Yamaha XT550 regulator [Archive]

Wired1

25th May 2008, 18:26

Hi experts, I'm on the final leg of rebuilding an XT550 that came to me in a lot of boxes. I have fitted a pretty nifty looking headlight and want to power it off the charging circuit. Measuring the output from the single phase alternator gives me about 30 volts ac so that is a bit big for my 12 volt lights. I could change the bulbs to 24 volt ones and leave it as ac or I could fit a regualtor/rectifier and hope that it will happily shunt the excess voltage away - is this right? I don;t want to fit a battery so is there any other options? Cheers...

FilthyLuka

26th May 2008, 00:27

Your best bet is running lights on DC, so setting up a rectifier circuit with some caps to even shit out. Then using appropriate resistors to get the voltage to 24 for the headlight :)

Motu

26th May 2008, 19:12

You could use a zener diode like the Lucas system on British bikes - it shunts voltage over 14.75 or there abouts to earth.But your system probably puts out too much,so you'd need 2 zener diodes,as some of the later Triumphs and Nortons did.Use a cheap rectifier from Jaycar or Smith the Dick.

These work as a full shunt to earth,so the alt is working full out all the time - a voltage regulator would be better....run with a drain all the time,lights and maybe a resistor or capacitor to take some of the output.

Wired1

26th May 2008, 19:35

Yes I think I need a regulator/rectifier. I bought one last night on turdeme so hopefully it will handle the input voltage and output load OK. Anyone know where I can find a generic wiring diagram for this? It appears to be a single phase rectifier and I'm hoping it's got a regulator built in as I think most of them do these days. If it goes bang it was only $13 to find out!

Motu

26th May 2008, 20:06

What is the wiring on the bike? Usually yellow is ac from the stator,black is earth and red 12v DC out.So the important thing is how many yellow wires? 2 yellows will be a 3 wire reg,3 yellows a 4 wire reg.I'd say the yellow and green will be AC...but how many wires on reg,how many on the bike?

Wired1

26th May 2008, 20:25

The XT has two white wires that weren't attached to anything and measuring them running I get 30 volts ac so I'm guessing these are the alternator output from a single phase alternator. Actually I've just checked the manual and this is right, two white wires are the alternator. The original bike had a five-wire regulator/rectifier - two ac in (white), a ground out (black), a red to the battery, and a brown to the rest of the load.

I haven't received the rectifier yet but it looks like it has red, black, pink, white and green. I guess the red and black will be the same but the other three might be a case of trial and error. I'm not planning on running a battery so I think I have to add an electrolytic capacitor from red to earth to simulate it.

FilthyLuka

28th May 2008, 14:06

FilthyLuka

28th May 2008, 14:10

three phase rectumfrier

Wired1

28th May 2008, 17:43

Thanks, it is definitely a single phase alternator. I had it running tonight on an old yamaha regulator/rectifier that I'm not sure the history of - and it produced 30-odd volts dc which tells me the rectifier bit works fine but the regulator bit doesn't bugger it. I still have to try the cheap chinese regulator/rectifier I bought the other day. It arrived and only has four wires (2 x ac input and 2 x regulated dc output?) so I have hooked it up ready to test tomorrow. The first regulator blew my low beam headlight so I'll use an old indicator as a test load before getting too carried away!

FilthyLuka

28th May 2008, 20:26

Wired1

28th May 2008, 20:39

you could try a potential divider setup for getting the voltage right?

http://www.iop.org/activity/education/Teaching_Resources/Teaching%20Advanced%20Physics/Electricity/Images%20100/img_mid_4087.gif

something like that?

Yes that's a possibility. That way I could leave it ac and no need for a regulator or rectifier. The only catch is the lamp filament has a very low resistance (if it's 50 watts then it must be 2.88 ohms) so I'd need a 4.6 ohm resistor rated at 50 watts and that's a heater.
Another more barbaric approach would be to put the tail light and headlight in series, which would split the 32 volts to 16 volts across each more or less (depending on the wattage of each), but 16 volts would probably blow them anyway.

Wired1

29th May 2008, 18:36

I have had success with the new chinese regulator. I tried an old Yamaha regulator I had first just to check it was really buggered and it is so I blew all the bulbs! The buggered regulator was rectifiying but not regulating so it was pumping 30 volts dc into everything.

Next I experimented with the voltage divider but the resistors I was using were only rated for 5 watts so they quickly got bloody hot. If this had worked it would have been a nice simple fix as I wouldn't need a regulator as I don't need to charge a battery etc. I added a diode to chop out every second half wave and effectively halve the voltage but the peak voltage was still too much for the bulbs.

Finally I fitted the new regulator with my best guess for wiring and thankfully it worked. I am not switching the lights as they may as well be on all the time, and I have read some regulators need a minimum load to make them work so this way there is always a load connected. It works a treat and the regulator only got comfortably warm after half an hour or so of me buggering around connecting it up properly.

Wired1

2nd June 2008, 12:58

Bugger - blew the new regulator up.
It was working nice for about five minutes, measured around 14 volts at the output of the regulator and the lights were working. No increase in brilliance with revs so I figured it was sorted.

I didn't bolt the regulator to the frame, just left it tucked under the seat so maybe it needs some more heat-sink?

I took her for a blat up the road (it has shitloads of grunt, what a blast) but by the time I got back, maybe a minute of high revs, it had stopped. My first thought was that I had blown the bulbs again but they work with a seperate battery so it's the regulator bugger it.

