Building a small A123 Battery Pack

[ELECTRIC AVENUES]

Just got confirmation from some dudes over at ES that the Dewalt 28v do in fact contain 8 A123 M1 cells. Nice. These are going cheap because they are being phased out over some trademark issue or something. In the meantime, UK tool retailers are still asking huge money for them.

 

[trepo]

Trepo nice pics BTW. The DeWalt packs have the advantage of being ready soldered together mostly with tags incl.

I get about 8-10 miles (13-16 kms) on my 2*6s pack depending on how much I pedal. What are you powering ?

I guess my Brompton/Tongxin combination are a low demand setup.

PS Aah I wonder if that is why my Turnigy screen messes up soemtimes in the cold ?

PPS Hopefully your Tongxin will turn up soon

Regards

Jerry

Thanks Jerry! Yes, your range seems to be about twice compared to mine.

It's probably due to the higher weight of my bike, its 35 kg all together (25 years old steel-framed trekking bike and SLA batteries worth of 15 kg). I myself weigh a little over 90 kg... yes, I know, I should eat more healthy and cycle more to get fit.

So the bike and rider are about 130 kg together, no wonder it takes 10 WHr / km. And my controller is a 14 amps unit, your Tongxin one probably eats less current.

It's now two weeks since they picked up my payment for the Tongxin kit in China. Hopefully the kit gets on the way this or next week! I already have all the other bits ready.

Today I had my second ride with A123 batteries (2060 mAh consumed until weak motor performance) and this time I am charging them with the same ebay charger as yours. Charging is going through Turnigy meter so I will update charged capacity to this post later.

I just have to monitor the end voltage that it doesn't get too high. Build and adjustment tolerances seem to be quite wide on these cheap chargers. My unit even had a bare negative charging lead inside, it had been chafed to the heat sink. I just insulated that part of the wire and the charger seems to be working fine.

The charging has just ended as of writing the post. Unfortunately I did not notice the peak charging voltage but the charger had green light and the pack rest voltage was 42,87 V.

Poli max B6 was able to push in only 20 extra mAh to the first pack and 27 mAh to the another one so this 36V charger seems to be doing good job. The cells were also quite well balanced (20-30 millivolt maximum difference).

Regards

Taisto

 

[jerrysimon]

Thanks for the update. My Tongxin/Controller are rarely pulling more than 5-6amps so that probably as you say explains the range.

Fingers crossed that your Tongxin will turn up soon. As I said he seems reliable and its been new year so probably things a little slower.

My charger seems ok and as you say it does not seem to over charge. Not state of the art finish I agree. I put a new three pin plug with a 3 amp fuse on mine for safety and am rarely far away from it when it is charging. I always turn it off after the green light comes on and never leave it on when the charge is complete.

Regards

Jerry

 

[ELECTRIC AVENUES]

eBay.ie: Hobby Spot HS300A2 Capacitive Discharge Metal Welder (item 170453925159 end time 10-Mar-10 20:37:36 GMT)

Nice hobby welder, the very thing for doing tabs. Obviously quite expensive but I am sat here, thinking about it.....

 

[jerrysimon]

Well that money would get you quite a few tabbed A123 cells

Regards

Jerry

 

[ELECTRIC AVENUES]

Well that money would get you quite a few tabbed A123 cells

Regards

Jerry

Ain't that the truth! And that is one way to look at it for sure. Biggest mistake I ever made was buying a job-lot of non-tabbed when I should have got the better tabbed versions in the DeWalt packs.

Lives and learns, I suppose.

Anyway: the reason I was looking at it was because I wanted to go into further education as a provider of bespoke e bike solutions for the private market.

Cheers.

 

[Fecn]

Capacative Discharge welders are easy and cheap to make if you know a bit about electronics. I built one for myself a few years ago, but never managed to get hold of any nickel strip to use for the tabs. It's still in the garage gathering dust...

$100 CD Battery Tab Welder

 

[ELECTRIC AVENUES]

Yes, I heard about these welders, and I am making inquiries about them.

Here is a link for some nickel tabs......eBay.ie: 50 Solder Tabs. Build your own battery packs. (item 350316912267 end time 16-Mar-10 00:28:44 GMT)

 

[Fecn]

Thanks for that link... I should have more accurately said.. "The only place I could find Nickel strip was in the States, and I was too lazy/stubborn to order any for myself"

At the time (2004/5) I phoned round a dozen different metal suppliers in the UK, but couldn't find anyone with thin enough nickel in sheets (I wanted sheets so I could cut out L-shapes etc). If you're ordering from the states though... please get some for me too

 

[ELECTRIC AVENUES]

Thanks for that link... I should have more accurately said.. "The only place I could find Nickel strip was in the States, and I was too lazy/stubborn to order any for myself"

At the time (2004/5) I phoned round a dozen different metal suppliers in the UK, but couldn't find anyone with thin enough nickel in sheets (I wanted sheets so I could cut out L-shapes etc). If you're ordering from the states though... please get some for me too

The tabs are quite cheap, and shipping is probably very low.....most sellers send stuff by USPS Priority Air Mail and that takes around 2 weeks or 12 days. I will order bulk and then come back and see if anyone here is still interested....

