Building a small A123 Battery Pack

[trepo]

trepo,

I look forward to watching your build thread/diary. Lots of pictures needed

The round A123 cells are more robust it seems than the Turnigy lifepo4 packs so I think you have chosen wisely.

Did you order a couple of motors as the cost of postage is the same for two or even three, so it worthwhile getting a spare ?

PS it took about 2-3 weeks for the motors to turn up after they withdrew my payement. Like you I used westernunion which does require an element of trust but they seem genuine. Although it will probably be delivered without an import/VAT charge I received an invoice from DHL in the post about 2 months later. The actual charge was quite small about £10 I think and no admin charge. I ordered two full sets of everything.

Regards

Jerry

Thanks for encouragement, Jerry!

I only ordered one motor because shipping fee quoted was 150$ for one and 250$ for two, the kit itself was quoted 140$.

How well Billy communicated with you during the order process? I can see that my payment has been picked up and I asked him if he has got the money, but no answer yet... of course I understand that he might have something more urgent going on than just a order of one motor to european private customer. Shame we can't get these motors from Europe for decent price.

Did you get a detailed invoice by mail (I think that will be needed for customs office once the kit arrives)?

I specifically asked to get a motor without that splined part and with shorter axle, we'll see what's in the package (hopefully) in a few weeks.

 

[jerrysimon]

Thanks for encouragement, Jerry!

No problem. Billy's english was not bad and communication is good. When I realised I had ordered the wrong one we had extrensive email exchanges though I could not seem to explain about the roller break flange unfortuanately. He does seem to now understand though as I have since spoken to him a few times about it. There were a few times when I did not get a response for a day or two. Remember their Chinese New Year celebrations have only just finished. As I said he has proved reliable to date.

The invoice was complete with the package, so DHL will sort it out don't worry.

Its a step of faith to order I know, but I am sure it will work out

At least I have led the way already and you can learn from my mistakes lol

Regards

Jerry

 

[ELECTRIC AVENUES]

A123 Build, Large-Scale, Advise and Help Needed!!!

Hi again, I thought I would post this here as a follow-on to Jerry's own A123 build thread, as this will be larger scale. I cannot do it on my own , and it could also serve as a valuable guide to anyone who attempts a similar project.

I expect to get 44 A123 in the post tomorrow, and another 20 in a week or so. They are not the green tabbed ones that Jerry had, 40 of them are left-overs from a job-lot that an American user had from building a motorcycle and the remainder were harvested from some Dewalts.

That will bring me up to 64 cells, though I expect 4 of them to be bad, from the Dewalts.

So call it 60 cells.

I have an Aotema Senorless Hub, the controller can handle around 30A and 50 volts or so.

My overall goal is to find a way to make up individual packs such that they can be joined quickly and then chopped-changed into larger packs {let's call them batteries} of varying voltage and capacity, from say 72v 4.5Ah to 48v 10ah, as an example.


I was looking for, initially, a list of everything I would need to start making the base packs.

Charging will be via an 8-plug Turnigy Accucel....

I understand I will need a power supply for this...can anyone recommend one? Thanks.

Can anyone recommend a source of good balancing strips?

How should these be soldered together? Do I need to get some copper strips, or nickel strips?

I will leave it at that for the time being, many thanks indeed. If anyone has any questions about anything, just ask. Thanks.

 

[jerrysimon]

ELECTRIC AVENUES,

Any 12v power supply for the Trunigy should fit the bill. Depends on how fast you want to charge them and the max charge current of that Turnigy 7amps ?

Faster charges will require more amps. I would say min 2amp power supply.

I use an old PC power supply that I have adapted that outputs 12-15v at 5amps max I think. But you can buy cheap ones of ebay for less hassle.

Like this

In terms of balance taps depends on how many cells you are going to put in each pack. With that charger you can do 8 max I guess. Earlier posts in this thread give links to 6s balance taps.

