[TheForge] Inverters

[Steven Smith]

Ben Barrett wrote:
> Well certain [electric] motors are induction-run.... things like
> lights, most heaters, etc, are resistive... I'm pretty sure the
> standard arc welder is resistive.  Induction uses EMF from a coil, and
> often involves pulsation (some frequency, similar to AC [vs DC]) and
> sometimes higher voltage as well.
>
> I'm very curious about DIY induction forges, esp. after seeing the
> nice commercial model at my first conference recently.... I hear some
> rice cookers use induction for their heat, and am wondering about
> scrapping some broken-down rice cookers, to try to adapt for small
> metalworks.  Any thoughts or ideas?  I presume I'd have to isolate the
> heating element, remove surrounding plastic, change/remove the temp
> sensor, and so forth, only to be able to heat up a very small amount
> of metal... but very efficient if tuned.
>
> If anyone has experience building their own induction forge, please
> contact me off-list.  This *might* be a topic worthy of the list, in a
> new thread.
>
> But anyway, yeah, resistance loads are the "common" ones that make
> most sense, the resistance loads are sort of "sinks" for electrons, a
> simple heating element is a classic example.
>
> ciao,
>
> ben
Ben,

What little I know of induction heating--
It relies on resonance to pump power into the load (i.e. the piece of 
steel you want hot). Your work piece will have to be a certain size and 
shape. Something different will require rebuilding your coil. I 
guarantee you will not make any headway adapting rice cookers. What does 
a rice cooker burn, a couple of hundred watts? I bet you need to max out 
a 220 outlet to get a piece of steel up to temp in a reasonable time.

Here is a commercial example:
http://www.blacksmithsdepot.com/
Scroll down to the bottom of the page and click on the Induction Forge 
Basic Kit. I would have given you the link, but it is of a silly length. 
Notice the closely shaped coils. Notice that it consumes 6kW.

If you build switching power supplies to drive such a thing (I've built 
and tested supplies that size, but not for an induction furnace), please 
wear goggles while testing.

Steve