Question on portable generator usage

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

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 alone.

You'd be wasting fuel.
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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 constant load. ^^^^^^^^^^^^^ 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.
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Hi David
How much power do you expect the generator to provide to the furnace when it is ON??
Jerry
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Normally about 1.5kW but maximum would be 3.5kW if the gathering hole is left uncovered for sufficient time.
Jerry Martes wrote:

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Hi david
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 voltage.
Jerry

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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.
Dave
Jerry Martes wrote:

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Anything above 5kw is not very portable. With wheels, you can go to 10 kw but after that it is trailer time.
David Billington wrote:

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David Billington wrote:

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 a time.
John
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On Sat, 25 Mar 2006 12:40:09 +0000, David Billington

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
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