My BMW M3 E36 glovebox flashlight has not worked for years, so I decided this weekend to do a teardown and repair. BMW is the only car manufacturer that I know that puts a flashlight in the glove box. It is a nice idea, but the simple design guarantees that it will need replacement in 3-6 years. When do you ever need a flashlight in the car? However, when you do, you probably want it to work. In this post, I’ll show the teardown, the circuit description, how I repaired it and put it back together.
Teardown
To get into the case, use a small flathead screwdriver and pry open the case down the middle starting from the end that plugs into the glovebox. Also, use a plastic pry tool (like the ones for iPhone Screen Replacements) to work the opening down the length of the case until it comes apart.
Carefully take out the two cell coin battery from the enclosure taking note of the copper switch and the L-shaped steel foil
Now comes some fun stuff taking apart the battery to get to the copper switch piece and the steel upper L-shaped steel foil that the blue ground is attached to. Use a set of pliers to break the metal welds to the battery enclosure for these two pieces. You won’t need the battery enclosure so don’t worry about bending it.
Circuit Description
The circuit is quite simple and took all of two seconds of video to draw. The Kicad schematic tool a little longer. You can download the schematic from GitHub.
When the car is on, the two NiMH batteries are charged by through the 1.47k resistor giving a trickle charge rate of 6.5mA. This constant trickle charge is one of the main reasons the batteries failed. A similar 250maH NiMH coin cell battery from Varta, the original manufacturer, shows that with a constant trickle charge, the lifetime is 3-6 years depending on temperature.
Because the circuit is attached to the 12v battery, I’m sure that there were several design challenges for this charging circuit. 40v Load dump, reverse voltage protection, all need consideration. Since the charging port is always on, the lifetime profile is not more than 6 years. While I don’t recall the exact time it failed in my E36, I don’t think it was much past 6 years.
Repair
Two new 200mAH cells and a roll of copper foil were purchased from Amazon. As will be shown below, copper foil is useful during the reassembly.
Links to the replacement battery and Cooper tape:
Reassembly
During reassembly, it is important to keep the two coin cell stack up as flat as possible. This is where the thin copper foil comes in to keep the connection between the two cells flat. A powerful iron also helps to keep the solder flow as thin as possible.
step 1: Solder the copper switch to the positive terminal base of the coin cell
I made the mistake of taking off the green insulation on one of my NiMH batteries. This insulation helps to ensure when stacking the coin cells you don’t short the positive and negative terminals. You can easily remove just a portion of the insulation so that you can solder the copper foil, but try to leave the rest. You will see later where I had to add some electrical tape (can you see it below?).
Step 2: Use copper tape to tape the top of one cell and bottom of the other cell
Remember to stack them so the positive terminal of the top coin cell is connected to the negative terminal of the bottom terminal. The positive terminal has a “+” stamped on the end. Do you see the black electrical tape to ensure the copper foil did not short the bottom NiMH battery. Try to keep the green insulation on and this will not be an issue.
Step 3: Solder the copper foil to the coin cells.
You may not need to solder, just using the conductive tape. But I did this step to maximize reliability in case of oxidation. Inspect and work to ensure the copper foil is as flat a possible
Step 4: Wrap the L-Shaped steel foil in copper tape.
With even a super hot iron, I could not solder to this L-shaped steel foil. By wrapping it with copper foil, the connection should be very low impedance and now the assembly can be soldered to the top of the coin cell stack.
Step 5: Fold the tape connecting the coin cells so they are stacked.
Step 6: Solder the L-Shaped steel foil to the top of the stack.
Step 7: Reassemble the battery into the enclosure
Step 8: Test the operation and the fit with the second half of the enclosure.
By testing, you can adjust the copper switch to provide a solid connection to the bulb. Also, use two rubber bands to see if the enclosure can completely close with no air gaps around the edges. You may need to make the battery enclosure thinner by inspection.
Step 9: Glue the enclosure together with plastic adhesive.
I used Plas-T-Pair adhesive along with the rubber bands to allow the glue to dry 20 minutes.
Extending the Lifetime of the Flashlight
A detection circuit that only charges the device when needed can extend the battery life past 10 years. Another approach is to only charge the device when the car is on. The duty ratio in this scenario could extend lifetime way past 10 years. With the current design, the flashlight is always being charged. As shown on the datasheet, this continuous trickle charge will reduce the lifetime of the battery.
In any case, a simple and fun repair. It is nice to have it repaired in the unlikely event I may need it. I will need to do this in another 5 years unless I can hack something to extend the battery lifetime. Of course, now I have a blog entry with step by step instructions. 🙂 Let me know your comments and questions below.
NEW: I show how to extend the lifetime of the flashlight in the Hacking a 1996 BWM E36 Flashlight for Longer Lifetime blog entry .
SUPER NEW: Do you need help? At Surfncircuits we offer a repair and upgrade service that follows the instructions in this blog and the next so you don’t need to. Please visit our Surf-Shop for more information.
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Thanks,
Mark
E36, E34, E30, E3, E28, E23, E21, E12 BMW Glovebox Flashlight Repair Service
Repair and upgrade your BMW Glovebox Flashlight to last. (updated Dec 2022)
Awesome, so stoked you showed me the blog. I see that the resistor’s there for controlling the current but because of it’s simple design, is there no protection from overcharging of the flashlights batteries (thus decreasing its life-span)? If so I suppose a reverse biased 2.4V Zener Diode in parallel to the two NiMH batteries may increase the lifespan of the batteries.
Awesome, so stoked you showed me the blog. I see that the resistor’s there for controlling the current but because of it’s simple design, is there no protection from overcharging of the flashlights batteries (thus decreasing its life-span)? If so I suppose a reverse biased 2.4V Zener Diode in parallel to the two NiMH batteries may increase the lifespan of the batteries.