I guess the regulator I bought was designed for a lower input voltage as two bulbs is hardly a heavy current load. The problem is whenever you buy these things off the net the sellers never know the ratings of them or can supply wiring diagrams. I guess I can get the same sort of thing from an autoelectrician but at what cost?

FilthyLuka

2nd June 2008, 15:38

Doesn't cost anything to ask em eh? Under the seat aint really a good place, you need somewhere with lots of airflow. You can do the old bonneville trick and bolt the reg to the front of the lower triple clamp, lots of airflow there :yes:

Wired1

2nd June 2008, 16:30

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.

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

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...

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

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

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

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...

FilthyLuka

2nd June 2008, 21:48

try a Yuasa YB10A2 or similar, they are pretty compact.

Wired1

2nd June 2008, 22:03

try a Yuasa YB10A2 or similar, they are pretty compact.

Is there a website with their specs etc on it? can't find the fucker

FilthyLuka

2nd June 2008, 22:26

Is there a website with their specs etc on it? can't find the fucker

Its the battery outta a GN250, i know cause i have a spare one and its pretty small :)

Your not running anything massive, so go into a dealer and ask about a battery for a little electric start dirtbike, that will work. If they aint got one, pull the battery used for a GN125, smaller still.

As far as specs go, as long as its 12v i wouldn't worry. You don't need to crank a starter motor so don't worry.

xwhatsit

2nd June 2008, 22:27

FilthyLuka

2nd June 2008, 22:33

Oi Wired1, my CB250RS is running a Big Fuck Off electrolytic cap in place of a battery. It's quite happily been running for tens of thousands of kilometres like that. I did have a problem when, after the headlight blew (just vibration and old age), all the other bulbs followed within 10km. However, as long as the headlight is on (and working), the electrics are about as reliable as one can expect. And no getting a sore leg trying to kickstart a bike on a cold morning with a flat battery!

I've got a few spare CB250RS reg/recs, do you want one? They're large and well-finned. Also used in the CX500 and various other quality Honda motorcycles ;) Can't kill the bastards, people buy old ones from wreckers and fit them to modern bikes. Also have a spare Big Fuck Off cap -- Surplustronics on Queen St is heaven -- want it as well?

Check that you don't have a threephase generator, the rec is considerably different, and wont help a single phase.

xerxes, a coil might be a good investment. Caps and AC can get "resonant frequencies" that generate fucking MASSIVE voltage spikes (15 thousand volts plus), but if its running all good i don't think you should worry much. Just a thing to keep in mind if it starts doing random things.

Wired1, if a 250rs runs a single phase generator,i would take xerxes up on this offer.

xwhatsit

2nd June 2008, 22:39

Check that you don't have a threephase generator, the rec is considerably different, and wont help a single phase.

xerxes, a coil might be a good investment. Caps and AC can get "resonant frequencies" that generate fucking MASSIVE voltage spikes (15 thousand volts plus), but if its running all good i don't think you should worry much. Just a thing to keep in mind if it starts doing random things.

Wired1, if a 250rs runs a single phase generator,i would take xerxes up on this offer.
Showing my ignorance here, I seem to recall it is a three-phase. Should know better than to get into these threads :D

On the subject of voltage spikes, isn't the rectifier turning it into DC before it gets to the battery/cap?

Mike from Cycletreads (Drury Tyres now) has been running his multiple 250RSs with no battery or cap whatsoever, claims no problems, but that worries me slightly (don't understand the technical reasons why/if that's a problem, but it just seems bad :laugh:). 5-wire rec/reg, three yellow wires coming from the generator.

When I blew all my bulbs after my headlight went, Ix suggested I get a beefy truck 24V bulb and wire it inline with the generator output, so it's always on. Enough of a voltage drop to keep everything else happy.

Wired1

2nd June 2008, 23:03

Thanks guys, all good stuff. I have already bought a couple more of the regulators and I'm going to weld a backing plate to the frame where the regulator can get some air so I'm thinking this will all help. I had the regulator loose and tucked in behind the side cover so no cooling help there.
I'm a bit limited in space for a battery - I don't know where they put them normally - but I can probably squeeze a gel cell under the seat as long as it doen't mind which way up it goes!

xwhatsit

2nd June 2008, 23:11

Looks shit hot!

Can you get the regufier at the top of the downtube?

Wired1

3rd June 2008, 08:41

Looks shit hot!

Can you get the regufier at the top of the downtube?

It's a long way from the wiring, but I'll have a look. That's where the one on my sportster was and I guess that explains why it was there. My SR has it at the front of the air box behind the engine... I've also got a lot of empty space under the side cover.

Wired1

4th June 2008, 17:41

Right. I welded a plate just behind the driver's leg to keep the wiring nice and short, and to act as a heat-sink for the regulator. I picked up the smallest battery the battery man could give me and it is 1.2 amp-hour so running the 3.2 amps I measured with both lights on it should last for 20 minutes or so without charging. I made a battery box out of an old battery acid bottle (how ironic) and wired it all together.
I took the bike for a blast up the road and it was all still working when I got back, until I dislodged the battery negative and this blew the fucken regulator again. Bastard.
Fortunately I bought two of them so I banged the second one in, bolted everything down again and this time soldered the connections onto the battery. Tested it running and it's charging at a nice 14 volts.

Anyway it's been a learning exercise but I've gotta sell this bike to fund the restoration of my SR400 so I've listed it on Trademe for $1500 start price and $2000 buy now - lets see what the public think. http://www.trademe.co.nz/Browse/Listing.aspx?id=158927160&ed=true

Thanks for all your help on this guys.