Building a regulator/Rectifier for a motorcycle

[Monkleys]

I hope this is in the right forum. This looks about right.

Okay so I've bought an old motorcyle that I've started to build up from scratch, and finally, I've made it to the eletronics.
I've posted on a few other forums looking for some help with this project as I have little experience with eletronics, I can pretty much solder things together.

I'll provide a diagram and anything else that might be necessary. As well as everything I've learned so far.

I'm going to start off with the wiring diagram for my motorcycle, it's a yamaha xt350.



Okay, and here is some background to my problem.

So recently I bought an XT350 which pretty much starts and runs perfectly. With only one small major problem, its eletrical system, surprise!


Okay so, the headlights never worked, that's problem one. Problem two, the battery never charged. Oh, it didn't come with a battery.


Naturally, I bought a battery, plugged it in, with a bit of wiring, fixing the connectors, getting some rust off the switches(she was neglected for a good year). I managed to get the turn signals, odometer lights, tail light and horn to run off the battery, as it was wired originally. Though, the battery never got recharged from the magneto, I jumped past the rectifier/regualtor because the headlight wasn't working either.


I opened up the flywheel, found the charging coil disconnected from one of the poles(It's very thin wire) and the lighting coil has a small cut across it shorting the connections together, as well as a few fried wires. I unwound the lighting coil, just until the cuts, soldered on a fresh piece and rewound, then fixed the charging coils connector, and any fried wires. I put it all back together, and it worked, somewhat. So the lighting coil should've given me 0.39 ohms, I get 0.8 ohms. I used the same wire, don't judge me, I tried without breaking it further.


Okay, I've explained myself, here's my problem. With the regulator/rectifier plugged in, I only get 3v to my lights, yeah, an entire 3volts, which isn't enough, this is AC. So even with the rectifier/reg plugged in, guess what, still not charging my brand new battery. So I figured that's broken.

Alright so my problem is the rectifer/regulator. I want to build a new one specifically for my bike, but I need advice and a circuit diagram to follow to put the components together. The reason I can't buy a new one is because I live in South Africa and it's incredibly difficult to find one with importing, and almost always, import fees mean its $100+ which is way too much from my student budget.

As for parts, my local eletronics store, any components that I have access to, can be found here: https://www.communica.co.za

The system is bascially a stator with 3 coils, all AC. One for the pickup which runs the bikes spark. Then a coil for the charging system, and one for the lighting. The regulator/rect takes in from two coils, one wire directly from the charging coil and then a braunched wire from the lighting coil to shunt off any extra voltage as to not blow the AC headlight. The other braunch from the lighting coil heads into the headlight.
It's a shunt type reg/rec.
Here are the readings I have:


This was with the engine running at about 2.5k to 3.5k RPM

The lighting coil: 29.5 - 30VOLTS | 7.9 - 7.95 AMPS
The lighting coil with the headlight on: 14- 14.5 VOLTS | 6.43 AMPS => The light got hot very quickly and the volts dropped to 3.2VOLTS
The charging coil: 15.8 - 16.3 VOLTS | 11.10- 11.15 AMPS (yeah, I checked more than once)


I did notice that if I revved up to about 6k RPM one of the lights on the odemeter than I had connected got very bright and popped.

Okay, so at about 6k RPM:
The lighting coil: 66VOLTS | 8.9 AMPS
The charging coil: 41 VOLTS | 13.3 AMPS

Could anyone come up with a circuit for a rect/reg that would work? Please, any help would be appreciated.
If you need anything more from me, just ask.

 

[BradtheRad]

It sounds as though the field coil is getting too much juice (assuming your motorcycle alternator is like an automobile alternator). It carries a few A. It creates a magnetic flux field around the main coil which then creates all power for the vehicle, and charges the battery.

The alternator contains large diodes rated for several amperes. These must all be good or your DC is not healthy. Can you open up the unit that contains the diodes? Can you check them one at a time by running a couple of Amperes through each one in one direction? (Nothing should go through in the other direction.) If circuitry does not permit testing each one individually, then you may need to disconnect each diode from circuit, which is not necessarily easy.

Suppose you try reducing current to the field coil (assuming I'm on the right track)? Then you might avoid overloading circuitry.

Since you mention AC and rectifiers, do you expect AC in any circuits? The lighting circuits? An oscilloscope is the proper way to check this. Or can your meter let you confirm whether you get DC where you need it, and AC where you need it? There are analog meters with an 'output' jack which removes DC component from an AC voltage.

 

[srizbf]

Will it be possible to trace the component/circuit diagram of the rectifier /regulator unit ? Having done so much of patient tracing/work , it will be easy for you to do that .(provided the unit is not sealed)

 

[Monkleys]

It sounds as though the field coil is getting too much juice (assuming your motorcycle alternator is like an automobile alternator). It carries a few A. It creates a magnetic flux field around the main coil which then creates all power for the vehicle, and charges the battery.

The alternator contains large diodes rated for several amperes. These must all be good or your DC is not healthy. Can you open up the unit that contains the diodes? Can you check them one at a time by running a couple of Amperes through each one in one direction? (Nothing should go through in the other direction.) If circuitry does not permit testing each one individually, then you may need to disconnect each diode from circuit, which is not necessarily easy.

Suppose you try reducing current to the field coil (assuming I'm on the right track)? Then you might avoid overloading circuitry.

Since you mention AC and rectifiers, do you expect AC in any circuits? The lighting circuits? An oscilloscope is the proper way to check this. Or can your meter let you confirm whether you get DC where you need it, and AC where you need it? There are analog meters with an 'output' jack which removes DC component from an AC voltage.

The alternator is pretty much three coils inside the flywheel that spins and has magnets inside of it.
This is here is the coils

And this here is the permanent magnets that spin around them. As far as I can tell, there's no diodes in the alternator.
AC current is producted by all the coils. The AC runs directly to the front headlight from the lighting coil, but braunches off into the regulator/rectifer to shunt any excess and to convert to DC to charge the 3ah 12v battery.

Will it be possible to trace the component/circuit diagram of the rectifier /regulator unit ? Having done so much of patient tracing/work , it will be easy for you to do that .(provided the unit is not sealed)

Unfortunately, it's a completely sealed unit. This is the first thing I hoped to do.

 

[Monkleys]

Please excuse my amazing paint skills, though this is pretty much the bike circuit, from the battery it all goes into the back lights, indicator, ect, which is dc. I've left out the pickup coil which powers the bike.

 

[BradtheRad]

Since you mention a shunt regulator, here is a simple illustration for DC. I don't seriously believe this to be useful for your situation, since my concept is too wasteful to be realistic.

Your generator puts out a healthy supply of volts and amperes. The goal is to reduce it to safe operating levels. The regulator/rectifier does this with sophisticated circuitry, but apparently it has gone kaput (since you report it puts out 3VAC).

If you cannot open it, diagnose it, and repair it, then you probably wish to find a substitute. There is no simple easy method, but you might combine methods.

* Make DC voltage regulators for DC devices. This can be a series type using a zener diode, transistor and resistors.

* Make series AC voltage regulators for the lamps. This requires more components than a DC regulator.

* An inductive choke, since you have AC going to the lights. You might create a value which is correct for a range of engine speeds and loads, but not all engine speeds and loads.

* Diode to block one-half of AC waveform, thus lights get 1/2 the power. Or, diodes in anti-parallel plus resistors in parallel, as a partial method.

* Buck converter regulators. Efficient and lightweight. It can be store-bought, but it needs to handle all possible supply conditions, and deliver ample power to all loads single or combined, without overloading them.