Thanks, and a good idea. Have you tried this before? I was thinking a slightly higher voltage like 2.8v may give more charge on the batteries, but I see how this can extend the lifetime. A good experiment to try.
No, I have not tried it but I was trying to come up with ideas that would lengthen the life span of the batteries without needing a circuit redesign, thanks though. I thought 2.4V was the best value to go with because it would match the voltage of the two batteries in series. Also I would like to add that a current limiting resistor should probably be in series with that Z-diode.
Thanks , I’ve come up a zener type design that works well in simulation. I need to see the voltage that gives the best battery % charge, But right now 2.8 looks good . If it works, I’ll publish in a blog shortly. Good idea.
This is actually very interesting and from your detailed instructions, even a novice like me, could attempt this repair.👍🏻
Well written, attractive looking article. I have a flashlight in my 14 year old BMW. I wonder if it works? If not, now I know how to repair it. Thanks!
A 14 Year old BMW was part of the next generation of cars from the E36 family. The flashlight design is slightly different, but similar in how you open up and replace the battery. I’m not aware if they changed the design to improve lifetime. So if you open it up, please send me pictures and I can decipher. Thanks,
Can I send you $35 and my non-working flashlight to fix & send back?
Hi Brian. Thanks for the interest. Have you checked ebay? They may have something for that price. Is there some help I can explain to help you do it?
Thank you for the kind note. No one on ebay has taken the time to document the process like you did and provide a viable solution that someone could have confidence in. Given the two options, anyone would take your solution over an unknown ebay seller. That said though I did take a shot at it and used a couple of different NiCad button cells and an LED and hack-soldered something together that produces light. I’m not crazy about it. Even as an LED, it does not seem to shine for more than about 10 minutes. Maybe after a few cycles it will get better. I’d still have rather given you the $ just for the effort to document it and have something reliable.
Great write up. I just bought a 2016 Z4 and some maroon stole the flashlight. I ordered a replacement and figured it would be dead on arrival and I’d have to fix it. Not sure as I haven’t gotten it yet. But in preparation, I figured I would search if anyone repaired one yet. I didn’t think I would find such an eloquent document. The diode is a good idea. I’m surprised that you didn’t swap out the bulb for a high output LED. The light might actually be used then. You can never have enough flashlights! Thanks.
Hi. Great write up! Pretty clear instructions. Any tips on how to solder the battery to the copper switch properly? I can’t seem to manage to solder those two together
The biggest tip is to have a powerful iron with a large tip in order for the solder to flow. I’m guessing that you need to either turn up the heat on your iron or use a larger tip in order to transfer the heat to the battery. For a good iron, I use the Hakko FX888D (https://wp.me/P85ddV-B8).
Good luck and let me know.
This is awesome! The task seems a bit daunting for someone with no electrical skills or experience but I will follow your steps and hope for the best haha I was also wondering is it possible to upgrade the bulb to a brighter more energy efficient one? If so do you have any suggestions?
Thanks in advance,
A first time BMW owner ^_^
Yes. Use an LED bulb. Saves draw on the battery and lasts forever. Just find a bulb that’s about the same size. There are dozens of providers. Just be aware that polarity matters with the LED and you may need to change the power flow from how the filament light bulb was originally configured. If you just swap the battery connection polarity, that may affect how it charges.
For the final assembly, to make everything stay in place, I used a hot glue gun.
Solder some wire together as practice before moving forward.
Hi Jake, Good luck and let me know if you have any questions. We also just started a repair service for those don’t have time or equipment. See https://surfncircuits.com/kiosk/ for details.
Great instructions and followed to a tee. I now have a rebuilt, working 25 year old original light. Thanks !
Anyone know what battery I need, as the link no longer works? I tried the CP300H / 250H NiMH batteries but they are slightly to tall. Thanks in advance!
Hi Jay, the repairs are done with the Varta V250H cells. The height is about 6.1mm and this fits well. I just searched for varta V250H on the internet and found a local supplier.
Hello Mark, I don’t understand the step to use a plier to tear the battery from the copper part. I am trying to wedge a blade between the side of the battery and the copper part. The L shaped part was easy to remove. Mine is from a 37 years old E24, the flashlight corrosion inside is impressive. Thanks
OK got it, but the welded copper part broke, too corroded
Thanks Christian for notes. I have also had a flashlight where the copper pieces that attached to the battery broke apart due to corrosion. I replaced this with a solid copper wire that soldered between the battery and copper spring and it worked well.
It may not be obvious, but most flashlights have the copper piece soldered to a battery sleeve, not the battery itself. This sleeve can be removed to help with separation with the weld. I have been successful this way when a simple screwdriver method doesn’t work. Let me know how it goes.
Hello Mark, thanks for the info. I managed to clean it all, install new batteries and weld the wires. The problem is finding the replacement bulb. BMW tells me it’s discontinued and even BMW Classic does not sell it anymore. Apparently, it’s replaceable with a LED, but you have to reverse the batteries wiring. Now trying to find out what is the spec of the replacement LED.
Hi Christian, I have found many Incandescent bulb replacements on Amazon. Look for CEC #222 0.56W E10 base models. I’m not surprised BMW doesn’t sell them anymore, But it seems there are many after market vendors . Let me know if you find them? Thanks
Hi Mark, I found a couple of bulbs in the UK, same spec as the old one. Now struggling to get the whole thing rebuilt as the copper piece that is actuated by the ON/OFF switch is difficult to adjust with precision. Easy to have it ON all the time or OFF all the time. Just hard to get the proper angle.