Help me design a flashlight for work.

I'm a millwright(industrial mechanic) and have been on a never ending search for a decent flashlight which is an integral part of my everyday tools. I had the idea that I could make one, but would need some help, so I came here, hope that is ok. Here are what I consider the must haves:

1. Fits inside a large pocket.
2. Rechargeable without removing the battery.
3. Magnetic.
4. The "bulb part" must pivot/swivel so I can point it while it's stuck somewhere.
5. Reasonably inexpensive, less than $50. There's a good chance it will get dropped or lost.
6. Doesn't need to be super bright.
7. I just want on and off, doesn't need to have variable light levels, strobe, play the violin, or anything else.

So I think I can handle making the case but am really looking for suggestions as to what battery/charger I should use and what "bulb" arrangement I should have?

I thank in advance anyone who takes the time to reply.

Welcome here, EtienneNavaar! :wave:

2. Rechargeable without removing the battery.

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As a diy project, that might be a tricky one. Especially if it must be pocketable. A charger circuit inside the light would be complicated; such circuits are usually custom-made to suit a particular flashlight / battery type. And often bigger lights (law officers duty gear, search & rescue type lights etc).

For use with an external charger (but battery inside the light): common NiMH and Li-ion chargers don't have a connector to charge batteries outside the charger (an exception would be hobby chargers).

As for "bulb", ehm... bulb? :thinking: LED you mean?

If you want to focus on the mechanical design, perhaps creating a P60 host might work? That way you can drop in a module that combines electronics + LED + reflector into one. Any idea on what power source you'd like to use?

Thanks for your welcome and your reply RetroTechie.

After much googling and ebaying I've found a few rechargeable headlamps that might work for me. The ones I'm interested in have a light part and a separate battery part. I would have to fashion a more traditional tubular type battery holder onto which I could affix the already pivot-able light assembly. The ones I saw had a charger that required you to unplug the power source from the light part and then plug the charger into the power source. I would have preferred to just jam the flashlight in a slot or hole to charge it but at least this way I don't have to remove batteries.

So, the ones I looked were powered by 1 or 2 18650 batteries. They also claimed like 1800 lumens. I have no idea how bright that would be? How long would those battteries last?

The other issue with these is that I have found none that would work for me that are only 1-mode. My current flashlight is 3 mode and there are countless times I've left it on because I didn't cycle thru the various modes till I got to off. So if I understand things right the mode part is integral to the driver and not readily alterable. How easy would it be to change the driver?

Once more thanks for the reply and I hope you can help me with my follow up questions.

If they are claiming 1800 lm from a single LED, it's probably a CREE XM-L, perhaps an XM-L2, and the claim is quite exaggerated. More likely you would be getting 800-900 lumens out of the light (the LED can generate 1000 lm, but the reflector efficiency is probably no better than 90%). For comparison, a regular 60W light bulb is around 800 lm. Some cheap lights don't even drive the LED to its max, and you might get as little as 500 lm.

Run time is hard to define in most lights, because they give you full output for a while, followed by a period of declining output. Some run quite a long time at quite low output, some don't.

Also, 18650 batteries range quite a bit in quality and capacity. Just capacity can differ by a factor of 2:1. So depending on the driver you get, and the capacity of the battery, you could get anywhere from 30-90 minutes on full with one battery, double that with two. In most cases, the output will begin to drop before that, and the light will continue to run well after that, though at reduced output. If you have modes, they will extend the battery life by the inverse of the amount they reduce the output. So 1/3 output will give you 3 times the life.

Some lights are easy to modify, some are not. I'm guessing that a headlight would be on the 'not' end of the spectrum. Some drivers can have the modes removed relatively easily, but most can't.

1800 lumens is a lot of light, but as DIWdiver mentioned, it is most likely not true. The real brightness would probably be somewhere around 700-900 lumens (which is quite a lot, too). If the brightness is somewhere around that, you could expect something like 1 hour / 18650 battery. A bit more if the batteries are good.

You didn't say anything about the runtime requirements.

EtienneNavaar said:

The other issue with these is that I have found none that would work for me that are only 1-mode. My current flashlight is 3 mode and there are countless times I've left it on because I didn't cycle thru the various modes till I got to off.

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What is your current flashlight? My lights have 2-7 modes (8 different flashlight brands I think) and none of them requires any mode cycling. One click or twist and they are off. Some of them could easily turn on in a pocket though.

Anyway, you have been searching for a suitable light a lot and now you found some cheap ebay headlights. Is there something fundamentally wrong with the actual worklights? For example, I believe that Milwaukee M12 Led Work Light would fulfill all the requirements except that it will be closer to $100 with a battery and the battery needs to be removed for charging (removing takes less than 1 second and you have the possibility to use spare batteries when needed). You also wrote that it should be inexpensive because it can be dropped or forgotten. Unlike the parts in cheap ebay lights, these kinds of lights should be pretty well drop proof. Of course, there is no light that would be "forgotten proof", too (except perhaps the bluetooth light that FourSevens has been developing).

Thanks for your reply Esko.

As far as runtime requirements go, I think at least an hour on a charge would be enough for most of my days.

The flashlight I have has only one button and each time you click it, it goes to the next mode (there are 3).

You're right about the Milwaukee light, it does look good. The price is a bit steep but I would be in if I knew I would never lose it. The only other issue I see is the magnet. The magnets on the lights I've had so far have been just strong enough to hold up the light, even the slightest bump and they were gone. Not sure about the Milwaukee one, would have to try it out first, but it is definitely an option I haven't seen yet.

EtienneNavaar said:

Thanks for your reply Esko.

As far as runtime requirements go, I think at least an hour on a charge would be enough for most of my days.

The flashlight I have has only one button and each time you click it, it goes to the next mode (there are 3).

You're right about the Milwaukee light, it does look good. The price is a bit steep but I would be in if I knew I would never lose it. The only other issue I see is the magnet. The magnets on the lights I've had so far have been just strong enough to hold up the light, even the slightest bump and they were gone. Not sure about the Milwaukee one, would have to try it out first, but it is definitely an option I haven't seen yet.

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They must use super cheap magnets. I have an Olight S20 baton - small 18650 light.
Magnet in the tail holds light horizontally quite well.

For what you want, if your prepared to do a little work, I'd consider a cheap photographic ball head.
They make them very small. Make or find magnet for base. Make or buy flashlight holder / adapter.
Then you can attach any small light and adjust direction simply.

Google micro photographic ballhead - $15 -$20 should be good enough for small light.

Seems to me you might be looking for something modeled like the Streamlight Sidewinder ? If you do most (all?) of the casing yourself, there isn't much in the way of headlamp / bicycle light you'd need as parts. LEDs, drivers and reflectors (electronics) are available both as individual parts, or combined. Optics are a different animal, but for (from what I understand) a work light of sorts, super floody (read: perhaps just a bare LED + glass to protect it) might be equally useful as something with reflector and some throw.

Charging in place is another matter though, especially if you'd like the light to stay on while charging (nothing's impossible ). I'm guessing you might need some help with the electronics here? :thinking: