T-Max blowing after market regulator rectifiers (and how to fix it)

One thing that is annoying lately on my (now elderly) 2007 T-Max is how often the Regulator Rectifier is dying. I've had what are significant and expensive problems caused by this in the recent past and even going back years its stood me up in the past too with a previous model.

I believe that the problem is the construction of the after market ones compared to the original ones, right now (in Australia at least) getting genuine ones is "special order ex-Japan" and they are now AU$360 - fark!

So how can I make do with what's available at sub $40 price, which BTW the genuine ones used to be $80).

What happens?

Thermal failure is what seems to happen. When you pull the regulator you can see that its "popped" up at the back (opposite end to the plug).

Wanting to see what was there I worked at prising it open ...

The first thing that stands out is that its got thermal paste (badly applied) to a heat transfer plate to marry it to the sink body ... so that's a step back from the yamaha design because only one side can shed heat. Next you can see that the backing of the heat sink is not polished at all and so will have even greater reduction of heat transfer capacity (and NO thermal past should not be used like tooth paste, it requires a very clean joint and is only to fill tiny imperfections).

Next we can see that the thermal (tooth) paste application has boiled off and sunk down into the bottom of the crevice meaning that the regulator (encased in plastic) can shed even less of the heat.

Meaning that the thermal paste changes to become "thermal insulation" ... this just can't work for long if it gets hot.

Why will it get hot? Well simply put if the generator (three phase AC stator type) puts out more power than the system needs it can only get rid of that excess energy as heat ... so yes, the regulator becomes a little heater shunting the extra power off. This happens at higher RPM much more so than lower RPM (when the stator is generating less power), and I believe that 5000RPM is the threshold for that: meaning that on the highway is when it will pop. 

AND THAT FITS MY EXPERIENCE

Understanding the problem

Looking at one of these things its pretty clear that its intended to be air cooled:

... with fins all over it like that (note the temperature sensor "blu-tak" puttied in there).

However its located under the rear cowling cover ... which essentially prevents any air flow (where it pinches tight just where it joins at the front).

obviously this provides it some weather protectection, but as you can see also prevents it getting air circulation. This overlay shows where things are under the cover.

(Note the masking tape) 

The isn't much air flow possible, which is even more clear when viewed from behind that it sits in a "warm air" bubble of whatever air can leak through from the engine bay...

Sealed in a pocket of warm air from the engine, its heat shedding possibilities are low. This is verified by a quick run with the cowling on and off (recall that temperature sensor??)

So I did a highway short run with the cowling on, came home, took it off (had to unplug the sensor briefly) and took off again and did the same run with the cowling off and air flow around the regulator / rectifier.

That red arrow indicates a temperature which I consider on the threshold of operation before thermal runaway (meaning it pops) is likely.

So how did the original survive? Well I'd say because its actually not only better made but better designed. You see quickly (if you compare them) that the after market one just looks cheap and has a resin back. Resin is not a good conductor. So lets look at the old regulator (old picture I'm afraid, I've already binned it)

See that nice aluminium backing? That means that heat can go out through the back too. So now lets look at where it was mounted...

... and we can see there is not only an area for the metal backing to press against (and shed heat into the frame a bit) but there are signs (discolouration) that its been doing exactly that.

Solutions?

Well if I could be sure that a genuine part for nearly AU$400 would do the job I might be more tempted to give that a go, however my measurement suggest to me that an alternative exists; which is cooling the existing cheapie better. 

Having already established that running without the cover results in a remarkable cooling difference I'm inclined to believe that as long as I can get air in there it will work. So with that in mind I decided to try a little pipe directed ducting

I looked at the overlay diagram I'd made and determined where to drill a hole (the masking tape), and with a hole drill, put in a 24mm hole to take some small flexible ducting

which then comes out on the inside.

where I can then see where it comes out from by using the above overlay technique

Which I sub sequentially tuned it to point more down after this shot. I have found that using my thermal camera that the lower portion of the heatsink generates the most heat. "Tuning" was just bending (its flexible hose right?) and I used a cable tie to hold it down there.

When fitted up to the bike its pretty neat

and I'd say that if you didn't know it was there you would likely not spot it

Lastly I did another run into the next village and did some 6000prm run in a few places (you'll see two spikes in the middle)

which is quite a good result, although not as good as fully open was ...

So for now I'm calling this sufficient but when summer comes I'll need to check that its still safe in temperatures. If it turns out that the 40C days we get bring it too high then I'll consider an option where I cut a section out of the cover and expose the fins directly to outside air.

For now though, this is good enough.

POST SCRIPTUM

I was riding around and thinking about how close that graph got to 50C and thought that since the air temperature right now is like 20C (middle of the day) and that in summer its going to be nearly 50C (coming directly off the road) that will drive that temperature up closer to limits again. So I decided to look for power and attach a small case fan to assist cooling.

See the video for details. Sorry about the mistake in speech, I find it hard to juggle a camera, focus and know what to say on an unscripted quickie. Please find below a video, which may not appear on mobile viewing (because mobile is still shit compared to a desktop experience).

for the screws I used I had to

1. drill out the holes in the CPU fan I had lying around
2. bevel the edges with a bevel tool (so that they'd sink in  to look cleaner and have enough depth to bite into the cork
3. there are no screws at the bottom because there the heatsink "next rail" was too low to support the cork ... I might add some and glue it in place if I feel the need. The fan over hangs on the stand but is vertical when riding so it should be ok (bumps ...).

make sure the cork is in snug (not loose) and apply the hotmelt glue to the join of the edge of the CPU and the tip of a cooling fan. Make sure you do not get overspill which blocks the blades (I have experience using case / cpu fans for a few things). Add a little more on the outside and smear it in with a screwdriver blade as you go. The heatsink will cool and set if faster than the plastic case.

I used both because a synergy of two methods is better than one.

HTH