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Extending the Life of the Regulator/Rectifier...

31080 Views 15 Replies 15 Participants Last post by  Penfold
[align=center]Extending the Life of the Regulator/Rectifier[/align]

The regulator/rectifier (or reg/rec) converts the power the alternator generates into the voltage the bike needs. The rectifier part converts the AC (alternative current) to DC (direct current) and the regulator stops the voltage going higher than a certain amount, typically 14.5V for a CBR250. If the reg/rec dies, it usually stops power getting through, or it doesn't limit the voltage :cool:.

If the voltage gets too high, the battery boils and is damaged, and all the bulbs in the bike will burnout, including the headlights, tailights, instrument backlighting etc... Worst case, you get a few nasty spikes through and the engine controller and tacho will die [xx(].

If the voltage gets too low, the bike will have trouble idling, may not start, you might not be able to rev very high, lose performance and have missed ignition events.

What causes it to fail? Bad design for one... Honda did a crap job of making this part, and its a common problem for the CBR250's.

The damaging component is heat!

These things can get really hot, and the longer than run at high temperatures, the shorter its life will become.

There are few things that can cause it to run hot. The primary culprit is an old or worn out battery. If the battery doesn't hold much charge, or is in otherwise poor condition, it will sink LOTs of current, and never properly charge. The reg/rec has to supply all this current, and this high current causes it to get hot. A good battery will charge up while riding, and not take any more... the easy life for the reg/rec!

The other problem is high wattage bulbs in the headlights. Normally the CBR250 has 35/55W bulbs. So with normal driving lights, it's probably drawing about 6 amps. Now if you upgrade to 60/55W bulbs, that goes up to 9 amps. Considering the CBR250 puts out about 18.5 amps with some revs, thats half the budget!!! Now you may wonder why it would make a difference, given the highbeam is 60W. It comes down to use... how often are you sitting at the lights with your high beam on? Not often. At idle, the battery is supplying most of the current. The rpm has to be few thousand revs to start contributing significantly... and it will have to contribute back to the battery when you take off from the lights. So it comes down to higher wattage bulbs are going to generate more heat in that reg/rec... most likely while your sitting there idle without any airflow to help cool the reg/rec.

What you can do, is to provide better 'thermal relief' for the reg/rec. See it here in the picture, bolted to the frame.

The underneath side of the reg/rec is metal, and the frame sucks the heat away and keeps it cool. If you left it unbolted it wouldn't last long [B)]. You can definitely improve how well the heat gets drawn out to the frame by putting a 'thermal transfer compound' between the reg/rec and the frame. You can buy it from Dick Smith and other electronic shops.

Silicone Heat Transfer Compound, 10g tube
Dick Smith, N1205, $3.69

Just a note... some of the stuff is carcinogenic, so check the labelling and use gloves to be on the safe side ;)

Clean the frame and reg/rec throughly... remove any bumps etc... and apply a thin layer.

Make sure its bolted back firmly, but definitely don't over-tighten and strip the threads :rolleyes: Make sure that when you put it back on, you don't trap a big air bubble in there. That would act as an insulator. So touch the bottom edge first and the top edge last, squashing the compound out the sides as you go. Below is a perfect example of having enough on there to get a small amount ooze out the sides ;). If in doubt, put a slightly thicker layer of compound on and clean it up later :dodgy:

This will make a big difference! You can also get rubber thermal transfer pads, however they are difficult to find for the general public in this size, and more expensive.

I have seen some people put CPU fans on these... but I personal don't think thats a great solution, and a bit over the top :cool: Besides, the metal sink on the reg/rec will likely transfer more heat than a fan will by blowing on the top of the epoxy.

The alternative is to find another reg/reg from a different bike that fits. I've never needed to look into this myself, but I believe your best option will be to visit the wreckers and ask them what they have and will fit. You might need to do some re-wiring to actually fit it! If you have to replace the reg/rec... definitely consider this option, and compare prices. Worst case, you could be up for new battery, bulbs and replacement reg/rec. Spending $3 on some thermal paste and 10 minutes of basic work to prevent failure is a good investment IMHO :dance:.


If the terminals of the reg/reg and/or plug terminals are dirty or loose, it can cause problems. This picture is of a VFR400 regulator which had a bad connection with one of the alternator wires.

The poor connection generates quite a lot of heat. So much heat, that the wires fused together and shorted.

The yellow cable ties didn't help either, as they caused the addition pressure points pushing the wires together in spots.

Make short the terminals are difficult to push on, and if not, squash the terminals to make them a tighter fit. If there are any signs of charring or meltage, something is wrong and likely to leave you on the side of the road cursing at some stage ;)

If the wiring has fried, you can always replacing the wires. I did this for my VFR400...

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Here ya go. Some light reading on the topic!

I am going to be checking my (fiancee's) new Cagiva Raptor tomorrow. Apparenty the TL100S is pretty notorious for bad reg rec wiring.

Eclipse you are a guru. Bloody good idea!

Good write up as well, thanks!
I am going to be check doing that to mine asap
I think i'll do this just in case.
Thank you
Yea thanks bud, i'm getting right on to doing this mod.
Thank you so much for sharing a wonderful post on about life extension of regulator. I always get low voltage problem after some time. And it threatening me to solution.
I hate when they threaten you to solution!
The charging system is the alternator, regulator rectifier, and the battery. ..... while running cooler, and possibly extending stator life.
that's bloody genius - turning the frame into a heatsink :)
I have thought about cooling it by way of a Corsair H100 Watercooler just to be a complete NERD!! i have a spare sitting here.
Un19ue said:
I have thought about cooling it by way of a Corsair H100 Watercooler just to be a complete NERD!! i have a spare sitting here.
Where are you going to put the radiator? Also, are you sure that the H100 can deal with sudden shock? I.e. Pot holes. I mean, most PC's are stationary most of the time. But, corsair does make quality gear.

:) :p
It was a stationary though, but sounds like a challenge now. The rad could go where the vent is next to rear seat. i might actually have a look tomorrow.
Had the same problem before I though that the rectifier is a busted so I bought a 2nd hand part and plug it and still doesn't work, check the fuse and its blown check the harness found out the wires are burned.
My fuse went in my bike and I have replaced my battery and regulator now I go to start it and all it does is make a winding noise anyone know what the problem could possibly be ?
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