Seeking: ~120V DC 20A supply

Looking at the

From reading mentions of GFCI's, it sounds like this design is not isolated. We have debated that issue, and for now at least, we want isolation.

I don't know if the other 2 folks have seen the thread, but I will point it out to them.

A thousand dollars for that joke in conduit box?

It's not isolated. Why not just do a triac phase control, if isolation isn't needed?

The switcher in the VFD's I know are switching rectified line voltage to create 3 phase; there are thus six sets of power semis. The control function is to vary the frequency while firing the semis in sequence. The output is 3phase AC, but hardly sine waves.

I can't see what that has in common with a high power multi-tens of KHz switcher, with a transformer suitable at the frequency & power level.

While I've not repaired any VFD's, I've read a bunch of spec sheets while seeking one. None I saw alluded to a HF transformer.

The UPS's I have scraped have real, 60 Hz, transformer iron.

We want isolation. That means a transformer. At 60 Hz, that is huge, but at 100 KHz, far less so.

Modified sine or the ancient six-step? That must have been a real cheapo VFD. The ones I dealt with had a real clean sine wave coming out. You do not have to buy three-phase, they also come single-phase.

Well, it's been a while but the ones I saw had that in there. Plus a bridge which you'd have to disable or bypass.

If you mean a big ferrite transformer, all the ones I looked at had those.

Wow, those must be from the days of Fred Flintstone :-)

Fast forward 40 years and check out a modern "real" UPS in detail:

Still, kilowatts of drivers and transformers and rectifiers is non-trivial. There will be hundreds of watts of heat to get rid of.

There is another thread where someone showed a 3kW charger. Here are the

specs:

The thread is:

Meanwell makes battery chargers up to 1000W standard, and possibly up to

Maybe you can use three chargers.

Paul

Meanwell supplies are cheap and seem to be very reliable. A mess of them might be a good basis for a charger. We are paying under 25 cents/watt for an open-frame PFC supply.

Not necessarily. I just sim'd another converter, a step-up to 28V. Including magnetics losses it clocks in at slightly above 97%. When the boards come back they are usually about where the sim said.

I still think Mike Engelhardt should get a Nobel prize for LTSpice.

Electronics needs their own prize system: The Decibel! That way you can not only recognize someone, you can rate them. Some may reach 100 dB, while others hit the noise floor at -100 dB.

Reminds me of a much needed SI unit--the millihelen, i.e. the amount of beauty required to launch one ship.

Cheers

Phil Hobbs

You also have to factor in the size of the ship and how ugly it is, if you really want to get the right number. :)

someone

Many years ago HP used to sell them. They were very expensive for what they did.

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