Yamaha XT550 regulator

**davereid** · 2nd June 2008, 17:06

You won't be able to use a voltage divider, it would provide F.all regulation, and as a rule of thumb, your voltage divider needs to draw 10x the current your load does, so its just not going to work.

If you are blowing the RECTIFIER you have too much load.

Paradoxically, if you are blowing the REGULATOR you don't have enough load.

Your bike has fixed magnets, rotating around a winding. The faster the magnets spin, the more electricity you make.

Your rectifier converts it to a sort of DC, thats' suitable for charging a battery.

The regulator generally comprises a big transistor, like a 2N3055. This transistor is wired directly across the battery, just like a light would be. A zener diode provides current to the base of the transistor from battery positive.

The zener only conducts when its rating is exceeded. So, a 14 volt zener would not conduct until the system voltage exceeds 14 volts (plus any voltage lost across the base-emitter jnction of the transistor.)

So, as you hoon off down the road, rpm go up, and system voltage exceeds 14 volts. The zener conducts, and turns the transistor ON.

The transistor is now like a big load across the electrical system - it draws current. This current is sucked out of the alternator. This pulls the alternator voltage down.

As the voltage goes down, the zener turns off, and the cycle is set to restart.

The regulator dissipates the power it draws as heat. If it draws too much, it will fail, as it will get too hot.

So, if you have no lights on, at high rpm, the regulator has to turn all energy produced by the alternator that exceeds the 14 volt threshold to heat.

If you have a 55 watt headlight on, the regulator doesn't have to work as hard. The headlight has saved it 55 watts. Got two headlights ? you have saved the regulator 110 watts of work.

Of course, at low rpm the alternator may not be producing enough juice to keep two headlghts at 14volts.

Hope this helps !

**FilthyLuka** · 2nd June 2008, 17:06

Originally Posted by Wired1

I'm also running without a battery, adding even a small one might help to reduce the alternators load and it would certainly smooth it out.

Didn't you put in a capacitor? That should do the trick.

What davereid said about the transfering of energy into heat is very true, hence why putting the thing under the seat isn't such a smart idea. Most bikes have to power a charging circuit aswell, so alot of the energy is put into that circuit. If you are running just lights, all that energy needs to be diverted into heat instead of going into a battery. Wire in a "big fuckoff cap TM" and see if it helps

Another method may be to use a stepdown transformer, take 30VAC to 20VAC then run that into the reg/rec.

A battery kinda acts like sort of a "buffer" if you will, so hopefully "big fuckoff cap TM" should do the same thing. Make sure you get one rated correctly though. 600volt .2 Farhad cap (no, not micro farhad) should do the trick. But if you are looking for a cap of that size you might aswell just wire in a battery...

Originally Posted by davereid

The regulator generally comprises a big transistor, like a 2N3055.

I built a distortion pedal around one of those transistors, sounded freaken metal \m/ (><) \m/

Blew up shortly after, hehe.

**davereid** · 2nd June 2008, 17:13

A battery will help, as it draws curent to charge, and helps runs those headlights properly when rpm are low, and the alternator can't do it.

Assuming no load, just alternator, rectifier and battery then...

a) Batteries stabilise voltage, and when connected to a rectified AC source will tend towards the mean applied voltage.

b) Capacitors on the other hand like to charge to the peak of the applied rectified voltage, not the mean. You will measure about 30-35% higher voltage.

Of course you don't have any more energy - as soon as you connect a load, voltage will be determined by the battery and alternator.

**Wired1** · 2nd June 2008, 17:18

Thanks for that, the one thing I have learned about automotive wiring is I'm glad I'm the other sort of sparky.
I had the headlight and tail light going - they are permanently wired on - and they would be around 70 Watts all up so I figured this should be enough load to make the regulator work. I should have put a capacitor across the output to smooth it out a bit but that doesn't seem to have been a problem as the bulbs didn't blow. The thing I can't quite get my head around is why I should put a battery across the regulator output - surely all this would do is take more current when charging - or is that the whole point? I could just as easily run the lights from the battery without the charging circuit but the idea was to do without the battery.
Should I try again with the regulator exposed and bolted to the frame plus a capacitor to replace the missing battery?

