Building a small A123 Battery Pack

[Scottyf]

Discharge + Charge = 1 Cycle.
Basically everytime you re-charge. But a full cycle should really be from full to virtually empty.

I balance charge each time. Only because it takes me an extra 30 sec's to plug in the balance leads and generally as I'm not using a cell log etc I'm just trying to keep each of the cells inline.

So far there all equal bar one cell which appears to be alittle weaker by 0.02v but nothing to worry about!

 

[jerrysimon]

Scott,

So do you split the packs down to charge them/have a couple of dedicated lipo charger/balancers ?

The LiFePO4 chemistry is definately safer than Lithium Polymer (I have used lipos a lot in my RC hobby), remain in balance better, can cope better with under/over charging and can be left safely unattended to charge.

I guess what this proves though, is it is worth balancing the A123, LiFePO4 packs occassionally.

I would only recommend A123 cells though for smaller packs as say, a 10ah one would get expensive and pretty big/heavy. In my application of a pretty flat 10 mile round commute, they have proved excellent.

Regards

Jerry

 

[vhfman]

Jerry

I hope your A123 battery pack is holding up OK with the new/old cell configuration.

I have some 2.5 year old Headway 10Ah cells that I have still been using this summer. The original battery came with a built in BMS which at first seemed to work OK. But after a few months use I noticed I was not getting the expected range with the battery. Investigating the lack of range I measured the cell voltages and found that the BMS was not balancing the cells correctly. I saw that one or two cells were always taking longer to charge and a couple would appear to charge much faster. Although the BMS details indicated that it would protect against over charge at the cell level. I was concerned that the two cells that charged faster would shoot past the over charge 3.65V limit going well over 4V. I was not happy with the BMS so I decided to remove it completely. Since then I now manually charge the battery cells with 2 dedicated Lipo/LiFe balance charges (icharger 106B+) I split the battery up into 2 X 6S packs to charge and monitor, I then connect them in series 12S on the bike. This has allowed me to charge and monitor individual cells and balance each 6S pack, which I do on a regular basis. I have found that the cells are now holding up much better than they were with the original BMS arrangement. The cells seem to hold their charge more consistently and despite now being over 2.5 years old are still giving very nearly the full 10Ah capacity.

Earlier this year, thinking that the Headway cells would be on their way out soon, and wanting a more flexible battery pack for different trips which I can alter from a small 12S1P to a larger 12S6P. I followed your example and made up some A123 packs, like you from OMG. This arrangement is working well, I think that the A123’s hold their voltage under load better than the Headway cells, but of course they are much newer.
I suspect that OMG cells are not the real A123 Systems ANR26650M1-B’s at the price they are. But they do seem to be a good buy and your small packs have done well over nearly 2 years of daily use.

I hope your new/old pack will continue to work OK for you, but it’s worth keeping an eye on cell balance for a while.

Chris

 

[jerrysimon]

Interesting read Chris. I am not sure as you say if the OMG cells are genuine. That said I have found a video on Youtube that claims OMGs batteries are not genuine. I took the wrappings off and they seem to be match the battery he is holding. All a little confusing.

[video]http://youtu.be/t6WPzcz-FQg[/video]

As you say though even if they are not, they seem to perform and work well and have more than paid for themselves over my last 2500 miles.

Regards

Jerry

 

[Scottyf]

Scott,

So do you split the packs down to charge them/have a couple of dedicated lipo charger/balancers ?

Generally yes I do each night. I could just bulk charge but for the 5 mins it takes me to actually pull apart my wiring harness and attach the para board its really not worth it.

The below image shows how I generally charge the Lipo.
Obviously this setup is not really portable unlike my old Ebike battery that was in an alloy shell plus a nice compact AC/DC convertor @ 2amp 42v (84watt).

But this does give me close to a 185watt charging power which is about the cheapest setup I could get without buying larger power supplies / lipo charger etc.
I don't have the space in an apartment or a garage to really tinker around properly. I'm forever in the bad books with the wife.
This allows me to effectively balance charge the 4 lipo bricks @ a total of 440watt nominal in about 2.5 hours. In the future I'm sure I will go to something bigger but for now its proving to be reliable.

I do miss the ease of clicking in a charger and battery BMS combo and forgeting about it while it charges. But i've swapped ease of use with flexibility and weight.

So Xbox 360 Power supply (12v 16.9amp), 3 PC fans @ ttl 3w for cooling, Lipo charger, Paraboard for parallel charging Lipo bricks.

 

[jerrysimon]

Well although the cell seemed to have recovered (though never really took a full charge after I knackered it) I found that whenever the pack approached discharge, the suspect cell got hammered and its voltage went down to below 1 volt!

I fully charged the pack and then took another new spare cell I had and this time fully charged it before I replaced the dodgy cell.

That seems to have done the trick. Oh well you live and learn

Overall I am still very pleased with these little packs. So much so I have ordered a third pack. I especially like the fact that they can be easily disassembled and the odd/duff cell replaced. Just need to make sure the pack and specifically the new cell, are fully charged before you use it.

This pack seems to still have plenty of life in it at two years old, 2500 miles and about 500 cycles to date. I will keep the thread updated when the pack finally fails.

Finally as said before, I think its worth balancing the pack every few month or so if using daily.

Regards

Jerry

 

[NRG]

Hi Jerry, could you remind me where you got the cells from please...

Thanks.

