A123 20AHr Pouch Cell Battery Build & Info Thread

[deVries]

Hi JD,

I just wanted to get your answers into this thread too, beyond your thread topic, since it will cover here the various methods to assemble cells into a battery.

For those of us that don't have our cells yet, when you have time, could you please measure the L x W dimensional area of just the tab area that sticks up? This will give us an idea how much tab we have available to work with.

Thanks!

[ohzee]

You see any of those 35$ welders now ? looking at ebay 136.99 is the lowest I found.

Was not sure if maybe they called it something else.

[deVries]

You see any of those 35$ welders now ? looking at ebay 136.99 is the lowest I found.

Was not sure if maybe they called it something else.

You misunderstood. There never were $35 dollar welders on ebay. You can *save* $35 dollars by buying the same welder on ebay, which is also the same welder that you can also buy for $35 dollars more at Harbor Freight.

[ohzee]

ahhh haha thanks for the clarification..

I should have put that together wtf would sell a 35$ welder.

[deVries]

I don't have my cells yet to personally do the measurements, but Dr Bass did them and hopefully I copied them correctly into the solid models.

Just for verification purposes, and for those of us that don't have our cells yet, when you have time, could you please measure the L 1.772 x W 1.027 dimensional area of just the tab area that sticks up?

Does it seem possible to fold the tabs right down to the edge of "cell body" where the tab exits, or is there some additional support "inserts" where the tab exits not allowing for folding the tab all the way down to the "cell body" ??? (This will give us an idea about how much tab "sticking out" we have available to work with by bending or folding the tabs.)

Doc's measurements shown above go to three decimal places. No need for that, when you do "the verify". Just want a good estimate if it seems "close enough" within a 1/16th of an inch or so.

If you don't have any loose cells readily available, then maybe JD or someone else has some to measure one.

Thanks!

[Doctorbass]

Hey Bigmoose, I have a friend from Montreal that is building a suzuki swift with a AC150 kit from AC propulsion and he plan on using the A123 pouches.

We discussed alot about the connections about a way to be able to get up to 500Amp burst connection from 3p pack for his and our projects.

We wanted to have an easy acces to from the top of the cell connections and to have the optimized pressure on the most of the cell tab surface but without having the need of multiple screw and holes on each tab.

André( that have the swift) did some test with the connections and got really good results about temperature and low contact resistance.

The principle is to use some concentric aluminum half moon that press teh cell tab together and to have only one or two screw pre connection.

After all tests, the half moon principle seem to be the best we found.

Because it is circular, it can not really bend and will keep all the pressure againdt the cell tab surface uniform. But the two I.D. of these half moon must be calculated depending on the number of "P" , to preserve the match between both I.D.


Doc

[jonescg]

Doc that's awesome! Glad to see you got some good results out of it. I love this place

[oatnet]

The principle is to use some concentric aluminum half moon that press teh cell tab together and to have only one or two screw pre connection. After all tests, the half moon principle seem to be the best we found. Because it is circular, it can not really bend and will keep all the pressure againdt the cell tab surface uniform. But the two I.D. of these half moon must be calculated depending on the number of "P" , to preserve the match between both I.D.

Very Cool approach Doc. If you have a batch of these made up, please let me know.

-JD

[docnjoj]

Absolutely clever, Doc! Any chance of commercialization? Perhaps for 1P?
otherDoc

[ohzee]

With my cells so far I created 2 12S packs via compression with a cell_man high power BMS. It worked well , but with the diodes &
wires it was somewhat a pita to use. Not to mention only good for my cargo bike and not my mountain bike because of size.

So I had ping send me one of his high rate 20S BMS which is a signalab. I really liked the lights and how this BMS bleeds off all the cells.
The bad part is the most I am seeing AMP wise with it is peaks of 50-60 which is only on initial acceleration.

I am thinking now I may use the BMS just for charging and bypass the BMS for discharge so I can get the most amps from the a123 cells.

Anyone see a problem with this ? I have an email out to cell_man asking if he has a 20S or 24S high rate BMS and I may also go that route
tho the lights are nice.

Just wanted some input on bypassing the BMS for discharge.. I think I know my own answer , but wanted to be 100% thanks.

2nd question should I be concerned with regen on any of these BMS ?

May not look pretty. I used saran wrap for 1st layer. Filament packing tape for 2nd and duct tape for outer.
covered it all up so I can drop metal parts and not worry.. Need a 12x8x7 plastic case now.. Cool thing is it fit in my rear topeak trunk bag.

[dnmun]

why not try to solder up the shunt on the BMS and see if you can overload the mosfets? not too much solder, a little on each end, and then you can also solder a heatsink on the to the tabs of the mosfets to spread out some of the heat, and keep the hot end of the BMS out in the air flow.

[acuteaero]

Hmmm- I was doing some searching around tonight and realized that anyone who is reading this thread looking for answers should really read this thread too: viewtopic.php?f=14&t=15408 from a couple years ago, many good answers and ideas are put forth.

I had a bad failure on my Kokam packs on Friday due to allowing excessive movement of the cells- pounded one cell into leaking, bringing up an important concern besides electrical terminations,--- physical mounting of the cells. I made a long rambling post about that here viewtopic.php?f=14&t=40658#p594151

[Grinhill]

Well, I've recently joined the club! I bought 70 cells, will eventually be used in an e-motorcycle but may find themselves in other projects before then.

All cells measured 3.27 V (+/- 0.01 V), undamaged except for the following:

Two cells which were on the top tray of one of the boxes were deformed in a "dished" shape. I haven't read of anyone else having similar faults. My guess would be it may have occurred during shipping, perhaps this tray was on the bottom when the boxes were dropped. It's really not worth chasing replacements.

