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Probably rubbish ...but worth a punt?
Should be good enough for a Feather.
http://www.dealextreme.com/details.dx/sku.5105http://www.dealextreme.com/details.dx/sku.5105
A quick Google around gives a probable continious discharge rate of 15C.
BUY 10 or more ...go to checkout click BULKRATE and the price drops to $34.69 including shipping!
I think i will need to get my money back from robotmarketplace. My A123-cell packs arrived and after removing the shrinkfoil, it seems they solered all the vent holes from the cells. Tomorrow i will put a picture online. :sad:
They dont supply what they promise on there website:
These packs are constructed with highest-quality triple-welded tabs, wiring strain-releif, and 3M Polyolefin Mil-Spec rubberized finish.
There are no triple- welded tabs used and only wiring strain relieve for 1 cable. I would advice not to buy it.
(Message edited by tough_as_nails on September 15, 2008)
Note that the blue dot on the button (negative) end of the cell is not actually a vent - apparently it is where they are filled. And there is no vent on the flat (positive) end either. So shouldnt be a problem where they are soldered.
If you can have a look at the individual cell voltages when discharging and check that they are all similar capacity and that you can get at leat 2 Ah out of them, then I would suggest they are OK.
Would be good to see a pic.
Just out of interest, could you post a picture of the cells please?
Looking at their site, im not too sure they are actually A123 cells. Which ones did you get? the spec on their site says the higher capacity cells are only 20A discharge, 30A max. And they state the 1100mA cells as being A123s, but im pretty sure they only make 1 size.
Nope 3 are listed.
http://www.a123systems.com/#/products/http://www.a123systems.com/#/products/
They dont actually make the 32 series. And doesnt look like they will be either, unfortunately. Just the 18650 and the 26650 - 18 mm or 26mm diameter, both 65 mm long.
Started making up the packs for beta
http://www.b-e-t-a.com/2008/images/a123-6s4p.jpghttp://www.b-e-t-a.com/2008/images/a123-6s4p.jpg
looks good john. Do you glue the cells together or just rely on the tape you use to hold it together? Also what is so special about the tape you seem to use? heat resistant? Im making my own packs sometime next week, you still upfor checking them when there assembled? Im getting the same cells you just ordered via Grant..
Hopefully this link works:
http://picasaweb.google.com/Jeroenvdlo/Firestarter1#http://picasaweb.google.com/Jeroenvdlo/Firestarter1#
These cells are glued with hotglue it seems.
Dave, no havent bothered gluing them together. Theyre only card tubes, so wouldnt make a great deal of difference.
Yup, Kapton tape is good stuff - you can attack it with a soldering iron and it doesnt melt. Great for building packs, particularly for keeping the balance wires separate from the main connectors.
See http://www.terrorhurtz.com/a123/build.aspxhttp://www.terrorhurtz.com/a123/build.aspx
Thanks for the pics Jeroen. Those wheels look rather nice... what is the polyurethane that you are using? Whats the blue stuff, mould release? How did you decide on what hardness of PU to use?
The base of the wheels is 7075 aluminium. The surface is roughend with the crosshatch ( i dont know the English word) and later on roughend again with a steel wire brush (again i dont know the English word). Directly after roughning it, it is degreased with thinner. Then i coated it with one layer of FL-10 primer from Devcom. This is hazardous and smells so bad that i put on a mask with medical oxigen against the smell. This coating was left to dry for 1 - 1,5 hour.
The blue stuff is the first mould i tried to make and its made of Smooth-sil 950. It is a shore 50, 2 component sillicon, special for making moulds. The dummy for the wheel was made out of HDPE, but the sillicon will not stick anyway. I mixed the whole 5kg can at once, but it was curing so fast that after 10 minutes i could not poor it anymore. This was the most expensive mistake i made. I wanted to fill 5 moulds, but only the first one seemed to have succeeded well enough. The sillicon works perfect, but i should have used 5 small cans and mixed each can in a wooden box before pressing the HDPE dummy into the sillicon. I had already made 5 wooden boxes.
