Building a small A123 Battery Pack

[NRG]

For balance charging I use a Turnigy 8150 and for normal pack charging a modified Mean Well CC/CV psu set for 29v to give me a 4.15v cell charge on my 7s3p battery. I parallel connect the balance taps when using the Mean Well to help them keep even better balance.

So far I've only needed to balance charge once every 10 charges and in fact I could leave it to 1 in 15 as the cells seem to stay within 20mV of each other. Keeping the Lipos within the 4.15v ~ 3.2v region extends their life apparently 800~1000 cycles possibly more, so I'm very happy with the setup at the moment.

 

[jerrysimon]

Thanks NRG, cool setup.

Ok been out in the workshop and built the second 6s pack. Here they are on the scales connected togther.

They still both need to be shrink wrapped and with this the total weight is probably going to be around 1kg.

This is the series lead to connect the 2 * 6s packs together for the final single 12s * A123 pack..

Both packs have been fully charged and balanced so connecting them together we get a voltage of 43v

43.2 = 3.6v/cell allowing for the inaccuracies of my cheap multimeter.

I tested the battery with the motor in the forks and everything works great. On the actual connection to the controller I will probably use a better connector and put in a fuse and an on/off switch. I noticed the voltage drops pretty quickly to 41 volts after I ran the motor for a while.

Just need to build the motor into the wheel and I will be ready for the first test ride

Regards

Jerry

 

[daniel.weck]

This is going to look very good !

Please let me know what switch you will use to isolate the battery. I read on the German Pedelec forum about using a MOFSET circuit to make the switch operation safer (apparently the kind of spark that occurs with certain switches may damage the controller...I don't really know).

Anyway, I have an inline car fuse on the red positive wire coming out of the battery, a high-quality connector between the controller and the battery, but I'd like to add an easily-accessible switch near the battery so I can "turn the bike off" when I temporarily park at the shopping center / whatever (otherwise the back-lit Cycle Analyst remains on and of course the handle bar throttle is active).

My most important requirement is that the switch must be splash-proof and big-enough so I can use it with gloves. I currently disconnect the main connector but it's a hassle.

Many thanks, Daniel

 

[jerrysimon]

Well its Christmas Eve and the heat shrink turned up today beating the last day of Christmas post as did the nipples so we are set to go

Not sure if I will get to build the wheel though, as being Christmas Eve there is a lot to do with familiy arriving tomorrow.

This is such a great forum for sharing and getting info on our hobby.

Happy Christmas and the best for the New Year to you all

PS My A123 cell suppliers now sell rather nicely made up 6s packs here

Regards

Jerry

 

[daniel.weck]

PS My A123 cell suppliers now sell rather nicely made up 6s packs here

Thanks for the heads-up, and merry xmas to you all !

 

[Herb]

PS My A123 cell suppliers now sell rather nicely made up 6s packs here

Support Britsh Industry - Order from Jerry

 

[jerrysimon]

Lol it was traumatic enough making up my own packs, not sure I would want to turn it into a cottage industry. The margins would never be worth it.

Those made up packs are excellent value and take a lot of DIY hassle out of the equation.

Regards

Jerry

 

[jerrysimon]

Ok now that I have had my first test ride on my E Brompton a few final posts on the batteries.

Here is a battery taped up and then covered in some 100mm shrink wrap

They weigh between 480g and 485g so total weight including serial lead is about 0.97kg. I need to sort out some velcrose to strap them together.

After the first 3 mile ride (using a lot of throttle but mainly on the flat and a couple of inclines) I put them on charge using the cheap ebay charger referred to before. Within 40mins they were charged and the light went from red to green. Note for this charger the two 6s packs are connected in series. Thus this is charging them at 36V/1.6amps. Intially I don't want to run the pack right down. Once I have a few charges through, I will then test the full range.

After the first ride the voltage was down at 39.7V i.e. nominal voltage of 3.3V/cell. Checking with the Turnigy they were all still in balance. After charging with the above charger I checked with the Turnigy and it had again brought the cells up to a balanced voltage of 3.6V/cell. So all looks good.