My 6s packs have not needed balancing since I first completed and balanced the cells some 20 charges ago. Each cell has remained within a few mV of each other. That said I am not really loading then that hard drawing on average only about 6-7amps.

If you want to charge them all connected together though your going to need a charger that can charge to whatever the voltage is.

Soldering direct onto the cells is possible but you need to be carefull. Again I think there are some earlier links in this thread for advice. I would also test each cell first to make sure they are all similar voltage/charge before you start connecting them all up.

Hope that gets you going.

Regards

Jerry

 

[ELECTRIC AVENUES]

ELECTRIC AVENUES,

Any 12v power supply for the Trunigy should fit the bill. Depends on how fast you want to charge them and the max charge current of that Turnigy 7amps ?

Faster charges will require more amps. I would say min 2amp power supply.

I use an old PC power supply that I have adapted that outputs 12-15v at 5amps max I think. But you can buy cheap ones of ebay for less hassle.

Like this

In terms of balance taps depends on how many cells you are going to put in each pack. With that charger you can do 8 max I guess. Earlier posts in this thread give links to 6s balance taps.

My 6s packs have not needed balancing since I first completed and balanced the cells some 20 charges ago. Each cell has remained within a few mV of each other. That said I am not really loading then that hard drawing on average only about 6-7amps.

If you want to charge them all connected together though your going to need a charger that can charge to whatever the voltage is.

Soldering direct onto the cells is possible but you need to be carefull. Again I think there are some earlier links in this thread for advice. I would also test each cell first to make sure they are all similar voltage/charge before you start connecting them all up.

Hope that gets you going.

Regards

Jerry

Cheers Jerry.

I was going to charge/balance each pack, once at a time. Maybe get two accucel. It is a real one-off job. These A123's are going to be the "flagship" of my battery collection.

8 cells to a strip, two strips per pack, each with a balance tab, encased in heat-shrink, and with 2 power wires for each.

That's 16 cells, then. Suppose now that each 8 cell block provides 24v@2.26 Ah. Thats 8 in series. 24v {just taking the round figure} per strip.

What I am wondering is IF I have a choice between the overall pack {of 2 strips} being a 48v 2.26 Ah unit or being a 24v 4.5 Ah unit, if you see what I am saying.

In other words, can I connect sells in series into columns, and then connect those columns into parallels within a pack, and then connect the packs themselves in parallel or series as I see fit.

Or is all this a departure from scientific reality??

Thanks again.

 

[trepo]

Hi all,

here comes my report about A123 cells taken out from used Dewalt DE9360 36V power tool batteries. I read a tip about those here in this forum (thanks danielweck) and went ahead and ordered 8 pcs. from ebike-solutions.de. Have to say that customer service was great, it was Sunday afternoon when I asked about these by email and 10 minutes later I had paid them using Paypal and they were already posted next day. Delivery took about one week and here they are:

Of course you have to open the case to get the cells out. You will need a star-shaped Torx-bit with hollow center to do that, correct size is T10. You'll also have to drill some plastic away from the case to get access two recessed screws:

Just drill slow speed until torx bit gets grip with the screw head:

Lift the case lid and you can see the cells under the charging/discharging control circuit:

 

[trepo]

Next you have to unplug the balancing lead connectors. They can be found from the both sides of the pack under the tape:

Now you can tilt the bms circuit and take take away the temperature probe:

Now it is time to cut the actual power wires (the red and two black ones). Just don't short-circuit them! I remember when I was repairing electricals on my car some 20 years ago and somehow the ring in my finger got between + and - wires, that did burn and hurt enough. Take away rings and metallic wristwatch if you are wearing one to be on the safe side.

Now we still have to get the cells out of the black plastic bottom part. Just use flathead screwdriver and pry the cells up little by little:

 

[ELECTRIC AVENUES]

Wow. Do you mind telling how much you paid for 8 of them? You can PM if you want. I paid £83 for 20 cells contained in 2 36v packs from a guy on Ebay who was selling them "as is"....I think 4 of the cells were broken and the packs were useless for power-tools because of bad wiring.

