Voltage Regulator for a Small Motorbike, 6V AC Current

I have an idea: My guess, it's just the brake lamp, So, what lamp is used? Is there one or two?

That will give me some info. I'm thinking of the possibility of replacing it with an LED (replacement lamp) and a diode or better yet two LED lamps and a diode to work on both halfs of the 1/2 cycle.

An 1156 is a typical brake lamp. This lamp https://www.superbrightleds.com/mor...d-bulb-single-intensity-18-smd-led-tower/163/ actually says 12 VAC, so I'm thinking that this may work with little or no modifications.

Some of the replacements I have used #194 for side markers, only work when oriented the correct way. There are two resistors that could easily be changed in this lamp. Lowering or raising the voltage if necessary.

It would be very easy in eny event to make a small low current - current regulator if necessary.

A single LED has a reverse voltage about 5 V or so, but they are in series, so say 4 LEDS in series might have a reverse voltage of 20V and then they could use a single resistor for these 4 LEDS and have 2 strings in parallel. These would only work on DC.

I am used to buying indicator lamps that will operate on 24 VAC/DC, so it's nonetheless possible.

The two advantages af LEDS are they generally don't burn out, but reduce in intensity and the more significant advantage is turn on time. The turn-on time is a safety improvement.

Just changing the light to a LED will make the design of a regulator easier and more compact if it's necessary.

The taillight is a 1157 two filament bulb; 3w running light, and 15w brake light. When it dramatically burnt out, I left it in place. Didn't think of removing roadside, but would be interesting to see if it'll run w no bulb.

Shunt regulator = the circuit I'm referring to is a shunt regulator then. As good as it is, I'd like something simpler and more compact. The circuit I have will be almost as large as the taillight itself. **broken link removed**

LEDs = They are voltage sensitive, and I'm not aware of any that work for a 6V AC current. And the AC compatible LEDs merely have a diode in the base, dumping 1/2 your current anyway. So no gain in luminescence there.

My goal is a simple and compact AC 6V regulator. Converting to DC isn't worth the effort in rewiring and adding more devices.

7.3 * 1.414 0-peak for the regulator makes it about 12 V, sort of, if it were filtered and rectified.

In any event, what I am advocating is to:
1) Change the resistor(s) is a stock LED lamp to lower the voltage.
2) Add a current regulator if necessary
3) still carry a spare
4) You might have to change the socket
5) The bike, I think, would have to run if the bulb is removed.

Caveots: Accessibility of the resistors. I have in my possession a #194 replacement lamp that works on 12V when installed din the proper direction. I KNOW I could change that voltage to anything by changing those resistors. To make it operate on an AC voltage would take a bit more work.

What they actually could have done is to use a lamp as a current dependent resistor in the ignition coil circuit. In that case, it is a real active device and a regulator would be the best choice, but I still doubt it. Getting it small would take some effort.

Just being suggestive, a box such as https://www.polycase.com/wa-series might be able to be used. I had an electronic ignition which did have a heatsink and a single TO-3 transistor exposed, so I doubt that is much of an issue to have it exposed. There were plastic covers available for the transistors. So, it would take some effort. Making a PCB would make it more reliable as well.

My initial thought was to build it into the tail lens, but I don't think that will happen.

So, I still like the idea of making a LED replacement work, Just not sure how to go about it without more info:
1) bulb type #
2) pictures of the tail light assembly

Worst comes to wose, you might have to "home grow" your own socket. One connector that comes to mid is this https://uk.farnell.com/molex/38330-0503/plug-socket-connector-female-12pos/dp/1164039 one.

Ok how about a series resistor and two back to back zeners at ~6v. If it's simplicity your after and not efficiency this couldn't be much simpler.

Does the lamp provide license plate illumination as well? https://www.superbrightleds.com/mor...ual-intensity-25-led-motorcycle-bulb/170/767/

An 1157 is still a 12 V bulb, so not sure what's it's doing in a "6V system"?

Figure 53, here https://www.google.com/url?sa=t&rct...lsoO0mtjdqIw6Ug&bvm=bv.76943099,d.cWc&cad=rja is actually a current regulator.