Over the next few weeks I will post updates on the condition of the pack. I am hopefull that this is a really neat, light and inexpensive battery solution for short journeys. We will see. To build this 2 * 6s, A123, 39.6V. 2.3Ah pack yourself incl the cheap ebay charger works out at about £75 using new cells, cheaper if you use ex Dewalt tool pack cells. If they don't need balancing that is not bad. If they do then the Turnigy charger adds about another £40. I may build a second pack later depending on how this pack performs. Even then as I said a second charger at work would work too.

Regards

Jerry

 

[daniel.weck]

I like your 12s battery layout, as the individual 6s packs (each with their own cell header connector) can be balanced individually using a cheap charger.

I'm looking into a layout that would allow me to use my spare Tongxin-powered 36V e-bike as a short distance runabout (i.e. low A/h capacity), but that could also be used as a booster pack for my main Bafang-powered 36V e-Brompton (i.e. not to add more capacity to my 10Ah battery, but to add extra voltage above 36V => more power)...just thoughts, I need to check whether it's technically doable (I'm not even sure my controller can handle anything above 36V nominal).

Cheers, Dan

 

[emissions-free]

Hi Daniel,

I've run 2 identical 24V LiFePO4 packs in series to make 48V but I believe the series packs should be the same type or at least similar. This setup ran just fine and didn't cause any problems. I don't know what would happen if you ran a much smaller capacity battery in series, which also had very different discharge characteristics.

Were you thinking of putting the 2 * 6S packs, paralleling them and then in series with your main pack? You might get away with that, but putting 36V of booster packs in series with your main pack, might make some probs...

 

[daniel.weck]

Thanks ! I thought it would be a bit more complicated and I intend to do a bit more research before doing anything stupid

 

[jerrysimon]

Ok another finalish pic of the 10amp blade fuse I have put on the 2 * 6s1p connected packs.

Once I get my Turnigy meter I may reduce this to 7.5amp if I can show that it does not draw more than that in my Tongxin/Brompton application.

Regards

Jerry

 

[daniel.weck]

Don't forget to keep spare blade fuses (of various ratings) with you when you go for a ride

 

[NRG]

Ok another finalish pic of the 10amp blade fuse I have put on the 2 * 6s1p connected packs.

Once I get my Turnigy meter I may reduce this to 7.5amp if I can show that it does not draw more than that in my Tongxin/Brompton application.

Regards

Jerry

Don't go too low in value, you may want to rate the fuse at 150% of your peak current draw but no more than the current rating of your wiring.

 

[jerrysimon]

Thanks guys. Yes at the moment I am carrying a 15amp fuse out when I go

All my wiring is rated at 15amp at the moment. Lets hope that when I get the Turnigy meter and find its pulling 20amps, I won't have to upgarde it all

Everything is running cool at the moment but then its below freazing outside

Concensus is that the Tongxin should not really have more than 10amps pumped into it anyway.

Regards

Jerry

 

[NRG]

There's a power chart here:

Hangzhou Zhejiang University Tongxin Electricity Company

Not sure if this applies to your motor Jerry but this seems to indicate approx. a max. 13A peak draw so maybe you have the correct fuse already....certainly no more than 12Amp at 80% efficiency....

 

[jerrysimon]

Thanks for that NRG. I reduced the 15amp to a 10amp one today though I did not try it on any hills just the level. I have a 15amp one in the bottom of the bag should the 10amp blow whilst out riding.

Once I get the Turnigy Meter I can test everything in real time to comfirm

Regards

Jerry

 

[john]

I found that the Tongxin controller limits to 12A, as per the spec., with a brief peak of about 15A when you open up the throttle.

 

[jerrysimon]

Just a quick update the 12v, 10amp fuse blew today so the 15amp fuse is back in

It happened when I let a colleague at work ride it and I think he just opened the throttle up to full. I also spoke to the electronic guys at work and they said its probably because its a quick blow fuse and the occasional surges progressively damage the fuse.

Anyway once I get my meter I can test the actual currents involved.

EDIT** oh thanks John I just saw your post which lines up with what your saying.

Regards

Jerry

 

[NRG]

...and the chart I linked to earlier LOL!

Just fitted a Watts UP to my DIY special and was shocked to see an 850W and 30amp peak 30amp is the current limit of the controller maybe I need to think about heavier gauge wiring