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6V DC motorcycle regulator

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Mike711

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I have a vintage motorcycle (1934 Levis 500cc model D) with a BTH mag generator which I have just fitted. The dynamo is a small permanent magnet DC type, but chucks out about 6v at tickover rising to about 15v when revved. I need a voltage regulator for this machine to avoid blowing all my bulbs and frying the battery. I tried a simple circuit from internetland but this sdoesnt contrrol the voltage at all with no load, and if I apply a load (i.e. a 6 v bulb) there is no output!

I'll try and find the circuit diamgram for the one I used and add it here.

any help much appreciated.

Mike
 

MikeMl

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Hi Mike,

There have been previous threads on these forums about exactly this topic... Try out the "search"

Here is one I participated in, but there were others...
 

Mike711

New Member
Thanks Mike, the one you pointed out is an AC alternator, I found several of these but nothing for a DC machine when I tried the search before posting this....
 

alec_t

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Does this describe your generator?
Snip1.JPG
 

alec_t

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Here's an ultra-simple shunt regulator :-
Simple6Vreg.JPG
The MOSFET needs to be a logic-level type, generously rated to handle ~50W or more for extended periods and must be mounted on, but electrically insulated from, a big heatsink. The bike's chassis could be part of the heatsinking arrangement.
 

MikeMl

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Thanks Mike, the one you pointed out is an AC alternator, I found several of these but nothing for a DC machine when I tried the search before posting this....
If it uses a permanently-magnetized field, then the shunt-regulator will work. Put it another way, a shunt regulator doesn't care what is pushing the electrons. As pointed out in the linked thread, you can dump some of the excess output current into the head light.

Does your device have a segmented commutator and brushes? What rotates, the magnets or the output winding?
 
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Mike711

New Member
MikeMI, the winding rotates with a segemented commutator and carbon brushes, thanks I'll have anther look at the link.

Alec_t, thanks for the circuit looks nice and simple.

I have attached a file of information for this machine which is quite a rare beast, and if tou read through it I didnt think it would need regulating.... but maybe its been rewound, or rebuilt during its lifetime.

Very prompt respones form all you gentlemen, most helpful thanks very much.
 

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spec

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Most Helpful Member
Hy Mike711,

I know you haven't asked this but I would recommend changing all the bulbs on your motorbike to LED types: http://www.dynamoregulatorconversions.com/led-headlamp-bulbs-shop.php

Not only will this give you far superior lighting but it will radically reduce the current load on the dynamo. It will also lighten the load on the bike's wiring, contacts, and switches. LED lights also last indefinitely in practical terms.

In addition, I would recommend that, rather than fitting a Zener Diode, you fit a precision regulator, which will be cheaper, will keep your battery properly charged and in good condition. One of us on ETO can do you a decent circuit.

spec

PS: fancy posting a picture of the Levis.:cool:
 
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crutschow

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...............
I know you haven't asked this but I would recommend changing all the bulbs on your motorbike to LED types: http://www.dynamoregulatorconversions.com/led-headlamp-bulbs-shop.php

Not only will this give you far superior lighting but it will radically reduce the current load on the dynamo. It will also lighten the load on the bike's wiring, contacts, and switches. LED lights also last indefinitely in practical terms.

In addition, I would recommend that, rather fitting a Zener Diode, you fit a precision regulator, which will keep your battery properly charged and in good condition. One of us on ETO can do you a decent circuit.
...................
LEDs reduce the load on the generator which you generally don't want, since the excess charging current has to be shunted away.

You can't use a normal series regulator with a permanent magnetic generator as the generator voltage will get very high if you restrict its current.

Alec's shunt regulator should actually work reasonably well, since the negative temperature coefficient of the MOSFET's threshold voltage will help compensate for the drop in voltage with temperature of a lead-acid battery.
 

Nigel Goodwin

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LEDs reduce the load on the generator which you generally don't want, since the excess charging current has to be shunted away.
I suspect that's not a problem, as the dynamo appears to be such a low output so it probably couldn't over-charge the battery :D

Obviously, adding a shunt regulator would prevent any chance of that, but may well not be required at all? - a simple ammeter from dynamo to battery would show the charging current for different engine speeds, and any potential chance of over-charging.

The LED bulb idea might even make the electrics useable? - instead of externally charging the battery when you want to use the lights :D
 

spec

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LEDs reduce the load on the generator which you generally don't want, since the excess charging current has to be shunted away.
You have to lose all of the generator output current whatever bulbs you use. In daylight the lights are not on.

You can't use a normal series regulator with a permanent magnetic generator as the generator voltage will get very high if you restrict its current.
I am well aware of that. I made no mention of a series regulator.

Alec's shunt regulator should actually work reasonably well, since the negative temperature coefficient of the MOSFET's threshold voltage will help compensate for the drop in voltage with temperature of a lead-acid battery.
The accuracy is not sufficient to do the job and keep the battery in good condition. The MOSFET is not defined anyway. I do not know of any MOSFET that could reliably dissipate 50W especially taking into account the temperature extremes on a motorcycle. The MOSFET temperature would bear no resemblance to the battery temperature.

The battery will discharge through the dynamo when the engine is not running.

spec
 
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MikeMl

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...
The battery will discharge through the dynamo when the engine is not running.
Replace the original cutout relay with a high-current Schottky diode (rectifier).
 

crutschow

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You have to lose all of the generator output current whatever bulbs you use. In daylight the lights are not on.
In the USA motorcycles normally run with their lights on in the daytime, supposedly as a safety device.
 

spec

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In the USA motorcycles normally run with their lights on in the daytime, supposedly as a safety device.
It is odd that in the 1990s UK bikers often rode in daylight with their lights on, but now they no longer do.

Yes, you could leave the lights on all the time, but I think then you would find that the dynamo would be struggling to keep the battery charged with the original filament bulbs.:arghh:

Also, the lighting on most old bikes is pretty feeble and not consistent with conditions on modern roads. I wish that LED lights and solid-state electronics were available when I had an old motorbike.:cool:

spec
 
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Nigel Goodwin

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It is odd that in the 1990s UK bikers often rode in daylight with their lights on, but now they no longer do.
Many bikers still do, I always used to, and I would now if I had a bike.

But even with lights on, I could guarantee at least twice a week someone would pull straight out in front of me when I was going to work.
 

spec

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Many bikers still do, I always used to, and I would now if I had a bike.

But even with lights on, I could guarantee at least twice a week someone would pull straight out in front of me when I was going to work.
Yeah- know what you mean.:eek:

spec
 

alec_t

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It is odd that in the 1990s UK bikers often rode in daylight with their lights on, but now they no longer do.
Maybe they don't down there in deep Somerset, but they do here in Wales ;).
 

crutschow

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Many bikers still do, I always used to, and I would now if I had a bike.

But even with lights on, I could guarantee at least twice a week someone would pull straight out in front of me when I was going to work.
For that reason I added a headlight modulator to mine, which causes a periodic change in brightness of the headlight (240 ±40 cycles per minute between approximately 20% and 100% of full intensity, and is legal in the USA).
Much harder for the vehicle driver to ignore a flashing light.
I haven't had anyone pull out in front of me since I installed it. :banghead: (knock on wood).
 

spec

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Maybe they don't down there in deep Somerset, but they do here in Wales ;).
:p I have been over the bridge many times; we have relations in the Aberdare region. Also been to Cardiff many times, but must say I didn't notice any bikes with lights on in the last few years.

spec
 
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