Arduino Forum

Using Arduino => Motors, Mechanics, and Power => Topic started by: Tofer on Apr 10, 2019, 11:24 am

Title: 3S or 4S Li Ion for a 12V led 60W
Post by: Tofer on Apr 10, 2019, 11:24 am
Hello!

I thinking about making a battery for my 12V video light. I can't decide which way is going to be more efficient.

1. Making a 3S battery pack of a bigger capacity and putting a step-up DC-DC module to have stabilized 12V

2. Making a 4S battery pack of a smaller capacity and putting a step-down DC-DC module to have stabilized 12V

Title: Re: 3S or 4S Li Ion for a 12V led 60W
Post by: Robin2 on Apr 10, 2019, 12:10 pm
Whether you step up or step down you will waste energy. Why not use the LiPos directly? Three LiPos will give a voltage between 12.4 and 10.8v depending on the state of charge.

Do you really mean you have an LED lamp that takes 5 amps at 12v? If so the battery will discharge very quickly. That seems more like a job for a large lead-acid battery.

This does not seem to have anything to do with Arduinos!

...R
Title: Re: 3S or 4S Li Ion for a 12V led 60W
Post by: Tofer on Apr 10, 2019, 12:35 pm
First of all it has everything to do with arduino. My project is completely based on an Arduino board. It is supposed that we discuss power sources in this forum section. So, please don't say it.

LiPo charges up to 4.2V each battery, and discharges to 3V. In case of 3S it will be 12.6V - 9V. This is a too much big difference for the video light.

5Ah will be enough for my purposes I can achieve it by having 3 couples of Li Ion batteries.
Title: Re: 3S or 4S Li Ion for a 12V led 60W
Post by: slipstick on Apr 10, 2019, 01:42 pm
Are you talking about Lipo or Li-ion batteries? They're not the same. Lipos are readily available in 5Ah capacity or greater. Also there's nothing stopping you from recharging before they get anywhere near 3V/cell. By 3.6V/cell there is almost no energy left in them anyway.

Steve
Title: Re: 3S or 4S Li Ion for a 12V led 60W
Post by: Robin2 on Apr 10, 2019, 02:21 pm
First of all it has everything to do with arduino. My project is completely based on an Arduino board.
How was I to know. You did not mention that in your Original Post.

...R
Title: Re: 3S or 4S Li Ion for a 12V led 60W
Post by: vinceherman on Apr 10, 2019, 02:37 pm
+1 on running 3s directly.
Want to avoid the 9v complete discharge voltage?  Add more capacity by running multile packs in parallel like you mentioned.  For the same run time, you will only pull half the capacity of each pack.

How long are you looking at running this?
Title: Re: 3S or 4S Li Ion for a 12V led 60W
Post by: Tofer on Apr 11, 2019, 11:16 pm
+1 on running 3s directly.
Want to avoid the 9v complete discharge voltage?  Add more capacity by running multile packs in parallel like you mentioned.  For the same run time, you will only pull half the capacity of each pack.

How long are you looking at running this?
I need 12V stabilized. On each volt the current changes dramatically in case of LEDs I use. So the brightness is going to change from 100% to let's say 60% in one hour. This is an unacceptable condition for a video shooting.

The question was different. What is more efficient for the project either to have 3S and one step-up module or 4S and a step-down buck?
Title: Re: 3S or 4S Li Ion for a 12V led 60W
Post by: MarkT on Apr 12, 2019, 11:55 pm
Doesn't matter whether boost or buck, you should select the most efficient from a set of available
converters, using the efficiency ratings in the datasheets.  And definitely get something reputable,
not unbranded rubbish.

You might want to look at LiFePO4 too, nominally 3.2V per cell with a flatter discharge curve
and less eager to catch fire.
Title: Re: 3S or 4S Li Ion for a 12V led 60W
Post by: hammy on Apr 13, 2019, 01:03 am
A 60w led is very large , are you sure that's right ?

Led street lamps for example can be 30w or less .
Title: Re: 3S or 4S Li Ion for a 12V led 60W
Post by: slipstick on Apr 13, 2019, 10:18 am
The question was different. What is more efficient for the project either to have 3S and one step-up module or 4S and a step-down buck?
Depends entirely on the efficiency of the specific converter and there are no general answer. If your input energy is supplied as (nominal)11.1V @ 4Ah or 16.8V @ 3A you still have the same 44.4Wh of energy.

Steve