Sciencemadness Discussion Board

Building An Carbon Arc Furnace

symboom - 26-1-2012 at 19:14

so im getting one more 12v battery together for a total of 36volts in series ive seen people use batteries for welding so maybe this could be used to make calcium carbide
combining calcium oxide and carbon.
any suggestions.

White Yeti - 27-1-2012 at 08:06

Pessimistic opinion:
It's not worth making a carbon arc furnace to make calcium carbide, you're better off just buying it. Not only do you need high voltage, but you also need massive amounts of current. The best you could do with 2 batteries is a miniature for demonstration purposes.

Mr. Wizard - 27-1-2012 at 08:11

You may get a arc, and you may reach high temperatures, but the large amount of heat and energy you will need on a sustained heat of anything more than grams of carbide will be hard to reach. The batteries will deliver the high current for a short time and then either be overheated, destroyed or need a recharge.

A carbon arc starts with a high voltage in the range of your 3 battery combination, but another battery would make the arc easier to start and maintain. Once the arc starts the resistance of the arc is very low and represents almost a direct short to the batteries, which then are overloaded. Lead acid batteries are a better impedance match for the low resistance load than any other type of battery, but even they are not designed to do this for any length of time or very often. What will also happen is the arc will start and melt or heat up your carbon and CaO mix and form a conducting path that may have a similar low resistance. Your plan will work for a short time or for a demonstration, in my opinion. The cost, bulk, and time involved with automotive batteries is high.

Here are some other options:

First would be an old fashioned 'stick' welder, operated from the mains. They have a 'duty cycle' that may allow continuous use on the lower amperage settings. A variation of this would be a rewound microwave oven transformers (MOT) wound with heavy gauge wire to deliver more current. A few of these could be wound in parallel to deliver kilowatts of power. There are many net sites describing MOT welders.

Second and cheapest is using a resistance load to safely limit current directly from the AC mains. My first arc furnace used a 1500 watt light bulb as its current limiter. These were used in school auditoriums as overhead lighting back in the 1960s. The way it works is the cold resistance of the filament is low, but once the current starts to flow the filament heats up and increases resistance, and cuts the current. Since the bulb is designed to handle the full 1500 watts, a direct short of the arc carbons just results in a bright bulb, and no damage to anything. Other resistive loads such as space heaters or even banks of 100 watt light bulbs in parallel can be a fail safe automatic load limiters. The down side of this is that full mains voltage is on the carbons when they are exposed, and you can get a lethal shock. The other downside is all the power used in the resistive load limiters is wasted. Since you are not doing a commercial set up, that shouldn't matter much. Do be careful with the mains voltage. A good safety rule is to keep one hand in your pocket, and only use one hand to touch or reach for things. Light bulbs are cheaper than 12 volt batteries. and MOTs are found in discarded microwave ovens.

quicksilver - 12-2-2012 at 10:02

I've worked a bit with high energy electronics and I have found that when you start dealing with such things the electric meter starts spinning faster than a DVD drive. You can very easily drive a month electric bill up to the four figures with common SMAW welding if you worked full days on large projects. Any level of current needed to spread heat enough to melt and keep melted most materials is simply not feasible for the private individual.
IF you actually want the ability to work with metals: coal is fantastic. A simple hole in the earth lined with thick, high lime concrete and an air in-put duct will do most anything you may want. :P Seriously! Coal works damn well!
The wiring and safety issues with current boosting transformers is a very serious thing & needs quite a bit of study before setup. Full bridge designs also require certain high capacity passive components that can cost a LOT of cash.
I have tried working with high current tools at a private residence and after a certain time period, it just get much too expensive.

Mr. Wizard - 12-2-2012 at 11:19

Coal has it's advantages, especially for the traditional metal heating, and smelting, but he mentioned trying to make calcium carbide. Nobody can argue electricity is a cheap source of energy, but it sure is convenient and indispensable for some jobs.
I pay about $0.11 for a kilowatt hour at my home here in the SW USA. This is about 0.0834 Euros on 12 Feb 2012. What are the rates of other members ? I have relatives in northern California that pay 3 times as much! I agree running an aluminum or carbide manufacturing plant would be expensive, but running an arc furnace at 1-2 KW for a few hours wouldn't cost that much where I live.

Gasoline with 10% ethanol (regular 89 Octane) costs about $3.60 a gallon here, diesel fuel is slightly higher. The ethanol ruins the gas milage. I've had the opportunity to buy gasoline from mountain towns in northern California and the milage is up to 25% better. I can speculate they don't put ethanol in the gasoline there.

condennnsa - 12-2-2012 at 14:54

In Romania we pay 0.4 lei for 1kwh, a dollar is 3.3 lei so that's $0.12/kwh.
I would have thought that in the US electricity is much more expensive than here, guess i was wrong.

Gasoline is $1.8 per litre , and methane $0.38 / cubic meter.

I find that for most hobby projects, if it can be done electric than that's the way to go.
Sure, like quicksilver mentioned, if you're dealing with large projects full days it will go damn expensive, but maybe then it's not just a hobby anymore. Electricity is just so clean.
To give an example, when I built my 2kw resistance electric furnace, it was love at first sight. Sure, it took 1.5 hours to bring 2 litres of Al to 800C but there was no mess, no smoke, I used to work with it next to my bed! And when it was cold outside, the cooling furnace was actually helping in warming the house

quicksilver - 13-2-2012 at 08:29

Best working number is 4 cents (on the US dollar) sounds about right for the southwestern USA (non-California) with surcharges and taxes. California would be higher.