im going to put some load on it this afternoon on 40 metros....I'll post the results....Thanks...Steve

UPDATE:   7290 khz... I ran the transmitter into the dummy at 2.5 KW carrier level ....yallos etc got all tuned up.. Transformer cool to the touch..No Buzzing, or flamage...got on the antenna..retuned...worked Calif on AM got a good report from Tom...then I .got an unsolicited report from an unidentified station that I was 10 kcs wide and had a hum..  So the transformer is working well...but I need more filtering ...the filter section is designed for 3 phase and comes up lacking on single phase...I'm happy...

Very interesting! I wuz talking with Tim of HLR fame and he was explaining to me a way to hook up 3 phase to single without tearing it apart to do so. He also stated that the output in current would be about 2/3 of original. On my big Westinghouse MW-2, I had been using a 17 KVA  3 phase BC pull plate transformer. It can be wired wye or delta. I think it may have to be wired delta for it to work on 1 phase? At my camp where the big Westinghouse is located, I had to generate my own power to power it but the big 3 phase gen set has been broken for about 8 years now and I want to get the transmitter back on the air. My working gen set is a Generac at a rated power of seven KW. I need to get a real wiring diagram on how to change the connections on the transformer for it to operate on 240 volts AC. Can anyone on here draw up a diagram that I could use?

Thanks Terry
W2PFY

Terry ..there are a couple ways to run that big transmitter on single phase....see the link in the first entry in this thread  for the cap method and there is an article in electric radio on how to do it by wiring the single phase into the transformer to get the best flux patterns...I will look for a link to the ER article...neither method requires cutting....I have used the ER method...It gives full voltage at reduced amperage..

Running it on single phase is pretty simple, pick two legs and fire in.  Your problem will be the rest of the PSU...it used to look for 360Hz ripple, now will be seeing 120Hz.  More cap necessary, and most 3PH supplies don't need a swinging choke as the source impedance is so low.  Get ready to add more iron, too.

73DG

First, get a Variac for 240 volts.
Then find the primaries for each winding. Get out the clip leads, at reduced voltage, experiment to find out how to get the two primaries in phase to generate a secondary voltage. Then figure out the phase of the secondary to series the windings to generate the most voltage. Just ignore the third phase, it will not be used. Once you have everything in phase at low voltage you can crank up the primary voltage and adjust the taps on the primary and secondary to get the voltage you are looking for. All the transformers are a little different buy experimenting with a lower voltage and getting the phase figured out of the windings will get you there safely. This gets you 4000 Volts at a few amps easy with surplus 5K FM transformers. Just be careful. This stuff is lethal.
Keith
WA1HZK

The ones with a choke will use a small one. I saved a 2.3H choke from a 5-7KVA 3-phase klystron power supply. I want to use that or a similar choke for use as a resonant filter. I'm not sure about voltage ratings needed. There is a difference between volts-to-GND and volts-across-winding.

The original 3 phase setup had a 5 H choke input and a 5 uFcap...after converting the transformer to single phase, I paralleled in  another 5uF.  Ripple looks much better on the scope...no more reports of hum... I would like to have about 20H and 50 uF...  I'm having a difficult time finding components rated for 10KV+ locally

You know where to go for that sort of stuff, Steve...:-).

73DG

Thanks Guys, I wuz at the camp on Thursday up in the Adirondacks and there was still three feet of snow in my driveway! Looks like I'll try again in about 3 weeks  when the snow melts and then start experimenting with single phase on the plate transformer. I'll need to use a four tube bridge circuit from the original six and see how that wiring is going to go? I'll have 8 henrys of inductance and the original 15 uf 5000 volts cap to work from. The rectifier in this thing was rated at 4 KV at 4 amps. It was a multi channel system.

Wish me luck!

