LED Bulbs DIY!

I have been working on my BMW R50 to get it ready for this summers riding season, and this time I was tinkering inside the head light housing. I had a small issue, my key plunger would not seat the contact correctly and thus the motorcycle’s lights and engine were intermittent… which is not good when riding as you never want the engine shutting off thus I was unable to ride the past few weeks until I got this figured out and fixed permanently.

Lucky for me it showed up in my garage right after I replaced the chrome cover for the key hole with a newer one.  I wanted to fire the engine up and check stuff out… but it wouldn’t stay running.

Removing the headlight and looking at the plunger key area on the ‘inside’ of the housing, I noticed a very light contact was being made. This was an easy fix… I looked at the copper “finger” that was making contact with the key plunger and notice is was barely making contact, thus I bent the thicker copper contact up and verified that when my key was inserted a good contact was made… a bit of cleaning and an emery cloth over the contact point to ensure the mate of copper was clean and with no build up of carbon.

Mess of wires in the head light housing.

I was on to my next project… the little bulb for the speedometer was out, so while I was in there I figured it would be good to fix it!

Try to find this size of bulb anywhere local would be a joke…(it is small and 6 volts) … PN 07119978270… I guess I could order it online and have it in a few days, or I could use a super bright LED and build one out of the blown bulb.

I found this bulb for sale on http://www.bmwhucky.com/

 07 11 9 978 270  bulb 6V 1,5W speedometer  all 6V  $ 5.50

So here is the quick and dirty when putting together your own LED bulb… First go with super bright LEDs, next do some very simple calculations, purchase resistors, LEDs and shrink tubing (Or as I did, dig around in my electronics bins and find the parts)  and prepare to hone your soldering skills!

Note: when purchasing your LEDs be sure to open the data sheet and find out the Maximum forward current and the voltage of the LED…. this will be important! You will want to have a really bright LED “light bulb”so the next step is to calculate the smallest resistor you can use and not damage the LED (The maximum operating current, typically 20 to 40 mAmps).

So to get to the heart of the topic, and to not have a bunch of calculations… I will describe my design.

Using a quick calculator I can verify my design and the size of the resistor (OHMS AND WATTAGE)

My motorcycle is 6 Volts DC, I have an LED that operates nominal at 30 mAmps (That is milliAmps)!  I will use a 220 OHM resistor (1/4 watt)… and that puts the current at 27 mAmps… which is good because when the generator charges the battery, the voltage can go up a bit and thus at 6.5 Volts the current is at 29.5 mAmps, just below the max current.

Super Bright LED
Super Bright LED

Be careful and  break the glass off of the old burnt out bulb. I use a paper towel and wrap it around the glass before I break it to capture the glass fragments. Try not to break the filament in the bulb, you will use this! (Unless the bulb has a solder tab on the bottom of the connector (photo below).

Bulb ‘tit’ that allows soldering the leads of the resistor and the LED

Next find the positive lead, mark it so when you go to put the LED on it is in the right polarity! If you are using the bulb like the one above, the outer metal is usually ground the the center is positive. The nice thing about making your own LED bulb is that if you want to go back to the Bulb type light, you can take out the LED bulb and the housing (holder) is the original.

Bulb housing for the Speedometer
Bulb housing for the Speedometer

Now with the resistor, LED, heat shrink tubing and the bulb housing you are ready to solder it all together. Try and make the leads short and cover all leads with heat shrink tubing to protect from shorting out.

Check the polarity of the LED and try it on a power supply or a battery before installing.

LED bulb, Finished assembly!
LED bulb, Finished assembly!

So, in a few minutes I had an LED bulb that is very bright and works great.

Here is a few photos of a multi LED bulb I did for a brake light.




The Goal of course is to put enough LEDs to get the brightness of the bulb to the same or better LUX .


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