Potential Transformers

[Emma Black]

Hey all, I scored some potential transformers. They are surplus from a new biomass power plant and even though I only paid scrap prices, they turned out to be brand new with a full testing report. Maybe these are a bit over the top given the much smaller and smarter options now available.

For a fusor would these be ok ran at the 50Hz grid frequency or would I be better off increasing it to smooth things out? Obviously with suitable rectification , grounding ballast etc.

[Richard Hull]

If the voltage rating of the primaries is 33kv like it says, You have struck it rich!! These are even better than x-ray transformers! (no oil!)

Potential transformers operated in reverse are ideal and even though rated normally around 500-1000VA they will gladly supply 2-3X their rated power in regular use. I have used them extensively in my Tesla coil work and have about 5 hanging around the lab. The issue in filtering and can only be done once rectified by very high voltage capacitors to create stable DC at loads. You need not have stable DC for fusor use!!! Reduced performance can be had by suitable full-wave rectification!! This again demands some very expensive diodes.

Another key issue pops up here. The base plate on many of these transformers is grounded and the center tap of the high voltage side (the top terminals) is connected to the grounded plate. This is a big issue and creates all manner of issues for fusor use where safety grounding issues raises its nasty and deadly lethal head.

With 33kv out of the top terminals, you might only have 16.5kv from each to ground, ( bottom grounded plate.) You must ohm this out and report back to us here!!

Take an ohmeter and measure from each HV terminal to the metal plate if the readings are about the same, you have a center tapped ground to the base plate. If open (no ohmddic reading) you are in great shape. However, I bet you will get readings.

Do not proceed to use these without getting back to us! With their power rating they will kill instantly if not used in a proper manner!

Richard Hull

[Emma Black]

Hey Richard, thanks for the info.

I wondered about that to, as initially there was a bolt on the back which looked like it went right into the plastic. On closer inspection though, it doesn't, there is a weird hollow in the mounding.

Anyway I just went out and tested. Nothing, triple checked, they are not grounded to the baseplate

[Richard Hull]

Neither top bolt will be grounded to the base plate. There might be some high resistance to the base plate of a number of kilohms! As half of the secondary, (midpoint in the winding), might be grounded to the base plate. Example: Across the two high voltage terminals 70k ohms....One terminal to the base plate 35k ohms.

Only special transformers with only a single HV terminal have the bottom of the HV secondary winding grounded to the base plate. Example: 70k ohms to base plate.

Richard Hull

[Emma Black]

Apologies, I meant theres no connection, not grounded! It's an open circuit between the baseplate and either top bots and 22k ohms between the two.

[Richard Hull]

If this is truly the case, you have a totally unground referenced HV winding. A four diode bridge of sufficient voltage will supply your fusor at full voltage on the 110 volt line with a peak voltage of 33X1.414 = 46,000 volts DC unfiltered at 100 HZ. You wound need to ground the positive output of the bridge to the plate and also electrical ground the plate, as well. This will make the negative of the bridge your hot fusion lead.

If you do this, take your bridge grounded system up to full voltage before you hook up the fusor. If your secondary is ground referenced, at least two of the diodes will explode! If no explosion you should be good to go.

HV knobs on potential transformers are traditionally ground referenced, (center tapped winding to ground). You have a rare beast.

As you acquired three at once, they may have been 3 phase types and could not be ground referenced in a leg.

Richard Hull

[Matt_Gibson]

I work for an electric utility and we have tons of these. I need to see if we have any 69kV ones that have just been sitting around needing to be taken off the books

-Matt

[Richard Hull]

Matt sounds like he understands. I always was amused at what the power companies call the primary, we call our secondary. The power company had them made up and due to the usage, they are correct. We are using them backwards and as such, the design in our use is not magnetically optimum, but they function great for our purposes.

Richard Hull

[Emma Black]

Followed your suggestion Richard. Im pleased to report no diode explosions. After this, added a big resistor and threw together what I'm calling the "1 minute fusor". Will add the obvious that I didn't dare run this completely ungrounded wired safety nightmare of setup for more than a few seconds (at a distance) and the voltages were comparatively low.

Next step to wire up everything properly under oil with all the metering etc.

[Richard Hull]

That entire head is lethal! I sometimes am amazed at what is presented to me. 24 gauge clip leads can handle any current during normal fusor runs but act as fuses during any arc conditions. The 300 volt wire insulation adds to the illusion of the entire scenario of transporting and insulating up to 33 KV to the Hot feed thru gauge set. The gauge sitting at full high voltage does indeed show you have a vacuum of unknown pressure.

