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.

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.

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.

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.


You'd be wasting fuel.

"David Billington" wrote in message
...
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.


Hi David

How much power do you expect the generator to provide to the furnace when
it is ON??

Jerry

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.



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

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.

Normally about 1.5kW but maximum would be 3.5kW if the gathering hole is
left uncovered for sufficient time.

Jerry Martes wrote:

"David Billington" wrote in message
k...

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.


Hi David

How much power do you expect the generator to provide to the furnace when
it is ON??

Jerry

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
Spamtrapped address: Remove the python and the invalid, and use a net.

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




"David Billington" wrote in message
...
Normally about 1.5kW but maximum would be 3.5kW if the gathering hole is
left uncovered for sufficient time.

Jerry Martes wrote:

"David Billington" wrote in message
. uk...

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.


Hi David

How much power do you expect the generator to provide to the furnace
when it is ON??

Jerry

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:

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




"David Billington" wrote in message
k...

Normally about 1.5kW but maximum would be 3.5kW if the gathering hole is
left uncovered for sufficient time.

Jerry Martes wrote:

"David Billington" wrote in message
.uk...

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.

Hi David

How much power do you expect the generator to provide to the furnace
when it is ON??

Jerry

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:

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:

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




"David Billington" wrote in message
...

Normally about 1.5kW but maximum would be 3.5kW if the gathering hole
is left uncovered for sufficient time.

Jerry Martes wrote:

"David Billington" wrote in
message ...

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.

Hi David

How much power do you expect the generator to provide to the furnace
when it is ON??

Jerry