Battery for LP

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thanos_37
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Joined: Fri Aug 12, 2016 7:54 am

Wed Oct 26, 2016 2:36 pm

[Hello forum !!!

i want to power my LP for my project with a 6V, 4,5 Ah, it is a Lead Battery...,

the question is.., It is ok to do that ,to use that type of battery and a DC-DC LM2596 power Supply Buck Converter step-down??
i attach some photos to help :)


Thanks Thanos
RoboticsArt

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LazyBunny
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Wed Oct 26, 2016 4:47 pm

Using a 5v step down regulator from 6v with that chip would work, but as your lead acid battery got lower your regulator will have trouble since it wants +1V over output, even so you may have trouble as soon as the battery gets to 5.8v or so. You might be able to find an ultra low drop down switching regulator that can do 5v from as low as 5.5v.

Alternatives could be using 2+ cell li-po/li-ion batteries and a drop down regulator that has a low power cut off.

But here's what i would do, You could use a voltage divider with the onboard arduino(ADC) and a nice little arduino program to have a program run if the voltage gets too low. for example 10k/12k voltage divider will take 8.4v (fully charged 2 cell 7.4v lipo pack) down to 4.5v. And then when the battery hits 6v (lowest you want to take a 2 cell lipo), the divider will give off about 3.27v and you could write a script to shut down the LP.

To summarize, a 10k/12k voltage divder will take a 2C 7.4V battery
Maxmimum Charged
8.4v to 4.5v

Normal Rated charged
7.4v to 4v

Minimum Permitted
6v to 3.27v
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thanos_37
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Wed Oct 26, 2016 5:21 pm

Hello and thanks for reply ...., :)
1st i don't want to use an arduino board , i use another micro-controller.
2. for my project i want to use a lead acid battery 6v , 4,5Ah but you are right .. when the voltage is low the LP Board can not continue not even open!!!
RoboticsArt

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thanos_37
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Wed Oct 26, 2016 5:38 pm

Lazy Bunny ..., i read again your post and i have some questions ?

About your alternative propose ."be using 2+ cell li-po/li-ion batteries and a drop down regulator that has a low power cut off."

Can you be more specific ?

My consept is : i want to power my LP with a lead acid battery 6v 4,5Ah or a li- po battery 7,4v 2000ma and when the battery is low i can charge the battery ...
Like a lap top PC!!
RoboticsArt

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LazyBunny
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Wed Oct 26, 2016 8:07 pm

The LattePanda has an arduino built right into the board. No need to use another micro controller for this task.
http://www.lattepanda.com/docs/#Inputs_and_Outputs
You can program it to act as a usb keyboard and mouse, even going as far as to making it use Win+D and Alt+f4 to and some other key combos to shut down the PC as to protect the battery from overdraining it. Or have it have a blinking light or both.
You can still use another microcontroller for other stuff.

And sorry about my wording.
I'd use a 2+ cell lipo battery, 1cell is 3.7v, 2cell is 7.4v, and 3cell is 11.1volt
I'd use a step down regulator, much like yours, but i'd use one with a low power cut-off. So it doesn't drain your li-po past the safe point. Generally you don't want to take a li-ion/polymer cell below 3volts per cell usually.
So you'd use a step down regulator with a configurable li-po safety cut-off. Or you could make your own shut down code using the onboard arduino, that makes the LP shutdown automatically when the battery is too low.

7.4v 2000mAh lipo battery is still pretty small. With other stuff, you might get an hour at most.
I'd personally use a 7.4v 8000mAh.
Though i'll personally be using an 11.1v 12Ah - 16Ah battery, but i need mine to last many hours.

If the panda takes 2amps, and your other stuff takes 500mA, you can do the math. so a 7.4v 2Ah battery may be too small.
7.4v @ 2000mAh = 5v @ 2812mAh with a 95% efficient stepping regulator. with 2.5A power consumption, that's 1.12 hours.

