Bulb voltages... maybe a stupid question?...

rzgkane · Post by **rzgkane** » Mon Mar 26, 2012 5:50 pm

I installed my HillHudson neutral light LED today and it was a huge improvement. Thanks HH.

In the process of poking around during the install I found that my speedo light bulb was a 6V 3W bulb and the high beam indicator bulb was a 12V 1.5W. The 6V is bright and the 12V is dim. Is it OK to use a 6V bulb in a 12V system? Any downside?

12V bulb on left and 6V on right.

IMG_0798 by rzgkane, on Flickr

CliffC · Post by **CliffC** » Mon Mar 26, 2012 6:11 pm

In my experience there is nothing wrong with it, it just won't last as long. Cliff

Wilf · Post by **Wilf** » Mon Mar 26, 2012 6:13 pm

Using Ohm's Law, the 6 volt filament has a resistance of 12 ohms and draws .5 ampere. In a 12 volt circuit, the bulb will draw 1.0 ampere with a power consumption of 6 watts.

The 12 volt bulb draws .125 ampere with a power consumption of 1.5 watts.

Possible downsides: decreased lifespan of the 6 volt filament, increased heat in a confined space and less current available for your charging system.

Wilf

rzgkane · Post by **rzgkane** » Mon Mar 26, 2012 6:26 pm

Wilf wrote:Using Ohm's Law, the 6 volt filament has a resistance of 12 ohms and draws .5 ampere. In a 12 volt circuit, the bulb will draw 1.0 ampere with a power consumption of 6 watts.

The 12 volt bulb draws .125 ampere with a power consumption of 1.5 watts.

Possible downsides: decreased lifespan of the 6 volt filament, increased heat in a confined space and less current available for your charging system.

Wilf

Thanks Wilf. I appreciate the scientific approach.

Given my bike's less than stellar charging system I might not want to rob the system of that additional .875 amps, especially since in CA we have to ride with the headlight (and therefore speedo light) always on. I think I'll get me another 12V 1.5W bulb and see how dim the speedo gets.

What is the stock wattage for the three mini bulbs in or about the speedo?

Where's the best place to pick up these bulbs? Are they scarce? Plentiful? Any auto parts store?

48lesco · Post by **48lesco** » Mon Mar 26, 2012 8:57 pm

1445 auto bulb works, but you can get the Stanley bulbs from Honda for cheap and they are brighter and last longer than the Chinese versions. Should be 12V / 3W and draw 1/4 amp each.

rzgkane · Post by **rzgkane** » Mon Mar 26, 2012 10:22 pm

48lesco wrote:1445 auto bulb works, but you can get the Stanley bulbs from Honda for cheap and they are brighter and last longer than the Chinese versions. Should be 12V / 3W and draw 1/4 amp each.

Thanks. I found a place locally that sold me a couple of 1445's. They list in the book as 14.4V bulbs, though, and I have no idea what the ramifications of that are.

Edit: I just ordered a few of the ones you mentioned straight from HONDA. I forget sometimes that some of the more generic stuff is still available from them.