Wiring lithium polymer (LiPo) batteries

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Life of Brian
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Wiring lithium polymer (LiPo) batteries

Post by Life of Brian » Thu May 14, 2009 8:02 pm

Thinking about how to power your portable? I suggest lithium polymer (LiPo) batteries. Not only do they come in a variety of shapes and sizes to match just about any project's needs, their prices just keep dropping as time goes on.

One important thing LiPo batteries need is a protection circuit. A major downside to LiPo batteries is that they must never be overcharged or overdischarged, and a protection circuit helps prevent that. Combine the following circuit with a smart charger that is also designed to prevent overcharging, and you have a (relatively) safe setup that is small, lightweight, and can power your portable system for hours and hours.

This guide details a typical layout for a 7.4v system, which consists of two standard 3.7v LiPo batteries wired in series.

This is what a typical protection circuit looks like (obviously much larger than life size):
Image
Image taken from batteryspace.com

It's not rocket science. Simply wire the batteries' terminals to the appropriately labeled pads, making sure your polarity is correct. P+ and P- are what you connect your charging jack and system to. They are your protection circuit's output.

Perhaps this (not to scale) diagram will help:
Image

Please note that how the batteries are connected to the system and power switch is just my suggestion - there are other ways to do it but I have found this to be an effective and simple setup.

Keep in mind that if your system needs 5v to operate, you will need a linear or switching regulator to drop the voltage down to what you need.


Now that you know how to wire the protection circuit, it's time to determine which protection circuit you will need. Your battery will be rated for a maximum amount of discharge current (rated in Amps, A, or milliamps, mA) that it can handle. Select a protection circuit that matches or is under that value.

A website I highly recommend is http://www.batteryspace.com - they usually have very fair prices and all the parts you will need to make your very own LiPo battery pack. There are other online stores as well - Google is your friend here. There are tons and tons of cheap single LiPo cells and pre-assembled LiPo packs on eBay, but whether or not you trust Hong Kong craftsmanship sold at discount prices is up to you.

Warnings, Disclaimers, etc.
Be very careful when working with lithium polymer cells. These are very energy dense batteries that you DO NOT want to mishandle. This YouTube video should provide the caution necessary when working with these cells. I know that BatterySpace includes safety information with every battery they sell, so heed their warnings! When working with the batteries, tape loose wires down so no accidental shorts can occur. After you have wired your batteries up, I suggest putting electrical tape over the batteries' contacts and then a thin layer of hot glue around the edges of the tape to make absolutely sure that nothing will slip loose once inside your portable.

An ugly, but effective demonstration:
Image

If the idea of wiring up LiPo's makes you nervous, then I highly recommend you take a look at li-ion batteries or NiMH RC car batteries, especially if you are just getting started with electronics. The trade-off, however, is that they are generally larger and weigh more. If that does not scare you off and the promise of long-lasting, amazing batteries seems like just the thing you need for your next portable, then you now have the information you need to use lithium polymer batteries.
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Re: Wiring lithium polymer (LiPo) batteries

Post by grahf » Fri May 15, 2009 2:01 am

Nice work Brian. This is the kinda stuff that first timers sustain themselves on :D

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Re: Wiring lithium polymer (LiPo) batteries

Post by Life of Brian » Sun May 24, 2009 12:10 am

Update:

Apparently BatterySpace has started offering a whole lot of LiPo packs with protection circuits already built in to them, for prices pretty comparable to doing it yourself. I recommend you give them a try, especially if this is your first foray into using LiPo's. Here is one such example.
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Re: Wiring lithium polymer (LiPo) batteries

Post by XCVG » Sun May 24, 2009 10:38 am

The problem with your switch arrangement is that it's impossible to run your portable off wall power.

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Re: Wiring lithium polymer (LiPo) batteries

Post by Life of Brian » Sun May 24, 2009 1:29 pm

XCVG wrote:The problem with your switch arrangement is that it's impossible to run your portable off wall power.
True. I like using large capacity batteries so I don't usually need wall power, but another schematic here would be handy for those who are teaching themselves. Please draw a picture for us and post it here!
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Re: Wiring lithium polymer (LiPo) batteries

Post by ShockSlayer » Sun May 24, 2009 8:32 pm

Easy.

Image

Now it does.

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Re: Wiring lithium polymer (LiPo) batteries

Post by wajimba » Thu May 28, 2009 9:05 am

The only thing left is getting a charger- would you recommend a 1.5A charger for your 2500mAh battery suggestion?
http://www.batteryspace.com/index.asp?P ... rodID=3379

Oh- also for clarity on the diagram by ShockSlayer- would you connect the charger (7.4v) to the 7.2v AC adapter, and then you can charge, or play and charge? Or would you need a separate 7.2v adapter for this?

edit: What kind of charger do the psone screens normally come with?

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Re: Wiring lithium polymer (LiPo) batteries

Post by ShockSlayer » Thu May 28, 2009 1:42 pm

Charger and AC adpater would have to be separate.

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Re: Wiring lithium polymer (LiPo) batteries

Post by Basement_Modder » Wed Jun 03, 2009 7:46 pm

What, like AC adapter for playing while its on and charger for charging?
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Re: Wiring lithium polymer (LiPo) batteries

Post by AfroLH » Wed Jun 03, 2009 8:05 pm

Hey, for a DPDT switch can I use this:

http://poolsmartpools.amazonwebstore.co ... FRE1E8.htm

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Re: Wiring lithium polymer (LiPo) batteries

Post by wajimba » Wed Jun 03, 2009 8:39 pm

AfroLH wrote:Hey, for a DPDT switch can I use this:

http://poolsmartpools.amazonwebstore.co ... FRE1E8.htm


Ummm, it's kind of called DPDT on that site- not sure what the question is....Plus that thing is a monster! 20 amps!?!

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Re: Wiring lithium polymer (LiPo) batteries

Post by AfroLH » Wed Jun 03, 2009 8:43 pm

wajimba wrote:
AfroLH wrote:Hey, for a DPDT switch can I use this:

http://poolsmartpools.amazonwebstore.co ... FRE1E8.htm


Ummm, it's kind of called DPDT on that site- not sure what the question is....Plus that thing is a monster! 20 amps!?!


Ok.
Well what do I use as a DPDT switch?

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Re: Wiring lithium polymer (LiPo) batteries

Post by wajimba » Wed Jun 03, 2009 9:23 pm

Look on radioshack for "DPDT Switch." Something like this:
Image
DPDT Submini Slide Switch
Doing the math, it's rated for 37 Watts- if you're going to run upwards of 12V across it, you should be able to push 3 amps- plenty for a portable.

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Re: Wiring lithium polymer (LiPo) batteries

Post by AfroLH » Thu Jun 04, 2009 7:16 am

wajimba wrote:Look on radioshack for "DPDT Switch." Something like this:
Image
DPDT Submini Slide Switch
Doing the math, it's rated for 37 Watts- if you're going to run upwards of 12V across it, you should be able to push 3 amps- plenty for a portable.


Thanks :D

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Re: Wiring lithium polymer (LiPo) batteries

Post by ShockSlayer » Thu Jun 04, 2009 3:54 pm

Basement_Modder wrote:What, like AC adapter for playing while its on and charger for charging?


Yes.

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