 

[jerrysimon]

Just a breif update.

I have just passed the 250+ discharge point of these cells having used them for the last 13 months or so.

To date they have performed faultlessly in my application, retaining both charge and cells remaining balanced to within 10-20mv of each other (no BMS fitted).

Specs state that they will give 1000+ discharge cycles, which in my application would last me 4 years. The pack cost me about £70 to build + £50 for the chargers, though I have only used the Turnigy charger/balancer once when I first constructed the packs.

I agree my application is less common than many i.e. a daily 10 mile round commute on pretty flat terrain, but carrying two of these 12s1p packs may provide others more flexability. It seems the solution represents a good value for money option.

Maybe I won't be saying this in 3 years time


Regards

Jerry

 

[John L]

Thanks for the update Jerry Your set up does seem to be very good value and a realistic option.

John

 

[jerrysimon]

There is an interesting article in that magazine being linked to in another thread page 46.

ExtraEnergy Magazine Issue 2 (english)

By chance, I am using my battery in a very simlar way to which they recommend.

I usually charge twice a day once at home and again i.e. before each journey either way. My battery is therefore never fully discharged, I am guessing about 1/2 to 2/3 before it is then recharged.

I am wondering if this also effects the balance of cells if no BMS is used

Regards

Jerry

 

[Pedalo]

It's good to hear your battery is holding up well. In particular as I use mine in almost exactly the same way!

 

[jerrysimon]

What's better than my DIY A123 12s1p (2 *6s1p) pack ?

Two of them

This turned up the other day (there is another one in the box) from my previous supplier. The only difference this time, is I got them to spot weld them up into two 6s1p in my previous flat parallel side by side config.

I have enough 6s pigtail balance taps and connetors left over from the last build I did over a year ago.

Not only will this provide me twice the range for those longer rides, but also keeping the same config profile of the 6s1p packs means I can swapped out between each of the single packs if one fails.

Regards

Jerry

 

[daniel.weck]

Nice !

Mhmm, green battery cells...

 

[MalcolmW]

Controller voltage ratings

I am really bad at these threads so tell me if i am doing it wrong.

as i am a beginner i have many questions but be patient.

Controllers, in particular for a 5year old Sprint initially NHMI. I want to build batteries for it but do not know the max voltage it is safe to use with this controller. Or the drop out voltage but this is less important.

What do they mean by "reboot", is it sw off and on again?

So much to learn, so little time.

Malcolm

 

[jerrysimon]

Kinda of a double post (but you can't seem to edit old posts in this new forum software ?) from another project I did building an Ebike for my daughter with M.E. (CFS), but worth adding to this thread for completeness. This provides a more robust solution for the battery both in terms of a connector, isolating switch and enclosing the battery pack in a tupperwear container.

Here are some final pics of the battery and how I installed it inside a tupperwear box with a seperate switch and connector (Speakon 2 pole rated to 40amps) available form Maplin here.

Finally I had to make a seperate charger lead to enable it to be charged from my chargers with Deans connectors fitted.

Regards

Jerry

 

[jerrysimon]

Well after 22 months, 2500 miles and approx 500 charge cycles, one of my cells seems to have died

Interestingly the battery still worked ok on my 10 mile round commute but I had noticed a drop in power overall and sometimes for no reason it seemed to slow right down. Clearly there was a reason. I guess the low voltage cutout did not kick in because I have 12 cells ?

Over the last week I had noticed that one of the cells voltages had been dropping. I test occasionally using the excellent little CellLog meter and here it shows the complete failure error. It was easy to identify which of the two 6s1p packs had failed and being a DIY pack, was just a case of then stripping one down to identify the suspect cell.

Measuring 0.51 volts instead of the usual 3.3 volts!

Cell removed and taps protected from shorts.

Regards

Jerry

 

[jerrysimon]

Ok battery pack rebuilt with a spare cell I had and hooked up for inital balancing.

I was told these were genuine cells but I noticed they seem to be double wrapped

I had hoped to get at least 1000 charge cycles and probably more. Anyway its good that they are DIY packs and thus I know how to dismantle and repair them. I had purchased a few spare cells when I first built them so I can replace any faulty ones as and when. I guess for the cost (about £40/6s1p pack) nearly two years use, still represents good value for money and its not as if the whole pack is wasted.

Will be interesting to see if another cell fails. I will keep you all posted.

PS I just went out for a test run and noticed a big difference in power

I guess as the failure was gradual I had not really noticed the drop in power.

Regards

Jerry