New to the forum, Long time believer in OU

forest · March 13, 2015, 07:39:44 AM

As you posted for example at 46,9khz 1000W of power is dissipated on this heater. Is there any energy dissipated at this frequency by inductance magnetic field ?

MarkE · March 13, 2015, 07:52:43 AM

Quote from: forest on March 13, 2015, 07:31:31 AM
MarkE

Can you explain how you get the formula for apparent power PAPPARENT52.9E3 V2/Z.
What does 52.9E^3 factor mean ?
How did you got that nice graph ?

P_APPARENT is the product of the rms voltage: 230Vac rms, and the rms current: 230Vac rms/Z. It is the apparent power uncorrected for the phase shift caused by the inductance.
52,300 is (230Vac rms)².
I made a spreadsheet to generate the graph. It uses the same formulas that I posted.

MarkE · March 13, 2015, 08:07:28 AM

Quote from: forest on March 13, 2015, 07:39:44 AM
As you posted for example at 46,9khz 1000W of power is dissipated on this heater. Is there any energy dissipated at this frequency by inductance magnetic field ?

Inductance by definition only stores energy. It does not dissipate energy. Any energy dissipated will look like resistance.

The more important thing here is that there is no reason to try and drive high frequency current through the heaters. Build a power converter at whatever frequency is convenient, then filter that and feed it to your coils. Steady DC puts the least mechanical stress on the ressitance wire anyway, and it makes filtering the EMI easier.

I assume that building multi-kW power converters is something new to you. The old school method would be a triac type heating control which you can just buy off the shelf for relatively low cost. Instead of PWM'ing the triac heater controllers operate complete half cycles. They switch at the AC zero crossing. As a result, the EMI is low as is the cost. They rely on the thermal inertia of the thermal load to average out the temperature. If it takes 10 minutes to heat something up by 200C, then the 1/100th of one second represented by a 50Hz half cycle with the heat on or off only changes the temperature by a fraction of a percent.

forest · March 13, 2015, 08:10:42 AM

Hmm..I've got 1096W real power at 46,9khz from your formula. Why such difference of 96W ?

forest · March 13, 2015, 08:20:26 AM

MarkE

Thanks for advice.Sorry, but I will try that stupid path of high frequency first - it simplify many aspects. Actuall I think it may be easier then I thought.
You said inductance store energy. That's correct, but at such high frequency it will flip poles 46900 times per second. I hope you see what I'm about ;-)
I've got what I've got - plenty of coil wound resistive heaters and only few expensive (fortunately found at scrap yard at low price) diodes.

Thank You for your help MarkE. You are GREAT!