Need help to build a 12V 40ah battery pack

[robypez]

Hello everybody, my name is Roberto and after some useful lecture here I'm trying to build my first battery pack.
I need to power a trolling motor for a catamaran, and at this moment I'm using a Lipotech 45 Ah battery LiFePO4. The battery is perfect for my engine, but the weight and the "shape" is not so easy to manage on my small boat. In the sealed marine box the battery is huge.
So I thing to build a light battery pack in a small and long shape to "hide" under the structure, but I have some questions.

I think to use Panasonic batteries, 2900 mAh and 3.6V. Using 40 batteries, 4 in series and 10 in parallel I will obtain, If I understand some FAQ here, 14,4V and 29 Ah.

First question: is there a way to obtain a lower voltage, maybe with a different cell type?
Second question: I'm trying to find a PCB to manage my battery pack but I don't understand which type of PCB could be ok for me.

Thank you su much, I'm trying to learn here but there are a lot of topic about 24V or 36V battery pack...

Here some data of the engine:

power 32lb, 312 watt(max speed), 0,42cv, 12volt, 26A,

 

[e-beach]

robypez Hello, first things first...

I think to use Panasonic batteries, 2900 mAh and 3.6V. Using 40 batteries, 4 in series and 10 in parallel I will obtain, If I understand some FAQ here, 14,4V and 29 Ah.

Those batteries would work. How-ever they are expensive. When you order them from your vender, inquire if they have tab welding services so you don't have to solder them together.

First question: is there a way to obtain a lower voltage, maybe with a different cell type?

Ok, my question is why do you want to lower the voltage of your pack? Fully charged lead batteries are 14.4v and fully charged 4s LiFePO4 is 14.6v. So why do you want a lower voltage.

You also have the option of using a balance charger instead of a BMS/PCM. Undercharge the batteries a little to achieve your lower voltage. I would recommend something like a Cell-log 8M to give you notice when the battery is drained in-case you can't see the volt meter has reached 12v under load. The Cell-log has an alarm to remind you.

Second question: I'm trying to find a PCB to manage my battery pack but I don't understand which type of PCB could be ok for me.

If you want to get a protection circuit board you could find one on ebay, although some of us have bought them from Bestech Power http://www.bestechpower.com/148v4spcmbmspcbforli-ionli-polymerbatterypack/

 

[robypez]

Thank you so much. I added the location to my profile, Italy!

So I can keep 14.4V...

I want to create a cylindric like shape, so I think that I can align 4 batteries in this way ---- placing a conductor between them.

I already look and that website for the protection circuit board, but I don't understand which model is the best for me (how many ampere?)

 

[999zip999]

26 amp so a bms like 40a with spikes. Just a guess but a watt meter it will tell you. Plus it will tell you the ah you have taken out of your battery or as a fuel gauge.
In the ebike technical section look for "ebike tool box bargains" by DrAngle. Cheap Solutions.

 

[e-beach]

99zip999 makes a good point. A 100 amp RC watt meter inline with your existing battery will tell you a lot of useful information like Amps peak watts peak ect. They can be found on eBay for under $10 USA.

So before you purchase a BMS/PCM get a RC watt meter and look at your current draw and that will tell you what amperage BMS to purchase.

If you can find complete specs on your motor please post them.

Also, the balance circuit of the BMS may not kick in until the cells reach 4.2v so if you don't fully charge the cells to the saturation point, in this case 4.2, then the pack might never balance correctly causing problems and loss of battery life down the line, not to mention the outside risk of a fire.

This is why a good balance charger and corresponding power supply might be a better option for you. With a programmable balance charger you could set the charge to say...3.6v per cell and then you won't over volt your motor.

You will probably lose some of the rated amps due to a lower then standard charge so consider a 5s or 6s 10p pack to make up for the lack of a full charge.

 

[Willow]

...easiest solution is 4 of these cells - http://en.calb.cn/product/show/?id-626