After that 140 pound mistake, a friend of mine sugested to use casting plaster/gypsum. This is the cheapest i could find at the hardware shop. It about 7 pounds for 5kg and it works well, with plenty left.
The urethane is Flexane 60 which is being produced by Devcon aswell. This was the softest i could find on the RS-components website. Also the shore 50 from the sillicon was just a little bit to soft. So it was a bit of a gues. I have some anti vibration mount that i thought was shore 60 and that rubber looked very sticky, but still hard enough.
The urethane is very easy to cast and it does not cure that fast, so plenty of time to fill all 5 moulds. The air bubbles will go to the surface by themselves. A vacuumpump would have helped aswell. I casted it at 18 degree celsius room temperature and it is cured after 2 days.
After breaking the plaster mould there is still a thin/1mm rubber/plaster layer on the urethane, but it is easy to remove with a steel scraping tool. On advice of the Devcon manual and by Mario i bought a cheap tablegrinder to put on my lathe to machine the rubber. Mind you that 150W is not enough. The biggest parts i had already cut off before gringing. With some experimenting it seems that when running the lathe on 750 rpm and with the 2900rpm from the grinder you get the best result. The surfaces of the grindingdisk and the urethane where going in the same direction, like with spurgears. The diameter of my wheels is 90mm.
I added some more pictures to the link here below.
http://picasaweb.google.com/Jeroenvdlo/Firestarter1#http://picasaweb.google.com/Jeroenvdlo/Firestarter1#
And some images of the first scetches. I will need to update these soon.
http://www.bugs.nl/media/album/index...lyZXN0YXJ0ZXIv
(Message edited by tough_as_nails on September 18, 2008)
crosshatch ..knurl... is the English word Jeroen.
Thnx woody, that is good to know. I only knew this word for using on technical drawings, but i did not know that it was called the same when machining parts.
Is the steel wire brush also the right word?
Wire wheel or wire rotary brush would possibly be a better technical description.
Diamond knurl is the correct term for your cross hatch pattern.
Ah, ok, it is clear now. :) thnx for the update. But i did not mean rotary brush, i meant the handtool.
Anyway the most important thing is, that it worked :)
LOL ...Wire brush is correct.
Jeroen, do you still need to get back to Robotmarketplace?
As it seems that it is not a vent, what they soldered, i see no reason yet tosend it back. :) But i still have to measure the cells voltage and capacity.
I am curious as to what the guys experimenting with A123s here think of the zip charging method discussed in this thread on an RC forum
http://www.wattflyer.com/forums/showthread.php?t=25492http://www.wattflyer.com/forums/showthread.php?t=25492
If I am reading this correctly, A123s are pretty dam robust both on the discharge and charge and can be charged with little more than either a homemade charger (check out the terminator 2 from Dan Baldwin) or even just a car battery or two with a length of cable to act as a resistor to limit the charge.
Yup, looks like the A123s are taking the abuse.
400 cycles, proably regularly over-charging cells at very high currents and only 11% capacity drop. 400 cycles... probably at least four years of fights for the average robot.
The Zip charging (basically just fast charging with a power source voltage matched to the pack voltage) is probably only suitable for 3 or 6 cells. Who wants to carry around 3 car batteries? Or even one... and you have to re-charge the car battery at some stage.
Probably only really worth it if you really need to charge in 6 mins.
But then we generally re-charge our A123s in less than 10 mins (at 5 Amps), because we dont take that much out of them.
We use a cheap 48V, 10Amp power supply (to charge two 10s packs), a light bulb for each pack to limit the current and a dapter for each pack as a voltage cutoff. The dapter is similar to the Terminator but can handle up to 10 cells at up to 10 Amps - http://www.slkelectronics.com/lipodapter/http://www.slkelectronics.com/lipodapter/
But we try to make sure the packs are well balanced before each competition.
I find that the packs tend to go out of balance when left for a while, so best to balance them right before an event.
Thanks for putting it all into perspective John.
I am very glad to see that the A123s are up to taking the demands of robotic combat! :)