Fixing Bike Flashlight


A few nights ago the Filini team was at our place for strategizing about our next two MTB challenges:

  • St Helens
  • Mohab
Company, fire, backyard chilling and some impromptu parmigiana by my WIF-i led to pretty late night. Tim had shown up with his bike and wanted to go home, without lights.

I remembered I had bought lights for night rides with my WIF-i (Vickie). After grabbing I realized the batteries exploded for sitting for too long in the hot bike shed.
How to Clean After Corroded Batteries – Eastern Massachusetts ARRL

A new set of batteries didn't resolve the issue since the corrosion was all over the contacts. Several random advice from the crew were tested, one of them was "scratch the contact with a car key"... yah that didn't work either.

Tim went home and bravely survived the low light sidewalks. Such a big boy our over 50s team player!
Today I decided to look into this issue and this is the story of how I got it back on track. Don't throw away corroded electronics, this recipe will work for the vast majority of exploded battery compartments.

I disassembled the bike flashlight and quickly realized that the corrosion was way far beyond the battery compartment, it had reached the PCB all the way through the wires.

I put some white vinegar inside an ultrasonic cleaner with some water. Distilled water would have been better to avoid rusting after the process but I didn't have it readily available and with this pandemic going around I wasn't going to mask venture for a corroded plate... so I figured I will deal with rust with a small metal brush if it happens once it dries and oxygen will take its course (the day after did...)

The liquid almost immediately got murky and it was frizzing like a tarantula on steroids over its web.
The vibrations reduced as the corrosion was coming off the contacts.

Since the parts on the PCB were very basic, mostly secured in their own shell (LEDs) I took the risk to bathe also the PCB because the stains of corrosion were too much to clean with a cue tip. 

The final result is awesome and sparkly. After soldering back the original wires it wasn't working. I scraped the wires to see if they had green gue inside, typical color of corrosion for copper-like materials. Sure enough, they were fried to the bone. I replaced them and that was very tricky because the corrosion had reached such deep layers that the iron couldn't melt or visibly affect the existing solderings.

With some patience and some markings on the plastic at the end, I managed to get the job done.

In the cleaning process, I lost some reflective layer that was on the head of the flashlight where the LEDs sit on. It further bounces light when the LEDs are on. I wanted to shape a little piece of aluminum foil but the WIF-i kept calling for lunch while I was on the phone with Cristiano that wanted to murder a door (another post will tell the tale of that). So I quickly put it all together and went to enjoy a lovely meal.

The light works again as intended. There's some rust on the contacts that causes a random flickering, I ordered some chrome spray to recoat the contacts. Hopefully will get it here before this shitty year ends. And as for Tim, he still alive and well. A bright spot in this corrosive story!

;mE Out.


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