On Sat, 25 Mar 2006 12:40:09 +0000, David Billington
wrote:

A glass blower I know expressed interest in my electric glass melting
furnace, he mentioned wanting one to take to events for demonstrations
and powering it from a mobile generator. Now the controller uses a
solid state relay zero crossing switching and burst firing and I imagine
the generator may not like the rapid switching from load to no load and
back. Does anyone have any knowledge or experience of this type of
application. I had wondered about having a dummy heater load the same as
the furnace and switching between to two so the generator saw a constant
load.

Here's an idea or three, free for the taking: If your design has
multiple heating elements in parallel, you might build a 'portable'
version of the furnace and rig the elements so they run in stages. #1
is on almost all the time unless it starts to overheat. And it kicks
elements 2, 3, 4 on as needed.

And they sell multiple-stage time-delay relays meant for electric
resistance furnaces, so a single temperature controller input kicks
the elements on in stages. One element section every 15 seconds or so
till it hits full load.

Only two elements? Rig them with a contactor so they go in series
for a 'low heat' setting (I'm guessing 60% power instead of 50%, since
there has to be a resistance curve on the nichrome wire), and the
contactor parallels the elements for high.

There will be a jump in the load, but the generator is already at
half load so it should take it in stride. You'll hear the grunt for a
second as the throttle opens up. It's slamming from no load to 100%
where you have big problems like stalling the engine.

And consider the effects of voltage spikes coming out of the
generator plant on the temperature controller or other misc. loads if
you suddenly drop the furnace load from 100% to 2% with one control
stage. Might want to add extra way-huge-oversized MOV's for voltage
spike control, and stage the load drops at the 'off' setpoint too.

-- Bruce --
--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
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