Yep, not much to it it is there? The only thing I'd do different is use four wires of the same length to trigger the FET gates (instead of the current bus arrangement). This would sync timing between the FETS a little better.
Steve Tyng On Aug 10, 3:35 pm, "Phil Downs" <[email protected]> wrote: > Hi all, > > I had a bit of spare time on my hands, so I started looking at a speed > controller for my ‘Pile of bits’ > > I have done some reading up and now know how these work, looking at the > price (and features I don’t want) I decided to have a little play about. > > As my motors cant be reversed by swapping the supply lines round, and are > case grounded anyway, all I need is the speed controller bit. > > I found a cheap 9-24v dc PWM controller board, assembled and tested for > about £5, so I got a few to play with. > > I got a couple of packs of automotive mosfet’s off ebay and sat down to see > what I could come up with. > > The ‘As Purchased’ board:- > > PMC Board.JPG > > After some playing and testing, I removed the original POT (a cheap and not > very good one) and replaced it with a bigger (still 5K) one with a proper > spindle. I didn’t put this on the board but put a 2’ lead on it to simulate > it being at the other end of my tank. > > The meter now shows the controller working much more accurately. > > The next thing to do was to add additional mosfet’s to the gate feed, ‘I > wonder how many it can drive?’ was the question. > > After adding a jumper point on the gate side of the on-board mosfet, I > connected it to the new chip, and it worked perfectly. After adding another > and making sure that both new chips were operating independently and > identically, I kept on going, eventually I got to 5 additional mosfets plus > the on-board one, all working fine. > > After a bit of a tidy and fixing the whole lot to a bit of scrap wood I > ended up with this:- > > PROTO1.JPG PROTO1A.JPG > > Now the original board was rated at 3a (the chip can handle 12a, the PCB 6a, > so sold as 3a), each of the new IRF2804 Mosfets is rated at 75a at 10v (62a > at 12v) so with suitable heat sink (I’m planning to use the motor mount, > that’ll save wiring the –ve as the tab is the –ve drain) this simple > collection of bits should be capable of running a motor of 250a at 12v > (3Kw!) now my new motors shouldn’t even reach half this maximum load. > > All I have to do is gear the throttle servo to the new POT shaft, and I have > a speed controller for under £10. > > What have I missed, it seems too easy? > > I can get away with only using two additional chips, but I always > over-engineer everything I do, if things are only running at 30-50% of > maximum, it’ll last longer (in my mind at least). > > Just in case you’re wondering, to reverse my motors I have to change the > terminal the +ve line is attached to, a chunky relay and a battle switch for > each motor will do the trick. > > Any comments? > > Phil. > > image003.jpg > 31KViewDownload > > image005.jpg > 28KViewDownload > > image007.jpg > 23KViewDownload -- 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
