Simple Calorimeter

Why not just use simple electrical measurments and math to figure it out. Volts times Amps in and out that sort of stuff.

Well, we tried but we need to know the phase angle of the output as it's ac and being a square wave on the voltage and a non pure sine wave on the current makes it a little difficult plus a non straight resistive load also doesn't make it easy. The swiching on the output is at 100KHz so simple power meters are giving us odd mesurments at high current.

OK - here's the obvious question: why is a circuit running on 100kHz square wave voltage and non-pure sine wave on the current? What does this circuit actually do?

It's an inverter and 100KHz is an efficient frequency to run at. You get a square wave on the voltage when you chop dc however without getting into proprietary info we are running a fets for precision control for the turn on and off so it causes a non sinusoidal sine wave on the current when it's running. We have tried a Yokogawa WT120 power meter and also differential voltage probes with Pearson current coils and we don't get correct readings even after running a calibration on the scope and probes.

And why is the thermal information needed?

It looks like the only way to get an accurate power measurement of the power consumed in the circuit. By knowing how much the liquid temp rises during operation we then can hold the fets on as in a short and get the same temp rise by carefully controlling the dc current through the circuit we can now know the power. I was thinking some Pure Silicone Fluid 20cSt would work. But I was also wondering if there was a simpler way that I didn't know about. I was hoping that the smart folks on cr4 knew of something as I have run out of ideas. We need to know the efficiency of the circuit is what this is leading to. With the ac signal out we are having a hard time measuring that power so we were going to measure the power used by the circuit in the form of heat.

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Given you have a 380 volt DC source thats easy to measure and calculate your input power from. Then just use a fixed value non inductive resistor for the load bank.

If your input wattage is known and your load wattage is known then its just simple math to figure out the difference.

We thought of that as well but if it changes the current signal then it would change the power out. Sense I am unsure where the exact discrepancy is in the measurements whether it's the current or voltage or both that is being given by the scope. I am having a hard time measuring the voltage and current. Some of the measurements are saying I am a 100% or better in efficiency. So without knowing if the current or the voltage or both is not right how do I come up with a non inductive resistive load to put on the output? A non inductive resistive load would there for change my phase angle of the circuit and according to the math if I change the phase angle in an ac circuit would then change the power. I also need to make an efficiency curve as the loads moves up and down. As I said before I am driving into a non straight resistive load so I have all kinds of capacitance of the boards of the loads and inductance of the traces and not to mention the circuit on the load. It would be better to run the loads I have and then by measuring the temp rise on the fluid I can plot a number of liner curves, then by locking on the fets causing a controlled short I can then calculate the power in the circuit by getting the same temp rise.

Hi Guest,

Do you want to build this calorimeter yourself? Or will a shop bought one do? And what is your price bracket please?

Good luck and happy holiday.

First yr voltage waveform is square and even yr current waveform is a non pure sine wave,how do u expect to read out the exact power.

U need to go back to yr inverter cct and improve yr waveforms to be pure sinusoidal wave for both voltage and current,then u can get the accurate power wt yr meter or by calculation.

Patrick Whowha

Simply pot resistors and place it in a water bath. Do this for the input and the output. Use the same resistance for both. Test the resistors and find identical resistance parts - this is key. Compare temperatures. Be careful. Make certain you potting material is sound. Enjoy. You must run the experiment long enough for the separate water baths to stabilize. Monitor the temperature outside the baths also.