## Portable DC source for electric arc-Ruby synthesis by the Henry Moissan method

I am looking for a DC portable power supply for an electric arc with the following parameters 50V,25 to 30A so that it can work for 15 to 20 minutes continuously for the melting of chromium-doped Al2O3,it is Henry Moissan's experiment with the synthesis of ruby in an electric arc furnace.I am not experienced in electrical engineering,can anyone advise me?I thought of implementing the project with four 12V car batteries and placing inductance to them.Or use supercapacitors,maybe it would be a cheaper and more elegant solution??Thanks!

RU_KLO - 22-12-2022 at 09:55

1st: Im no Engineer, but do electronics as hobby from the last 30 years. mostly below 5 Amp circuits. So take this as a guide for consulting even further.

2nd: You are asking 50V 25A, did you meassure the resistance from the inductor coil? Where the circuit comes? Was it tested? its your own invention?

For the great amout of Amps needed, your 4 battery is very dangerous, taking 25-30 Amps for a long time more (than few seconds). from battery is no good - heating /explotion hazzard.

"What happens if you pull too many amps from a battery?
Drawing lots of current from a lead Acid battery will simply make it hot, it may in some circumstances melt the terminals or part of the internal connections"

If you have a 12V battery and you're asking how much amperage can it kick out, the answer is however much or little it has to to satisfy Ohm's law, V = IR. The less resistance you have in a circuit, the more current will flow and vice versa. The absolute extreme of this would be if you had zero resistance (an ideal short circuit), then the poor battery would try to crank out infinite current to maintain the relationship. That means kaboom.

Of course, there will always be some resistance in the real world so your battery will probably only have to try to crank out thousands of amps - still kaboom.

To answer your question: How many amps a battery supplies depends entirely on the voltage of the battery and the resistance in the circuit. It is not a fixed value for any one battery or class of batteries. Even the resistance of the circuit is not necessarily a fixed value, it would depend on factors like the level of corrosion in the terminals and the temperature of the conducting wires. If you want a ballpark of how much current your battery sometimes supplies, check the cold crank amperage rating.
"

some ideas:

other way is to have a motor/dynamo (aka generator) to get the desirable voltage/ amps

also : 220V/110V generator + step down SMPS (you will need to find a suitable SMPS. goggle: 50V 30A SMPS and you will find some.

please keep in mind that: 50V x 30A is 1500W. if SMPs has a 80% efficieny this means you will need 1875W add 20% headroom: 2.250W, lets keep it at 2.5KW (your generator should be capable of generate 2.5KW)

and also a fan (things will get hot) 25A is hot. (melting hot)

High current / short cables should be used.

rounding up: if you do not have experience with high ampere (> 5A) circuits, my recomendation is : do not attempt this or search for professional help.

Fulmen - 22-12-2022 at 12:11

1500W of power is about 10 times more than you should be starting with.
blogfast25 - 22-12-2022 at 13:03

 Quote: Originally posted by Admagistr it is Henry Moissan's experiment with the synthesis of ruby in an electric arc furnace.

So you have a reference for this method? Share!

Quote: Originally posted by blogfast25
 Quote: Originally posted by Admagistr it is Henry Moissan's experiment with the synthesis of ruby in an electric arc furnace.

So you have a reference for this method? Share!

I am sending it as a pdf attachment;-)

Attachment: Rubies by Moissan..pdf (896kB)

Sulaiman - 22-12-2022 at 16:10

1 from the pdf it seems that you are going to vapourise Cr2O3 so you need to avoid any fumes generated.

2 you could use a.c. or d.c. as it is only for heating, not electrolysis.

3 what vessel and electrodes do you intend to use?
(I guess that carbon electrodes may introduce unwanted carbon into the mix etc.)

4 I also guess that the voltage and current are used to create the required temperatures,
so by my guesswork you could use higher voltage and lower current.
The current being determined by electrode spacing, so you have many options.

I imagine that a significant problem will be current-limiting the power supply when starting an arc.

I wish you good luck - take care

blogfast25 - 22-12-2022 at 16:38

Quote: Originally posted by blogfast25
 Quote: Originally posted by Admagistr it is Henry Moissan's experiment with the synthesis of ruby in an electric arc furnace.

So you have a reference for this method? Share!

I am sending it as a pdf attachment;-)

Thank you...

It's definitely something to pursue. Moissan's a hero of mine...

[Edited on 23-12-2022 by blogfast25]

 Quote: Originally posted by Sulaiman 1 from the pdf it seems that you are going to vapourise Cr2O3 so you need to avoid any fumes generated. 2 you could use a.c. or d.c. as it is only for heating, not electrolysis. 3 what vessel and electrodes do you intend to use? (I guess that carbon electrodes may introduce unwanted carbon into the mix etc.) 4 I also guess that the voltage and current are used to create the required temperatures, so by my guesswork you could use higher voltage and lower current. The current being determined by electrode spacing, so you have many options. I imagine that a significant problem will be current-limiting the power supply when starting an arc. I wish you good luck - take care

Thanks a lot! For the first experiment I want to use a crucible of chemically pure carbon (graphite) with an approximate purity of 99.99-99.999%,fortunately I have it and electrodes of carbon with a purity of 99.9%,I want to place the electrodes just above the mixture so that they are not in direct contact with it.Later I would perhaps use tungsten electrodes in an argon atmosphere if the results with carbon are not good. I recently got magnesite bricks from a dealer,who operates near where I live,I think they are much better for furnace construction,than the air and moisture reactive CaO,which Moissan used. Can you think of a suitable, relatively cheap power supply that you would recommend for me:-)?It's really about the right temperature...Do you think I could use the mentioned battery of supercapacitors,maybe with some current regulating resistor?Have a nice day and thanks!

