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VOLTAGE REGULATOR RECTIFIER
Achilles' hell for the desert queen (1/4)
(wait....there are many pics to load)
I'm an Honda Africa Twin 750 mod. RD04 '91 owner: a tanker under a mechanical point of view, but it has an electrical problem: the voltage regulator - rectifier.
Surfing on the web it
seems that the regulator - rectifier problem is a common problem between many
About AT, it seems the RD04 model suffers more than others; after I've payed 200 euro for a new one, I've investigated the problem.
Well, after some search, I'm going to suppose most of the motor-cycle rectifier regulator use a 3-phases bridge to rectifier the AC output of the alternator and 3 SCR diodes to regulate voltage at 13-15V; a simple comparator (may be a single transistor+diode+capacitor - I've opened the broken regulator) drive the SCR gate;
The SCR short-cut to
ground the signal when it exceed 13-15V and so doing it produce heat: heat
and vibrations is the worse thing for an electric device......and the regulator
In RD04 model the
regulator - rectifier is on the right side, just above the coolant reservoir and
above the exhaust system; try putting you handle near it and you'll note how
much heat the silencer produces;
More, the right side seems to be very hot (think to the heat your right foot feels when running), heat wich goes away throught the right side.
Add the own heat of the regulator and you'll understand why the regulator's' life is too short.
Infact in the next model (RD07) it has moved on the left side;
I don't understand why Honda engineers have used a power dissipator only in one side: the other side (where you can see a black resin) produce a lot of heat too!
Other enemy of
electrical devices are vibrations and sure on a bi-cylinder like our AT there
are many vibrations, but the regulator is mounted directly to the frame with
just 2 bolts.
Well, if that's' the situation, we have to eliminate heat and vibrations.
About heat, the position is not good: under the instrument cluster will be a nice place but very far; so I decided to move the regulator bsck, on the left side; you just need to add 40cm of cables.
It's mounted trought 2 "collar bolt" (1/2 inch-see pictures for details).
Use anti-vibrations washer, nylon insert
nuts and thread locking compounds;
Use some rubber between the frame and the bracket to breack vibrations.
I've added an other power dissipator on the other side of the regulator ;
it'a 90x85x25mm but remember: bigger is better.
Because there're some millimeter of empty space between the regulator and the added dissipator,I've used a copper-sheet and siliconic grease (that used in electronic) for a better heat exchange;
Well the first test gave me good results but heat was still excessive;
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73 de iz7ath, Talino Tribuzio