Following on from the discussion about Franks blown tongxin controllers i decided to make a current limiting device to have more control over battery consumption.
I bought a 0-50A LCD display (complete with Shunt) from ebay as the base for the project. The voltage drop is 0-75mv for the complete range 0-50amps.
The next step was to design a simple comparitor circuit with a variable threshold(current limit) which turns on a transistor to 'clamp' the throttle voltage. When i say simple, it really is...
Having tested the LCD meter on a bench i found it's calibration was wildly inaccurate. Simple solution was to add a 24swg copper wire to the shunt to make it good. (You can see this on the first picture)
Next step , monitor my Tongxin motor setup and see how much current is being drawn under certain conditions.
Amazing...when you think you are being careful and prudent with power, at the low speeds the meter was telling me different. On occasions i saw 18A being drawn (wide open throttle) and nothing unusual to see a constant 11-12 amps being unnecessarily drawn because of lack of throttle control. Experimenting on one hill, the controller and wiring was warming up nicely.........actually getting very hot indeed.
With my new accrued data and a few 'suck it and see' ideas. I came up with a circuit compromising of a few resistors, 1 transistor, a linear potentiometer and 1 dual op amp. All very simple.
It works like this. The voltage drop across the shunt resistor gets amplified by the first part of the op amp (a). The amplified the signal is then compared to threshold voltage (set by the Pot) which will send the output of the second op amp (b) either high or low. This will switch on (or off) a transistor which in turn, connects a resistor to 'clamp' the throttle voltage.
This in theory was the idea.
Does it work?
Well after bench testing and playing around with different resistors to set gain and voltage clamping. It appeared to work. However until it was on the bike i wouldn't know.
As usual with my bike.....liberal use of tape, cardboard and cable ties, it was installed......don't laugh!
btw no throttle being applied in this picture
First time out everything appears to work very well, but i had to make a few changes to the output resistors. It would reduce the throttle voltage ok but i could still make the controller draw 10amps.
Its was tricky to work it out as the impedance of the controller was unknown to me
However, a few more trys, and i have now found the ideal value for throttle voltage clamping.
With the adjustment at the minimum, wide open throttle. 13.5 mph, level ground, no pedaling. 2.6A
I'll continue in a reply as i've reached my 4 pics limit
I bought a 0-50A LCD display (complete with Shunt) from ebay as the base for the project. The voltage drop is 0-75mv for the complete range 0-50amps.
The next step was to design a simple comparitor circuit with a variable threshold(current limit) which turns on a transistor to 'clamp' the throttle voltage. When i say simple, it really is...
Having tested the LCD meter on a bench i found it's calibration was wildly inaccurate. Simple solution was to add a 24swg copper wire to the shunt to make it good. (You can see this on the first picture)
Next step , monitor my Tongxin motor setup and see how much current is being drawn under certain conditions.
Amazing...when you think you are being careful and prudent with power, at the low speeds the meter was telling me different. On occasions i saw 18A being drawn (wide open throttle) and nothing unusual to see a constant 11-12 amps being unnecessarily drawn because of lack of throttle control. Experimenting on one hill, the controller and wiring was warming up nicely.........actually getting very hot indeed.
With my new accrued data and a few 'suck it and see' ideas. I came up with a circuit compromising of a few resistors, 1 transistor, a linear potentiometer and 1 dual op amp. All very simple.
It works like this. The voltage drop across the shunt resistor gets amplified by the first part of the op amp (a). The amplified the signal is then compared to threshold voltage (set by the Pot) which will send the output of the second op amp (b) either high or low. This will switch on (or off) a transistor which in turn, connects a resistor to 'clamp' the throttle voltage.
This in theory was the idea.
Does it work?
Well after bench testing and playing around with different resistors to set gain and voltage clamping. It appeared to work. However until it was on the bike i wouldn't know.
As usual with my bike.....liberal use of tape, cardboard and cable ties, it was installed......don't laugh!
btw no throttle being applied in this picture
First time out everything appears to work very well, but i had to make a few changes to the output resistors. It would reduce the throttle voltage ok but i could still make the controller draw 10amps.
Its was tricky to work it out as the impedance of the controller was unknown to me
However, a few more trys, and i have now found the ideal value for throttle voltage clamping.
With the adjustment at the minimum, wide open throttle. 13.5 mph, level ground, no pedaling. 2.6A
I'll continue in a reply as i've reached my 4 pics limit
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