 Quote: Originally posted by Sulaiman 1 from the pdf it seems that you are going to vapourise Cr2O3 so you need to avoid any fumes generated. 2 you could use a.c. or d.c. as it is only for heating, not electrolysis. 3 what vessel and electrodes do you intend to use? (I guess that carbon electrodes may introduce unwanted carbon into the mix etc.) 4 I also guess that the voltage and current are used to create the required temperatures, so by my guesswork you could use higher voltage and lower current. The current being determined by electrode spacing, so you have many options. I imagine that a significant problem will be current-limiting the power supply when starting an arc. I wish you good luck - take care

I found this power supply recently,but it is expensive and dependent on the 230V electricity grid.
https://www.ampul.eu/cs/spinane-zdroje/2327-napajeci-zdroj-5...

Thank you for your honest answer!I haven't tried it yet, it's still my theoretical, unrealized idea, but I asked a man who is an experienced electrician and he told me that he once built such a device as a welder from car batteries and it worked great and without problems...

violet sin - 22-12-2022 at 17:29

If you were going to spend a decent chunk of money, see if you can get something useful for other things. Like a small generator instead of some batteries, or a small TIG welder instead of just a power supply.

I see some generators at 4kw range for as low as 200\$. Don't imagine they gonna last forever but the price point is right. That's for me in USA though, not sure if the availability in your area. Thanks for the post card Admagistr

Here's a welder, stick and TIG from closter to you vendor.
https://m.aliexpress.us/item/3256802881378736.html

unionised - 23-12-2022 at 01:11

How did Moissan get those currents and voltages?
Can you copy that?

 Quote: Originally posted by unionised How did Moissan get those currents and voltages? Can you copy that?

Moissan used a dynamo.I send this very interesting book attached.It's on page 4

Attachment: Moissan The electric furnace.pdf (6.4MB)

I wish everyone a Merry Christmas!
Junk_Enginerd - 23-12-2022 at 13:26

I may be mostly useless in this forum, as a pretty poor chemist, but I'm at least a damn solid electrical engineer!

1500 W for 20 minutes, that's 500 Wh. Standard 60 Ah 12 V batteries times 4 gets you roughly 3000 Wh, so that works. Car batteries are never actually 60 Ah in practice though, but you've got some margin.

The problem is you wouldn't have anything regulating the current and that's problematic. AC is convenient for this purpose since you can both limit the current, voltage and power and you also get a bit of the arc stabilizing effect that an inductance provides thanks to using a transformer.

While a typical welder(the go to device for this process) is indeed around 50 Volts, that's not at all the voltage you should supply. You see, welding machines aren't really voltage regulated at all(MIG welders excepted). The voltage just is whatever it is as the current is regulated. Open circuit, in a non loaded state, this is about 50 V. 50 V happens to be about as much voltage as can be considered safe to touch. It's good to keep this as high as possible because it makes it easier to strike an arc. Once an arc is struck however, the voltage supplied by the welder will not be anywhere near 50 V. In a normal welding situation it'll be more likely to be about 12 V, because that's about the voltage drop of a continuous arc of that size. If the arc is about to go out, the voltage drop will rise, and the welder will raise its voltage in response, to try and keep a constant current going.

A pack of batteries won't do this. If you use a 48 V battery pack and strike an arc with it, you'll get pretty undesirable results once the arc is struck. Because again, the voltage across the arc drops to maybe 12 V. But we are feeding it 48 V. Sooo... We have 36 V more to burn! The arc is roughly 12 V regardless. That means the current will rise to whatever is needed to create a 36 V drop across the circuit as a whole, whether it's in the batteries internal resistance or the cables. That's A LOT of current. It'll probably soar to many hundreds of amps and either your cables are gonna catch fire, or if they're properly dimensioned the battery will catch fire instead...

It all boils down to that batteries are ideally a voltage source, while for your application you need a current source.

A battery powered constant current driver at these power levels isn't something you'll be building yourself, nor something I can imagine existing as an off the shelf product.

The best compromise I can think of is using only a 12 V battery, which hopefully will match the arc voltage better. Striking the arc will be finnicky, and sustaining the arc will require careful regulation of the arc gap distance. An inductor would help with both of these issues, but ho boy that's going to be a really big inductor. Could be done, but I think it might be quite annoying and difficult to use.

blogfast25 - 23-12-2022 at 13:42

 Quote: Originally posted by Junk_Enginerd Could be done, but I think it might be quite annoying and difficult to use.

