Bike rectifier.

[Diabolical Artificer]

A while ago the "rectifier" on my motorbike, a 94 Yamaha XV535 virago, died. As a new Yamaha part is about £100 I got a cheap jobbie off ebay. Went to start the bike yesterday, battery flat, thought I'd forgotten to turn it off. Charged the battery up, started it, got 50 yards, battery dead. There was a short between - and + which turned out to be, you guessed it, the rectifier. One diode was shorted.

Looking at the bikes electrical system in more detail, AFAIK the alternator is three phase, havn't had it on the scope yet, but the schematic shows three windings in a Y shape. I took the original "rectifier" apart, which was potted. It is basicly three diodes on a heatsink. So as diodes capable of handling a few amps at 12v are cheap, why not make my own rectifier?

Again looking at this in more detail, the bike "PSU" has no smoothing cap, but does have a regulator, which from the size of it is probably nothing fantastic. So I'm thinking why not pop a big cap after the rectifier and maybe build a better regulator too. The old "system" is crap. The connector from the rectifier to the battery is burning out, being one of those multi horrible spade connectors. I've already had to replace the LH coil twice and the TCI and solder the coils to the loam as the old spade connectors were loose dirty etc. An up rated charging/supply system would e the way to go I think. Bike electrics are pretty basic and horrible in comparison to the PSU's we use on the bench or even in basic consumer gear.

Any thoughts, much appreciated. Andy.

[boater sam]

The alternator is 3 phase as you found, in star mode. A diode on each leg to + and another on each leg to - is the normal way with cars anyway. 6 diodes.
If your battery is sealed, most are, then the regulator simply shuts off the charge at 14.4 volts, should be easy to build or use a regulator out of an old car alternator. The sensing wire connects to the ignition warning light so it sees 12v when the ignition is on.
The control wire goes to the slip ring brush which is not connected to either + or - ( this depends on whether the alternator is =or- sensing ), that's how it shuts down the alternator output.

[Diabolical Artificer]

thanks for that info Sam. I think the rectifier on mine is simpler, it being three diodes connected to each end of the Y, probably to the anodes. Each diode is joined at the cathodes, a red wire comes off this junction, which I presume charges the battery.

I need to investigate further.

Andy

[boater sam]

That really is crude, its half wave rectification. Is there any sort of regulator? I've never done bikes at all.

[Kalee20]

Presumably there is a return from the star-point connection. Yes, 3-phase half-wave.

Is it a permanent magnet alternator? If so, then there's no way to control the output, and the regulator just has to switch the rectified output on or off, according to battery voltage.

[chriswood]

It's a long time since I did mbike electrics but regulation was often done with a zener diode shunting away the excess power to protect the battery often seen on a heat sink mounted under the headlight or somewhere in cool air. Rectifier can be made from 3 stud types mounted on some aluminium angle.
Chris

[Diabolical Artificer]

Finally got around to having another look at this and opened up the "rectifier/regulator" . This one picured is a cheap Chinese jobbie I got to replace the original Yamaha one. It's different to the Yamaha one, it had a little "sub" board in, the Yam one didn't. On the sub board were a few SM diodes and resistors, nothing else. I suspect the diodes are underneath the potting.

I've knocked up a schematic. as you say Sam there are six diodes in pairs in series. Getting a likely diode to replace this box was tricky. most dual diode packages  are common cathode or anode. These are the ones I bought, should do the job - http://uk.farnell.com/ixys-semiconductor...dp/1080104  These are dual series, meaning they have a tap at the junction of cathode and anode.

What is puzzling me is that there isn't any regulator of any sort elsewhere on the bike. So current/charge is constant to the battery. There's no smoothing cap either, which I guess is pretty standard for bike charging systems. I don't suppose it needs it exactly, but it seems like a good idea to put some sort of regulation inside the box if I can get it to fit. A simple fold back/feedback into an op amp which controls a series pass tranny.

However current demand isn't constant. For normal running a trickle charge is sufficiant, but when the lights are on you need full charge. Any ideas for a simple regulator?

Andy.

[Crackle]

If that is how it is wired with 6 diodes then it appears to be a full wave 3 phase rectifier
Similar to car rectifier packs but I seem to remember they often used to have a separate set of diodes to power the field winding and regulator.
You used to be able to buy car regulator diode packs as spares.
http://www.ebay.co.uk/itm/322519933551?

Mike

[boater sam]

So 3 phase alternator, star connected, with 6 diodes rectifying. To regulate you need to control the field which is on the armature with 2 slip rings usually. 
Some are + sensing, some - sensing.
Assuming negative ground battery, if its + sensing, one brush will be to battery positive, you control the other brush voltage between ground and battery +.
If - sensing, one brush is ground, control the other. I may have that a about face.

Now its been a while since I played with these so don't assume I am correct please.
For a good explanation and some idea as to how it all works, read   

https://www.scribd.com/doc/119790895/THE...NATOR-BOOK

Hope that helps,
Sam.

[Diabolical Artificer]

Thanks for those links Mike and Sam.

Don't think this has any sensing. It is AFAIK a fixed magnet alternator, no field coil. A zener across the OP has been suggested as regulation.

I'm wondering if there is a correct order that the windings have to be connected. If each winding is 120 degrees out of phase with the previous one, then wouldn't windings two and three have to be in the right order as connected to the diodes? i'll get a scope on it over the weekend.

A.