You said that your contactor is switched by the microswitch on the throttle pedal. What will happen when you apply throttle with no power is the duty cycle will rise to increase current. ...
-Adam
It is very important to get the timing correct when activating the main contactor with the throttle. As Adam says, if the controller starts outputting power before the contactor closes, you'll damage the contactor, caps, etc... It can be done - I have mine set up this way. The main contactor opens everytime I let off the accelerator.
One characteristic of incorrect timing is jerky starts. Since the car had been working before, we should be able to answer this question.
Also, here's a guy who had this problem (though, I also think he didn't have a precharge resistor) and this is a picture of his contactor contacts.
Paul
That sounds great. I willalso keep in touch via e-mail. The answer to your question about reversing the supply is no. That could not happen as I have two packs of 60 v each so even if I did reverse the second pack there would only be zero volts across the controller. I drew a pic in corel and converted it to a PDF for you to see. Atteched also pics of the reverse side on the controllers control board. See the diodes there. I have no idea what they do either, and no, up until now I have never done any work on this controller other than mount it on a huge heat sink.
I have the contactor connected through a timer which connects the pre-charge resistor (49 ohm 10watt) for six seconds then it allows the contactor to engage when the accelerator pedal is pressed. It dis-connects when the accelerator is let up. I have read what Adam said and it sounds plausable to me. I will check the contacts out and report later.
At around 500amp, there is a voltage spike of around 15 or 20 volts from drain to source. So, if there was even the TINIEST throttle while the contactor was open, it would immediately drive the pwm to 100% duty. And with a motor that's not spinning, it's almost a short circuit. So, you would have maybe 2000 amps or even more for a very short instant, and the voltage spike from 2000 amps would be more like 80 volts instead of like 20 volts. That's because the voltage spike is proportional to the current. So 4 times more than 500 amps would have 4 times the voltage spike. So, if you had 120v nominal, that would put the total voltage (counting the spike) over 200v, which would short all of the mosfets.
Another way to test if this is what happened is to measure the resistance of the potentiometer at the instant that the pedal contactor closes/opens.
Hey Paul. Was wondering if you had any idea what I may have done wrong on my control board. I did find a few loose components and the heat was
mostly around U1 (thru the bolt). Thanks, watt.
Hi again Paul,
The resistance when the contactor comes on is 687 ohms and it is a 5k pot. I was going to take a picture of the pitting on the contactor, but I then realized that it would not be a true reflection of how it was working with the controller attached. When I first contacted you about the controller not having enough go, and later found it to be the pot not moving enough, I decided to connect the 60volt battery pack directly to the motor through the contactor and using the microswitch on the accelerator pot setup to engage it. This caused a lot of contact arcing so I will not be able to tell if any of this was caused whilst the controller was connected.
Adam,
Thank you for you contribution to my problem, I like your conclusion very much and obviously you know a lot more about electronics than I ever will. It is great that there are folks like you around willing to give a helping hand. Thanks too to all the others who are partaking in a solution to my problems.
Thanks again to all,
Doug.
HI Watt! If you can mail it back to me, I can probably narrow down the problem. I'm not sure based on your description though.
Yo Dwiffy! The software was designed to have about 10% dead zone, which means that 0 to 500 Ohms translates to 0 throttle.
So... 687 Ohms is definitely in nonzero throttle territory, so I think that makes the "100% duty when the contactor closed" theory very plausible. But just think! You figured out a whole new failure mode! This needs attention! I never even thought about that. Way to take one for the team! I'll get you a new one shipped soon! I need to add that to the help documentation. Man, motor controllers are touching little things. It's like a wild mustang that needs to be tamed. I'm feeling so poetic tonight.
Paul,
What should the range in ohms be for the pot from min ohms to max ohms for best results. It will be difficult to get the pot to swing 270 degrees using a lever to go grom 500 ohm to 5k. If the travel was to be 500 ohms min to about 3.5k max that would be easy to do mechanically, or maby I should look to fittied a log pot rather than linear. Pls advise and could you tell me where you got your pot from. It most probably will be better for me if I have the identical type to yours.
Thanks,
Doug.
Hi Doug! The software is adjustable for any pot range you want, so that's not a problem. If the contactor comes on at around 700 Ohms, I can just have the "zero throttle" zone be like 0 to 900 Ohms or so. Then the max throttle can be whatever you want. 3.5k Ohms max is no problem. I'll just program your microcontroller for that, so you shouldn't have that problem again.
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