12V charging system/regulator for 125 motorcycle

Hello GroupDIY,

This is not audio related but i'm sure someone here can help me 
I would like to test and build a 12V regulator from my 1977 yamaha RD125 motorcycle. i don't know how to do it.
The regulator is connected to one input side of the rectifier and the case is connected to the chassis/frame.
its a monophase half wave regulator.
it uses a thyristor.
Thats all i know.
Someone from our club here in france said he once melted an old broken regulator to see what was inside and said there is only one thyristor, two capacitors, and two resistances.

Can someone help me to design or share a similar circuit so i can build one?
There are plenty of combined rectifier/regulators on ebay for only 6$ ! but most of them are full wave. Mabe it works if i connect it directly on the battery positive connection?  but i would prefer to build one half-wave version like the original and keep the separate original rectifier.

This is what i know :
the battery is 12V 5.5A/Hour
the alternator delivers about 60-100VAC at high RPM
when switched on "night position" (or when the main lights is switched ON, depending on model)  there are x4 additional coils that add up in parallel to compensate the lighting consumption (around 60Watts) So the alternator has two "main" or "always active" coils, and x4 additional coils in "night position".
attached is a copy of the earlier schematic (RD 1975) but uses the same part number for the regulator as model 1977 (my model)
Original regulator was made by stanley in the 70s.

Thank you for your help !

Interesting perhaps a shunt regulator... is it in a heatsunk package capable of dissipating several watts?

Might be a simple clamp at 15V or so, but I am just guessing.

JR

My 1967 BSA 250 was just a 50 Watt 15V Zener bolted to the frame.

I'm unclear about the rectifier connections on your Yama schematic and suspect there are errors which may not have mattered when all was fresh but are misleading now.

If this is not your go-to-work bike, you can disconnect the alternator, put a good full battery in, and re-charge every time you ride.

*Maybe*! My BSA had a separate dynamo for spark, would run fine without battery lines, battery was just for lights/horn. I just realized your Yama gets spark from "battery" so without a generator the run-time may not be great.

Yes the circuit is drowned in epoxy resin, in oval aluminium heatsunk/housing (photo attached)

Yes this is my everyday bike since almost 10 years now and running without regulator!
This regulator is known to fail at some point and make a strange behavior in the working of the bike. so many people disconnect it and run without regulation. Older model of this bike had NO regulator installed from factory, next generation used wire wound resistor as a regulator, and later models (my model) uses electronic one made by stanley.
I have a spare original regulator i would like to test, how can it be done?
Variac + rectifier? but in reality the frequency also changes with RPM...
I imagine the best solution would be to make an experimental bench with a spare original alternator attached to a variable motor...

anyone know a simple electronic software or simulator for mac please?

thank you!

If the shunt regulator is disconnected the battery could overcharge and be damaged.

I was just guessing about 15V clamp... IIRc a 12V battery is nominally 13.6V.. add a volt or so for diode drop and we are close to 15V

You should be able to determine the clamp voltage of a working shunt regulator empirically by feeding it with a current through a few hundred ohms resistor in series from a roughly 20V DC power supply.

JR

Thank you John,

So you mean i could test the regulator with linear power supply?
What you call clamp voltage is the "limited" or maximum output voltage from the regulator right? i believe it should be around 14VDC feeding into the battery/charging system (i mean, in the case of 12V battery)

I don't understand how linear power supply or direct current can work for testing this regulator? the regulator seems to work from half wave pulsing and connected to one side of the bridge rectifier. As i see it, the circuit is cutting off half wave alternance to limit the current into the charging system.

I wish i could experiment with a simulator software, i admit i have very limited knowlege with electronics, but i can understand the concepts. Like we say in france, i understand very quikly, but someone has to explain for a very long time  ;D

I know that lead battery and charging systems is a whole science of its own, and not so simple.
My bike is actually running well without the regulator attached, and since many years. The batteries on my bike have normal life span of about 3 years, which is the normal age for these batteries and as described in the manual of the bike.

Apparently, the battery actually acts as a regulator itslef, and naturally absorbs the excedent voltage.
Older models which had no regulators installed from factory, were known to "kill" light bulbs, and that they had to be changed often.
I always run my bike with the main lights ON, and seldom change the light bulbs.. light bulbs are rated 45Watts, i'm guessing its is helping in preventing the battery to over heat when traveling long distances at high RPM.
However, when the light is ON, the full x6 windings from the alternator are active to compensate electrical consumption, so that ignition system still gets some "juice" from the electrical circuit even when the lights are ON, so normally it shouldn't make a big difference...

Some experts of this model, say that in reality, it is extremely rare and difficult that the battery is over heated and boils, when running without regulator.
They say this could only happen in very extreme conditions, like running full RPM for hours with very hot temperature. and that these conditions never happen...

I hope someone can help with this, its been years that i'm trying to somehow "demystify" this circuit. and can't seem to find much info on internet, even on specialized motorcycle forums It seems most standard regulators are full wave, and connected at the output of the bridge rectifier or battery positive terminal. This very circuit seems to be a bit special as it uses a thyristor and connected to one side or halfwave of the rectifier...

