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Author Topic: Understanding Li-Ion Batteries and Packs  (Read 6003 times)

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Offline IndustrialAction

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Understanding Li-Ion Batteries and Packs
« on: August 10, 2012, 06:43:11 PM »
Back in April, I posted a thread at Imperial Royal Arms with information regarding Li-Ion batteries and packs. I heard some of the information was re-posted here which lead me to the realization that there isn't a thread on FX with this kind of information. If I had done a search earlier I would have posted it here as well. I've posted the thread below and will update it as things evolve. I hope you find it useful!

This morning I noticed something that made me VERY happy. TCSS now carries several new Li-Ion battery packs. I already had some questions about them so I'm going to post up some information for everyone's benefit rather than one-on-one.

The first place to start is with some terminology. Li-Ion is short for Lithium Ion. Li-Ion batteries are my battery of choice for saber building. They cover a broad range of cells that use varying chemicals to store electricity. All Li-Ion batteries are not created equally. Understanding what the specs mean will help you determine what batteries are best suited for your build. When you are looking at cells or packs to use in saber builds, my recommendation is that you stick with packs made from Li-Ion cells (not polymer packs) and they MUST have a PCB or you must install (or use the stock) one if you are building your own pack.

Once you've decided that you need a Li-Ion cell or pack, you need to determine the voltage your build needs. The two options we should concentrate on are 3.7V and 7.4V. You actually get more voltage when the cells/packs are fully charged but you generally see them listed with one of those two nominal values. There are 5V and 6V regulated packs available and they could be an option for someone doing an MR conversion as MR boards can't take 7.4V. Builds using Igniter, the Petit Crouton or Crystal Focus generally use 7.4V set-ups (though 3.7V is acceptable in most cases). When I do an MR build, I use a 3.7V solution. When I use the other boards, I use 7.4V.

Now that you've determined the type and voltage, it is time to pick a battery size and mAh rating. Cell sizes are listed like this...

14500
16430
17670
18650

There is a wide range of sizes available. To see a chart of the most common, click here: http://en.wikipedia.org/wiki/List_of_battery_sizes and go to the last chart on the page.

The numbers in the "name" of the battery tells you the approximate size of the cell. The first two numbers indicate the width of the battery in millimeters (mm). A 14500 cell for example is generally 14mm wide (0.55"). The second two numbers are the length of the cell in millimeters. Therefore a 14500 cell is approximately 50mm long (1.97"). Each manufacturer has slight variations in sizes so don't assume they are exact. Knowing the size of your cells ahead of time will allow you to choose the best cell/pack for your build BEFORE you order. When calculating the approximate size of a pack, you simply need to do the math.

For example...

A two cell pack of 14500 batteries that are configured side-by-side would have an approximate width of 28mm (1.10") [14mm+14mm] and would have an approximate length of 50mm (1.97").

A two cell pack of 14500 batteries that are configured end-to-end would have an approximate width of 14mm (0.55") but a length of 100mm (3.94") [50mm+50mm]

You can see how a simple thing like the arrangement of the cells affects how they would fit in a build.

Additionally you need to consider the mAh (milliamps per hour) rating for your cell/pack. This is the amount of stored energy in your solution. The basic rule is the higher the mAh, the more run-time you get, the better the cell/pack is for your saber. The rule I use is to put the battery with the highest mAh in your saber that will fit. Manufacturers often put inflated mAh ratings on their cells so don't assume that your 3,000mAh 18650 really has that much capacity. It is probably very high but unlikely that it is truly that high.

Typically you'll find individual cells have mAh ranges like this...

14500 ~800mAh/cell
14560 ~1200mAh/cell
16430 ~700mAh/cell
17670 ~1250mAh/cell
18650 ~2200mAh/cell

Generally speaking, the longer the battery, the greater the mAh.

Often, you'll notice that 7.4V packs have the same mAh rating as their single cell counterparts. This is not a mistake. Your capacity is the same. An example is that a single 3.7V 14500 has approximately 800mAh while a two cell 7.4V 14500 pack also has 800mAh. The difference is when you get in to more than two cells in your 7.4V pack. A quad (four) 14500 pack now doubles the mAh rating, effectively yielding 1600mAh instead of the 800mAh that the two cell pack has. In the past, I would take two 14500 two cell packs and wire them together to get the 1600mAh capacity. Now, TCSS and others have four cell 14500 packs available. These packs are an excellent solution for many builds.