Terry

Here's a link to the Big W that some of you may not have seen?


https://get.google.com/albumarchive/110796788101790984942/album/AF1QipOu4bOtdDCyzFHlRd2Ors87hVgRkIdLFTdOcIdE?source=pwa (https://get.google.com/albumarchive/110796788101790984942/album/AF1QipOu4bOtdDCyzFHlRd2Ors87hVgRkIdLFTdOcIdE?source=pwa)

Hello
i've a three phase power transformers 3 primary with 240v and 3 secondary 2400v, i have an access to the wiring, i wonder if i could disconnect one column and leave it with out any change on the iron.

"
Looks like I'll try again in about 3 weeks  when the snow melts.     "

Hope springs eternal.


KLC

I like the idea of putting a cap in there or caps. I wuz a bit worried that the value needed might change with varying load under modulation,but welders at least the stick type, can be all over the place depending on the arc, metals used and amp settings. Welding may be may be more extreme than a class C transmitter with a class AB or B modulator with varying loads?

I am surprised that we haven't dredged up at least one electrical engineer who might say this is a bad idea ;D ;D


That's what this thread is all about. Why not try it on your transformer and let us know? I have also wondered that if you leave one winding isolated, could it have a useful output on its primary or secondary? Could you use it like a magnetic amplifier by placing DC to magnetize the core to vary the output voltage etc?? I don't have a clue but it would be fun to play with! Perhaps with a stick and rubber gloves :D :D :D

FG5FC:
"Hello i've a three phase power transformers 3 primary with 240v and 3 secondary 2400v, i have an access to the wiring, i wonder if i could disconnect one column and leave it with out any change on the iron."

Yes. Only 1/2 to less than 2/3 the power will be had at the same duty cycle and some power is wasted in the unused iron leg so it's inefficient and overly large.

W2PFY:
"Could you use it like a magnetic amplifier by placing DC to magnetize the core to vary the output voltage etc??"

I asked a similar question about the magnetic amplifier experiment but there were no useful responses. There may be some old examples of these uses on the internet.

To use the spare winding on the actual plate transformer itself will not work because as you saturate the core this looks like a short circuit as far as the primary input windings are concerned. It is, however, done in quite low-power circuits as sensing or control function where the power lost does not matter and the transformer is not going to be damaged by looking at a short, usually because the circuit energizing it can't blow it. That hookup just about always uses a transformer specifically designed for the purpose. Hobby use of common transformers works to some degree, when the power limitation caveat is considered.

My similar question was about using the two outer primaries of a separate 3 phase power transformer as the element in series with the plate transformer primary, and a middle leg winding, either pri or sec as the control element. I believe that is the right way to do the experiment.

In the past I had a Nobatron power supply with a 3-winding saturable reactor. A 6L6 on 300VDC fed into a high-turns winding on the middle leg regulated 28VDC/50A output. The two other windings, on the outer legs, were connected to oppose AC current. As the 6L6 magnetized the core in response to the output going lower under load, more AC mains juice was allowed through this reactor into the power transformer to bring it back up to 28VDC. The range of adjustment was smallish. There was a mains input transformer ahead of all of this, that gave about 160VAC. This is because otherwise the normal loss in the saturable reactor's series inductance would not have given the desired output voltage. I believe it was also because the saturation did not proceed linearly over the regulating range.

Trying different things out with the Nobatron's circuit is part of my education on this subject. Unfortunately I was too young at 14 to understand the beauty of that power supply and ended up parting the thing out. Still have the rectifier transformer, choke or input voltage booster, and nasty old selenium rectifier redone into a battery charger.

Also, one of the major transformer manufacturers sold a 'companion' saturable reactor type unit to go with their plate iron. In the AM transmitters they shewed, it served as a form of syllabic carrier control.

I do not have an electrical engineering degree. If I'm wrong on this then someone should point it out for everyone's benefit!