Lead acid: 6v 4Ah -> 5v 4.5A with a 95% effecient regultor. That's 1.8 hours. This battery is much larger and heavier though.

3 cell lipo,11.1v 12,000mAh (probably still weighs less than your 6v lead acid battery.)
11.1v @ 12Ah = 5v 25,308mAh @95% effecient regulator. = 10.1 hours at 2.5A power draw..

the math goes like this.
7.4 ÷ 5 = 1.48 (7.4v ÷5v)
1.48 * 2000 = 2960 (2000mAh -> 2960 mAh)
2960* 0.95 = 2812 (voltage regulators aren't 100% efficient, switching regulators are usually 85%-95%)
2812 ÷ 2500 = 1.12 ( 2812mAh battery, 2500mA power consumption = 1.12 hours.)

Your power consumption will vary from other stuff you have connected. I'll be pulling closer to 3amps, so i'll end up using a 95% efficient BEC or something that can handle 5A. and some BECs have built in sensors for Lipo batteries.

Long post i know, i try to make sure people have all the information i need. I'm much better at electronics than i am at programming etc.
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thanos_37
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Thu Oct 27, 2016 2:11 pm

Hello again ...

it is a very specific reply..., thanks :)

I want to use the Lead acid: 6v 4.5Ah because it is cheeper for our "product" and the size that we want and also i belive that can halt a lot of hours of use!!

1. You propose to use a step down regulator with a low power cut-off, Correct ???
and witch one you believe it is bettere for use???
http://www.ebay.com/itm/LTC3780-DC-5-32 ... Swys5WWQQ5

http://www.ebay.com/itm/LM2596S-Step-Do ... SwrklVNQN-

http://www.ebay.com/itm/5A-Automaticall ... SwjVVVm0Re

Thanks a lot for your help :D
RoboticsArt

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LazyBunny
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Thu Oct 27, 2016 3:49 pm

First one: From the spec sheet looks like it needs +1v over your output, so 6v minimum for 5v output. Which is fine so long as you keep your battery above 90% charge. :(

Second one requires 1.5V above your output. so if you want 5v out, you need to put 6.5v in, so it wouldn't work.

Third one:
Wide Input Voltage Range: DC 6 ~ 35V
Output Voltage: DC 1 ~ 35V
guessing it can go 6v down to 1v, or step up 6v to 12v, but probably not 4v up to 5v.


Can you find a small 12v lead acid battery instead? 12v 2.5Ah = 2.28 hours when dropped down to 5v. And should still cost around the same price as the 6v 4.5Ah, and be about the same size.
It would be easier to use a switching regulator on it to go from 12v down to 5v. Since 6v down to 5v is kind of hard using a switching regulator.
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thanos_37
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Thu Oct 27, 2016 4:08 pm

Hi again ,

i found that one, take a look please!! :)

http://www.batteries.gr/en/product.asp?catid=2660
RoboticsArt

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LazyBunny
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Thu Oct 27, 2016 10:03 pm

Yeah that should work, you should get 2 and a half hours out of it. Maybe more if the software isn't under heavy load, maybe less if you have a lot of other stuff attached. I don't know what 'product' you're making this for, but that looks like a better choice than the 6v battery.
My Gameboy: http://imgur.com/a/lhY1x
My SBC Joystick: http://imgur.com/a/vtc5C
My Rockin' Dreamcast: http://imgur.com/a/kI50p
I'm Kiera, the Laziest Bunny in all of Bunny Town.

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thanos_37
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Fri Oct 28, 2016 2:57 pm

Hi LazyBunny :)

allow me to be more specific for what i have in my mind "product". it may help to understand what i do...

with one power supply (Lead aced Battery OR a Lipo 7,4V 5000ma ) i want to give power to the PB Boar and to Micro controller 32 bit with sensors and two servos 5V and two DC Motors .

But i try to find what solusion is the right for my project.
RoboticsArt

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