The AM Forum

I have read the theory on combining 2 or more power supplies for increased voltage output....I would like to hear from someone who has experience with combining high voltage supplies....I  need 7200V at 2A  single phase 240 input...  I haven't been able to find a suitable transformer or a pole pig @ 15KVA. So I have been wondering about combining a couple of 3500V supplies...? 

Insulating the "upper" supply components would be the bugger, obviously. I think, rather than stacking two separate supplies, I'd run the two transformers in parallel input and series output, then rectify and filter from there, after hipotting the secondary windings to make sure they'd handle the stress.   If t'were me, I'd grab a chain saw and get a good pole pig from down the road.  Seriously, there must be some out there in the back of the garage that could be had if you cast the net wide enough.  HV supplies need to be simple, not complicated.
73 de Norm W1ITT

KL7OF said:Just musing here, but could you parallel the supplies and build a doubler that would satisfy your requirements? Serious RF being generated into the aether with7200V @2A!  ;D

A 10-15 KVA  single phase240V / 7200V pole pig would be perfect...I'm a serious buyer..

 https://www.ebay.com/itm/Pole-Mount-Transformer-25-KVA-General-Electric-120-240/313370644150?hash=item48f6588eb6:g:M3kAAOSwCZ9f14uu (https://www.ebay.com/itm/Pole-Mount-Transformer-25-KVA-General-Electric-120-240/313370644150?hash=item48f6588eb6:g:M3kAAOSwCZ9f14uu)

They’re out there....

Ed

Main page
https://eaglemade.net/

https://eaglemade.net/collections/transformers/products/copy-of-transformer-4800-volts-7-5-amps-37-5-kva

https://eaglemade.net/collections/transformers/products/copy-of-transformer-4800-volts-5-amps-25-kva

Check them out I have seen his stuff it works. Don't fry yourself have fun.

Johnathan N8QPC

I second Eaglemade.  Floyd has some excellent surplus pigs.  He also has a serious amount of parts as well.

--Shane
KD6VXI

He says he is a serious  buyer. Well you aren't going to find any  cheaper. I've know Floyd for over 20 years he is a straight up Christian guy.  No BS all about business. He could go ahead and have something wound. The last transformer I had wound 17kva was 1700.00.

Johnathan N8QPC

On a different note I have had good luck w rectifying each transformer, then putting the DC side in series.

Did that on an xformer with 4. 5kv out the rectifier. I put a 440 volt secondary control xformer into a voltage doubler. That gave me another 1300 or so volts and then took the - side of the doubler to the + of the Dahl rectified supply.

3000s like high voltage on the anode.

--Shane
KD6VXI

is  that  7.2 kv  loaded..or un loaded ?     Either  5100  with a  FWB.... or 2550  with a FWD.

A  4.8 kv pole pig will  give u  6.7 kv  un loaded.

Don't  go cheap on the  wire gauge..from main panel to xfmr.  Don't  go cheap on contactors  either.  Use  2  poles  of a  3 pole contactor.   Buddy used  135 amp,  3 pole  contactors... he got em at an electrical surplus place in the se of the usa...  $50.00  NIB.   He paralleled  all 3 poles to make a 400 amp contactor, repeat for  2 more  of em.    One in each hot leg of the  240.   3rd one is the step start.   Easily paralleled with  1" x 1"  x  1/8"  thick  angle  aluminum. 

I used  1-0   RW-90 cu from main panel to  HV  supply, aprx 25'  run.  Easy to work with, and has  37  strands.  Rated at  170 amps  ccs.   I noticed on all the  RW-90  power cables, the  actual real gauge is one size  bigger.   IE:  6 ga  RW-90  is actually  4.98  ga.   10 ga  is  really  9 ga.     8 ga is  7 ga.

It's also  600 V  rated, and waterproof, and uv proof. 

3  ga is  readily available anywhere, like home depot  ( hot/neutral/hot/grnd)  and good for  100 amps  ccs.

Most of my V drop is  from the street  to main panel,  like  95%.    From panel to  HV supply is a non issue, but that  depends on current  draw.... and length.

Jim   VE7RF 

77000 V loaded....center tap wud be nice for the screens..I have a 400 amp service..and lots of big cu wire..

Good luck

Hi,

the following schematic is working for years in my installation. I use 5 transformers for 10Kv/3A. You can use as many transformers as you wish in order to reach your desired dc voltage. You can energize them from one phase or from different phases and in case you wish less voltage, you can use part of them. You can of course energize them randomly, no problem at all who will be the first or the second or the last one.
Use bridges and caps for at least 3x the secondary ac voltage of each transformer.
High voltages need very special care … TAKE ALWAYS THAT CARE ….

Stefano

Stefano
 
I see the potential for exceeding the voltage rating of the insulation on the transformer. Do you have the transformer mounted on insulators or just wing it. Even on insulators there is the risk primary to secondary arc. IF you are using 2500 vac transformers do you think that that insulation will handle 7kv or more? I'm just curious.

Johnathan N8QPC

Jacob used to put 6 or more microwave oven transformers, with secondaries in series, in a vat of oil. Not exactly safe.

Jonathan,

I haven't connected the transformers' secondaries  in series as it is suggested in previous comments.
My supply with multiple transformers in series connects the regulated dc of each supply. This way there is not stretching to any ac secondary. There is not also stretching to any of the bridges and capacitor banks as far each of them is enough for the regulated dc. Per example if the lowest transformer - the closed to the ground one - is let say 1000vac we'll need 8 diodes bridge and 5x450v electrolytics in series, if the next one is 2200vac we'll need 16 diodes bridge and 8x450v electrolytics and if the upper one - the closest to the B+ - is 3500vac we'll need 28 diodes bridge and 12x450v electrolytics. This way diodes and capacitors will have a good safety factor for 1.41x ac to dc regulation. I of course have the transformers on plywood but not because they need extra isolation just for mechanical reasons. On the contrary there is isolation problems if you connect the secondaries in series and then you regulate the total dc with a single bridge and a single capacitor bank. In such a case the top transformer isolation will have to stand the total secondaries dc voltage which is dangerous for the irons but mostly for the humans.

Stefano

If the the transformers are wired as shown. The. DC of the prooceding supplies will be on the secondary of the following transformer. The negative end of the following bridge provides  a path to the secondary of the following transformer. If you don't belive me make the same circuit with some low voltage transformers and make measurements at the secondaries to ground. Stay safe and have fun. Don't be a ground.

Johnathan  n8qpc

This is not a theoretic schematic, this was a working project for many years in my very demanding linear amplifier with a 4cx15000. The transformers were floating - not grounded - as I said and their isolation primary to secondary was enough to withstand the total output dc voltage. I had never problems and I could each time decide how many of them to use in order to get any desired output dc voltage. On the contrary I had faced different problems when I tried to connect the transformers' ac secondary in series and then to regulate with a single bridge and capacitor bank.

Stefano