The BMW E30, E32, E34, and E36 have space in the glove box for the white flashlight (torch) 63171375457 or 82119413147. The later BMW models provide the black flashlight 63316962052, which is not compatible because the flashlight contacts are male.
The original electric circuit is extremely simple. There are two 1.2V NiMH coin cells, a resistor to constantly charge them, an E10 2.4V bulb, and a switch.
You can read an article about Teardown and Repair of the Simply Designed BMW E36 Glovebox Flashlight.
All white flashlights that you can get now have dead batteries. You can replace the batteries with similar NiMH batteries, and they should work for a few years.
My project replaces the original circuit with a more sophisticated circuit that has a charger chip, Li-ion 4.2V coin cells, and an LED bulb.
The charging chip is LTC4079.
The LTC®4079 is a low quiescent current, high voltage linear charger for most battery chemistry types including Li-Ion/Polymer, LiFePO4, Lead-Acid or NiMH battery stacks up to 60V. The maximum charge current is adjustable from 10mA to 250mA with an external resistor. The battery charge voltage is set using an external resistor divider.
The chip is tiny, but it’s possible to solder the QFN chip using hot air.
Two ⌀24.5mm RJD2450ST1 200 mAh rechargeable coin cells are used.
Charging Current – Standard: 95 mA
Charging Voltage – Maximum: 4.2 V
The RJD2450ST1 has contacts for soldered wires. But it requires cutting two small slots in the plastic circle in the middle of the flashlight. The RJD2450 without contacts can be used if there is a battery spot welder for the original contacts.
The resistor divider R2=1.54MΩ and R4=249kΩ provides the 8.4V charging voltage.
The resistor divider R1=1.2MΩ and R3=130kΩ disables charging when the battery voltage goes down to less than 12.17V. VIN(REG) = 1.190 × (1 + 1200000 ÷ 130000).
The resistor R5=12kΩ sets the charging current to 25mA. RPROG = 297.5 ÷ 0.025. The maximum charging current for the coin cells is 95mA. When I tested this amperage by using a 3kΩ resistor, the LTC4079 was very hot as the PCB is too tiny to dissipate all heat.
The timer capacitor C2=0.1µF is set to disable charging after approximately 5½ hours. CTIMER = 5.5 × 18.2.
The 10k NTC thermistor is NHQM103B375T5.
I used a 4-layer 1.2mm-thick PCB.
The flashlight uses E10 bulbs.
The default polarity of the BMW E30 flashlight bulb is to have – (negative or ground) at the tip of the bulb and to have + (positive) at the screw body. Most LED E10 bulbs have the opposite polarity: + at the tip and – at the body.
It’s relatively easy to change the wires, but the original connectors around the coin cells must be isolated well.
I checked a 1W LED light. It was really hot when it was on. The body of the flashlight is plastic and there is no airflow, so the plastic can melt.
I selected this LED: 0.5W, Screw E10, Nopolar, 12V Warm White(4300K). It can be connected to – and + both ways. It doesn’t get warm. It also has the same height as the original bulb: 22mm. It even has a lens.
The flashlight is pretty bright and works for more than 10 hours on one charge.