Thanks for the comments guys, My main reason to build rather than to buy is all the scooter controllers I have found have been 30a or less, a little weedy for my tastes!
I only stuck it on wood to be able to play with the layout and be able to take a picture that wasn’t just a pile of spaghetti with some stuff buried in the middle. The Fet’s will be securely mounted on the motor mounting plate, this will act as a large heat-sink and the ‘Load’ connection (as my motors are case ground) the ‘load’ leg of the Fet will be cut off and the stump insulated to further isolate it from the ‘Supply’ connection. As I will have quite a large plate to mount the fets onto, I think I’ll mount the board then place them in an arc around the connection point on the board, that way they’ll all have the same wire length attachment without coiling anything. (Good tip guys!) If I include a fan blade on the motor shaft, I can get a huge air-flow over the mount and fets and I’ll end up with about a square foot of 3mm steel (or brass?) heat sink, to suck the heat from those little buggers! That enough to keep them cool? Yes, each motor mount will be electrically isolated from the hull, and each other, that bit I’ve thought through already! The controller is switching at 20MHz according to the spec, my meter shows it running at 19.74 MHz, so that’s about right, it certainly has a very smooth output curve (with the better POT, the supplied one is, how can I say, a bit crap. But what do I expect; the whole board is cheaper than a cup of tea and a scone!!) Another ‘benefit’ for having the controller physically separate from the fets is that when one decides to die, even if it catches fire, it can’t harm the controller board. Having an array of smaller fets seems to me to allow a fault tolerant set-up. When one fet dies, if it’s locked closed then the motor will speed up, when I then throttle back, the other fets in the array will close down so only the ‘dead’ one will be running the motor (now flat out) and will rapidly burn out as it’s now trying to carry 3 or 4 times it’s design load (probably just explode thereby breaking the circuit). As it cannot damage the board, I should be able to throttle up and carry on (with the remaining fets). If it fails open-circuit then I probably won’t even notice. That’s another reason for building it with a load rating several times that that’s necessary. I’ll have a think on the ‘Flat-out’ relay idea, would it really help, if the PWM is at 100% then you’ve already got a solid-state relay (I cant measure any voltage drop across my fet array when at 100%) Regards Phil D. -- You are currently subscribed to the "R/C Tank Combat" group. To post a message, send email to [email protected] To unsubscribe, send email to [email protected] Visit the group at http://groups.google.com/group/rctankcombat
