I know we have a few motorbike riders on here, but this may be of general interest anyway.
For a few years now there has been an improved motorbike R/R ( rectifier / regulator ) that is a lot better than the standard bit of kit. The newer one is called a 'series' type, and brings bike electrics more in line with car stuff. Bikes have a similar 3 phase AC alternator to cars - but where modern cars have a wound rotor ( the bit that spins round ) so that by varying the voltage applied to it you can control the output of the stator ( the fixed heavy windings ), bikes still have a permanent magnet rotor so that the amount of power output is basically uncontrolled and just depends on the engine revs.
The normal OEM R/R is a 'shunt' type ( electrical speak for 'in parallel ) where full power is drawn from the stator coils and any power not needed by the bikes electrics was basically wasted by 'shunting' it through thyristors to earth, this means the stator is always fully loaded and runs hot, and the R/R heatsink also ran hot because of the power through the thyristors, next generation of R/R was a 'mosfet' ( metal oxide semiconductor field effect transistor ) which was faster switching than thyristors and generated less heat, so the heatsink ran cooler on mosfet type, but the excess power was still 'wasted' and the stator coils were still fully loaded all the time, so the stator was still running hot ( many bike stators use engine oil for cooling the coils ) a burnt out stator was a fact of life to many motorbike owners, as was a melted R/R and a destroyed battery. .
Now to the latest ‘series’ type R/R, well it works on the 3 phase AC side like a light dimmer switch, and actually blocks a certain amount of the voltage from the stator when it is not needed by the bikes electrics, this means that it takes a lot of the load off the stator coils and also the heatsink runs a lot cooler. I have just fitted a Electrex world ( made in Oxford, UK ) ‘series’ type to my bike to replace the OEM shunt type and the immediate effect was that the voltage to the battery was much better controlled throughout the rev range and the heatsink ran 30degC cooler ( OEM was getting on for 80degC the series one was just under 50degC ). This latest 'series' type R/R brings motorbike system more in line with car systems. I often wondered why you can get a 5 year warranty with a car battery, but with a bike battery, even the most expensive ones, the best you can get is 12 months. It was simply because motorbike charging systems were so crude compared to car ones ( but recently car ones seem to have become very overcomplicated ).
Have attached a PDF of an R/R basic dimensions are about 110mm x 80mm x 30mm – one plug with 3 yellow ‘AC’ wires from stator coils and one 12VDC plug with black and red wires to the battery. All the rectifier diodes and other stuff in this heatsink will be contained inside the normal car alternator.
Just to add, many smaller bikes ( probably less than 250cc ) are only single phase AC from stator, bigger bikes get 3 phase like a car and about 35amps total capacity, and some bigger adventure bikes may get 50amps to cater for all the extra lights and other kit they may have fitted.
