Rear bike lights with 18650

Hello everyone!

first post post although I've been browsing for a while and learning from all of you.

I'm working on my first battery light project and I was hoping you'd shed some light (boom boom!) on a few questions I have. So here we go!

i want to build a rear light for my bike modifying 3 existing aaa powered lights to be all powered by two 18650 batteries. The lights are to retain their own individual circuitry and switches. I hate the fiddly aaa batteries and dont want to have to negotiate 6 of them. On top of that I want the whole setup to be fixed to the bike permanently and the standard fittings are very flimsy.

So what I would do is bolt and glue the slightly modified lights to a waterproof junction box, put the batteries inside the box (in appropriate holders) and fix the whole box to the seat post with some kind of theft proof fitting.

As as far as the circuit is concerned, the batteries will be in parallel and the lights in parallel, and a master switch between the two. So, correct me if I'm wrong, 3.7v of the batteries will power the 3v lights. Would this work? Or will the extra voltage damage the lights?

Also, will I need an extra circuit of some kind for the batteries? I plan to buy protected ones, and I have a separate charger. I am a bit worried about them as I've read a lot of horror stories on here!

Is there anything I've missed out?

apologies for the long post, thanks in advance for your help.

Jon

Bump... Any help with this, please?

I don't want a ticking time bomb under my seat!

Thanks

jop85 said:

Bump... Any help with this, please?

I don't want a ticking time bomb under my seat!

Thanks

Click to expand...

Can you post pictures of the lights you plan on using? You might be able to get away using 3.7 volts if there is already some sort of current/voltage regulation built into the lights.

Yes, I think the main concern is the voltage difference. Are you planning to wire in series three separate rear lights into one assembly? My other questions is, what is the use of this? I do mostly road biking here in Phoenix, Arizona. Too much rear light (or front, for that matter) would really upset the drivers

Not one but two 18650's for a tail light? It will run either run forever or rival a good headlight in output; the former is of questionable benefit while the latter presents an annoyance for other road users.

Otherwise ... at 2.2 - 2.8V Vf on most red, you'll need to drive them individually with parallel 18650's; with series 18650's and a nice combination of Vf's you could drive them in strings of 3... you'll need some sort of means of limiting current regardless. You're probably not going to want to be driving a giant cluster of 5mm LED's at max current nor multiple power LED's at 1W.

Unless you're planning on extracting multiple amps at a time from the cells or expect the light to regularly take a tumble down a mountain (or under the wheels of city busses) and keep on ticking, I wouldn't worry about making the housing bomb-proof.

But what's the rub with AAA's? I find that the typical 2xAAA tail light is good for more 45-60 minute rides on a charge than I can be bothered to count (as opposed to the headlight's pair of 18650's which are good for 2, perhaps 3 such rides). I use a PDW Danger Zone that's a wee bit obnoxious with its semi-random strobe pattern. It's survived a pavement crash unscathed last year that f_cked up my kneed badly for almost a month and it's also easily removable from its rigid seatpost mount. I wish I could find a nice tail light that runs on AA's since I have scads of those, but it's not like the 2xAAA form-factor is coming up terribly short on utility.

DrafterDan said:

Yes, I think the main concern is the voltage difference. Are you planning to wire in series three separate rear lights into one assembly? My other questions is, what is the use of this? I do mostly road biking here in Phoenix, Arizona. Too much rear light (or front, for that matter) would really upset the drivers

Click to expand...

Hi Dan, thanks for the reply.

The lights will be in parallel so the overall voltage will remain 3v. And the batteries will be in parallel too so that would stay at 3.7v.

My morning commute is at 5:30am in small country roads and I need to be seen by sleepy drivers. The 3 lights will be on in this way: 1x fixed beam, 1x slow strobe, 1x fast strobe.

Thanks

idleprocess said:

Not one but two 18650's for a tail light? It will run either run forever or rival a good headlight in output; the former is of questionable benefit while the latter presents an annoyance for other road users.

Otherwise ... at 2.2 - 2.8V Vf on most red, you'll need to drive them individually with parallel 18650's; with series 18650's and a nice combination of Vf's you could drive them in strings of 3... you'll need some sort of means of limiting current regardless. You're probably not going to want to be driving a giant cluster of 5mm LED's at max current nor multiple power LED's at 1W.

Unless you're planning on extracting multiple amps at a time from the cells or expect the light to regularly take a tumble down a mountain (or under the wheels of city busses) and keep on ticking, I wouldn't worry about making the housing bomb-proof.

But what's the rub with AAA's? I find that the typical 2xAAA tail light is good for more 45-60 minute rides on a charge than I can be bothered to count (as opposed to the headlight's pair of 18650's which are good for 2, perhaps 3 such rides). I use a PDW Danger Zone that's a wee bit obnoxious with its semi-random strobe pattern. It's survived a pavement crash unscathed last year that f_cked up my kneed badly for almost a month and it's also easily removable from its rigid seatpost mount. I wish I could find a nice tail light that runs on AA's since I have scads of those, but it's not like the 2xAAA form-factor is coming up terribly short on utility.

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Hi, thanks for taking time to reply.

Yes, the idea is for them to run for as long as possible between charging!
Also, using the lights as they are means removing them when I get to the station to avoid theft, which makes it extra fiddly when you have helmet, gloves etc to think of.

Ideally the whole assembly will remain fixed on the bike until I have to charge the batteries (hopefully once a month or less!).

As I just mentioned in my previous reply to Dan, batteries will be in parallel and the lights will be in parallel. Would this work voltage wise?

Thanks

jason 77 said:

Can you post pictures of the lights you plan on using? You might be able to get away using 3.7 volts if there is already some sort of current/voltage regulation built into the lights.

Click to expand...

Sorry, won't let me upload from the app. Make because I'm new?

jop85 said:

Hi, thanks for taking time to reply.

Yes, the idea is for them to run for as long as possible between charging!
Also, using the lights as they are means removing them when I get to the station to avoid theft, which makes it extra fiddly when you have helmet, gloves etc to think of.

Ideally the whole assembly will remain fixed on the bike until I have to charge the batteries (hopefully once a month or less!).

As I just mentioned in my previous reply to Dan, batteries will be in parallel and the lights will be in parallel. Would this work voltage wise?

Thanks

Click to expand...

I guess I can appreciate not wanting to remove a light every single day. Mine clearly isn't designed for that kind of regular use.

Unless you have a nice DC-DC circuit in mind (ideally a boost circuit at that) for driving the LED's, running the cells in parallel will be less efficient than in series since you end up wasting so much voltage on regulation ala the humble resistor.

My old Vista Lites ran on two AA batteries and powered 5 leds. Blinky, chase and solid on. The light came with a clothing clip as well as a seat tube attachment. The AA batteries powered the ligh for a couple hundred hours.

idleprocess said:

... I wish I could find a nice tail light that runs on AA's since I have scads of those, but it's not like the 2xAAA form-factor is coming up terribly short on utility.

Click to expand...

I bought a Cateye taillight last year that just uses a single AA. Very nice, and comparable to a Superflash in terms of output (according to my eyes). I think I ordered it through the Cateye website. It's an older design, so you never know when they will kill it. Seems like everything is going to USB charged lithium batteries.

Anyone here who owns the Ituo Bolt?
Since it's out of produvtion since summer 2017, the only alternative for 18650 is the Orfos FlarePro with an Thrunite C2 18650-cell powerbank.