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klugesmith

Thu Apr 25 2013, 08:22PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

Ash, this magnet (which I have no room to build) is driving me to distraction.
The 3/0 Al wire was just put up as an example of being flexible if the goal is to minimize materials cost.
You're right about it being better to match more convenient power supply voltages.

I found that heavy gauge copper building wire goes for less money per pound (of Cu) than magnet wire. The thicker insulation makes it bulkier, but as stranded wire it's easier to wind. And could always be unwound and re-sold as useful building wire.

AWG #2 copper is about right for 12 volt designs of this diameter. There's a 500 foot length (whose wooden spool was damaged) on ebay for $600 or best offer; that's 100 lbs of Cu at $6/lb.
Just right for my original Version 2 design: same 1923 watts, now 186 turns x 155 amps, 12.4 volts.
As I explained yesterday, one could use a shorter length of that wire to make the coils more compact.
Voltage requirement would be unchanged, but current and power would go up.

At my day job we use large numbers of compact 12 volt 200 amp SMPS's.
There are also mains-frequency transformer options (e.g. for low voltage lighting),
MOT rewinds (perhaps 2 in series to get the power; easy to air-cool),
and heavy-duty car alternators. How 'bout driving around with a mobile cyclotron instead of an earth-shaking amplified sound system?

[edit] For a better match to your welder, coils made with AWG #6 wire would take about 31 volts.
If you use the full 43.6 kg of Cu, that would be 470 turns x 61 amperes, with 0.5-ohm coil R.

Ash Small

Fri Apr 26 2013, 08:57AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

That's an interesting point you make about car alternators, Rich. It's the voltage regulation that limits them. It's quite easy to 'hack' them to produce higher voltages, easily up to 120V (you may have to fit diodes of higher voltage rating for rectification).

I assume you'd still be able to pull 60-80 amps from them at higher voltage. There are numerous 'how to's' on the internet.

Steve Conner

Fri Apr 26 2013, 09:34AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I believe the original cyclotrons had their magnets powered by motor generators, as they were built before good high-current rectifiers became available. A car alternator might be a vintage-correct solution.

The problem with building wire is that it has PVC insulation that softens and shorts out at a relatively low temperature compared to "real" magnet wire.

A cost-benefit analysis should include the cost of any power supply parts that you don't already have lying around the junk box (shed, 40 foot container, warehouse

)

Ash Small

Fri Apr 26 2013, 12:38PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Steve Conner wrote ...

I believe the original cyclotrons had their magnets powered by motor generators, as they were built before good high-current rectifiers became available. A car alternator might be a vintage-correct solution.

Would these not have been dynamo powered? Alternators still require 'good high-current rectifiers'.

Steve Conner

Fri Apr 26 2013, 12:58PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Yes, a motor generator was a kind of primitive mechanical rectifier, a 3 phase induction motor driving a brushed DC generator. You also got a "rotary converter", which was the same thing but combined into a single machine. In both cases the rectification was mechanical by a commutator and brushes.

So if you want to be pedantic, an induction motor driving a car alternator isn't really vintage correct, you would have to use a dynamo from an ancient car.

Noah Hoppis

Fri Apr 26 2013, 03:57PM

Registered Member #10072 Joined: Thu Feb 14 2013, 05:12AM
Location: seattle wa
Posts: 21

True that most alternators are rather flimsy nowadays, I have seen several horse power DC motors that are about 1.5ft in diameter around but they went of to scrap long ago

. Wonder about welding transformers, I have on rated for 250A @ 2.5V and given enough transformers in series then a good output could be achieved. Aluminum wire was a clever idea, I recently bought 90ft for $15.

...

Fri Apr 26 2013, 09:50PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

For power, just get a vicor megapak off ebay (then usually go for $100-200). Most of them will run from single phase, although I think some of the higher power ones will shut down if you try and draw the full 4kw from a single phase 240v line. Most of them are adjustable (they don't state it, but there is a header for 'trimming' the output) 90-110%, although some of them are adjustable 10-110% (unfortunately, it is almost never stated on the sticker which type of vicor brick is used internally), but if you get one that is like 10x 5v modules you can tap to the nearest 5v and use a large resistor (or transistor + opamp system) to do the fine tuning.

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