RECTIFIERS

[mizzytheman]

Posted on behalf of Alan H

Rectifiers.
I’ve had a few calls lately regarding different bikes (mainly triples) not charging much or at all, and in fact on a T200 that I got last year that didn’t charge properly when I originally got it ended up with a similar issue.
Now I’ll not go into all the wheres and whyfores about the three phase charging system on the triples here – maybe on another post that could be ‘stickied’ so that it’s easy to find.
Anyway, we do need to understand the basics of a charging system.
A charging system usually consists of a rotating magnet inside a coil (or coils) and when the magnetic lines move over the coils, a current is induced in them. As the magnet consists on a North pole and a South pole, the current generated changes from positive to negative each half revolution of the magnet so the current generated alternates – hence the term ‘alternator’.
This alternating current is no good whatever to charge a battery and this situation has to be ‘rectified’ by inserting a diode, or series of diodes between the alternator and battery. If there’s only one diode, it will be a half wave charging system which is very basic, low charge rate so a bit pants really. Found on old bikes with early Villiers engines and does the job – just.
However we need to power an ignition system, better lights, indicators, brake lights and horn, so needs more power – always more!!
A series of 4 diodes in a square formation with all the diodes ‘facing in the same direction (towards the positive) is known as a simple bridge rectifier and will give a much better charge rate so will allow more power to be used.
Unfortunately, the charging systems on our bikes are knocking on a bit – some well over 50 years old – and over time the connections have deteriorated and develop resistance so all the power doesn’t do what it’s supposed to and merely gets warm where the connections aren’t as good as they were originally. Heat isn’t a friend of electrics and can cause items to melt, burn out or even worse – to burn.
We’re concerned with burning out in this case, and if a rectifier gets hot, the heat can cause one or more of the diodes to overheat and go open circuit so there’s no circuit through them and obviously they don’t work. A new rectifier is the way to go, but even if you can find one, they ain’t gonna be inexpensive.
It is possible to buy decent quality replacement individual diodes to repair a bridge rectifier, at about a fiver apiece. Then they need to be built into the original unit and to be honest it’s an expensive way to go and a lot of trouble, so what’s the alternative?
Rectifiers are available for lots of purposes and are rated at voltage and current. So if we think about an engine at full revs when all the bike lights are on and using brake and indicators (on the way home at night), the voltage might be as high as 35 volts from the alternator, and maybe 15 amps current. That’s over 500 watts of power trying to get from one side of each diode to the battery, so the bridge will get hot and fail again. We need a higher rating then.
A simple bridge rectifier rated at 1000 volts and 50 amps is overkill you might think, but really it makes the job of allowing a possible 500 watts dead easy and only gets a bit warm doing it – and it’s less than a couple of quid and dead easy to fit. Or if you look on everyone’s ‘favourite’ on line auction site, 4 for £2.59 currently (no pun intended!!)
Rec3.jpg
The 2 terminals marked ~ are AC so come from the alternator, - goes to earth and + goes to battery positive. The 6mm mounting hole is perfect as most original rectifiers have the same size mount.
Job done then. Of course the anoraks will be offended, but if we don’t tell them, they’ll never know and we don’t care if they do anyway.......
Ah but, I hear you thinking, the triples have a 3 phase alternator so that’s no good.
Well there’s summat we can do there too.
A 5 terminal/3 phase rectifier rated at 1000v/35amp is a massive £2.89, or 50 amp is £4.19. (Both similar other than the current rating).
Rec2.jpg
BUT one rated higher – at 1200v/50A (because it has cooling fins – or ‘a heat sink’ is a massive £4.59 and does the job perfectly.
Rec1.jpg
The three ~ terminals need the yellow wires on them, the – needs a black wire connecting to earth, and the + terminal needs a red wire to go to the battery positive.
Anyone needing any more information on the subject, please send a PM, don’t try to post on the thread please

[mizzytheman]

Sorry for the late response in posting an update on this thread but part of the problem has been getting hold of sundries to complete the work. Simple stuff like wire and spade connectors taking twice as long to arrive in the post. I’ve been waiting over two weeks for brake pads to arrive for the Z1300. Anyway, rather than do a step by step guide some simple photos should be enough for you to follow what I’ve done.

The only parts I’ve salvaged from the old rectifier is the cable sleeve and the plug. The other parts required are as follows.

Cable is 2.5mm

Spade connectors are 8mm instead of the standard 6.3mm which is the most common size used on this bike.

I’ve soldered and crimped the spade connectors just for the sake of going OTT.




Here it is fitted to the bike.

Additional earth lead required

Total cost of parts including the rectifier is about £9.50.

It was a bit late to carry out any tests but I’ll post the results sometime tomorrow

[mizzytheman]

Hi Gents,

Finally got round to carrying some testing on the bike/rectifier and here are the results.

At 1000rpm 13.5 volts. (With lights on 12.6 volts).

At 1500rpm 14.2 volts. (With lights on 13.6 volts).

At 3000rpm 14.3 volts. (With lights on 14.4 volts).

These are closely in line with the Suzuki manual so pretty happy with the results.

Rectifier temperature after 15 minutes 27 degrees C/80.5 degrees F which I don’t think is anything to worry about but I’ll recheck the temp once I’ve been out for a long run.

It’s worth noting I didn’t just jump straight in and assume that the rectifier was at fault. I carried out extensive tests on the stator and rotor and also the voltage regulator and finally the rectifier. Most modern multimeters have a setting for testing diodes. After various tests it was clear that the rectifier was at fault. One of the diodes was allowing voltage in both directions.

Just goes to show with a bit of research and help from some Yorkshire guy there is always a way to solve these faults without having to buy new or opt for a RR77.

I’ll let you know if it develops any issues over the coming weeks.

[mizzytheman]

For further details click here

http://www.kettleclinic.co.uk/kcforum/v ... 13&t=12685