LEDs on a 6V bike, Help!

[CALfeRacer]

I am looking for tail light options for my 1979 CB125S Cafe project, and am running in to problems. I want something slim to mount under my seat, since the rear wheel travels pretty far up, and i don't want my light to get smashed by the moving wheel. I saw LED light strips on Dime City Cycles, and was wondering what I would need to do to use them on my bike. I know from physics and some internet surfing that LED lights use a resistor to drop the voltage down to the right amount, and that I could use V=IR to calculate the resistance needed to go from 12V to 6V. Only thing is, I'm not quite sure how to go about this. Is the resistor built in to the unit, or do i need to buy an in-line resistor to use? Anyone have some experience with the DCC light who could point me in the right direction?? Thanks!

 

[Sonreir]

Actually, you're after the opposite. You need to remove resistance to get a higher voltage device to run on a lower voltage system.

Unfortunately, that's not usually possible.

You'll need to undergo a complete 12V conversion for your bike or find 6V LED options.

 

[CALfeRacer]

So reayyly, it would just be easier to find a small tail light and use a 6V bulb in it? I know ledlight.com has a 6V led bulb I can use in a tail light application. DCC has a slim cateye that I might be able to make work.
Thanks!

 

[Sonreir]

No problem.

 

[nrcb125]

I'm in the same boat, except I might be switching to an EFI kit on my CB125 so I'll have to go 12V at some point. From the research I did, there weren't many 6V options even for normal incandescent bulbs.

 

[CALfeRacer]

I'm in the same boat, except I might be switching to an EFI kit on my CB125 so I'll have to go 12V at some point. From the research I did, there weren't many 6V options even for normal incandescent bulbs.

If you do go 12V, look in to CB350 Stators. I have heard that they will give you the charging capacity for 12V and fit in the CB125 Stator Case with no problems.

 

[MatthiasSalzburg]

If you do go 12V, look in to CB350 Stators. I have heard that they will give you the charging capacity for 12V and fit in the CB125 Stator Case with no problems.

Yes. I did this to my 1980 125 and it worked great. 35w H4 bulb, Kohler reg/rect., & 12v bulbs all around.

 

[nrcb125]

Yes. I did this to my 1980 125 and it worked great. 35w H4 bulb, Kohler reg/rect., & 12v bulbs all around.

Do you have a write up or a thread where you documented converting to 12V? Any other resources or a guide to do it? It would help me a lot with my conversion.

 

[Sonreir]

Get the CB350 stator from eBay and then a 12V Regulator/Rectifier from eBay as well (one of these: http://www.ebay.com/itm/REGULATOR-RECTIFIER-KOHLER-JOHN-DEERE-AM34738-AM106357-AHAKH6005-/180725719501?pt=LH_DefaultDomain_0&hash=item2a1417a1cd#ht_1007wt_932).

The white and yellow wires from the stator should be spliced together and then connected to one of the outside poles of the R/R. The pink wire goes to the other outside pole (doesn't matter which side on each of these). The middle pole of the R/R goes directly to your battery.

After that, it's just a matter of switching out all of the voltage-sensitive items on the bike (usually just the lights and coils) over to 12V.

 

[nrcb125]

Get the CB350 stator from eBay and then a 12V Regulator/Rectifier from eBay as well (one of these: http://www.ebay.com/itm/REGULATOR-RECTIFIER-KOHLER-JOHN-DEERE-AM34738-AM106357-AHAKH6005-/180725719501?pt=LH_DefaultDomain_0&hash=item2a1417a1cd#ht_1007wt_932).

The white and yellow wires from the stator should be spliced together and then connected to one of the outside poles of the R/R. The pink wire goes to the other outside pole (doesn't matter which side on each of these). The middle pole of the R/R goes directly to your battery.

After that, it's just a matter of switching out all of the voltage-sensitive items on the bike (usually just the lights and coils) over to 12V.

Thanks! I also found a pretty good writeup here: http://autos.groups.yahoo.com/group/CB125/message/3271

The important bits being:

So here's all one should have to do to convert an old 6V CB125S to 12V:

1. Purchase a stator from a Honda CB/CL350. Not hard to find since that
particular model was the largest selling motorcycle in history. There are a few
hundred thousands of them around….

2. Install the stator by removing the old one and inserting the new one. Fab
up a plug for the oil seal and solder the wires from the stator into the plug
you've cut off from the old stator.

3. Install a new rectifier if you haven't already done so (remember, they only
cost about $5). For heaven's sake, get rid of that old selenium rectifier.
Anything that requires cooling fins is just wasting that scantily generated
electrical power.

4. Install new 12V bulbs in place of the old 6V ones. You can probably do this
task for under $25.

5. You can keep the old 6V blinker: it'll just go faster. Or spend the money
to put a 12V winker relay in. A good electronic one costs $10 and doesn't slow
down at idle speed.

6. The horn? Well, I put a really nice Fiamm on my CB125S that I bought from
Aerostich. But that's just me.

Not too bad, huh?

 

[Sonreir]

That's missing possibly the more important point in the entire conversion: You need a 12V regulator. If you make use of your existing 6V regulator then you'll still have a 6V system.

 

[AgentX]

LED lights use a resistor to drop the voltage down to the right amount,

You don't need resistors with general LED lighting--that sort of defeats the purpose of using low-draw LEDs. And resistors don't change the voltage of your system--they increase the draw of current.

When resistors become useful is when dealing with LED turn signals, since old-style blinker units depend on resistance to control the rate of flashing. When your brake bulb blows and the bulb starts flashing faster, it's because there's less load on the system now that there's one less bulb to power, thus also serving as a convenient indicator that your, well, indicator is out.

So without a resistor, or a swap to an LED-compatible blinker, your lights will flash too quickly. I don't see why people would go the resistor route except as a temporary fix.

I have also read that diodes can be necessary in some LED turn signal applications to prevent unwanted activation of opposite-side signals, but can't speak to it.

 

[Sonreir]

You don't need resistors with general LED lighting--that sort of defeats the purpose of using low-draw LEDs. And resistors don't change the voltage of your system--they increase the draw of current.

Resistors drop current, rather than raise it.

 

[AgentX]

Resistors drop current, rather than raise it.

Sorry, I shouldn't be pontificating. Used the wrong terms when I didn't know what I was talking about although I thought I had the right concept. I'll go back to listening.

 

[Sonreir]

No worries.

Ohms Law: I = V / R

If voltage stays the same and resistance increases, then current drops.

 

[MatthiasSalzburg]

...
After that, it's just a matter of switching out all of the voltage-sensitive items on the bike (usually just the lights and coils) over to 12V.

Exactly what I did. I also switched over to an ebay solid state blinker relay. You don't need to switch coils. Just add a ballast resistor in series to keep the current draw the same as if it were a 6v system. My stock coil measured 1.8 ohm. Add two 1 ohm (10 watt rated) resistors in series to bump the coil to 3.8 ohm. 6v/1.8=3.3amp or 12v/3.8=3.2amp