DIY Battery

48Volt 10AmpHour DIY Battery Howto
An example build of a high power battery system for electric vehicles.

We've been building a DIY Battery System for our electric bicycle, an Ecospeed high performance electric bicycle.

The latest thing in high performance battery chemistry is Lithium Iron Phosphate,
and I just received my shiny new battery cells.

Warning : High Power Batteries are VERY dangerous!
These batteries can weld a nail (or your screwdriver) in seconds if you are not careful.
While Lithium Iron Phosphate battery chemistry is safer than most others,
there is always a risk of EXPLOSION if they are mishandled.
Take sensible precautions, like don't work on a metal table for example...
Always use eye protection and keep a fire extinguisher nearby.
Use the utmost care in handling these dangerous devices.
A good rule to follow (as with most high power electricity) is to use only one hand.
If you choose to use these simple directions as a guide,
Moxon Design will not be held responsible for any damages, black holes,
rips in the space/time continuum, or other maladies caused by your actions...

Shown below are the new Lithium Iron Phosphate cells that I received.

These are Headway 38120S 10AH batteries, where the "S" mean screw terminal connections.
As you can see from the picture below, I also ordered some plastic battery holders,
and some flat tie connectors, that will handle the large current (up to 60 Amps!) that
a high power electric vehicle system can draw.

Below are two of the 38120S cells in a holder next to an ordinary "D" cell battery for scale.

You alternate the Positive (+) and Negative (-) in each pair, so that they are all
connected in series. Each cell has a working voltage of 3.0 Volts.

Then you can use the flat tie connectors to join the pairs into a block.
I have 4 pair shown here (8 cells total), so that would be 8 x 3.0 V = 24 Volts.

Next I connect two of those blocks together, to make a 48 Volt battery.
The little electronics board in the front is the Battery Management System,
or the BMS for short. It makes sure the individual cells are balanced,
which means it keeps each cell's voltage between 2.7 Volts and 3.3 Volts.
It also acts as an electric fuse, if the battery should get shorted out by accident.
The BMS gets one wire run to it from each flat tie connection (i.e. each cell),
This allows it to balance the voltage on each each cell independently.

A view of the left hand side connections

A view of the right hand side connections

The local automotive/marine store had a simple, plastic, marine battery box.
It's mainly to protect the connections from shorting against anything metal
and provide an easier to carry around box.

And that's it, now you have a lovely 48V high performance battery that should
give you a range of 30-40 miles on your electric bike.

And for you geeky types out there, here are the battery specs.