I love the "high tension" connection to the gauge set in the first photo, as well at the high voltage chamber standoff, cardboard box! Nice.

Nice kludge to get a glow discharge. A poster image for how to obtain the most lethal possible demo setup. It appears even the shell might be lethal. A nice example of a hands-on assembly of a hands-off demo fusor. The one positive is It works!


I am glad you realize the danger of what I see here.

As I tell all working with HV here.....Enjoy life, it may be short.

Richard Hull

[Matt_Gibson]

Looks like your PTs and your pump works….Now that you’ve been bitten by the bug (assuming?), work on a more safe and reliable setup. You’ll need better gauges and some reliable ways to measure voltage and current.

Focus on ease of operation over cost, it’ll be worth it! Trying to fuss around with difficult controls/locations and not trusting your values can take the joy out of things…

Think about safety (#1) and accuracy.

I think that the reason that most people seem to achieve fusion and then bounce is because they kludged everything together and operating their fusor became a chore.

-Matt

[Emma Black]

To be clear I am very aware this is a totally inappropriate setup for anything other than very nervously double checking if the transformer was centre tapped and this was not intended as a serious post.

The wiring etc is completely inadequate and dangerous for a vast number of reasons and probably more I can’t even think of!

I was many feet away with the variac on a long extension lead and unplugged the thing before going near it.

As for using borrowing my resin casting vac chamber I think the 1 minute setup included taking it off the shelf, kinda surprised it made any plasma to be honest.

[Emma Black]

As a follow up, ease of operation sounds like a good thing to focus on.

Operating a fusor fully manually from my reading so far and very limited experience seems similar to driving a Ford Model T, where you have to manage the spark gap, hand throttle etc. Friends uncle has one and it’s hard work but very satisfying once you get the hang of it.

I have been thinking about some slightly automated controls for further down the line, I.e. being able to adjust the voltage and gas flow digitally.

[Matt_Gibson]

Digital controls are nice, but you should focus on taking baby steps. Once you get a reliable and easy to operate setup, then you can start upgrading each sub assembly/system one at a time. Keep your eyes on eBay and snipe!

[Emma Black]

Totally, want to go super slowly this is a very long term project after all. First step is to make a lovely power supply.

EBay is dangerous for bank balances. I already scored a nice diffusion pump and one of the Ludlum 2363’s…

[Alex Aitken]

Should the pump have any extra grounding on account of low pressure gas sometimes being a good conductor?

[Richard Hull]

As an auto restorer in the 80's (50-60s Lincoln Continentals), it is rare to hear someone speak to the model T, especially the need to work the spark advance lever to adjust as you drive. Later taken care of in the distributor's auto-vacuum advance.

If you stick with the fusor effort, you will learn that same feel for operation that is pretty cool once you master it, just like the model T.

For Alex...Yes, all pumps and electronics need to have a common ground to the home electrical system.

Richard Hull

[Emma Black]

Bit of an update, the bridge, big resistors etc have now gone into a nice neat box, with the PT output running though conduit all oil filled. Its vented and we will see how warm it gets.

People talk about mentioning the failures so I will mention my idiotic moment.

Before filling with oil I tested it dry, all good no issues at lowish voltage. One solder joint, right at the bottom looked a bit dry though so added some more solder . Without thinking poured the oil in immediately without letting the joint cool down.
Once the oil was in, suddenly nothing worked. The joint had cracked and wire had somehow come completely off. After a lovely mess of oil to cleanup later and we are back in business. I think crimp next time.

Next job, route the HV line through some pipes and put everything in one of the server racks I've liberated from a data centre decom

[Richard Hull]

Got enough oil for that diff pump? Looks like it could pump down a school bus interior. 14-16-inch throat?

Richard Hull

[Emma Black]

I know it’s massive (iso160) going to need a serious reducer - have enough dc704 to fill it once at the minute.

[John Futter]

that pump looks like a 1000/l/s edwards diff stack
more than adequate. To get full pumping speed out of it it requires an Edwards RV18 backing pump
I used two of these pumps on my 120kV ion implanter i built @ work

[Emma Black]

Wow! Thats an amazing setup. Pump is a 700c & lucky have an Edwards 18, need to figure out the cooling etc.