 

[trepo]

Once you have got the cells out the black plastic end parts drop off easily. Here are the cells exposed:

I am going to use two 6s packs on my bike connected in series. If you cut here (I used a Dremel-clone) you will get a pack with that needs only balancing leads and power leads added. You don't have to cut all through, just cut a little and the metal strip breaks with a light twist.

I added some electrical tape to keep the cells in shape. Next I added the balancing leads. I got 10 pcs. 6-cell ones from Electricwingman - Online shop for quality RC power systems and components for electric flights The price was quite cheap 0,80 each and delivery took a week from UK to Finland. It is important to connect individual leads in right order. The red wire goes to the positive end of the pack and each wire before that between the cells in the series. The last wire goes to the negative end of the pack.

 

[trepo]

Kapton tape is good to insulate and keep the wires in place. Should be heat resistant also, got mine from eBay for 7-8 euros / 33 m. Ideally you should not shorten the individual balancing leads, otherwise the charger may read false voltage when balancing the pack:

Here are all the leads soldered. The power wires are 14 AWG silicon wire. Just ordered some more, its great! So much more flexible than ordinary pvc-coated one.

At last we can add shrink-wrap to keep all in place. Again bought from eBay.

So now I have two 6s packs and of course you all are eager to know how they perform...

I charged and balanced the packs using Poli max B6 RC-charger. It was 28 euros delivered, again bought from eBay. By the way there seems to be many essentially same chargers around, I chose this as it was cheap and they sent it from Germany so no tax/duty. I had to change the charger settings and choose LiFePo battery type to get correct charging voltage which is 3.6 V.

Charging takes a little bit time but I used only 2 A charging current. With higher charging current the charger shows error message about low input voltage. It seems that the cheap ebay ac/dc adapter can only supply 2-3 A, but I don't complain, it was only 10 usd anyway.

All the cells get to 3,60 volts and the pack is full. After the another pack is charged it's time for a test drive. I made a adapter to connect two 6s packs together in series and there was powerpole connector for connection to my bike.

Start voltage 43,04 V, temperature -13,6 Celsius, no wind. I got 7,63 km until the bike suddenly started to feel very sluggish. Here is the big difference compared to SLA batteries, their voltage drops little by little, but these new packs gave plenty of power to the end. I just connected the SLA battery and drove back home to check Turnigy screen (it was cold and the lcd screen was messed up).

The pack gave 2086 mAh / 74 Whr. Minimal voltage during the trip was 29,72 volts. This means I can get 15 km if I double the pack, probably almost 20 km because I don't have the 15 kg extra weight from SLA batteries.

When re-charging the individual cells were around 3 volts, the difference between smallest and highest reading was below 0,1 V but the voltages became essentially same shortly after charging had started.

Eventually I am going to use 36V SLA charger for charging the packs. It charges to a little higher end voltage 3,708 V / cell so there might be a slight capacity increase also.

A note about the Dewalt packs. I ordered 8 pcs = 80 cells and there was 5 bad cells (voltage was under 2 volts, the good cells had over 3 volts and they were even pretty well balanced).

I remembered reading somewhere that bad A123 cells may be fixed by giving 12V zap to the cell. So I tried that and after connecting 12V to the cell with 1,25V voltage for 1-2 seconds I was able to get the cell voltage to 2.2 V. After that I was able to charge that cell, it took 2275 mAh. Haven't tried it though but I expect it to perform just fine.

OK, I have been writing for a while this long post. I just hope you bear my bad english and that I have been helping anyone building their DIY battery packs.