As I said earlier, it MAY be possible to access the resistor of the LED replacement like it is in the #193 bulbs I have.

It might be interesting to take a full wave bridge and a 100 uf capacitor on the output of the brake light and measure the DC voltage. Can you try to do that?

So, now you have two very simple circuits that could probably be built into the housing. An LM317, a full wave bridge and a couple of capacitors for each element of the bulb.. Each set at different currents. Modify the LED to work at a lower voltage.

Since I like to throw out all of the options, event he absurd otr expensive ones, here is one of those:

This https://www.digikey.com/product-detail/en/JTF1224S12/1470-2099-5-ND/4488478 is an unavailable DC-DC converter.

Yep, I know first strike. The specs say 20 mS of start-up - another blow, so you can't use two, one for each element.

What it does have for it, is a small size and little modifications.

So, if you could run a wire, rectify and filter, and find a DC-DC converter with a low enough input voltage (Which I don't know), then you would be able to create a small amount of 12 V inside the tail light lens for two #1157 LED replacements.

Now we just need a circuit that can turn on the lamp in the presence of an AC signal.

Again, this is a stupid idea, but may not be. It seems like the idea is to make it look stock on the outside and whatever is used has to be small.

It also means adding an extra wire to the bike, another blow.

Building a regulator has issues, because you have to possibly "re-wire" the bike.

See, I'm not too far off:

Making a 6V LED replacement for motorcycles.

This also suggests a DC-DC converter (150 W).

Both don't address the AC issue, but that should be easy to address.

This **broken link removed** is ALMOST what was in one of the videos. 8 V minimum and no idea what size it is.

Misterbenn said:

Ok how about a series resistor and two back to back zeners at ~6v. If it's simplicity your after and not efficiency this couldn't be much simpler.

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Ouch, you called my bluff. Yea, that's dead simple. But I'm weak in the knees for keeping power, so I'll suck it up and use the fuller regulator referenced in my link.

KeepitSimple, you are full of ideas. You suggestion that the tail lamp may function as a resistor in the ignition circuit is interesting. I don't know. I'll attach the bike's wire diagram, but in truth, the factory diagram may not be complete or accurate.

The lamp may actually be the "voltage regulator". I know that is not what you expected and I didn;t either. This https://electronics.stackexchange.c...ction-of-the-bulb-in-a-wien-bridge-oscillator may show the use of such a circuit is plausible. Hewlett-Packard used the lamp in their first audio oscillators.

I can;t tell if the stop switch is a simple SPST switch or not. I think it is. The warning really does suggest that the lamp is the regulator. Whether it's temperature compensation or whatever, I think it's an integral part.

It looks as if you don;t have two separate systems, but rather one coil is "regulated" by the stop lamp. As I said earlier, the lamp is a "current dependent resistor".

You might instead switch your thought to a dual lamp type of circuit, so that if the lamp fails, the other takes it's place and some lamp burn-out warning system is used.

Now, I don;t have any ideas at this point.

KSS, I'm not sure, but let me give some background info.

Antique Italian mopeds all used this system, where the brake/tail light was wired to the ignition circuit and caused a failure if the bulb burnt out. I don't think this was some grand plan, because they also used the cheapest way possible to build things. Actually sometimes they didn't, and built with quality. But...I don't know if this extended to their electrical systems. Idk.

My motorbike is like that; cheap, sort of. No battery, no regulator. But in other areas it's built very well. Your link is interesting, but I'm not sure they really gave the circuit that much thought. But I could be wrong, after WWI mopeds and small motorbikes were a huge industry for the Italians.

I'm not worried about the lamp failing, because you end up using the front brake most of the time anyway. But, I do want to improve the system. Would adding a real voltage regulator screw up their bizarre lamp-regulation control? Should I just wire in a second light and be done with it?

So, let's propose another function of the lamp. Basically the lamps resistance is 10-13x lower when cold. What if this cold resistance makes the bike easier to start? Thinking out loud here.

That STOP switch looks like it grounds the top coil or it connects the top coil to ground through the bulb. The coil voltage seems to come from the other coil, however, the capacitor is charged from the top winding. The abbreviations of HT and LT, or at least that's what they could be, could mean High tension and Low tension.

