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Old 09-17-2018, 06:38 AM
lotec lotec is offline
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Join Date: Feb 2012
Posts: 160
Originally Posted by Sawt2 View Post
Please explain
Thanks for asking. What I meant about impedance matching is, that if the output voltage is too low, then there won't be enough electromotive
force to push the amperage to where it needs to go, and if it is too high then useful amperage is being unecessarily sacrificed for voltage
that may not be particularly useful.

My observations were made in the context of using the motor itself as the target destination for the output, ie feedback. In the circuit
below, I opted for a high side switch, to prevent the motor coil from discharging in series with the battery, to keep the voltage down, and avoid
confusion as to where the feedback power was coming from. I used a fixed duty cycle of 50%, knowing that the optimum frequency is going to
produce the optimum on time for the motor inductor for feeding it's target destination. R1 is for measuring the current in from the battery
and R2 is for measuring the amount of current being fed back into the motor.

I started with a very low frequency of about 100 Hz, then started to walk through the frequencies. As the optimum frequency is reached input
current starts to drop off quite noticeably and the output current rises quite noticeably as well. When the input is at it's lowest and the
output at it's highest then it is tuned. The motor also had a surprising amount of torque as well.

Those are the upsides to the situation, but the downside is that once finding the optimum on time for the target destination, if the off time
is lowered, thereby increasing the duty cycle, then the amperage recovery declines. It seems to need the full 50 % off time to recover the
full amount of amperage. Maybe this has something to do with amperage lagging. The motor doesn't spin as fast as if it has 100% duty cycle,
but I think that the added torque and lower current draw and efficiency make up for that.

I was only using a small slotcar motor with permanent magnets, but am optimistic that this effect can be scaled up. It may be useful for
other types of target destinations that use amperage as well. I think it could be worth looking into. There are definite advantages to
doing this, as opposed to just randomly selecting a frequency to pulse the motor at. After the circuit is tuned this way, the
0.1 Ohm resisters can come out, but it's kind of fun to leave them in and see just how much amperage is being fed back in, when the motor is
under different degrees of load.

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