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Use of A123 cells are permitted providing that roboteers do so at the scrutiny of FRA event organisers.
Suitable charging equipment must be used and packs must be built to a safe standard.
Trials of the technology are still ongoing and while limited testing has shown favourable results the FRA advises, that this technology is used with caution particularly due to the charging requirements and energy density within this product.
Kan-opener team update on A123 trials
All parts have arrived now, the wait for the balancers has been tiresome.
Pack design has been approved and bench trials are to start soon.
If you already have a lithium polymer/ion programmable charger there is almost deffinatly a new download for it to charge A123 cells. I have looked a little into this as my purely Lipo/LiIon charger can now be updated to use A123s, nicads, NiMhs by downloading the new software from the manufacturers websites.
The standard balancers will also work very well with them, especially if used inline with the charger.
I have started a thread in FRA General Chatter (A123 Lithium cell use), where hopefully people can describe their proposed setup and we can all learn how best to use these cells.
quote:
I used the silver paste from MEC and it was tested at various loads on a 10 cell packs and it sounded like a kettle boiling at 45A from memory.
Ive never had this issue with the AS5, and I know its fairly good up to at least 90c, because Ive used the stuff on overclocked graphics cards which easily hit 80-90c when torture testing :).
Also, someone said in a previous post that the A123s are hard to solder. I originally made up a 4 cell test pack that I soldered. Since I dismantled my cells from Dewalt packs, I just trimmed the tabs back to the cell. This left a good 10mm x 10mm to solder onto. Even though this is just spot welded on, you can flow solder over the edges of the tab (and the centre) onto the cell face and it seems to flow quickly and makes soldering easier.
Having soldered some 5000 to 6000 NiCd cells, the A123s are by comparison far more difficult. So difficult that I will not be doing it again in the future. The A123s did not have previously spot welded tages and are in fact virgin cells direct from A123.
Having conducted tests on the cells in almost a lab environment, I can only state what I found when using the MEC paste. If it works for you then thats great but I wouldnt consider using the MEC packs for applications over 35A.
Paul, presumably it was the can of the cell that was tricky (the positive end)? Did these have the steel disc on that end?
The button end is very similar to nicads - nickel plated steel.
John,
The button end is certainly better than the +ve end but still requires more heat and takes longer to flow than NiCds - extra heat makes me nervous. For the +ve end, I had to remove the disc to stand any chance of soldering onto the can. To be fair, I have only soldered 10 cells but will be soldering plenty more shortly. May just need to perfect the technique but give me Nicds any time for soldering!
but will be soldering plenty more shortly ..personal use I hope!
Hi Woody,
Im afraid not, theyre for someone else. In fact I would go retro now and go back to SLAs now NiCds are too hard to get. Trouble is I cannot afford another 6kg to use SLAs.
Hi Paul,
Weight is and always has been an issue in building.
Heres hoping that the Robot bug will re-infect you ... thus compelling you to arrive at a solution.:proud:
To the pessimist, the glass is half empty. To the optimist, it is half full...To the robot builder there is just to much damned glass!
(Message edited by woody on April 19, 2008)
Nice Lipo fire about half way thruogh the match.
http://youtube.com/watch?v=sdKlTaXXueYhttp://youtube.com/watch?v=sdKlTaXXueY
Impressive in the arena - I can imagine scary as [banned] if that happened testing on the bench!
(Message edited by kane on April 28, 2008)
I take it that those are standard lipo cells and not A123s?
Yes standard lipo cells just to show how dangerous they can be compared to A123s.
Pretty much every battery we have been known to use is vunerable. LiPo is such a technology that has a lot of power for a very low weight. These things like in Tonys clip can happen, but its not that every lipo used will burst into flames. If handled properly and cared for a lipo is just as safe/unsafe as any other battery. Ive seen them being used and abused in the antweight robots (where i must say some are a bit too reckless there) and in RC helicopters and 99% of the time there is no problem.
A123s just happen to be safer. That doesnt mean using lipos need be unsafe. Just to get some perspective on the case.
I agree with leo there!
Infact its actually quite difficult to get a lipo to catch fire, especially if they are more than half discharged. That is an unlucky case, but by all means in a robot, and then in an arena which is built to contain it. The fumes are not as dangerous as nicad though.
General use in pits should be often checked by event organisers, and a roboteer should be asked a few things about the batteries during tech check such as how to dispose of them after a fire or swelling as I know for a fact sme of the antweight lipo users do not have a clue, as demonstrated at RL with an antweight.
I had to dispose of the battery correctly.
I have never had a problem, or any form of puffing from lipos over the last 2 years, and i currently own about 10 packs with the smallest being 11.1v 2000mA.