OK, so here is another theory. Grounding out that top coil means no high tension for the capacitor (middle right) of the generator symbol. So, you're effectively grounding both sides. Now during run, the RPM is higher and therefore the amount of HV needed is lower. The unenergized bulb would be 13x in resistance closer to ground at this point, thus the voltage across the cap would be lower assuming the same RPM and same load.

When you put on the brake. The resistance rises, and therefore the voltage across the cap would be higher (at the same RPM), BUT since your stopped, the idle speed is greater.
Thus, a higher resistance from being on, effectively raises the voltage at the cap. Better put as, a lower RPM makes it easier to charge the capacitor.

The brake lamp would not be on when it has a high resistance. So, effectively, braking makes the idle more stable through the use of the lower resistance of the lamp.

I really think that's what's happening. Quite clever.

Stated again, the application of the brake light causes more voltage to be generated across the capacitor (cap), but at the same time the bike is stopped and at a low idle. It's harder to maintain that high voltage across the cap at a low idle, so they raise the voltage by making the resistance smaller. The lamp also acts as a fuse.

That's my best explanation I can come up with. This is surely an example of a diverged thread. Surprised the daylights out of me too.

PS: KISS works for KeepItSimpleStupid

My explanation doesn't agree with this one, http://scootrally.com/phpBB3/viewtopic.php?f=2&t=1738 BUT... not sure what to say.

KeepItSimpleStupid said:

My explanation doesn't agree with this one, http://scootrally.com/phpBB3/viewtopic.php?f=2&t=1738 BUT... not sure what to say.

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I've never seen any designs as poor as the one that this bike seems to use, perhaps it's just an Italian thing?.

But I have had bikes (trail bikes) where the headlight works directly off an alternator coil.

These had a small coil for the rest of the electrics, charging a small 6V battery - no regulator or any such thing, just a rectifier directly on to the battery.

The headlight though connected directly to a larger winding, and was 'self limiting' - they reach maximum voltage at a few thousand revs, and don't get any higher than that - even flat out.

sign216 said:

And the AC compatible LEDs merely have a diode in the base, dumping 1/2 your current anyway. So no gain in luminescence there.

Click to expand...

A massive gain, as they put out about 6 times the light for the same power, but as a I said before using a small battery and a rectifier to charge it would give you DC, and provide a suitable load for the alternator.

My goal is a simple and compact AC 6V regulator. Converting to DC isn't worth the effort in rewiring and adding more devices.

Click to expand...

As already suggested by someone - two LARGE zener diodes back to back - Triumph used one large one (mounted on a heatsink between the forks) to prevent overcharging of the battery on many of their bikes.

Post deleted

You could use a bridge.
Use fast diodes such as UF4001.

KeepItSimpleStupid said:

My explanation doesn't agree with this one, http://scootrally.com/phpBB3/viewtopic.php?f=2&t=1738 BUT... not sure what to say.

Click to expand...

KISS, that scooter link is pure gold. The way I read it the system is self regulating with bulbs of the correct watt/volt. Problems arise if a bulb burns out and isn't replaced, or is replaced with a different watt/volt. The thread goes on that voltage regulators aren't a solution, unless you put them all over, and that you may need 3 total! Rob Hodge, a scooter shop owner, is the one in that thread that seems to know his stuff. I quote:

"when piaggio designed the no-regulator systems, they balanced the wattage of the bulbs so that the impeadance of the bulbs functions to regulate the voltage so they could omit costly voltage regulators, and make the bike cheaper. ......
the best solution when a non battery bike blows bulbs or overvoltages is to first try another full set of bulbs (in case of manufacturing tolerances being off / bad batch of bulbs) and then increase the wattage but not the voltage of the bulbs in the system, while keeping the ratios between varying parts of the system as designed."

He goes on later in the thread to talk about regulators not being an easy solution for this system.

For me, the problem hasn't re-occurred after I changed the taillight bulb. I suspect there might be another light out, like the speedometer illuminating light or pilot light, that may be throwing the system out of balance. So I should check those minor bulbs.

Bottom line: It should work fine if I bring everything back to factory specs, and keep it there. At least that's my dream.