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Hi
Just changed the rectifier/regulator on my 2009 650 as it was not charging the battery. As I was testing the charging before I put the bike back together, I noticed that the rectifier/regulator was quite hot to touch.
My question is, is that normal?, do they get hot-ish. After the change the charging is ok now.
Thank you.
 

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Yes that is normal. It's why they have those cooling fins on them. They dissipate excess current as heat.
 

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I would smear the rec/frame contact surface with Heat Transfer Compound.
 

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The R/R turns surplus power from the alternator into heat, because the alternator is always working flat out.
This means that the more power you use on lights and farkles, the colder the R/R is operating. Light up that Christmas tree and let the R/R relax.
 

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Yep, shunt type regulators are good about dissipating extra power into thermal energy. Mosfet type regulators may be better about it but I have not installed one yet on this bike.
 

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My background and degree are in electronics. The white thermal conductive paste is what we called bird$hit. It helps to conduct heat from the device to the cooling fins.
I would agree when you're working on anything where the cooling fins and the heat source are separate like the CPU and the finned heatsink in a computer then thermal grease/paste/compound or bird$hit is a must. But the rectifier/regulator is a one piece unit and usually the back side of it is mostly potting compound so very little heat would be transferred to the frame. It won't hurt anything but I don't think it's really going to help that much either.
 

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Like model28a said, the compound is required when you want to transfer heat to the heat sink witch in turn dissipate heat by the fins large surface area.
The heat compound is located inside the rectifier not outside.
By using heat compound on the outside you will prevent heat from dissipate due to dust and dirt that will stick on the compound and coat the rectifier totally.
If you want to install a cooling fan on the rectifier i would agree.
 

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I haven't looked at the mechanical configuration of the R/R assembly but isn't there a possibility of the frame and mounting bracket offering some additional dissipation. In that case, the thermal grease on the frame face might offer some benefit. Really depends on the construction of the R/R. OTOH it isn't going to hurt anything so why not?
 

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Like model28a said, the compound is required when you want to transfer heat to the heat sink witch in turn dissipate heat by the fins large surface area.
The heat compound is located inside the rectifier not outside.
By using heat compound on the outside you will prevent heat from dissipate due to dust and dirt that will stick on the compound and coat the rectifier totally.
If you want to install a cooling fan on the rectifier i would agree.
The applied compound is not exposed, therefore it would not collect any dust or dirt.
 

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Air movement driven by the rear-wheel motion cools the R/R (hopefully), hence its mounting location.

If you really want to reduce the heat generated by the R/R, then replace it with a series-regulator design. It's not a job for the faint-hearted though, and finding a source for the connectors is difficult.
 

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For those who are not familiar with electrickery:
There are two types of Alternator:
The permanent (constant) magnet. Here a magnet turns inside a set of charging coils (stator). The output is rpm related, up to a maximum. When the output is more than what is 'used' and more than the battery can ‘absorb’, the rest is shorted to 'earth'-the frame. A total waste of energy, but cheap to build. That is what the Burgman has. The volts available from permanent magnet alternators don't go up with RPM, in fact, if you have lights on and a bunch of electrical clothing switched on, the voltage may even go down at higher rpm because the power demand that the ignition places on the system varies directly with rpm. Cheap to produce. Great for the manufacturer. Burns up Voltage Regulators now and then, but that's the customer's problem once the warranty period is up.

The other alternator type has an electro magnet turning inside the charging coils (stator) Here the charge is controlled by the 'power' applied to the magnets via a ‘field coil’. That is what all cars and some bikes have. BMW boxers have this type.

 

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I have owned both a Guzzi and a BMW with the Bosch alternator with rotating regulated field armature.
On both bikes charging at low speeds was sketchy, and the field armature burned out twice on the Guzzi and once on the BMW.
I much prefer the total loss systems like Suzuki has.
 
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