 

[Scottyf]

How is the cell performing now anyway now that you've single charged it back in balance with the other cells?

I've decided to buy some more Winforce Lipo from Ebay to see if its any good in an ebike application.
There rated at 20c Burst, 15c Continous so really should have enough C rating to cope but there not that good in high draw applications in the RC world as well as the capacity not being as high as other makes like Zippy or Turnigy.

But for a cost of 3.8 watts for £1 its pretty good and would mean you could buy a 20ah @ 44.4v for £240 if it is a good buy for a lower C rating.
The above is also shipped.

Will see how it gets one.

 

[jerrysimon]

Hi Jerry, could you remind me where you got the cells from please...

Thanks.

I get them from this ebay seller.

He sells them individually or in packs made up with balance leads and power connector. If you do buy them individually, I strongly recommend you get them to weld/glue them up into the config you want as it saves loads of hassle and time doing it yourself. They do them nicely with a spot welder. They are still easy to seperate later if you have to swap one out.


I notice these are on speciall offer in the UK if you want them in the supplied configuration. They use an odd balance lead JST-PQ though that will require a converter JST-PQ-XH.

Regards

Jerry

 

[jerrysimon]

How is the cell performing now anyway now that you've single charged it back in balance with the other cells?

Scott that was the new replacement cell that sort of recovered after the single charge, but still whimped out when I took the pack to full discharge. I must have damaged it when it went down to 0.5 volts when I put it in the pack without fully charging it.

Now I have swapped it out again with a fully charged one this time that seems to be holding the charge fine

Regards

Jerry

 

[Scottyf]

Lesson learned then I guess. Must have knocked it badly taking it to that voltage.
I guess thats the nice thing about the Ni-hm batteries is the flexibility to give them a kicking and yet they still soldier on... to a degree.

Glad you got it sorted though!

 

[jerrysimon]

By chance my third pack turned up from HK today. Two 6s1p packs in the config I favour most.

I have to say their pack config/welding service just gets better and better. The complete 2 * 6s1p packs work out at just over £60 incl p&p though you then have to add leads.

I checked each cell voltage and they were all identical. For each 6s1p pack I just add a balance lead, a power lead, wrap it up in gaffer tape, run it across a Turnigy balancer/charger and I am ready to go

As I said you can buy them ready made in their 6s1p config wrapped with balance and power leads attached.

Regards

Jerry

 

[Scottyf]

Definetly one of the cheapest sources of a123 cells at a similar cost to the cheapest lipo so it's a very good deal.

 

[jerrysimon]

There has been some question over whether they are genuine A123 cells. IMHO they are and even if not, their performance in the ebike application is excellent.

Remember they are only 2.3Ah though, so not necessarilly the best choice for all ebike applications. However for longer journeys you can always take the associated number of packs you may need.

Equally they make a very good cheap backup/reserve pack for a regular larger battery if you are uncertain if your main battery will last a trip.

Regards

Jerry

 

[NRG]

Many thanks Jerry.

I get them from this ebay seller.

He sells them individually or in packs made up with balance leads and power connector. If you do buy them individually, I strongly recommend you get them to weld/glue them up into the config you want as it saves loads of hassle and time doing it yourself. They do them nicely with a spot welder. They are still easy to seperate later if you have to swap one out.


I notice these are on speciall offer in the UK if you want them in the supplied configuration. They use an odd balance lead JST-PQ though that will require a converter JST-PQ-XH.

Regards

Jerry

 

[Scottyf]

Yeah but you could ask them to make you a custom pack and then all you need to do is add a smart Bms and case and it's job done.

 

[Deleted member 4366]

What's the advantage of these cells when you can get 4 times the capacity of lipos for the same price and lighter?
18.5v 5200mAh 20C LiPo 5S 18.5 Volt RC Akku Battery WF | eBay

 

[Scottyf]

Lifepo4 chemistry and if you puncture them they don't explode lol.
I have brought some of the above lipo to extend range. The winforce batteries don't appear to get very good write ups but they might be very good for a cheaper lipo setup.

 

[Deleted member 4366]

Lifepo4 chemistry and if you puncture them they don't explode lol.
I have brought some of the above lipo to extend range. The winforce batteries don't appear to get very good write ups but they might be very good for a cheaper lipo setup.

I've been using these Winforce lipos for about 9 mont

hs and they work really well. Capacity is the same as always although was only about 8aH rather than 10.4aH from the beginning, but I'm not complaining at that price. If you're worried about puncturing, you can always put them in a box and they'll still be lighter than A123s.

 

[jerrysimon]

I agree at face value Lipos look the better option. I have extensive experience with Lipos when I use to do a lot of RC flight. I know many DIY ebike enthuiasts use them successfully and are content. If used with caution I am sure they are fine.

For me personally I want a battery I can just use and forget about. Using Lipos on my ebike is just a risk I am not prepared to take. My pack goes into work and is often charged at work too. I know that I can just leave them charging safely if I get called away. In my application I guess a larger lipo pack would not require charging at work though.

The A123 cells are also reported to have a longer life (1000-2000 charge cycles) than lipos and can be charged for several months using a cheap charger without balancing.

I have made my daughter, who suffers from M.E. , an electric bike and I would not want her carrying or using lipos on her bike either. For her I even enclosed the A123 pack in a DIY box with a more robust power connector and a switch. All my packs are also fused. Maybe over cautious but I wanted to make certain it was plug and play and all very safe for her.

Regards

Jerry