On Hass-Kamp, I opine that the 'created' phase's voltage will change with the amp load, and phase will change with inductor and or transformer tap changes. It might not be too critical for welding because they use a narrowly selected current range and can adjust the current with the control to get it there. After reading all of the articles it looks like they might be better served by adding a switch to cut in or out banks of capacitors and adding some kind of 'phase-o-meter' to see when the created phase is 'closest to the middle' once the arc is struck.

It would be a wild experiment to try it on an AM transmitter. Whatever effect it may have would probably not improve the modulation quality. For once I am glad to have a valid excuse not to try a wild experiment. spitzensparken und poppencorken.

Many thanks Opcom and W2PFY for your very useful inputs, for the moment i'm a little busy, i while make a try later.
Regards

I changed this post as it was not relevant? I don't even remember writing the post? I don't drink or drug...anymore.....Too old!

Speaking of interesting regulation methods:

I got the transformer and filter choke from a Motorola MSR2000 (14VDC/30A power supply designed to charge/float batteries to run repeaters or cell phone equipment) which used a ferroresonant transformer to a pair of big rectifiers and a pi-section filter (large caps and the hefty choke). But the regulation came from an (unfortunately missing) 65 mH choke switched across the ferroresonant winding and its 20 uf cap, through a triac triggered by an SCR and bridge rectifier (to conduct on both half cycles)! With no pulses to the SCR gate, the inductor is out-of-circuit and the available voltage at maximum... connecting the inductor across the resonant tank must detune it so the voltage drops. More on-time, less output. Never seen anything like it ;) I smoked a couple of smaller fractional-henry chokes experimenting with it, so there must be quite a circulating current.

If anyone's interested I have the manual, but it's a 7 MB PDF which is above the allowable attachment size.

I want to try the haas kemp on my frt39...the IPA and PA stages that run off the Plate supply are linear.   
  I have run this transmitter with the stock 3phase plate iron wired with all 3 coils hooked to single phase ..It worked to about 75% of its rated output..With the same transformer cut down to 2 coils , the transmitter works to about 60% of its rated output.  I am trying to acquire another suitable complete 3 phase transformer so I can experiment with the Haas-Kemp and I also have a homebrew 3phase converter made from a 15 hp 3 phase electric motor that I would like to try.. 

Hello KL7OF

Could you explain exactly how you made the wiring" I have run this transmitter with the stock 3 phase plate iron wired with all 3
 coils hooked to single phase"
Regards

By reflecting well, putting the 3 primary windings in parallel and in phase and the three secondary windings in series
is this the truth?

Yes...   once you get the phase(s) figured out for maximum output it works at about 75% of rated output.

Thanks KL7OF

I guess with a low voltage in the primary for instance 24 vac , i got the job!

Hello, know that is is an old post but will take a swing at it. Picked up a Collins 21E. Like to run it on single phase. Three phase is not an option since it is not even available on my street. Did anybody ever try the Hass-Kamp method from the welder guys? One plus is that I have 3 separate plate transformers for the 21E. So putting two or three in parallel is an easy cheap option. Ordered the ER back issue with the 3 phase to single transformer wiring but still have not received it. I know the primary is wired as Delta and the output is wired as Wye, each leg going to a rectifier. The center of the wye being B-. Don't really want to use a rotary converter since the size required would be big $$$$. Any ideas? Thanks

I have built a "3 phase generator" out of a 3 phase motor..A 15 HP 3PH motor has 3 legs...2 of those legs are attached to 220V single phase with a capacitor start and the motor will run...the 3rd leg on the motor "generates" the missing third leg..  I use it to run my lathe and mill..I tried it on the 3 phase transmitter and it works well enough...The "generated leg" draws a  more current than the other 2 legs so the 3 phase power is not completely balanced but no heating of components and no flamage...I got the plans for the generator from LINDSAY BOOKS...It  was cheap to build...

