LED product for a 6-volt AC bike's running/brake light.

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JimF
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LED product for a 6-volt AC bike's running/brake light.

Postby JimF » Wed Sep 12, 2012 1:17 pm

I have one of the DC electrical system 250s (Mach 1) and one of the AC electrical system 250s.

I have avoided the use of LEDs for tail lighting on the AC bike because LEDs are DC animals, meaning they can only light when the polarity of the power is forward biasing the LEDs, and they will not light if the power is reverse biased. In an AC system, the power changes direction constantly, effectively forward biasing the LEDs 50% of the time and reverse biasing them 50% of the time.

If a conventional LED appears to work on your AC bike, I would suggest that at that speed with which the LED is being turned off and on the LED only appears to be lit all the time, but in reality it is only being driven 50% of the time.

The other issue I have had is that the auto store LED bulbs are 12-volt units, requiring higher potential to reach full illumination.

Recently though I noticed that SuperBrightLEDs.com offers a 6-volt BAY15D dual-filament LED bulb in a 6-volt version. Also, the LED bulb is marketed as "non-polarized" such that it can work in both 6-volt negative ground systems as well as in 6-volt positive ground systems such as some British cars are.

It seems to me that an AC system motorcycle is merely a 6-volt negative ground system half the time, and a 6-volt positive ground system the other half of the time.

I am ignoring things here that are likely too complicated to argue, such as when the AC voltage swings across the zero-volt threshold there is not enough potential to light the LEDs. I have no clue what value of current limiting resistor the LED product is using and so the AC voltage level has to get even higher than the LED's bias voltage to account for voltage that is dropped across the mandatory current-limiting resistor. Lastly, another gray area is that the peak AC voltage is certainly higher than 6-volts which will overdrive the LEDs albeit for milliseconds.

So I tried the non-polarized LED bulb from SuperBrightLEDs and was pleased that it is brighter, both at the low running light intensity and higher brake light intensity than the 6-volt incandescent bulb it replaced. After several days it has not seemed to suffer from AC voltage peaks above the product's intended 6-volt operation.

Here is the part number: 1157-R19-6V

It's about an USD $8 item.

That part number is for a red LED product. They do sell the LED in a white version also with a larger viewing angle for a few dollars more, part number: 1157-W19-6V. Please note that white LEDs don't contain the full additive color spectrum like a white incandescent bulb has, so a white LED behind a red lens might not be as effective. The red lens of the taillight acts as a filter, serving to pass only light of red wavelengths. Red LEDs are emitters of primarily red wavelength light. Still though, in my estimation the two LED products are inexpensive enough that both could be purchased and evaluated on a potential recipient.

Keep in mind that if you have the brake light switch arrangement that feeds the ignition coil current through the incandescent brake light filament to power the brake lamp, you will need to change the brake light switch from an normally-closed (NC) to a normally-open (NO) and do a little re-wiring. I needed to ground the ignition coil, and put power on one side of the brake switch directly from a magneto coil, which I conveniently did by just tapping off the wire going to the running light side of the taillight bulb socket. I was able to get the switch I needed with the help of the fine people on this forum.

One more benefit: There is no more concern that if an incandescent brake light filament burns out or breaks from vibration that the bike will stop running when the brake is applied!

Disclaimer: I have no financial interest in SuperBrightLEDs. I am just reporting my results, your results may vary.

Jim

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