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 Li-Ion and Li-Poly

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fogdog



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PostSubject: Li-Ion and Li-Poly   Wed Aug 24, 2011 12:24 am

Based on what I have read, Li-Ion are safer to use with combat robots. That being the case, why is there such an overwhelming abundance of Li-Poly batteries on the RC market and very few Li-Ion (and A123 for that matter) if the Li-Poly are more dangerous? Do the Li-Poly have higher performance and are "safe" for RC cars/planes because they aren't being pounded by a spinning piece of tool steel?

Anyone know of a place to buy 12-19.2V Li-Ion batteries? Do you recommend the A123 over the Li-Ion? What are the pros/cons of each?

Sorry......still trying to figure this stuff out.
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rdubard
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PostSubject: Re: Li-Ion and Li-Poly   Wed Aug 24, 2011 5:16 am

You are not going to get a definitive answer here, because there is disagreement in the group about this. I am on the LiPoly side--they can and do explode and catch fire occasionally, especially if not balanced correctly, overdischarged, or physically damaged in certain ways. Of course, if you know this in advance then you make preparations. I have seen them go bad multiple times in a single competition, and the folks running it simply remove the bot and smother it in sand, or put it somewhere it can burn up harmlessly--then they move on to the next match. On the other hand, the newest of the LiPos can be charged really rapidly, have a high safe discharge rate (65C continuous--seriously, sixty five. You can fully discharge a fully charged one in under one minute safely, if you can find wire to handle it and a load that needs it), and LiPos have the greatest energy-per-weight and energy-per-volume (generally called energy density) of ANY battery commercially made.

I like ThunderPower. You can get them at RobotMarketplace, Horizon Hobby, or even look at their website directly.

We had a bunch of A123, and they all stopped functioning after 5-10 matches or so. It wasn't worth my time to investigate what went wrong, since the student who bought them didn't care either. No fires tho.
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fogdog



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PostSubject: Re: Li-Ion and Li-Poly   Thu Aug 25, 2011 1:44 am

Thought that might be the case. Thanks for the explanation of why Lipos are more common. 65C is pretty darn impressive.

The problem is that we only have NRL competitions in our state and the rules prohibit Li-Poly batteries. I am having trouble finding Li-Ion batteries that are 19.2V or 12V (need one of each for two different bots). Anyone know of a good place to get some?
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Stephen
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PostSubject: Re: Li-Ion and Li-Poly   Thu Aug 25, 2011 11:32 am

go with a123's we have used them for year and if made correctly they work great

what we did was we bought individual cells and wired them up
we had one pack at 17V or 18V
and another at 14V
so u can make them whatever voltage u need pretty much
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Cody
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PostSubject: Re: Li-Ion and Li-Poly   Thu Aug 25, 2011 11:52 pm

Most teams make or have there packs custom made
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fogdog



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PostSubject: Re: Li-Ion and Li-Poly   Fri Aug 26, 2011 12:22 am

From the looks of things, A123 are superior to regular Li-Ion batteries. Please correct me if that statement is false. Assuming A123 is the best option:

1. Any idea where I can purchase custom A123 packs?

2. Is it difficult or dangerous to build A123 packs?

3. If I decide to make my own A123, where can I purchase individual cells?

4. What is the charge time like for a "typical" A123 pack?
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Stephen
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PostSubject: Re: Li-Ion and Li-Poly   Fri Aug 26, 2011 2:29 am


1. i know i have the site we buy them from somewhere but i cant seem to find it right now ill try to think of it or i could ask frisco

2. its not difficult to wire up a battery pack you just have to know what your doing like i said in my other post on the other page about batteries if u dont wire them correctly the can smoke or blow up
but that will happen to anything you wire up wrong

3. i cant remember if we bought individual cells or if we got big packs and broke them down but i dont think it really matters

4. my 18v pack was around 10 15 min if u wanted a good charge

its all about pros and cons in the end u have to decide
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Evan Steeves
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PostSubject: Re: Li-Ion and Li-Poly   Fri Aug 26, 2011 9:34 am

fogdog wrote:
From the looks of things, A123 are superior to regular Li-Ion batteries. Please correct me if that statement is false. Assuming A123 is the best option:

1. Any idea where I can purchase custom A123 packs?

2. Is it difficult or dangerous to build A123 packs?

3. If I decide to make my own A123, where can I purchase individual cells?

4. What is the charge time like for a "typical" A123 pack?

Charge time is proportional to the discharge rating of the cell and theoretically as long as it dosent overheat it can take anything i have seen thermoelectric coolers becoming popular at rc car races to high amp blast charge packs past their rated current.

