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
Take your furnace to a generator dealer and tell them you want
something that will power it. Ask them to demonstrate that it does
before you make a purchase. Don't rely on generator specifcations
You'd be wasting fuel.
Get a phase angle firing circuit. The generator will run better with
it. Also, transformers dont like burst firing and zero crossing
systems. A phase angle control fires on every cycle so the transformer
sees an even load, not a series of on and off for a couple of cycles at
David wrote: (clip) I had wondered about having a dummy heater load the
same as the furnace and switching between to two so the generator saw a
Speechless wrote: You'd be wasting fuel.
If you can estimate the average power the furnace consumes from the on/off
times, you could adjust the heater resistance so the furnace stays on almost
full time. This would eliminate most of the switching and power waste. It
would also allow the generator to run with a lighter load, so it would be a
little quieter, and probably last longer.
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.
I'm building a load for a 100 KW generator right now. So, 3.5 KW seems
manageable with a realistic sized gen-sets.
How big can your gen-set be?? It seems that you can rent/borrow a
gen-set thats big enough to tolerate abrupt load/unload powers of about 3
KW. I assume the furnace can tolerate a little voltage variation while the
gen-set settled down while the power level gets adjusted.
Obviously you can test the gen-set with old heater elements or electric
stove heating elements if the furnace could not tolerate surges in the input
Thanks for the info. Various people have replied and given me some ideas
to think about so I can pass the info on to the chap that expressed an
interest in a portable set-up. The idea of renting and just getting a
bigger unit sounds good providing it's still fairly portable.
Thanks for the replies.
Jerry Martes wrote: