BMW glovebox torch / flashlight upgrade advice

Hi, new on here, had a search about these, but only one thread from 2005 came up. Looking for some advice on a project i am about to do, which is upgrade the rechargable torch from an older bmw e46, this is a fairly standard item on the older models.

The batteries had gone on both of mine, 2x varta v250h cells, and needed replaced. After cutting it apart and pricing up replacements for both sets of batteries around £15, i looked at bulb upgrades for the e10 incandescent bulb. I found the following e10 bulbs which looked promising.
http://www.ebay.co.uk/itm/1X-LED-1W...768826?hash=item3f66a1073a:g:J-0AAOSwyKxXhFVI
http://www.ebay.co.uk/itm/1x-CREE-3...728555?hash=item3f66a069eb:g:~uwAAOSwanRXhEvu
I then realised the batteries were 2.4v, and the minimum voltage for these was 3v, so I am guessing they wont work? Also the bulbs had a positive earth, so i would need to modify the circuit to make them work. I then found a similar bulb with swiching polarity, and a minimum 1 volt neededed
http://www.ebay.co.uk/itm/NICELITE-LED-LIGHT-BULBS-BICYCLE-CYCLE-LAMPS-FLASHLIGHTS-TORCHES-MAGLITE-CREE-/252527200107?var=&hash=item3acbcb476b:m:mgDUxO72a7Xke2B2ocxo8CA
These looked promising, but the project was going to cost me £40 for the 2, which made me think i could build something better for cheaper, with a little help!

here is a pic of the internals of the torch...


The two pins take the 12-14v from the car, and the circuit converts the power to charge the 2.4v battery pack. there is not a huge amount of room, as i have shown an AAA battery to scale. My first thought was to change the batteries for standard, add in a small boost circuit such as this, to power an led and driver intalled in the original location.
http://www.ebay.co.uk/itm/1-5-3-3-3...566471?hash=item41b0a65ac7:g:DvcAAOSwU-pXsTTx
Then I thought about ripping out the circuit, and installing a small nicd pack like a cordless phone pack or similar with suitable charging circuit, then adding a suitable converter to go to the led driver and bulb. The front opening is about 15mm, so a lightly modified cree bulb such as an xm-l2 would fit.

The problem is I am a little lost when it comes to this stage, I have spent a few hours researching, but no idea what i should be going for, plus my knowledge of cars is far greater than that of electrics/leds! I do enjoy a little project and making something custom. If anyone could point me in the right direction, it would be much appreciated, I am more building a torch from scratch this way rather than modifying it now! I just thought for less money than upgrading, i could make something better. The torch does not need to have a huge runtime, but would actually be useful if it was a lot brighter, for things like looking in the engine bay at night. the dimensions of the space i have to play with are about 45 mm x 31mm, and about 15mm depth in the unit, or 1 3/4" x 1 1/4 x 5/8". Any suggestions on battery packs, leds and drivers would be greatly appreciated, thanks, allan

We had that same flashlight from an old bmw. It isn't that easy to make it into something powerful.

I was toying with the idea of just replacing the batteries and installing a red / orange LED that can take a lot of current - like a rebel or similar. The reason is that you need an LED that will run at a low enough voltage, and that means - red or orange. If you use an LED rated for a high enough current, then you can just direct drive it from the batteries, as they cannot output all that much.

I enjoy playing with and building lights, but you should do it because it is a hobby, not because you will save money. At least in my case, I spent a lot. It would have been far cheaper to buy any flashlight on the market that you see.

Have the BMW logo engraved on an HDS Rotary and call it a day..

HarryN said:

I enjoy playing with and building lights, but you should do it because it is a hobby, not because you will save money. At least in my case, I spent a lot. It would have been far cheaper to buy any flashlight on the market that you see.

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Hi harry, thanks for that. I know a red/orange led runs from a lower voltage, i have done a few led projects with them before, some accent lighting in cars. I have had a look more at products and i was looking to install a non oem li-ion battery, with supporting voltage/charging mods, and a led driver as i want a white light. Yes I do enjoy doing it, I have just never modified a torch before, so thought i would come for some advice from more knoledgeable people!

I do enjoy modifing and personalising cars, and that is my hobby, but i would like to build a torch that suits my requirements for me. I am looking for maybe a 30 min runtime, a white led, and bright enough to light up/investigate a engine bay at night. My point of cost is that i don't want to go too extreme like a few of the projects I have seen on here, just something fit for purpose to suit my needs, and looks like a standard bmw torch, but seriously outperforms its woeful output, and lack of any real world use!

StarHalo said:

Have the BMW logo engraved on an HDS Rotary and call it a day..

Click to expand...

Thanks starhalo, what i want to do is use the existing case to make it look like an OEM bmw part, but actually have it so it gives a useful output, hence it being a project rather than buying a torch that will do the job. It locates as the picture below, in a charging socket, it doesnt just rattle around the glovebox as a cheap torch, it sits nicely in a charger as a cheap torch,!

A little update to this, i have started gutting the interior of the case, after deciding not to go with the original batteries. After spending hours looking at li-ion packs, I realised most will not fit, as i need enough room for the charging circuits too. I have bought the following and will modify the boards for size, making them as small as possible. This will drop the 12-14v from the car to charge a li-ion battery. I do have 2 of these flashlights for 2 different bmw's so will use the first as an experiment!

Step down voltage converter, i will remove the usb connector.
http://www.ebay.co.uk/itm/Fine-6-24...308117?hash=item4afadc1895:g:8toAAOSwvgdW4oZY

Li-ion charging circuit
http://www.ebay.co.uk/itm/2PCS-TP40...2d2ac1&pid=100011&rk=2&rkt=18&sd=181164645863

After gutting the case i am still deciding on what batteries to go for, i knew i had 16-17mm width to play with, and just shy of 40mm length, so looking at 15270 cr2 li-ion batteries, or 16340/ cr123as (rcr123a), which also seem to be notes as 17340's. Looking to put one in the case.

I had a look at drivers and cree leds, q5, xm-l2 etc, and this is where i am looking for some help. I had a look at calculating runtimes based on the cells, looking at different mah capacities, and it seemed like a black art. What i would like is maybe a 20-30 min runtime if possible. I also need a 16mm/17mm driver. Any helpful suggestions on what to look for would be great, thanks

There is a home built flashlight on here, I think called the ATL, that is pretty close in size to what you have. Perhaps you can do a guts transfer?

Here is a thread about it:

http://www.candlepowerforums.com/vb/showthread.php?401737-Micro-ATL-G3-and-G4

There is a bit of black art to it, but it is actually mostly a matter of running scenarios, lots of them. After running enough of them, then you can do it faster.

For a single cell light that doesn't draw too much power, and a single output power level, a resistor can be a very viable alternative to a driver. This is especially true in a small light. Let's take an example just for fun.

Starting with the LED and optics needed
- Since the light is fairly small, decent output is desired, and cost goals are modest, the easiest would be to use a 5mm LED, or perhaps 3 of them.
- The reasoning, is that 5mm LEDs are quite small, and they have already done all of the optical design and alignment for you. It can be a real pain to do this alignment when you don't have full control of the housing and design.
- They have pretty decent output, are available in many variations of white CCT and color quality, etc are reasonable prices.
- Buy a dozen so that you have some spares to play with

There are many suppliers, here is just one that popped up when I did a quick 5mm led search, and you can see that they are super inexpensive, practically free.

http://www.ledssuperbright.com/5mm-led-c-6

Picking a white one, the Vf is about 3 volts, and the forward current max is 80ma, so let's target 40ma to be safe.

Let's assume that you want to use a CR2 size, Li Ion. BTW, I have not looked lately, but a lot of them are not very well protected compared to 123 size cells.

During the "flat part" of the discharge, the cell voltage (Vbat) will be around 3.8 volts.

Vbat - Vf = the excess to be dissipated, so 3.8 - 3.0 = 0.8 volts

V= IR. 0.8 volts = 0.040 amps x R R = 20 ohms

Power rating for the resistor power = V x I = 0.8 x 0.040 = 0.032 watts. So nearly any resistor can work, even a 1206 in 1/8 watt or similar, or one with a lead.

A part like this is much less than a dollar, in quantity, about 10 cents. Better yet, it is quite small and nearly indestructible.

BTW - someone please double check my math.

Just for fun, look at how little wasted power there is using a resistor in this application. There are very few if any of the more complex drivers that would be more efficient.

Now, let's run a worst case scenario - battery is completely charged up, so max is going into the led.

Vbat = 4.2 volts
Vf = 3 volts

4.2 - 3 = 1.2 volts

V= IR, so 1.2 = 20 ohms x I ,,,,,,,,, I = 60 ma

This is still well withing the 80 ma max of the LED, so it is unlikely to be a problem.

These currents are so low, that you could put 3 LEDs in and still have plenty of run time.

I could not find it quickly, but for some reason I think that RCR2s have around 250ma-hr of useful power.

250ma-hr / 40 ma = 5 ish hours. 3 of them in parallel will run close to an hour.


This is just one example, but alternatively, find a single LED + reflector combo that you like which uses under 300ma and it should meet your goals. With that small plastic package, it is difficult to get any heat out, so I would not drive it with more than 1 watt, 1/2 watt is better.

Thanks for your suggerstion of the atl harry. These are slighly out of my budget for this project, at $85 for the cheaest one! I have gone and bought all the components i need for 2 of the lights, i have gone with Cree XP-G2 emitters, 3x amc71351050ma drivers and li-ion protected 16340 cells. Total cost for all components for both is £15, so cheaper than i can get to even replace the standard batteries which needed doing anyway.

Thanks for the calculations on the 5mm leds. I have used these in many projects in the past, and spent whiles calculating resistors for series and parallel setups. There are a few online calulators that really make it easy! I do have a lot of 5mm white bright leds left over from a project i was going to do as driveway lighting, running leds under glass blocks set flush into gravel, but i ended up swapping to 3x 5050 smd blocks which were already waterproof, and easier to solder and heatshrink in. I use many leds in car projects, and still use 5mm for converting some instrument bulbs in older vehicles from incandescent, where i need a soft glow, but have gone off 5mm/10mm leds, as they are nowhere near as bright as other things i am using now, like smd, cob etc leds. A project i did for a friend recently was 3w red leds, mounted to heatsinks, used as wheel well lighting. With the cars 12v output and 12w total led's, i soon found once you start using higher power leds, you need to use a driver, as resistors become too large for the power. I ended up using some current and voltage regulators to run these. My goal for this project was to run a useful light for looking in the engine bay, and i don't feel that 3x5mm leds would be bright enough. i know they would give a long runtime, but my goal was as bright as possible for a short time. My 5mm leds are measured in mcd's, difficult to convert but i think they wil be around 5 lumes per led, so 3 of them giving a 15 lumen output isnt really very bright. If i push the xp-g2 at 1050ma, it will output around 350 lumens, so a little different! I might have to drop the current and run a custom heatsink, but i do want a bright light. i will post up what i do here once i get everything delivered and get on with it. It was just my first flashlight project, and my first with batteries other than car batteries! So i guess i have a little more education on batteries, and flashlight leds/drivers.

Just checking in to see how your project is going. I was cleaning the garage and found an old BMW light, reminded me of your project.

HarryN said:

Just checking in to see how your project is going. I was cleaning the garage and found an old BMW light, reminded me of your project.

Click to expand...

Hi harry, i have received all the components, just waiting on the resistors to complete the charging circuit, and drop down the current. I have test assembled it and the light works great, I will do a full report with some pics once i am ready to complete it.