Re: low-cost 1800-amp heating source
- From: Winfield <winfieldhill@xxxxxxxxx>
- Date: Thu, 02 Aug 2007 03:38:34 -0700
MooseFET - Ken wrote:
Tony Williams wrote:
Perhaps no need to use a semiconductor. This could be
an opportunity to investigate the design of the old GE
theatre light dimmer, based on the saturable reactor.
There should be no net DC component from that, and
relatively soft waveform modulation.
La
ACin-----------/////////---------+
========= |
DC Control---////////------------- DC Control
========= |
ACout----------/////////---------+
Lb
The saturable reactor can be wound on E-I laminations or
on two toroids stacked together, with the control winding
wound on the stacked assembly.
Effective inductance control is just a matter of a variable
DC constant current source driving the control winding.
Just take two transformers and wire the primaries in series and the
secondaries in series bucking as the control. It worked fine some
40 years ago to control a light bulb so a bigger one should control
a heater quite nicely. DC in the secondaries makes the cores
saturate.
If you want to be a purist about it, you need to place a large
capacitor across the control winding. When you feed DC into
the control some AC currents flow in the control windings.
The capacitor keeps this out of the control circuit.
Actually, why can't the two transformer primary windings be
in parallel? That'd reduce the copper resistance. And
L(leak) for that matter, right? Editing Tony's drawing:
AC high + Pri - Load current
--+-----------////////-------+--->---,
| T1 ======== | |
| DC --+---////////---, | |(
| | + Sec - | | |( L(leak)
| +_|_ | | |(
| --- | | |
| | + Sec - | | / Win's Load.
| DC --+---////////---' | \ Rload
| T2 ======== | /
'-----------////////-------' |
+ Pri - AC low
OK, now I see that Tony took advantage of a series primary
connection to use transformers with half the primary voltage
rating. Hah, it appears there's no free lunch.
.
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