# Quick light maths



## HazeElctrc (Nov 7, 2021)

sorry i havent done electrical in a while ,but im trying to tune my light so if i have a 20v light that draws about 1 amp and runs on a 12v system , and i want it to last say 6 hours , will 9 18650 at ( 2000mah) work . 
I think i wire 3 groups in series of 2 parallel ?


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## Jay R (Nov 9, 2021)

Sorry, you are saying you want to run at 12v a light rated at 20v. So it will be dimmer than it should be?


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## Jay R (Nov 9, 2021)

3 cells in series will give you around 12v and 2Ah but you will need 6Ah to last you 6 hours so you'll need to run 3 sets of those in parallel. You'll actually need 4 sets in parallel for the full 6 hours due to efficiency loss and the fact you can't run the cells totally flat. So, 12 cells in total. 4 parallel sets of 3.
You'll also need a controller because if you just wire up like that, one will eventually be miss-matched and the while thing will explode.


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## HazeElctrc (Nov 10, 2021)

Jay R said:


> Sorry, you are saying you want to run at 12v a light rated at 20v. So it will be dimmer than it should be?


Im not sure , but the descrition says its a 20v light pod with 2x10v leds , it runs on 12v car power system, its brightness says 2000 lumens and a test result says it draws around 1.3 amps . My first build is just an on off switch .


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## HazeElctrc (Nov 10, 2021)

Jay R said:


> 3 cells in series will give you around 12v and 2Ah but you will need 6Ah to last you 6 hours so you'll need to run 3 sets of those in parallel. You'll actually need 4 sets in parallel for the full 6 hours due to efficiency loss and the fact you can't run the cells totally flat. So, 12 cells in total. 4 parallel sets of 3.
> You'll also need a controller because if you just wire up like that, one will eventually be miss-matched and the while thing will explode.


Ok im starting to see what i need , I plan on charging the cells on a separate wall charger with a display . SO I think i need a low voltage board to cut the power ?
What numbers should i look for ? ( im very new to the math side )
The light works really well at 3 groups in series , could i do 3 groups of 4 cells ?
Would you happen to know of any battery holders i could try out besides the amazon ones , I had a hard time wiring them I dont want to spot weld them because Im using scavenged cells from old electronics and I want to be able to pull them out to better match and charge them .


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## HazeElctrc (Nov 10, 2021)

HazeElctrc said:


> Ok im starting to see what i need what kind of controller should i look for ,is it a BMS ? I plan on charging the cells on a separate wall charger with a display and grouping them that way . SO I think i need a low voltage board to cut the power ?
> What numbers should i look for ? ( im very new to the math side )
> The light works really well at 3 groups in series , could i do 3 groups of 4 cells ?
> Would you happen to know of any battery holders i could try out besides the amazon ones , I had a hard time wiring them I dont want to spot weld them because Im using scavenged cells from old electronics and I want to be able to pull them out to better match and charge them .


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## Jay R (Nov 18, 2021)

Sorry, that's beyond my knowledge.


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