The discussion centers on the feasibility of a purely resistive energy storage load in electrical circuits, particularly in relation to induction motors. Participants agree that storing energy without any reactive components is not achievable, as energy storage and reactance are inherently linked. The conversation highlights the use of Variable Frequency Drives (VFDs) as a modern solution for controlling induction motor speed, rather than relying on resistive methods. Additionally, the discussion touches on the characteristics of batteries and capacitors in circuits, emphasizing the need for proper measurement techniques to differentiate between real and reactive components.
PREREQUISITESElectrical engineers, motor control specialists, and anyone involved in optimizing energy storage solutions in electrical circuits.
Hi,manzana said:Good question. What is your circuit? Normally you would put a bypass capacitor across the battery to keep AC out of it. Chances are, I don't understand the problem.
Not really, I accept that what I'm asking there probably doesn't exist any appropriate component or product (with a purely real characteristic). I'm sure you could do it via some sort of conversion, but that's not what I'm after.anorlunda said:Storing energy and being reactive are somewhat synonymous. So at first glance, I say no.
But a better answer depends on how strictly you mean pure. Can you elaborate?
Pure was a poor choice of word, I mean such that the resistive component is comparitively so large that any reactive component can be ignored.anorlunda said:I'm going to make a general statement here that applies to many PF questions.
Whenever someone uses the word pure with respect to real life electric circuits, he is begging for a contradiction of terms.Could your question be rephrased as "How can I reduce losses in an induction motor?"
Yeah, I am aware of a variable frequency drive, what I'm contemplating WOULD require modification of the rotor circuit, I think. I'm thinking about an arrangement that isn't a motor or generator as such, but a type of apparatus which doesn't really have a stator, relative to earth. Where the rotor and stator rotate, without a set frequency.anorlunda said:https://en.m.wikipedia.org/wiki/Induction_motor#Speed_control
VFD. Variable frequency drive is the answer. Controlling speed with resistors is pretty old fashioned.
tim9000 said:Yeah, similar question though: Does anyone know how capacitive nickel–cadmium or lithimum batteries (NiCd, Li battery) appear in an electric circuit?
Thanks for the link!Averagesupernova said:I think you want to look into double fed induction machines. https://en.wikipedia.org/wiki/Doubly_fed_electric_machine
-
There is an older type of brush type motor called repulsion/induction. It was known for being able to start heavy loads. When it came up to speed the brushes were short circuited so it basically became an induction motor. If you can find one of these you may be able to do some experimenting.
Ah, interesting points.CWatters said:If you look at the equations for a capacitor..
Q = CV
I = Cdv/dt
C = I / (dv/dt)
For a voltage source dv/dt is zero (because the voltage is constant) so it's not unreasonable to compare a voltage source with an infinitely large capacitor. In the small signal model of a transistor circuit the power supply is usually treated as a short circuit.
However real world batteries aren't ideal voltage sources. You would need to measure the specific battery over the frequency range of interest.
tim9000 said:So if I was to measure the source impedance of a battery, would that give me only the real part?
Ha, look, with respect I know the difference between impedance and resistance. I can remember off the top of my head:CWatters said:Google the difference between resistance and impedance.
Right'o. Thanks for the document!CWatters said:Depends what equipment you have. You can buy meters that will give you an answer or you can do it with a scope, signal generator and some maths. This from Tektronix explains how to measure the capacitance and resistance of an unknown capacitor.
http://goo.gl/6uN4u7