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Old 07-21-2002, 03:03 PM
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Mark Wilson Mark Wilson is offline
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Location: St. Paul, MN
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pete, it doesn't require more current from your 240VAC line, and it does not require a higher power scr or triac. and it doesn't require a higher current line and contractor to your furnace.

for example, lets say you have at 240VAC 100Amps line fed into a 4:1 step down transformer. the transformer steps down the voltage, but steps up the current to a 60VAC 400 amp output. if you connected to 4 parallel sets of elements( 1 or more elements in series on a leg) each parallel leg has 100 amps running through it. if you put all of the elements in series, the same 240VAC 100 Amp circuit will work the same way without the transformer.

i think it would help if i draw up and post a schematic. i will probably draw it up for a triac as that is much simpler to build and costs less.

another thing that i have been wondering about is using an scr on the high voltage side of the transformer. true this allows the scr to run with a lower average current, but then the scr is connected to the inductive load of the transformer. this might casue problems even if the switching occurs at the zero crossing threshold. in the case of the elements in series, it is totally resistive and has virtually no inductance so there will be less "switching transients" which should lead to the scr or triac running cooler and longer.
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