Although i wouldnt recomend for anyone who has no idea about them, but the biggest problem is that they are sold as a product like everything - they come with most RC models nowadays with no more safety notice than a rechargable battery.
I know the hazards of Li-pos Grant, and I take great care when using them. I agree that I should have bought along a Li-po bag and my metal charging case, and I shall from now on. It was ACCIDENT that caused Baby Hells Li-po to swell up, and I appreciate your help with disposing of it.
Ive learnt my lesson about leaving my robots near the audience, and it wont happen again.
But I resent that generalisation. I have not long used Li-pos, whereas people like Peter Waller and Simon Windisch have used them for much longer and know a lot about them, and their treatment, so dont go saying the antweight roboteers dont have a clue about them.
Now that thats out of my system :)
Li-po disposal equipment should be provided at all Live Events, Heavy, Feather or Ant. Vharging protection is the roboteers responsibility, but the EOs have an obligation to the safety of all roboteers and audience members to make the event safe, even from other roboteers :P
If you read the FRA Rules regarding them, you should bring all means off disposal and safety with you to an event. I have since day 1.
Im not generalising, you have kind of proven a point that some people know exactly what to do, and some people dont know until they have had an accident. I wouldnt leave an antweight where memebers of the public can touch them as 1) they may get broken, damaged or turns on and injure someone and 2) they will most likely get taken!!
Accidents happen, and lipos will at some point go up in flames, so before buying or using them you should atleast know everything about them.
What do you think of this charger
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=5606http://www.hobbycity.com/hobbycity/s...idProduct=5606
It is an OK low budget charger for up to 8 cells A123. It will not charge 8 cell very quickly, but the fact it is also a balancer makes it a very nice all in solution.
its just a cheap and tacky version of my e station BC8
http://www.brchobbies.com/?page=shop&category=7http://www.brchobbies.com/?page=shop&category=7
A UK source for A123 packs. From the pictures it looks as though they have balancing leads.
BRC packs are great quality and yes they do come with balancing leads, I highly recomend them. Great guys to chat to as well.
Chris
http://robotbirds.com/catalog/index.php?cPath=63&osCsid=86e97e111f0b28457539cc9d 07a182c4http://robotbirds.com/catalog/index....0b28457539cc9d 07a182c4
cheaper to buy from robotmarketplace. They sell them for £6 a cell.
Can someone give me the link to a source of battery bars suitable to solder to the top of the cells.. ive got to make a custom shaped pack to fit into my middleweight.
http://www.technobots.co.uk/acatalog/Online_Catalogue_Battery_Holders___Bars_23.htmlhttp://www.technobots.co.uk/acatalog...ders___Bars_23. html
perfect, cheers John.
poke
Dont poke a lithium cell, youll get electrocuted! :uhoh:
Enought with the spamming, alright!?
Chill Joacim just a bit of fun you see. the forum is pretty boring at the mo and just trying to spice things up a bit. its not spamming
No, its Swanning, and just as annoying.
Shane this is the Geek thread you must €œknow your onions€ before you say anything here, or they shoot you down in flames. :uhoh:
That€™s why you never catch me putting any comments here, I run cheap SLA batteries and I always loose.
:)
That is not true Craig, if you dont know your onions this is the perfect place to ask about them.
This topic doesnt need livening, there are separate threads and topics on this forum specifically for that.
just a quicky, can the a123 cells be charged in paralel?
for example, 3 cells in paralel wired in series with another load of paraleled 3 cells?
Yes. Though the connections between the cells need to be substantial.
http://www.killacycle.com/photos/battery-assembly-110s-x-9p/http://www.killacycle.com/photos/bat...bly-110s-x-9p/
Yup, you can do it with lithium cells, but not with NiCads, because the voltage drops when NiCads are over-charged.
This is one of the packs for beta (6S4P):
http://www.b-e-t-a.com/24cells.pnghttp://www.b-e-t-a.com/24cells.png
cells joined by 0.5mm copper sheet.
Makes it much easier to balance the cells (and only six balance wires to build into the pack) - you balance it as one pack, as opposed to four separate packs.
(Message edited by terrorhurtz on September 12, 2008)
Hyperion also do some battery bars specifically for A123 cells:
http://aircraft-world.com/shopexd.asp?id=5085http://aircraft-world.com/shopexd.asp?id=5085
Not that theyd be suitable for a parallel pack.
Laptop battery packs are also built with the cells in parallel:
http://www.b-e-t-a.com/LaptopCells.jpghttp://www.b-e-t-a.com/LaptopCells.jpg - 3S2P
(Message edited by terrorhurtz on September 12, 2008)