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.

I've actually done this to charge a traction battery pack. The only difference was that instead of a stepper motor, a student kept an eye on the multimeter and cranked the Variac down as the battery charged up. Works fine, if a bit labor-intensive.

Zivan makes exactly what you need, if you don't mind buying the charge controller and power supply all packaged into one unit. If you want to roll your own controller, Sorensen probably makes what you need for the power supply.

I just remembered another manufacturer of telecom-type supplies, Valere. Same problem as you have now, though; for most of their products, the world ends at 54 V. They do have a few that are available in 125 V DC output; they are the style where you buy a shelf and then buy modules to plug into it. Usually you can get some kind of data bus to the shelf.

Watchdog timer driving the I/O pin that goes to the big contactor?

Yow! At cell voltages of popular chemistries, and a 120 V pack, you've got somewhere between about 33 and 100 cells, or $4,455 to $13,500 in all.

Matt Roberds

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

Cheers

Phil Hobbs

With a selenium stack? I hope not...

But we don't want to blow oogobs of $$ on fullpriced new...

The 750W ones are $30 each, so we can tolerate some design pain at that delta-$

Not the BIG contactor; charge isolation one.

It's on the lower end but still the biggest investment...

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. :)

No, just a plain old square brick rectifier bridge with Si diodes, something like 600 V, 35 A. I found a piece of random sheet metal lying around the shop and bolted the bridge to that for a heatsink. Heat sink grease was in short supply, so we used a little wheel bearing grease instead. Worked fine, if a bit greasy-smelling when warm.

Understood. I was trying to supply some brand names that might be good keywords for Ebay, Craigslist, etc.

Are the outputs full floating? You could *try* stacking three of them, but as mentioned elsethread, that's generally a bit of a gamble with switchers.

Matt Roberds

I've got an 3 year old one here with a 50Hz transformer. the device weighs about as much in iron and copper as it does in lead. the badge says "Dyn-a-mix" which is the importer's mark.

It's just a little one. 1200VA output, 230Wh of battery.