[Ducati] Misc ponderings about regulators

[Dan Johnson]

My first fail on my ST2 was running down I-10 with high beams on and 
 >100F. So using max current, generating max current. That was when it 
was tucked in the marvelous stock location with no airflow at all. 
Queasy feeling when you're hundreds of miles from home and something 
like that happens. Since it was daytime, I removed the fuses from the 
headlights and ran without, bump started when I stopped for gas, and 
made it home fine. I've killed a couple in the stock location, and 
finally started trying to figure it out and do something better.

The regulator gets a certain temp at idle and lights on. It gets MUCH 
hotter if you rev higher and leave it for a time. The load from the 
lights, etc is about the same, and the ignition,fuel pump and whatever 
else that might change with rpm really isn't drawing much current, so 
isn't changing much. The voltage from the stator increases with RPM, so 
you're dumping more "extra" power than before, and that becomes heat 
exiting the regulator.

So I can definitely attest to higher rpm=hotter and lights off=hotter 
from playing with mine quite a bit, and trying to keep it cool.

I also noticed that as the regulator warmed then the amperage out 
decreased. Say you're at a stoplight and the regulator heats way up. The 
bike is going to start drawing power out of the battery to make up for 
the regulator not working. So if you aren't keeping the regulator cool 
enough, your battery is also going to work a lot harder. Even in the 
stock location at idle, with a good interface to the air intake housing 
and heatsink grease, it would get warm enough that it wasn't supplying 
enough current. In trying something other than stock, I did have it in a 
bad setup, and it was running hot enough that I'd go out for a ride and 
the battery was actually discharged compared to before.

You might not even notice if you try something and the regulator isn't 
cool enough. You'll get enough of a charge some of the times, but you're 
running off battery part of the time too. But you'll go through 
batteries and regulators. Having it work "enough" to charge, or just 
making sure the light is off, leaves you at risk to overheating and 
killing it.

What I did with mine was mount it underneath the airbox lid. I have the 
front of the airbox removed-huge hole. I also put a huge heatsink on. 
Stays plenty cool now. Another place might be somewhere near the battery 
between the fairing and motor. I played with putting it in the air 
intake, but couldn't keep it as cool. The heatsink (from a couple of 
computers) helps a bunch. The regulator doesn't have much surface area. 
You have to make sure there's plenty of surface area in contact with 
some metal-the regulator isn't going to stay cool enough on its own.

Having a heatsink or at least some metal also helps it not get nearly as 
hot when you're stopped at a light. You then have a reservoir you can 
dump some heat in to till you're moving again. The regulator doesn't 
have any "mass" to speak of, and so heats up and down quickly, and those 
thermal cycles are BAD. Keeping the temperature a little more constant 
will help make it live longer too.