On 11/7/2010 5:54 AM, Winston wrote:
Bill Noble wrote:
On 11/6/2010 9:00 PM, wrote:
On Sat, 06 Nov 2010 13:44:23 -0700, Rich Grise
wrote:

Winston wrote:


Aw, gawrsh, 'tweren't nothin'. ;-)

Thanks!
Rich
Variacs are MUCH more to be preferred (reccomended) for the job.

at the risk of being hostile, "nonsense" - variacs are NOT to be
preferred, unless you have no clue about electronics and are unwilling
to purchase a suitable thyrsitor or SCR controller.

Bill, help me understand please.

I have an autotransformer in good condition; sized
to easily drive my simple unregulated power supply.
The contact brush is nearly new and I have yet to
detect any contact noise or from it.

My Powerstat *is* much larger than a triac controller
and I agree that it does not self-regulate, but in this
application and with the stability of power that I
have available, I am not concerned about line voltage
variations or load current variations because I can
keep an eye on the performance of the hot knife and
tweak power into it as necessary.

I agree that it is a Lexus solution to a Corolla
problem, but the Powerstat is paid for, it is installed
and it works fine. Let me emphasize that it's lack
of isolation does not concern me because my downstream
power supply has a fully isolating transformer.

Would you agree that it is perfectly reasonable,
thrifty, safe, correct and honorable to use it to power
that transformer power supply, especially if it means
that I can work on my project instead of wait for a
triac controller to arrive in the mail?

Is there one reason that it would be either
unreasonable, wasteful, unsafe, incorrect,
dishonorable or somehow wrong for me to do so?

I ask the literal question without a trace of sarcasm
or snark.

What say you?

--Winston

There is absolutely nothing wrong with using what you have. I was
objecting to the blanket statement about a solution being better - from
a technology point of view, the statement was false. From a practical
point of view, if you have all the pieces to make a slightly less
wonderful solution, but it is an adequate solution, then of course you
can do it.

Here is the pro/con of your solution, whcih I assume is a variac driving
an unregulated DC power supply:

pro
you have the parts
it is easy to assemble
it will be reliable enough for your (non production line) use

con
heavier, more bulky
more likely to get damaged if power supply gets knocked off the table
if you had to buy parts, it would be more costly (but you don't)
no ability to regulate current/temperature of the wire automatically

so, for YOU, given that you have the parts, use what you have.