Quote:
Originally Posted by MPaulHolmes
The current sensor line to the microcontroller is an input (to the microcontroller). The output of the current sensor also goes to a comparator. As soon as the voltage output of the current sensor goes above the special trip point that corresponds to the maximum current, the output of the lm293 (or 393) changes from high to low. That causes the nands to latch into a state that gives a high output to the mosfet driver (which is OFF). The only way to clear the overcurrent fault state is to bring the "clear" pin low and then high again. As soon as the pin goes high, the nand latch is cleared and things go back to normal. The default setting in software is to clear the nand latch at about 4kHz. It's probably safer not to clear it at all, but you don't want to be driving down the freeway and all of a sudden, the car turns off for no reason other than a single spurious overcurrent event.
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Thanks for that Paul.
I almost got it right, I thought it cleared its self. which is how I used it, which could have been the reason for the fails, since the cct would be back on before the voltage spikes and currents had fully settled. You do in fact have a delay which I didn't. This is probably why I ended up with a high speed TIG welder or arc lamp under the bonnet.
I think I will go with my idea of reducing the motor drive at the throttle point rather than chopping it and delaying its return, as you say loosing all drive, all of a sudden is not good if its not for a majorly good reason. As I mentioned before I have a second cct which is a timer, a sort of watchdog, that is held reset normally but if the current rises above trip point continuously (pulsing will reset it) for about 1.6secs then I really do loose all drive/power, its a master kill. 1.6sec is a long time to electronics but not when there might be a wall coming up.
These two ccts are completely autonomous and take no instructions from any source other than the current sensor.
I am using an HTFS800, the next one down available was a 200 and I did not realise at the time that they read a lot higher than the basic reading (the 800 will read up to 1200A) I thought 200A was the max for the 200.
Anyway they work the same, mine has the main negative cable going thro it and gives me a voltage of 3.18 at 500A.
