I though to re-locate the rectifier off the rear fender until I saw that  it is deliberately flat mounted on the fender in a manner in which suggests Suzuki is using the fender as a heat-sink.  They could have mounted it anywhere, but did so on a large metal fender which is constantly in the air-stream.  Sure looks like its being used as a heat-sink. Someone even said his left a blackened area on the fender, which might indicate heat transfer. Any electrical engineers out there care to comment on this?

I've had mine stuffed in the airbox for about a year and have had no problems so far.

Using the theory of the fender as a heat sink, would'nt that also apply to the frame as a heat sink for the engine? The rectifier itself is made into a heat sink which is the metal case with the fins, the actual rectifier is incased in the epoxy you see from the bottom. If the fender was acting as a heat sink, then why would the rectifier be built into an actual heat sink? Now if the fender was made from something like aluminum, then maybe. I imagine why Suzuki engineers put it under the seat was pure aesthetics. Being under the seat actually inhibits the heat sink from doing its job. I moved mine for that reason, and upon removal of the rectifier, heat discoloration was evident on the fender, which is clear evidence that the rectifier was overheating. I'm thinking that when the rectifier overheats, the battery overcharges/overheats causing the electrolite to boil off. The muffler bracket makes a good open air mount for the rectifier, and only requires two wires to be extended, the rest can be re-routed.

I de-snorkled my air box, then drilled into the lip and through bolted the rectifier in place.  The air box has alot more room to for air to circulate than under the pillion seat.

When I did the seat lift, I removed the foam tape from the bottom of the seat to allow more air-flow below the seat, allowing more cool air into the air box.

No problems so far...

Hell, Billy wrote on 04/01/08 at 22:30:05:




It is constantly in an airstream as a result of the rear wheel rotating at high speeds.  If you look under the fender you will see dirt thrown up from the tire onto the underside of the fender.  That is why the fender is there, to prevent this thrown up dirt from hitting the rider.  Watch the videos of a stationery bike spinning its rear tire.  Watch the smoke as it is thrown up under the fender.  A rotating cycle tire continually cools the fender with air.  Additionally, air passing by any part of the bike will remove heat from the affected surface.

I guess the fender could act somewhat like a heat sink.  If Suzuki really intended this to happen, they sure did a lousy job of it.  You normally would want low thermal impedance between the heatsink and heat source.  Thermal grease or thermal pads are normally used between the device and heatsink if you are really serious about dissipating heat.  A painted surface generally does not have good thermal impedance characteristics.

Problem number two, the law of thermal dynamics.  Heat rises.  If Suzuki intended the fender to act as an adjunct to the heat sink, they would have mounted it on the underside of the fender.

Instead, its crammed into a cavity surrounded by 4" thick foam.  The only source of ventilation is the 5/8" gap between the pillion seat and the fender.  That sounds more like constructing an oven, than it does a motorcycle.

Just for kicks, I ran my digital probe thermometer down into the airbox to measure the running temps of my rectifier.  The immediate surface temp was 108* after running at 55mph for 30 minutes.  I think its perfectly safe being mounted in the air box.  Especially since I took the side door off to promote more air circulation.

skrapiron -FSO wrote on 04/02/08 at 16:26:25:

The principle you're talking about is convection.  Only happens when you're standing still.  Most of the time you have forced air convection.

Heat radiates, and conducts too.  The fender will conduct heat to cooler parts.  Where it will be radiated or convected off into the atmosphere.  

If you're having a problem with an overheating rectifier, put some thermoconducting grease under it or put it out in the air flow.