I'm hoping someone here has experience with vintage motorcyles and electronics, and could share a design of such a circuit?
I'm reading about thyristor theory and i'love to experiment with a simple software simulator but which one?
Anyone can recommend a simple one that works on mac?
Sorry for all too many questions and thanks a lot for your help!

isophase said:

Thank you John,

So you mean i could test the regulator with linear power supply?

Click to expand...

I believe that is what I said...

What you call clamp voltage is the "limited" or maximum output voltage from the regulator right? i believe it should be around 14VDC feeding into the battery/charging system (i mean, in the case of 12V battery)

Click to expand...

The clamp is applied directly to the high side of the AC generator. That gets connected to the battery through a diode so I am just guessing a major fraction of volt drop higher than target clamp voltage.  Battery voltage can rise while charging and I do not know how high will cause damage to the battery (but I suspect it can be found with some research).

I don't understand how linear power supply or direct current can work for testing this regulator? the regulator seems to work from half wave pulsing and connected to one side of the bridge rectifier. As i see it, the circuit is cutting off half wave alternance to limit the current into the charging system.

Click to expand...

my speculation is that is forms a simple shunt regulator. Below its threshold voltage it is high impedance, above its clamp voltage, low impedance prevents over voltage.  The AC output from the generator is smoothed by the relatively low impedance battery.

My understanding only explains voltage regulation for one polarity of AC output, the other polarity of swing seems unrestricted.

I wish i could experiment with a simulator software, i admit i have very limited knowlege with electronics, but i can understand the concepts. Like we say in france, i understand very quikly, but someone has to explain for a very long time  ;D

Click to expand...

Never used simulation (besides a filter design software program I wrote myself back in the 70s) so I can't help you there.

I know that lead battery and charging systems is a whole science of its own, and not so simple.

Click to expand...

optimal charging is indeed complex... I suspect that one is more crude... Like Paul shared his old bike just used a zener diode clamp.

My bike is actually running well without the regulator attached, and since many years. The batteries on my bike have normal life span of about 3 years, which is the normal age for these batteries and as described in the manual of the bike.

Apparently, the battery actually acts as a regulator itslef, and naturally absorbs the excedent voltage.

Click to expand...

No it acts more like a filter to smooth the voltage, but too much charging current can still result in over voltage damage.

Older models which had no regulators installed from factory, were known to "kill" light bulbs, and that they had to be changed often.

Click to expand...

too much voltage

I always run my bike with the main lights ON, and seldom change the light bulbs.. light bulbs are rated 45Watts, i'm guessing its is helping in preventing the battery to over heat when traveling long distances at high RPM.

Click to expand...

yup.. and helps cars see you..  8)  but like you said 3x generator windings when lights are on so not an obvious remedy. Depends on normal current consumption.

However, when the light is ON, the full x6 windings from the alternator are active to compensate electrical consumption, so that ignition system still gets some "juice" from the electrical circuit even when the lights are ON, so normally it shouldn't make a big difference...

Some experts of this model, say that in reality, it is extremely rare and difficult that the battery is over heated and boils, when running without regulator.
They say this could only happen in very extreme conditions, like running full RPM for hours with very hot temperature. and that these conditions never happen...

Click to expand...

if it never happened they wouldn't design a regulator.

I hope someone can help with this, its been years that i'm trying to somehow "demystify" this circuit. and can't seem to find much info on internet, even on specialized motorcycle forums It seems most standard regulators are full wave, and connected at the output of the bridge rectifier or battery positive terminal. This very circuit seems to be a bit special as it uses a thyristor and connected to one side or halfwave of the rectifier...

Click to expand...

looks only effective for 1/2 the waveform but I may be wrong.

A thyrister is just a type of semi conductor (4 layer switching device that once turned on stay on until current removed) these are commonly used for light dimmers and the like.

I'm hoping someone here has experience with vintage motorcyles and electronics, and could share a design of such a circuit?
I'm reading about thyristor theory and i'love to experiment with a simple software simulator but which one?
Anyone can recommend a simple one that works on mac?
Sorry for all too many questions and thanks a lot for your help!

Click to expand...

Most of my effort on old motor cycles was dealing with ignition systems (I put a hall effect points conversion on my old RD400). I didn't ride much at night and never had battery issues.

JR

An RD400!  8) 8) 8)

Time to build an variable power supply for testing,
i found more info by searching "charging system" instead of "regulator" on internet
Thanks a lot John for your help!

isophase said:

An RD400!  8) 8) 8)

Click to expand...

Yup... back when 2-stroke street bikes weren't regulated out of existence...  It sounded like an outboard motor, but went like a bat out of hell... Had to be careful when passing to not accidentally lift the front wheel when trying to turn... wheels can't steer when they aren't in contact with the road.

JR

Time to build an variable power supply for testing,
i found more info by searching "charging system" instead of "regulator" on internet
Thanks a lot John for your help!

Click to expand...