hefty amps-- DC 24-48V @ 1kA supply

Since regulation isn't important how about a big stack of paralleled lead acid batteries? Star topology wiring would probably be best.

Various manufacturers like lambda power and unipower-corp make SMPSU modules that work in parallel. Unipower TWRI series will do 9000 watts

Bob

Even expensive marine batteries will not supply that kind of current for long.

That's interesting, thanks. Big bus bars I guess. Perhaps $0.50-$1/watt? Best regards, Spehro Pefhany

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You can parallel enough batterys so that it is with the capability of the individual batterys, it's a question of run time between recharges and duty cycle because the batterys will take a while to charge. Can't comment on that without knowing the application.

Elecsol lead acid batterys with carbon fibre in the plates are reasonably priced and can do high currents, deep discharge and 1000 cycles. The limited number of cycles could be a problem. The safety requirements for liquid acid batterys may also be onerous.

Anyway I assume lead-acid is not going to work for you.

Those manufacturers are at the high quality/high price end of things. They are a bit more than $1/w here but we pay far too much tax. If you want cheap you need to be looking at buying direct from China. For example these

Cheap and cheerfull is a bit worrying that this power level. I'd want to fuse the individual outputs and check the individual outputs with a clamp meter and trim them so they balance the load.

Bob

A welding unit as a starting base?

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Most of the ones I've seen are not quite right, and the duty cycle is nothing like 100%, so it's not a great fit. Some welder mfrs make hefty DC supplies using similar technology, but they're still not quite there. Best regards, Spehro Pefhany

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tdipower makes big stuff. I don't know how affordable it is.

For non-surplus affordable, maybe a bunch of Meanwell switchers. Their stuff seems very good and is very low dollars per watt, as in $0.26 per watt for an open-frame pfc switcher. I think they have some kilowatt-range stuff.

I was/am considering stringing eight of their 48 volt switchers in series to get about 400 volts at 3 amps, for about $320 or so.

John

Heh, I'm reminded of the tray of 100 x 100V, 20A darlington TO-3's I saw at work (2N6287??). Would make a great amplifier for some 0.05 ohm speakers. ;-)

Tim

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My exact thoughts were: "that's a whole lot of 2N3055's" :)

[...]

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Mmmm... 2N3055.. shiny...

(but they're far from being darlingtons...) Best regards, Spehro Pefhany

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Have you checked with these people:

Meanwell is just one brand they represent. The supplies including parallel and redundancy operation are top dollar compared to the simpler products of the same wattage, something like 5x; the cost break with quantity is good though.

You could use three single phase welding or plating supplies, one on each phase, and the outputs tied together would have fairly low ripple. The magnetics would be rather large, but the concept is simple. I have worked on DC circuit breaker test sets rated at 1500 amps at 12 volts continuous (that was the small one), and a large one rated about 6000 amps at 20 volts continuous, with pulses to 30,000 amps. That one was in a box the size of a bathroom, and used 24 4000 amp SCRs with water cooling. The SCRs were originally phase-fired to adjust output, but when we replaced them, we used the gates just for on-off control, and a motor-driven Powerstat to adjust the input voltage.

I have seen high current industrial spot welders on sale cheap on eBay and surplus houses, and they convert the line voltage to DC, then use a high frequency inverter to much smaller transformers at 1000-2000 Hz or so. The output still needs to be hefty, but for 1000 amps a 1/4" x 2" bus bar should be fine. You could easily wind your own transformers from toroid cores. A 60 Hz toroid kit rated 1.4 kVA is available from

for about $100, but you would need to remove the 120 VAC primary and rewind it for 480 VAC at 2 kHz.

The basic toroid has 0.7 volts/turn at 60 Hz, so it would have about 23 V/t at 2 kHz. So the primary would be a total of 20 turns. The power rating at

2 kHz would be 46 kVA. You might derate a bit at 2 kHz due to core losses, but three of these puppies will certainly give you 24 volts at 1000 amps, and you can put two loops of bus bar through the cores to get 48 VDC. You will need some hefty rectifiers, but nothing extraordinary.

The devil is in the details, which are left to the designer. The interesting part will be making a 2 kHz 50 kW inverter for 720 VDC (rectified from 480 VAC), but a 20 HP V/F motor controller should be able to do the job with a bit of hacking.

Paul

Spehro Pefhany a écrit :

Not that I have the answer but is it one unit or production?

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I did a quick calculation, should be able to do the output inverter/ rectifier for around $6000, thats at the usuall inflated UK prices, probaly half that if you source the parts localy. You still need a DC supply, 3phase 12 pulse transformer rectifier around 600v DC. I can't do it for you though, too far away, too much aggro.

You might check out second-hand 60Hz plating rectifiers. There were a number going cheap not so long ago, as the domestic board fab businesses in your area went overseas.

They are typically 8-20V as I recall, and may look pretty seedy due to application environment, but were rated for continuous operation and sell by scrap weight + transport.

RL

5X 250 amp CV welders in parallel? ;-)

Good Luck! Rich

Submarine batteries or locomotive batteries would. :-)

Cheers! Rich

I say, divide and conquer. That's what the HV tension-line folks do, hundreds of small modules that can handle a portion of the MV and current, each taking a piece of the total voltage & power.

So, first, sets of 450 PFC DC supplies using 1.2kV components, then say 20 small sets of 2.5kW step-down modules using the 450V as input, and generating 50V (is that right?) and 50A output each. Bottom line, design & debug bulletproof 2.5kW PFC and 50A step-down current-mode modules. Parallel 20 of them for your 50kW 50V 1kA supply.

This is not ~ surplus and is not advertized as shippable outside US, but Atlantic sells it's stuff on the Canadian E-Bay site, so the shipping advisory could probably be extended, on inquiry, as it is not a strict company policy.

RL

Yeah, that one. How else is your 50 kW gonna arrive on site? All the other options for input are 'way expensive. And 'SMPS' for output is easily the best option, since you need to lower the voltage anyhow.

There are bunches of places where the scale of the problem permits economic solutions we low-power peons don't often see. Synchronous rectifiers, for example, might be applied to the

3-phase input power in the form of a motor driven commutator, with a few low-conductance-angle diodes to handle the commutation discontinuities.

You'll need some (small) energy storage at (assuming delta 480V) (480 * sqrt(2)) =3D 700VDC, and should expect ripple commensurate with the cosine of the half-conduction-angle ... which leads to the 'SMPS' part, where you want to use ganged multiphase converters (figure on 6 or 8 phases, and you can get down to '2% ripple' without much/any output filtering).

For an enclosure, see if Bud makes heavy-gauge concrete boxes...