I would purchase directly from
http://www.a123systems.com/ if you want the real deal, they wont be cheap and you may need to buy more than 20 at a time. I have seen people locally buy direct from them for their electric bike conversions running 40+ cells.

it is highly dangerous to build the packs if you ground them out in the later phases of cell building as they can carry up to 1000 amps of energy in some packs, the key thing is planning exactly what you want to achieve voltage and mah wise then draw a layout of the cells BEFORE you try wiring them up, when wiring individual cells I always have a bucket of sand and work gloves nearby just incase i make a mistake and short out a pack. i dont work with a123 cells but i wire up custom lipo packs so the saftey is just the same.

custom a123 packs can be purchased from the robotmarketplace, they outsource to a very skilled battery builder that will resistance match each cell before he makes a pack.
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SamM
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PostSubject: Re: Li-Ion and Li-Poly   Fri Aug 26, 2011 4:32 pm

Evan Steeves wrote:
custom a123 packs can be purchased from the robotmarketplace, they outsource to a very skilled battery builder that will resistance match each cell before he makes a pack.

Do you have some inside info? As far as I can tell, RMP doesn't sell custom A123 packs anymore. I think they used to buy from battlepacks, but battlepacks couldn't supply orders quick enough.

I've bought the materials directly from battlepacks, but wouldn't recommend them, as they've switched from A123 to K2 cells which are quite inferior for combat purposes. (20C continuous discharge compared to 40C)
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Koolaid64
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PostSubject: Re: Li-Ion and Li-Poly   Fri Aug 26, 2011 6:34 pm

how to make your own a123 packs

http://www.rcgroups.com/forums/showthread.php?t=599316
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Evan Steeves
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PostSubject: Re: Li-Ion and Li-Poly   Fri Aug 26, 2011 7:20 pm

SamM wrote:
Evan Steeves wrote:
custom a123 packs can be purchased from the robotmarketplace, they outsource to a very skilled battery builder that will resistance match each cell before he makes a pack.

Do you have some inside info? As far as I can tell, RMP doesn't sell custom A123 packs anymore. I think they used to buy from battlepacks, but battlepacks couldn't supply orders quick enough.

I've bought the materials directly from battlepacks, but wouldn't recommend them, as they've switched from A123 to K2 cells which are quite inferior for combat purposes. (20C continuous discharge compared to 40C)

Oh snap your'e right Sam they no longer have them, lame fail on my part. Rolling Eyes
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fogdog



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PostSubject: Re: Li-Ion and Li-Poly   Sun Aug 28, 2011 6:21 pm

Koolaid64 wrote:
how to make your own a123 packs

http://www.rcgroups.com/forums/showthread.php?t=599316

I saw that tutorial, but noted that the pack he was using was from a 36V Dewalt drill. Didn't even realize that those existed. If I purchase individual cells, what is the best way to solder the tabs? Cold soldering? With heat solder I'd be worried about heating up and destroying/igniting the cell.

FYI - Visited a sponsor of this site (http://www.all-battery.com/) and saw that they sell individual Li-Ion and LiFe cells.

Are LiFe (A123) batteries even allowed in the NRL competitions? The regulations only mention using LiIon.

Revision - Research tells me that spot welding would be the way to go to attach the battery tabs.

Anyone ever build their own Li-Ion packs?
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Koolaid64
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PostSubject: Re: Li-Ion and Li-Poly   Sun Aug 28, 2011 7:05 pm

from what i've read and done when making a123 packs a 50w temp control iron at 350-400 degrees with a big tip works well. just don't apply it excessively so not to damage the cell
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SamM
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PostSubject: Re: Li-Ion and Li-Poly   Sun Aug 28, 2011 10:16 pm

LiFe are a type of Liion battery and are considered legal for NRL events.
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Cody
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PostSubject: Re: Li-Ion and Li-Poly   Sun Aug 28, 2011 11:31 pm

fogdog wrote:
FYI - Visited a sponsor of this site (http://www.all-battery.com/) and saw that they sell individual Li-Ion and LiFe cells.




The forum doesnt have any actual sponsors, the ads above are randomly genereated by google off of what you've been searching and looking at so dont feel obligated to buy anything lol


Last edited by Cody on Mon Aug 29, 2011 3:14 pm; edited 1 time in total
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Koolaid64
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PostSubject: Re: Li-Ion and Li-Poly   Mon Aug 29, 2011 8:57 am

i think you messed up your quote on that one
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Cody
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PostSubject: Re: Li-Ion and Li-Poly   Mon Aug 29, 2011 3:15 pm

thats what I get for trying to quote off of my phone
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Chris R

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PostSubject: Re: Li-Ion and Li-Poly   Wed Aug 31, 2011 2:31 pm

What is the discharge rate for the Dewalt DC9180 cell in the 36v Dewalt battery pack that some of you used?
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