 

[trepo]

Wow. Do you mind telling how much you paid for 8 of them? You can PM if you want. I paid £83 for 20 cells contained in 2 36v packs from a guy on Ebay who was selling them "as is"....I think 4 of the cells were broken and the packs were useless for power-tools because of bad wiring.

I paid 197 euros including delivery from Germany to Finland, is that about 180 GBP or so for 80 cells? By the way the batteries are not listed on their shop but just ask by email if you are interested.

You could also try to feed 12 V to the bad cell maybe it "wakes up". At least my RC-charger refused to charge the bad cell until I did that.

The packs I bought were used ones but I believe they still have many charge / discharge cycles ahead and the capacity is certainly acceptable for the price.

 

[ELECTRIC AVENUES]

I paid 197 euros including delivery from Germany to Finland, is that about 180 GBP or so for 80 cells? By the way the batteries are not listed on their shop but just ask by email if you are interested.

You could also try to feed 12 V to the bad cell maybe it "wakes up". At least my RC-charger refused to charge the bad cell until I did that.

The packs I bought were used ones but I believe they still have many charge / discharge cycles ahead and the capacity is certainly acceptable for the price.

That sounds like an outstanding deal, even for used. Well done. I think I paid $6 per new cell for a batch of 44 that came from the USA, which I thought was a good deal, as I heard the retail on these cells is well over that, except for the cheap rejects they sell on Ebay.

Jerry's were not the rejects. The rejects are white and you can see where the old spot welds were on them. Anything that comes out of a DeWalt pack or out of the USA is usually fine.

The rejects probably work fine, it's just you can expect 2 in ten to be shoddy.

Thanks.

 

[jerrysimon]

I paid about twice that (£5) for my new cells with tabs.

I would have definately gone down the ex DeWalt pack, which are great value for money at those prices and are pretty much soldered up for you

I wanted to use new cells though to prove the concept (not original I know but original on this forum) so that other could follow on if they chose.

I am glad you have found it useful.

Regards

Jerry

 

[jerrysimon]

That's 16 cells, then. Suppose now that each 8 cell block provides 24v@2.26 Ah. Thats 8 in series. 24v {just taking the round figure} per strip.

I think that is wrong

At 3.3v nominal and 3.6v max that is 26v nominal and 28.4v max for 8 in series.

Regards

Jerry

 

[ELECTRIC AVENUES]

I think that is wrong

At 3.3v nominal and 3.6v max that is 26v nominal and 28.4v max for 8 in series.

Regards

Jerry

Yes, I just took the lowest figure of 3v per cell....I do this so the pack I end up with always has a few volts over what I want it to be.

For me, a 36v pack is one that has around 44 volts, if you see what I mean

 

[NRG]

Yes, I just took the lowest figure of 3v per cell....I do this so the pack I end up with always has a few volts over what I want it to be.

For me, a 36v pack is one that has around 44 volts, if you see what I mean

May not be wise to do that as you could end up blowing the controller FETs IE: for 48V using your calculation two 8s packs in series would give 48v and seem to be OK but when fully charged its 57.6v...that could blow some '48v' controllers out there which have a maximum 55v limit...

 

[ELECTRIC AVENUES]

Do these also contain the 3.3v-3.6v A123's??

Thanks.

 

[jerrysimon]

I don't think they do from what I recall reading. If you search the links in the earlier posts of this thread I think you can confirm.


Regards

Jerry

 

[ELECTRIC AVENUES]

I don't think they do from what I recall reading. If you search the links in the earlier posts of this thread I think you can confirm.


Regards

Jerry

So that's why they are so cheap...... Too bad I guess.

Cheers.

 

[jerrysimon]

Start voltage 43,04 V, temperature -13,6 Celsius, no wind. I got 7,63 km until the bike suddenly started to feel very sluggish. Here is the big difference compared to SLA batteries, their voltage drops little by little, but these new packs gave plenty of power to the end. I just connected the SLA battery and drove back home to check Turnigy screen (it was cold and the lcd screen was messed up).

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