Could you help me improve my diy Bike light?

HazeElctrc

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this is my first rough draft of my bang for bick light

I have a few improvements I need help and direction please , I can build it but i dont know the exact math and electric theories to apply to the project :(

The light pod is from amazon rated at 20v and i used a 10 $ car wiring harness kit for convenience , and i shortened some of the wires , its wired for 2 lights , ( though i might mount 2 on my bike for laughs on the night trail rides ) . Going with one for now and it works great . I got about 1 hour , its powered by 4 18650 cells scavenged from old banks and lights i dont use .

They are wired in series and I would like to know just exactly how many i could wire up and where the danger lies in over loading the system ?

(Most of the electronics are kept in a cheap water bottle in my bottle cage , for trails its fine but it could easily go in a water proof saddle bag !)

So First thing i need to do is get a reliable battery source , id like to get 5 hours give or take a bit , I dont know if thats too high expectations or what ? So i was looking to keep the cost down with scavenging old cells for now . I looked at some e-bike and water bottle battery packs at various ratings, and i really want to come in under 100$ for the battery as this is a bang for buck build .

Second thing is id like to know if its possible to get a high low setting or switch , Im not to sure on where to look for a solution that is water proof or resistant to water as it will be on the bike and sometimes exposed to the elements .

any tips are welcome thanks :)

test notes from a nice review on amazon :
Pic 1:
Readings taken @ 2 min
1.4Amps @ 13.1v (18.3w total)
Ambient temp: 75F
Housing temp: 104F
9.15watt per led

Pic 2:
Readings taken @ 2 min
1.42Amps @ 12.5v (17.7w total)
Ambient temp: 75F
Housing temp: 98F
8.82watt per led

Note: I took voltage readings at two diff voltages. Most cars run around 13.2v when the engine is on and 12.5v when just ran from a SLA battery (what I had on hand). But both are still drawing 1.40/1.42
 
Last edited:

DIWdiver

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Connecticut, USA
First of all, with this setup you MUST have a battery protection board or protected cells. Running cells with different histories in series dramatically increases the fire/explosion risk if you don't. Riding around with a bomb between your legs, you want the best safeties on it that you can get, even if you start with new, matched cells.

From the numbers in the reivew, it looks like the lights draw pretty close to constant current at different voltages. It looks likely it will draw a little less than 1.4A at full charge (16+ volts for 4 cells) and a little more at end of discharge (10-12V depending on your protection circuit).

To run two lights for 5 hours you need 1.4*2*5 = 14 amp-hours (or 14,000 mA-H). With salvaged cells you're probably looking at 1.5-2.5 A-H per cell. New cells could be up to 3.6. You don't need high-rate cells that would be lower capacity.

That means you need anywhere between 14/1.5=9.3 and 14/3.6=3.9 cells in parallel. So four good new ones, or maybe up to 9 or 10 old ones. Then four of those in series.

You could get 16 new, 3200 mA-H cells for under $60 (DLG INR18650-320 at LiIonWholesale as of this writing). That would be just under your target capacity. For an extra dollar each, you can get Samsung 35A (that's a model number, not a current rating) cells at 3500 mA-H, which puts you right on your target.

If you can go with a bigger cell, you can get a LISHEN 21700-LR2170SD at 5000 mA-H. Three in parallel would give you 15A-H so you'd only need 12 total, for $60.

By the way, I wouldn't buy cells on Amazon or any other internet discount house unless you know the brand and trust the seller. Any cells with "fire" in the name are guaranteed to disappoint.
 

HazeElctrc

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Messages
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Thanks for the reply, I'm sticking with 1 light pod for now , but I hope to give the guys a chuckle with my over kill at some point .
I plan on charging the cells from a external 4 bay slow charger with digital display . I grouped the cells that way .
I just finished rewiring 3p in 3s .
. so what kind of safety board should I go for ? I took out the relay , but I don't know if it was good or bad it just came with the cheapo wiring harness , I kept the fuse , but I don't think the fuse would stop a fire like you mentioned .
Does each pack need a protection device ?
. I'd really like stick with harvested cells from old battery packs .

I plan on doing a water bottle battery pack and a larger 4px3s saddle pack in a more traditional method with spot welds and bms with more convenient parts .
 

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