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Re: More DIY substrate heating cable questions

At 3:48 AM -0400 6/2/98, bickford at black-hole_com (Jay Bickford) wrote:
>Subject: Re: More DIY substrate heating cable questions

>The responses, however,  have brought another question to mind.  In the above
>mentioned article, the authors use an AC transformer, but Brent Harsh
>the use of an inexpensive DC battery charger like found at "WalsMart" for
>charging car batteries.  Does it make a difference if you use AC or DC?  Any
>electrical engineer types want to explain the advantages and disadvantages
>of one
>verses the other?  Are there any concerns about efficiency?  Is one type,
>AC or
>DC, more electrically efficient than the other?

There's no such thing as a DC transformer. All transformers work on AC. DC
is produced by using a rectifier at the output to convert AC to DC. The
rectifier will lose any where from 0.7 to 2.0 volts depending on
configuration and diode effiency. The wire doesn't care whether it's heated
by AC or DC, but you can get more energy to the wire if you dispense with
the rectifiers. Use AC if you can. If the cheapest way for you to get a
transformer is from a battery charger, then cut the rectifiers out and just
use the raw AC output.