At this point we've talked about type, voltage, size and capacity but there's still one more thing to talk about and that is discharge rates. For many builds, the max discharge rate (the maximum amount of power you can draw at one time from your cell/pack) is not an issue. Where it becomes a potential issue is with builds that support flash effects. When you're powering multiple high power LED dies at one time, you start drawing a LOT of power from your cell/pack. Depending on your set-up, you could be drawing close to 4A (amps). When you are looking at a pack for a high power build, you need to know what the max discharge rate is for your cell/pack. Many of the packs on BatterySpace.com for instance have a protection circuit that limits your current draw to 2A. If you put that in a build drawing more than 2A, you will trip the protection circuit and the battery will stop delivering power until you reset the PCB (plug it in to recharge). Each time you draw more power than the protection circuit allows, you'll have the same problem. In these cases, look for packs that have a higher max discharge rate. If you are using 18650 batteries, this is almost never an issue, however, it is a pain to get 18650's in most builds. After doing some additional research I found that the cut-off for most of the packs sold at TCSS is 6.6V.

The newest packs on TCSS have JST connections. These are "plugs" for the cell/pack making them easier to use in many builds, especially ones that use the modular wiring system. If you troop, these things are great. You can wire a JST connection to your soundboard and then plug your battery pack in and get rolling. When you run out of power, just unplug it and put a new pack in (yes, you'd have to carry charged packs with you). If you use a recharge port, you would wire your saber with the two battery connections on a JST. That way you can swap packs OR you can recharge your pack in-hilt. There are charging adapters for JST cells/packs so no additional wiring is necessary. It makes life much easier for builders that need this functionality.

That's it in a nutshell. I'll update this thread as things change. Feel free to leave comments, questions and corrections!



Offline LUMINARA UNDULI

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Re: Understanding Li-Ion Batteries and Packs
« Reply #1 on: August 10, 2012, 06:49:20 PM »
Thanks so much for posting this IA!  This is an extremely informative post :).  A ton of information here about the types of batteries we use in sabers. 



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Offline C-3P0

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Re: Understanding Li-Ion Batteries and Packs
« Reply #2 on: August 10, 2012, 07:05:49 PM »
This was exactly the information I was after a while back when I posted some questions regarding li-ion batteries :) its great to have it all here in this post, thanks IA!

Offline Jedibowls

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Re: Understanding Li-Ion Batteries and Packs
« Reply #3 on: August 10, 2012, 07:49:08 PM »
Great information!!!!  Thank you IA


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Offline IndustrialAction

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Re: Understanding Li-Ion Batteries and Packs
« Reply #4 on: August 10, 2012, 07:55:13 PM »
Happy to help!  ;D

Offline vulcan fox

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Re: Understanding Li-Ion Batteries and Packs
« Reply #5 on: August 11, 2012, 12:36:23 PM »
great post IA,,, useful for many budding saber smiths. :)

Offline Corran Horn

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Re: Understanding Li-Ion Batteries and Packs
« Reply #6 on: August 11, 2012, 01:04:11 PM »
I saw this posted at Imperial Royal Arms, I'm glad to see it here as well so it can be seen by as many people as possible, this is a great article and REALLY helpful.  For newer builders like myself it saves OTHER people from dealing with a thousand PMs from me. Hahaha.

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Offline Gil Gamesh

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Re: Understanding Li-Ion Batteries and Packs
« Reply #7 on: August 11, 2012, 01:53:42 PM »
Azmaria Dei posted something similiar a while back like this here as well for additional info as well as battery pack building info:

http://www.fx-sabers.com/forum/index.php?topic=29986.0

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Offline LUMINARA UNDULI

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Re: Understanding Li-Ion Batteries and Packs
« Reply #8 on: August 11, 2012, 02:03:17 PM »
Yep, that was a good tut also.



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Offline Mersenne

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Re: Understanding Li-Ion Batteries and Packs
« Reply #9 on: August 11, 2012, 09:32:46 PM »
Good clean information
Well done
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Offline Han Skywalker Antilles

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Re: Understanding Li-Ion Batteries and Packs
« Reply #10 on: November 13, 2012, 03:06:46 PM »
IA,

You're awesome! Thanks so much for this post.

I had a question about charge and discharge cycles. It seems like there is some conflicting info.

What is the optimum discharge and recharge cycle for a Li-Ion pack to max it's life? Should you fully discharge it every once in a while, or always try to fully charge it up before it gets that low?

Any tips?

Thanks!
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Offline Han Skywalker Antilles

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Re: Understanding Li-Ion Batteries and Packs
« Reply #11 on: November 13, 2012, 03:36:44 PM »
It might help a little if you know specifically what I'm talking about, but also interested in general good battery practice...

"2 TrustFire Red Flame 14500s, in a DIY battery pack. A 2AA holder adds too much thickness to cram in with the PC 2.0."
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