We have a biodiesel processor powered by a diesel generator.  The
maximum output of the generator is 4.8kw.  Unfortunately, a heating
element was added to the processor that wants 5.5kw, more than our
little generator can handle.  The heating element is wired to a 110v
AC circuit that in turn connects to a breaker box.  We have two or
more circuits available on 15 and 20 amp breakers.  The question: how
do we safely and permanently reduce the maximum power that can flow to
the heating element to, say, 2.5 or 3kw to accomodate the other power
demands on the system?  Changing the heating element is not an option
at this point.  We'd prefer not to add circuits at this point if
possible.

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Clarification of Question by biodiesel_bri-ga on 24 Jul 2005 11:41 PDT

I mistakenly posted that the heating element is wired to 110v, it is
in fact wired to 220v.

on 24 Jul 2005 11:41 PDT you ask:
So connecting this heater directly to 110v .. would be ok? 

Answer is yes.
 As long as heating element is just a resistor
    (i.e. just connecting wires and the heating coil, no electronics atd)
 it can be safely connected to lower voltage then nominal.

 What is shown on the apliance as 'wired for' - the nominal voltage -  
 is actually the maximal voltage the appliance can handle.

 At any voltage applied, the output is V*V/R  where V is applied voltage
 and R is resistance of the heating coil.

 If nominal voltage 220V would produce output 4.8 kW then
  R of the heater is 10 Ohms
( you can type into google:

  (220 V * 220V)/ 4.8 kW

to get that result)
( axel_wg-ga on july 13 was using 120 V to get about 3 Ohms)

 Therefore, if you apply 120V, your heat production will be 

((129 V) * (120 V)) / (10 ohm) = 1 548 watts

and it will draw current of 

(120 volts) / (10 ohm) = 12 amperes

The 50 amp breaker would work, but use 15 amp,
 as it is sufficient and safer 

Hedgie

The best way of reducing the current used by a heating element is to
reduce the voltage going to it, by means of a step-down transformer or
switch-mode electronic regulator.

simon2wright-ga is correct. To be more precise you have to reduce the
voltage to your 5.5 kw element to 84V to get a ~2714W heat output.
Your element has a hot resistance of about 2.6 Ohm. 84V divided by 2.6
= 32.3 Amps times 84V = 2713 Watts. If you find a 120V-36V, 35A
(~1.5kva,~$150) transformer and hook up the 36V winding reverse to
120V you get 84V. A good electrical contractor should be able to help
you connect it. This is a faily low loss solution. Electronic
regulators are very expensive unless you find some used ones, good
luck.

So connecting this heater directly to 110v with a 50amp breaker (with
appropriate gauge wire) would be ok?  The heater wants 5.5kw at 220v
right now, not 110.