I have a rotary phase converter for my bridgeport milling machine. I bought it several years ago on ebay from American Rotary, think the idler motor is like a 5 HP on mine, works fine for the milling machine. But to do a 5KW AM Transmitter that way properly it would require about a 50 HP idler motor, or combination of to get to 50 HP.  If I only had one plate transformer or other 3 phase equipment the big rotary converter either homemade or store bought makes sense. But since I happen to have 3 identical 3phase plate transformers the idea of running two or three in parallel to make the B+ would be easier and less expensive. Adding some capacitance to the B+ with a string of electrolytic caps that I already have a box of is also pretty easy as well. That is why I am asking about the transformer ideas to run the 3 phase on single. If not, being a plumbing contractor, I know several air conditioning and fire sprinkler contractors that deal with large HP pumps all the time, and probably have an old motor lying around that I can use as an idler and acquire for free. So I would just have to get some run capacitors and some start caps on a timer relay to get the beast rolling. The starting amps are also going to be insane. A a pair of 25hp may be better since i only need to single phase start one, and the second should start off the 3 phase generated by the first one. But still a ton of work, space, wiring, and effort to run a transmitter every once in a while. But then we are all insane if not I wouldn't be trying to do this to begin with and you would not be reading it having been there already before me. LOL ;)

Some of those ideas will work OK, others not.  You will have to decide what does OK, just watch out for harmonics in the AC pre-rectifier waveforms.  Break out yer scope, connect with caution around that HV.

A real Phasemaster is the most elegant solution, and they do show up from time to time on broadcast used-gear websites, i.e. https://www.thebdr.net/  eTc.

A word of advice:  Key the drive, not the plate supply.  Have the B+ on a timer, say 15 minutes on from first key up so it isn't constantly on-offing in PTT mode.  Your contactors will thank you.

73DG

I've got a 21E here that has been converted by W2INR, but I think by the looks he basically had a special transformer built by Dahl and just redesigned the power circuit.

Probably not much help as far as tweaking the original 3 phase circuit, but something to consider...

Yup, on me big Westinghouse MW-2 they always keyed the drive.The B+ was always on with HV contactor to key the desired transmitter and modulator.

If I were to key the plate transformer I would be keying a massive 100 amp contactor and the clunk it would make could be heard for about 100 feet. I think that sound would get old and the contactor would probably need to be repaired every once in awhile if you could find parts to repair it? When I UN-key the transmitter dumps -400 volts on all the big tubes preventing a melt down.

Dahl made a lot of single phase xformers to convert 3 phase boxes to single.

I bought an fm station a couple years ago, came with a 20kw phasemaster converter and a monster plate xformer!

No more worries about 3 phase, and cheap transformers are abundant in 3 phase!  Nobody wants em.....

--Shane
KD6VXI

Thanks for the Key The Drive idea. I like it. On the bauer I key the contactor that feeds the b+. but your idea is way more elegant especially at 100 amps on that contactor, just have to make sure the big tubes are happy with no drive. But i still have some time to get there. I am going to start experimenting with the hass kamp idea and go from there. will report my findings.  i even have a nice hv probe for the scope that i have never used. sure i finally will now.

I have a 5 KW continuous, 8 KW surge, military generator which provides 120 or 240 volts single phase, or 208 volt Wye three phase power.  Two cylinder overhead Onan engine.   New carburetor.  Available for any lowball offer.  It powered my home during hurricanes in Florida in the 70s and 80s, and during snow and ice outages in GA since 1990.  Needs 24 volts for starting, a couple lawnmower batteries are sufficient.  No longer needed at this QTH.

It might be possible to use a 3-phase motor driver that runs off the single phase power. variable speed drive - just using it for the conversion. Might need some filters on it. It might be hard on the plate iron. I don't know, just thought I'd throw it on the table.

