Rectifier/Regulator "Turbo" Modification Pictures
Choose a suitable 12V fan. This one is the type used in PC power supplies.
e.g. CPC part # MF54069 @ £5.98
It only draws around 120mA and has a high air flow rate.
An 80mm x 80mm x 20mm one fits perfectly but if you are using any other size fan, first check that you have adequate clearance to enable you to get it in place without fouling on anything.
Avoid using fans that have heatsinks already attached (CPU types). The most efficient heat removal is achieved by passing cold air directly onto the R/R's own fins.
With the R/R assembly still in place check how the fan will fit and make sure you know what orientation is the best. If it is the fan I have recommended a central position is fine.
Having removed the seat and cowling disconnect these two (lower) connectors and remove the rectifier/regulator assembly
Carefully mark the outer fins on the R/R unit and drill four holes about 4mm in diameter. A pillar drill makes this part of the job much easier. The fan can be offset to either end of the R/R assembly to achieve good clearance without compromising the performance of the cooler.
Use four tie wraps to attach the fan to the heatsink assembly. Make sure that you position the fan so that it Blows onto the heatsink. They are usually marked with arrows on the casing. If it is placed the other way around it will still work but it will be less effective.
Re-fit the R/R assembly then connect the wires. The negative wire needs to go to the framework. Use a crimp on wire tag and find a suitable bolt to ground to.
The positive wire (red) goes to the feed for the rear sidelight (brown wire) using an in-line splice connector. You could connect to the switched +12V at the fuse box, but it's quite difficult to get to a suitable wire without cutting into the loom. As I always ride with the lights on it seems like a fair compromise.
An alternative suggested by Malcolm Farrar is to run a wire across the front of the battery (behind the fuse box) to the brake light live side so the fan power is switched by the ignition key.
Thanks Malcolm.
Finally finish off by re-fitting the seat cowl and the grab handles, or topbox rack in my case.
Then replace the seat and hump (if you use one) and be happy that your Rectifier/Regulator wont overheat anymore!
FAQ ... well answers anyway!
There is almost no surface area in contact with the frame at the back of the R/R assembly. It is finned front and back too. I really don't believe that the mounting to the frame is supposed to conduct heat away as the frame has a nice thick coating of black paint. Not very thermally conductive!
My honest opinion is that Honda screwed up with the design of the vents on the seat cowl. The R/R unit is designed to be cooled by natural airflow but the cowl vents are cut the wrong way and so the R/R unit sits, shielded behind the plastic in still air, just cooking away..
Tie wraps are good to about 150C so no worries there, especially now that the fan is fitted!!!
The fan should be available for less than £10 if you shop around and fitting one could save you serious money on a replacement R/R unit. Avoid high street computer shops where they will try and extract from you £18 or more. Trade sales like CPC or Maplin will be cheaper or buy an old computer PSU and remove its fan!