Nice explanation, thanks!

So no handy-dandy circuit diagram we could use as a starting point?

Thanks a lot for the detailed analysis!I have the same question as my colleague blogfast25;-)!

Waffle_staffel - 23-12-2022 at 19:52

The cheapest and simplest method would be to make a salt water variable resistor/welder. As hair raising as that sounds, one can be made to operate safely. I believe both YouTubers NightHawkInLight and The King of Random have videos on constructing such power supplies and making rubies.

It's certainly safer for the novice than fooling with microwave transformers, which is another popular method. [I'm not saying either is safe or should be attempted without careful study and precaution] If you have access to a welder, you could use that too. A headstone or stick welder will do. A wirefeed welder should work, but would need some simple modifications.

I've seen cheap graphite crucibles used. I'm not sure whether an alumina crucible would hold up to the heat or react. The best and most readily available refractory material for holding in the heat/arc would be regular alumina firebrick. They're not very expensive, and get cheaper by the quantity. They can be carved and sanded easily. Kaowool is an inexpensive alternative, but may be difficult to shape without being coated with a sodium silicate solution and fired to reinforce. Shake the Future has a really good video on making DIY microwave kilns, which covers the fundamentals of working kaowool in this fashion.

Speaking of microwaves... you can also make rubies in the microwave!

Be sure and show us your results

[Edited on 12-24-2022 by Waffle_staffel]

wg48temp9 - 25-12-2022 at 09:08

There are some used server 12v power supplies on ebay UK selling for about £10. They range from about 570W up to 900W. For a carbon arc you probably only need two or three of them plus a ballast.

A salt water ballast may be simple but will be messy at 30A with the mist and corrosion. Perhaps strips of sheet steel could be used as a restive ballast.

see: https://www.ebay.co.uk/itm/195463881349?_trkparms=amclksrc%3...

[Edited on 12/25/2022 by wg48temp9]

[Edited on 12/25/2022 by wg48temp9]

blogfast25 - 25-12-2022 at 10:17

 Quote: Originally posted by Waffle_staffel Speaking of microwaves... you can also make rubies in the microwave! Be sure and show us your results

Thanks for all the info, Waffle!

Quote: Originally posted by blogfast25
 Quote: Originally posted by Waffle_staffel Speaking of microwaves... you can also make rubies in the microwave! Be sure and show us your results

Thanks for all the info, Waffle!

Thank you all for the information!

Twospoons - 25-12-2022 at 11:46

The difficulty you face with using server power supplies is the internal overcurrent protection - exceed the limit even briefly and its likely the power supply will shut down, and wont restart until its powered off completely.
Honestly, your best bet is to repurpose an arc welder and forget about trying to use batteries.

If you must go DIY, there is always the option of rewinding a microwave oven transformer: the HV windings get cut out and replaced with a few turns of really heavy gauge wire. Leaving the magnetic shunts in place helps limit the current when you short the new secondary winding. Quite a few spot welders get built this way.

[Edited on 25-12-2022 by Twospoons]

metalresearcher - 25-12-2022 at 12:51

I tried using a DC welder, using a block of graphite as anode and a carbon rod as cathode.
That worked somewhat.
https://www.metallab.net/jwplayer/video.php?v=L2NsaXBzL1N5bn...

Junk_Enginerd - 26-12-2022 at 00:32

Quote: Originally posted by blogfast25
 Quote: Originally posted by Junk_Enginerd Could be done, but I think it might be quite annoying and difficult to use.

Nice explanation, thanks!

So no handy-dandy circuit diagram we could use as a starting point?

The only circuit diagram I could recommend for "converting a battery from a voltage source to a current source" will be no sort of handy-dandy, I assure you haha. That would be a very complicated switched mode current regulator. Like full time several months of work complicated.

This gave me an idea though... I suppose it should be possible to make a battery powered welder by buying an inverter welder, and then substitute the part(switched transformer) where 230/110 VAC gets converted to a lower voltage, with batteries. Not simple by any means, but certainly more in the realm of amateur/enthusiast than designing a high current smps. That would give you all the convenient and user friendly features of the welder, and provide the battery powered freedom.

[Edited on 26-12-2022 by Junk_Enginerd]

Twospoons - 26-12-2022 at 13:44

One other advantage of buying a stick welder for this is when you have finished playing with your arc furnace you have a handy stick welder for joining pieces of steel.

I remember when I was buying a MIG welder so I could fix a rotary hoe, the store clerk asked why I didn't just buy a new rotary hoe - at which point I explained that this way I get both a hoe and a welder. And its been handy to have that welder available over the years.

wg48temp9 - 27-12-2022 at 02:45

If operating from the mains is acceptable, then yes the stick welder solution is the way to go. You can buy old hobby welders on ebay for as little as £10, the current is adjustable and the AC will burn the two electrodes evenly.

The wiring up three server power supplies in series is potentially difficult because to avoid revers biasing the input of any one off them you need series diodes between them and in parallel across each one. The diodes can cost more than the power supplies. However four of them will make a nice supply for a milti kilowatt induction heater.