I am reporting the findings of me experiments. The attached picture is the output of the Haas Kamp method. Maybe not a perfect implementation since I am feeding a plate xformer with single phase on the two outer coils, inverting the polarity on one of them. The center coil was fed in series with 400mf worth of capacitance from each of the 240 legs.  The three phase out delta (5kv) was fed into a second identical transformer to step down the 5kv back to 240 V so i can connect the scope to that. Needless to say the "fake" phase is a mess. I would even go as far as saying that with the amount of capacitance the welder guys say they are using, which is way less than the 400mfd that i used that their fake phase has voltage that is no low that it is not doing anything, but since in that process they inverted the connections to the second coil, they get 70% of the welders capacity, and the cap fed coil is doing more harm than good. That being said the transformers work great on single phase by feeding the outer coils (one with polarity inverted) and I did some restive loading up to a 10KW load on what was a 16KW spec on three phase spec xformer and it did not even blink. So with two of them in parallel I will feed the monster with no issues. Adding a second filter choke to the b+ and three times the filter caps as the original to get rid of the added ripple from the single phase supply. I also feed the primary's using the 208V terminals  with the 240V that my qth service has, which is bumping up the secondary voltage to very near the 3 phase level.  HAAS KAMP DOES NOT WORK!

This is very interesting...On your scope, I assume the light blue line is the "fake" phase...And you used AC capacitors...Thanks for the report...It will take me a while to digest this....Steve

Haas-Kamp as it was explained to me...
   The transformer is based on a 3 phase core having 3 sections and built so that the magnetic flow circulates thru the core in a figure 8 pattern.  Wire the far left and the far right cores so that they are operating opposite of each other.  (criss cross one)  wire the center coil in either orientationbut pass each leg thru a motor start capacitor of sufficent size to create a 90 deg phase shift AT FULL LOAD CURRENT.    This forces the core to function as it was originally designed and get the flux spinning in a figure 8.

This sounds almost exactly like what kc4mne did with perhaps more capacitance than the welder guys use....I can't help but think that there is still  more experimenting to be done and that this can be made to work...  I am trying to acquire some 3 phase transformers to work with..I appreciate the thought and time others have put into this....  Steve KL7OF

Yep that's the theory, but not what I saw. However my "load" was also inductive since I was not loading the 4+kv out directly, I was feeding it into another of the same transformer and stepping it back down to 240V and loading each coil with 5KW using electric range burners as a load. Loading the 4+kv directly would be more challenging and would require a much more elaborate "range burner in series" setup that i did not want to get into, especially at those voltages! One mistake and I could be a dead piece of bacon on the floor, getting an additional broiling from all the range burners as well! What I did learn is that firing the two outer coils in reverse polarity, completely cancels out the magnetic flux in the center coil like if it were not even there. Zero volts output on both primary and secondary. In my case I have three identical transformers, so with two in parallel running single phase I have more than enough current capacity. Adding a second choke and three times the filter caps to make up for the single phase ripple.

I just revisted this post as Im working with some 3 phase xfrmrs and single phase input....I want to thank you all for you interest and efforts on the Haas Kemp and transmitters..I have talked with a ham who tried several attempts at Haas Kemp on tx pwr supplies and had no results better than these other methods so I am going to let that one rest for a while..I'm not sure there is anything to be gained ...I do have a 3 phase welding machine that I intend to convert(some day)  just to see if the H-K claims are correct...I'll be able to tell...I have some experience as a weldor..I really want to work on transmitters however....Steve
 

I have been playing with some big 3 phase transformers.  Experimenting "Edison style" with a single phase variac input and voltage and current metered output.. I haven't learned anything new.  I did find something interesting.  I set up the input to the 3 phase trans with the end coils out of phase and the center coil in phase with the first.  I applied 20VAC  and got 300V out.  I then put a  series 25Mf AC cap in each input leg to the center coil and the output came up to 360VAC so those caps must be doing something to alter the flux flow in the core...I don't have any other AC caps on hand or I would try larger values...I haven't hooked up a scope to look at the output...
   The transformer draws current on the primary with no load on the secondary .  20 v in  300 out and about 4A draw on a clamp on meter...seems excessive on the current...any comments?