DIY A123 battery pack

Patmanbbe

Been Around the Block
Greetings!

I was hoping to get some feedback as I have seen a few people build them on this site. I am planning out how to build my battery pack using the a123 battery cells. I am not sure how many cells I should use in my pack. I have seen a couple builds using 6 and a couple using 8. I found this link on the web:

http://www.scriptasylum.com/rc_speed/lipo.html

The guy has a sort of calculator that tells you what the output is using different number of cells. By his calculations if I use 6 cells in my pack it would result in a pack rated for 22.2v @ 3000mAh with a max discharge rate of 60 amps. I don't want to put out too much and I also don't want to over charge the battery during normal use on the bikes charging system.

Can anyone offer any advise here? Thanks!
 

SONICJK

Reminds me of...me No, I'm sure of it. I hate him
DIY A123 battery pack

You have to wire them in a combination of series and parallel so that your output is about 12-14 volts. Any more will fry your bulbs and coils and won't even be able to charge from your charging system.
 

SONICJK

Reminds me of...me No, I'm sure of it. I hate him
DIY A123 battery pack

Each cell is rates at 3.6 volts.
So if you used 4 in Series the voltages are additive and you will get 4x3.6=14.4 volts. And an amp hour rating that doesn't change from the single battery so it's still about 2.3 amp hours.

Now if you expand on this and you take two of the batteries above and wire them together in parallel, you end up with the same voltage at 14.4 volts, but with double the amp hour rating. So 4.6ah.

So with 6 batteries you would wire two sets of two batteries in parallel and wire those two sets in series with the remaining 2 batteries. To get to your 14.4 volts.
 

Patmanbbe

Been Around the Block
Ok so based on the specs of the cell from A123 found at the link below

http://www.a123systems.com/lithium-ion-cells-26650-cylindrical-cell.htm

and the feedback from Sonic.

Individual battery cell out put is 3.3V and 2.5Ah

8 cells total wired with parallel pairs wired in sequence would output the following:

4 * 3.3V = 13.2V

double the Ah at 5Ah because of the cells in parallel.

it would look something like this:
batterycellconfig_zps2bf151be.png


So I would have a battery pack with 13.2V and 5Ah.
 

firebane

braaaaaaaaaaap
I thought about doing this for my bike but then realized it was just easier to invest in a small 12v 5aH battery
 

Patmanbbe

Been Around the Block
If you buy more than 10 they are about $7 per cell. They also sell very similar cells at any hobby shop that has RC Planes and RC Cars. Similarly priced at a local hobby shop where I live though not the same brand.
 

SONICJK

Reminds me of...me No, I'm sure of it. I hate him
Just a heads up,
they are very particular as far as charging goes. You absolutely have to upgrade to a good regulator rectifier unit so as not to overcharge them. Also use a standard lead battery for tuning, because if you kill them theres a good chance that they wont be able to be recharged correctly.
Test and tune with a 20 dollar lead acid, and then when you finish up swap over to the nice one.
 

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