How to switch HV between AC and DC

[FPS]

I'd like to build a power supply that will be able to be switched between AC and DC. I'd like to avoid changing leads around and since I think it's very difficult to switch the HV side, short of a massive HV relay, is it best to just use 2 transformers and switch the primary side? This is what I'm planning atm, as attached.

Now the left AC side should be about 30kV, and the DC side on right about 150kV.

What I don't know is how the DC side will effect the AC side since its effectively shorted through the AC transformers secondary. Is this a problem and how can it be fixed? Will a capacitor in series between the AC transformer and output terminal solve this issue? If so what sort of capacitor?

[Anders Mikkelsen]

Exactly what are you trying to achieve with this? Some more context makes it easier to give useful advice. How much power are you aiming for and what is the nature of the load?

You can't connect them in parallel, the rectifier would short the AC output, and the AC transformer secondary would short the DC output. The former can be addressed by a DC blocking cap (at the cost of some reactive current flow), while latter issue would require an impractically large AC blocking inductor in series with the rectifier. Relays would be a lot more compact and cheaper compared to a kilohenry 30 kV inductor

[FPS]

Yeh I had noticed the right hand side was going to be even more a problem then the left after posting that. I was hoping there was a solution that I wasn't seeing, but I guess there isn't.

A >30kV vacuum relay is looking to be about $2k, not really feasible at this time. There's a few open 40kV used Ross relays getting about for not much cheaper and generally 115v, not practical here. Making one may be an option but not one I'm enthusiastic about.

I've no practical purpose in mind for this I just want it.

[TizianoBll]

150kV DC is quite a lot, Did you already build the multiplier? I'm not sure if you'll be able to reach 150kV.
Anyway, you can use this simple schematic (image down) and build a diy high voltage relay for cheap using a DC motor and some basic materials. Just like this guy did -> youtube, but in larger scale.

[FPS]

Nah I haven't built the multiplier, but I don't think 5x is too much of a stretch. I was planning on using 50kV 2200pF capacitors in it, drawn from 2x 18kV transformers in series.

A fully enclosed latching relay would be ideal as I could just completely smother everything in resin, and it won't continually suck power out of the system which is powered by a 48v battery.

https://dc-components.com/wp-content/uploads/GIGAVAC-G61LC-HV-Relay.pdf

One possibility above but its only 60Hz rated I assume at 25kHz the rating would be lower.

[TizianoBll]

You need a 150kV make and break relay.
If you search online you can see that it's a common practice to have the generation circuit in resin and a custom relay/switch in air (teardown).

[FPS]

Yeh I think you are right, I hadn't bargained on this being so hard. I thought I'd be able to switch the 30kV before the multiplier but attempting to draw it out wasn't so successful at least not with a single DPST relay. The only sensible solution left is swapping leads around, if you switch it at the 150kV side but leave it energised it'll still be dumping corona.