**davereid** · 2nd June 2008, 17:23

Yeah, I would have thought that 70 watts of fixed load was enough to save the regulator from frying, so I'm not quite sure what is going on. The regulator should be bolted down - it helps keep it cooler, plus depending on design, the frame may be the ground. (earth)

Capacitor - not needed if you are just running lighting.

**FilthyLuka** · 2nd June 2008, 17:26

Originally Posted by Wired1

The thing I can't quite get my head around is why I should put a battery across the regulator output - surely all this would do is take more current when charging - or is that the whole point? I could just as easily run the lights from the battery without the charging circuit but the idea was to do without the battery.

Should I try again with the regulator exposed and bolted to the frame plus a capacitor to replace the missing battery?

The idea is to take more current. Excess electrical energy is given off as heat by the reg/rec. So once the revs pick up and the AC generator makes more juice, the thing fries itself cause of all the heat it generates.

Adding in a capacitor wouldn't hurt, it would help smooth things out atleast.

Put the thing in direct airflow and try again, you may find thats enough to stop it frying.

Mate, if i was you, i would just bung in the charging/light system outta something similar, like an SR500 or summat.

I wouldn't run the lights off the battery with no charging circuit, cause that means you need to bung out the battery and charge it when it goes flat, and who can be arsed doing that eh? You don't need to worry about starter motors and solenoids and junk so just wire in the charging circuit.

**Wired1** · 2nd June 2008, 17:29

It's still possible that I hooked it up wrong as it came without any diagram or labels, and speaking of SR500's - my SR400 has been blowing the headlight bulb, first high beam and now low beam, seems this bike may have a regulator problem too.

**Wired1** · 2nd June 2008, 17:32

Originally Posted by FilthyLuka

something like this?

Nice, how much current would the zener have to handle?

**FilthyLuka** · 2nd June 2008, 17:40

Dude, Use a fooken battery.

The faster your engine spins, the more shit it generates, the more crap the reg has to deal with, leading to it munching itself.

Because of the variable amount of voltage, you need something that can handle 0-14v DC and spit out 14v DC constant. What would do that? hmm, lets see, a battery.

The problem capacitors, you will need to deal with the inherent problem of Capacitance, so you would need coils to balance that shit out on the AC side.

Problem with regulators, they have a band in which they work in a specific range. like, it may take 20volts down to 14 no problem, but 18 volts it may not, and 30 volts it will have a hard time. Find out the range. The bigger the voltage range the more work it does

Problem with generators. They spit out constant voltage but the frequency changes, Bridge rectifier with cap in sorts this out. Make sure you get 30VAC at all revs.

How to work around all this foolery?

30VAC dump outta generator -> step down transformer (to 20 volts to make regulators life easier) -> Rectifier Regulator -> Battery -> All the other shit you plan to run.

That way will give you least amount of headaches. taking it down to 20 volts will make the reg/rec MUCH happier.

You need the battery to take variable voltage, smooth that bitch out, and spit out 14VDC smooth. Caps have issues that im too lazy to go into.

Battery is the easiest way

**FilthyLuka** · 2nd June 2008, 17:42

Originally Posted by Wired1

Nice, how much current would the zener have to handle?

fucking shit loads. Needs to able to handle the maximum amount of current drawn by the system. 1amp current draw = 1 amp zener, good luck with that.

(p.s: if you want to find one, they look kinda like a hockey puck)

EDIT: well, not really a hockey puck, 15 amp zener = hockey puck, they are more like a big diode size wise

**FilthyLuka** · 2nd June 2008, 17:46

sorry, post deleted, heres that wiring diagram again

**FilthyLuka** · 2nd June 2008, 17:51

Im not sure about AC generator though, weather it just changes frequency or voltage too.

Either way, step down transformer doesn't give a fuck, it'll spit out 20VAC regardless (if thats what its rated output is ofcourse)

**Wired1** · 2nd June 2008, 18:37

Right, enough fucks, I'll buy a new quality chinese regulator, bolt it to the frame, hook up the smallest battery I can find and cross my fingers. I'll let you know what happens...