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Old 07-10-2009, 03:33 AM   #1959 (permalink)
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Originally Posted by MPaulHolmes View Post
I just got back from the first test drive with ben's controller. I was really scared again. I started off easy for a few minutes. I had the overtemp shutdown start at about 60 degC just to be conservative, since I have never actually tested it in the car.

I drove it up some big hills, routinely doing 200-300 battery amps, so the motor amps were even higher. It did perfectly except for 1 time. I decided to floor it from 0 rpm. It latched up the microcontroller. I had to turn the controller off and then on again to reset it. Even the watchdog didn't restart it. That had happened on the other one I was testing in the garage.

We added some schottky diodes to prevent this from happening, and it was difficult to get it to happen this time, but it did happen. I'm of the opinion that when LEM 300 says 300amps, they mean it. It must have been around 450 amps when it latched up the micro-controller. I have a spare LEM 500 that I will install. Then I'll try to latch up the micro-controller again. My guess is that it won't have a problem with the LEM 500, since the LEM 500 voltage output will be lower.

What happens (I believe) is that the LEM output is a bit noisy, so when you are way over 300 amps, the LEM 300 output voltage has some spikes that are over 5v, making it no longer suitable to a 5v A/D input. That can latch a microcontroller (The EVTech list has told me that this can happen).

So, I believe we should change from a LEM 300 to a LEM 500 or 600. Sorry Joe! I mailed yours a couple days ago. It sounds like you will do some hard driving, so we probably need to get you a LEM 500 or 600. It's easy to unbolt the LEM and stick in a new one. You will have to reprogram the microcontroller with the new LEM in mind. I'll make the necessary changes and I can email you the program if you want. Those dang things are like $27! Makes me mad! I'm glad we haven't done a large group order yet! That would suck. I think I have enough from donations to order a LEM 500 for you, Joe. Adrian is sort of far away. Hmm... I'm not sure what to do about that.

Also, I was able to get the base plate pretty warm. It was just laying against wood, which makes for terrible heat removal, so I would also suggest bolting the base to a heat sink or something.
Paul, the LEM300 output is from an op amp that is fed from the +5vdc supply on the control board. The maximum voltage that the output can be driven to is +5VDC. What is more likely happening is that the cabling from the current sensor to the control board is getting induced voltage spikes from the main current carrying conductor. Have you used shielded cable for the connection to the sensor. The cable shield would need to be earthed at both ends of the cable to effectively shield at those currents. The other thing that can be done to make sure the A to D input doesn't go over the +5VDC is to connect a 4.7 volt zener diode accross D9, a 1N4732A would be suitable.
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