Inductor for AC to DC Welder Conversion

The best inductor to use is one made from an old battery charger transformer core , HID ballast core, or microwave oven transformer core. The second two are usually rather easy to split apart and rewind new coils on.

To get the proper size of copper winding just use multiple strands of what ever magnet wire you can get a hold of. You can buy it cheap from any electric motor repair shop.

There are charts on line that give you the cross sectional size of different wires so from that you can easily figure out how many smaller wires you would need in parallel to equal one of a larger size.

So what you suggest is to run say 5 parallel strands as one wire connected at each end? Making up the 22mm sq area of the original 4 awg. Would these be straight or twisted or does it not matter?

Doesn't matter so much really. Your choice.

Straight will lay in tighter but twisted will give you more air space which would help with cooling.

More inductance will make the weld puddle wetter and flow better so depending on what range and type of welding you do the most it may take a bit of trial and error to find what amount works best without going to high.

At the price of used equipment, WHY?

I converted a AC buzzbox to DC some years ago by building a bridge rectifier and buying a inductor that was used in a Miller AC-DC welder and added the necessary DC plugs. My box is a Linde but all the small welders are simular.

What you do here really depends on what you want out of it ! If you want smooth continous current then the choke needs to be the ~ same core size as the transformer. If you just want to lop off the peaks of the current then anything will do. When I did this many years ago (its still in the garage and gets used now and then) I used a core about half of the transformer size and wound it with a layer of 2.5 X 8 mm copper and played with the air gap. That worked so ~ so, but not as good as I had expected. In the end what worked best was to use a smaller choke and in parallel with the main DC output, a small DC supply about 50~70volts using a rectifier / capactor (10,000uF) arrangement and a series connected resistor which limited the S/C current to about 5 amps. The result was a nice smooth arc with good strike and continous current.

Bob

Sorry to resurrect this ancient thread, but I'm very interested in your solution.

"...what worked best was to use a smaller choke and in parallel with the main DC output, a small DC supply about 50~70volts using a rectifier / capactor (10,000uF) arrangement and a series connected resistor which limited the S/C current to about 5 amps."

If I understand correctly, your 50-70VDC supply and cap simply holds the voltage up, raising the floor of the output ripple?

If you need to convert from AWG, look here:-

http://www.engineeringtoolbox.com/awg-wire-gauge-d_731.html

Joining two wires of the same AWG, will give you the equivalent of the third step-up caliber, example: Two 18 AWGs will give you one 14 AWG, two 14 AWGs will give you one 10 AWG and so on.

As per the coil design, yes it is the same to use two paralleled wires as using the one equivalent.

Another less common option for winding your own high current inductors is to use a electric motor core or automotive alternator core as a large iron core toroid inductor sorts.

They are both easy to find and easy to wind plus due to their approximate toroid shape configuring your windings with multiple taps for changing your inductance ratios is a snap!

Just make sure you round of the sharp edges with a file or grinder first then cover the whole core in fiberglass and or epoxy to protect your windings.

Also if yo are looking for large diameter solid copper wire check with your local hardware stores electrical department. Large diameter copper wire is commonly used for the earth grounding on new electrical services and quite often can be found in sizes up to 2 gauge.

Granted its bare copper but stretching it out cleaning t and spray painting an enamel coating on it is rather easy.

GA for some good sensible and solid infos, thanks.

--"In the end what worked best was to use a smaller choke and in parallel with the main DC output, a small DC supply about 50~70volts using a rectifier / capactor (10,000uF) arrangement and a series connected resistor which limited the S/C current to about 5 amps. The result was a nice smooth arc with good strike and continous current."

How did you make the smaller choke? What was the core, how many windings? As I understand, did the 10,000uF capacitor kept up the voltage during the null section of the DC wave?