re. my blown controller:- IT'S FIXED!
Many thanks fechter and everyone else who's posted all the really useful info that helped me sort it out. I would have done it sooner but I've had a cold all week and soldering FETs while sneezing and coughing isn't recommended.
In the end it all went pretty much to plan: I swapped out the three 1000uF capacitors with new ones and moved them away from potential sources of heat such as the shunt resistor and the FETs, by keeping their legs long I could raise them up and away from these components. The gate resistors were still intact (rated 15ohm on this controller) so I just replaced the five middle FETs, which had the short, with IRFB4110s, plugged the controller back into the moped with a 5amp fuse on the power line and hey presto the back wheel went round when I twisted the throttle. One slight hiccup occurred when I replaced the other 10 FETs and put the controller back in and..... nothing.
Fortunately, I soon traced the problem to a dodgy connection with the throttle wires which had one of it's connector pins loose, just pushed it back into the connector block a bit and all done, totally working.
I've now done two runs of about 15 miles each on the moped and all's going fine. I'm sure it feels smoother and a bit nippier than before, it gets up to 30mph quick enough and tops out at about 35mph (eventually) on the flat. I've been riding in traffic with lots of stops and starts and some moderate hills and the hub motor feels only slightly warm at the end of the run. The controller however does feel significantly warmer than I'd like and I'm probably going to do some kind of forced air cooling on it although I might just move it so that it's getting more air flow over it. At the moment the controller is tucked away behind the under seat storage area and stuck to a plate metal box which holds one of the batteries. I'm concerned that the extra heat which this battery is getting will affect it's lifespan and pull the capacity of the whole pack down, so moving the controller to a better location is next on the agenda. The only slight gripe is the poor acceleration as the voltage sags towards the end of the run. I might have alleviated this by putting some solder on the shunt but I didnÃƒÂ¢Ã¢â€šÂ¬Ã¢â€žÂ¢t want to pull too many amps through these batteries, they're the silicone ones from Greensaver and I recon they're already operating at or above their recommended amperage rating, which will seriously reduce their life. This will not be a problem however when I replace them with LiFePO4 in the spring, funds permitting! I'll retire silicone batts to a small PV setup I've got planned.
Many thanks again to all on the forum for all the excellent info here. Did I mention ES ROCKS!