IMG_4954s.jpg (57.6 KiB) Viewed 456 times

I am thinking that it would be best to try and warm these by running at high discharge current for a while before attempting to press them between some flat plates.

Any other ideas?

[1000w]

I've had cells with similar bends, just gently press them flat by hand, check the voltage, they should be fine, the bend looks minor in the photo.
Good luck with the build.

[jamo96]

Well, I've recently joined the club! I bought 70 cells, will eventually be used in an e-motorcycle but may find themselves in other projects before then.

Grinhill - where did you purchase your cells from? What was the cost if you don't mind my asking? would probably be similar shipping costs for me (Brisbane)

Have you decided on a method of connecting these cells?

Wouldn't mind building a pack for my go kart - viewtopic.php?f=34&t=40631
cheers

[Grinhill]

Thanks for the advice Matt.

Hey jamo, the cells were from Victpower. I used DHL after reading someone else's experience with their slow airfreight - and I'm glad I did. Arrived pretty quickly, around 3 days (add a few days for multiple emails to Xin). Cost with shipping included was $25 ea, managed to avoid additional customs costs, although I'm not sure you could go too much larger a shipment than this before it gets noticed. They only accept telegraphic transfer, which will incur a few bank fees as well.

I'm liking Oatnet's methods so far, I will probably start with a small 1p pack and test on a pushy. I may even just fold and crimp without the spot-welding to start with. The large pack will be a 2p.

[jonescg]

Hi guys,

I have been looking at using EIG cells for my eCRX project, and they terminate in much the same way as the A123 cells. I put this picture in the Wanted thread but a mod can feel free to remove it if they think it belongs here.



Basically I thought about taking a PCB with pads I can solder M4-tapped brass blocks to. There are two slots either side of the block (1 mm wide) which allow the two paralleled cell tabs to slide through, and bend over the block; one one way, the other the other way. The tabs would be pre-trimmed and punched with holes at the right spots. 1.6 mm copper plate with 4 mm countersunk holes would hold the tabs down while making the series connection to the next terminal. I thought about putting traces down for the balance taps, but wires to plugs would work just as well.

[cassschr1]

Has anybody got there packs built yet and had balancing issues ? ( vic power a123)

[ohzee]

I felt like I had balancing issues with a cell_man BMS , but the ping BMS did a lot better job bleeding off until they were all
even so it could charge back up again. so depends if your talking with or w/o a BMS.

[cassschr1]

Sorry , should have mentioned that. I'm using powerlab 8.
I keep running into cells that go to 3.65 in a hurry while others are at 3.35 or so then it goes into a safety charge of like 500ma or lower which takes forever...even times out after awile. (few hours)

[dnmun]

doesn't it seem like that means that the cells with low voltage are already much more discharged than the ones the reach 3.65V first?

if you start by balancing the cells together, connecting all the anodes and cathodes together so they reach the same voltage and then charge up from there may allow the pack to balance faster.

i don't see how this is a problem of the BMS and i am of the opinion that the headway BMS is superior to the ping signalab. jmho. experts can now jump in and criticize me.

[ohzee]

Only thing I could think is try how oat was balancing his packs before putting them all together.
He had them all in parallel and charged/discharged them a few cycles (or more not sure) to make
sure they were in sync.

Ill admit I had some issues like you when I was charging with my icharger one at a time.. Some seemed to hang at the
right charge while some fell back down to .35 area.. The high power ping bms I have though does a great job of charging
to 3.65 bleeding off the highest charged to the lowest and charging back up.. the lights on the BMS make it great so I
know what's going on.. now if i unplug my balance cables and check the voltage they are all at 3.65.

GL - check out oatnet's older threads he has some good info on how to get em into balance.

[ohzee]

i don't see how this is a problem of the BMS and i am of the opinion that the headway BMS is superior to the ping signalab. jmho. experts can now jump in and criticize me.

yea I am by far no expert , but I have dealt with a cell_man BMS and a signalab BMS recently. the cell_man one looks identical to the headway BMS at least the way it's built.

my opinion in dealing with these is the cell_man BMS is much better at higher discharge rates and the signalab is much better at charging.

I left my cell_man BMS plugged in over night and it never even was warm which is what I would expect as it balances the cells. It also did not charge as long as I would have
expected it to do so.. maybe my cells were not as in good of sync as they should have been I don't know..

When i used the signalab BMS it was obviously warm after charging and did a great job of balancing the cells. That's why I considered bypassing the BMS for discharge.

Anyway that's just my experience so results may differ for others.

[dnmun]

you mean settled back to 3.35V i assume. people call that the 'surface charge', which dissipates somehow and the cells will settle to around 3.42V for the headways. these A123s i thought were able to hold that 'surface charge' without dropping the open cell voltage.

but yep, the trick JD followed is textbook for how you initialize the cells. when they all start at the same voltage then they can charge up together and not go far outa balance. that may be what you were fighting to get the pack balanced initially.

imo the headway BMS is superior because it would put all the cells right on 3.65V and the shunt balancing current is so much larger than the ping signalab. 160mA vs 60mA. jmho.

[cassschr1]

Just got done with second pack . On this pack I paralled all of em for 48 hours, then let sit 12hrs.
There still not all the same.I put the charger on,voltage would go up ta 3.65 ,level off,and charger thinks its done.
DOES ANYBODY KNOW IF THEREs A SPECIAL WRENCH FOR T-BOLT NUTS with 3 holes in it
Dnmum the cells never got to 3.65 and fell back.