SparkFun Forums

[dolphinair]

Hello,

I'm a 23 years old boy, and I started 2 weeks ago with arduino. I have a project in mind, and some things go wrong.

I have 6 Polymer Lithium Ion Batteries: https://www.sparkfun.com/products/8483
And I have 3 USB LiPoly Chargers: https://www.sparkfun.com/products/10161

I need the batteries to supply a Big easy driver: https://www.sparkfun.com/products/10735

I want to put the batteries in pairs to increase the cappacity, and I need to connect the 3 pairs of batteries in serial mode.

I want to switch from a circuit to charge the 3 pairs of batteries to the 3 chargers, to the serial mode to supply the big easy driver and the motor.

I understand that I can not connect batteries in series for the output 'Sys Out' shippers.

I tried to make a circuit with switches, but I'm lost when I have to connect the batteries in series. I have this circuit:



Can someone help me?
Thank you so much!!

[DakLak]

First, messing with batteries can cause fires. Ask Boeing.

To INCREASE VOLTAGE, you connect batteries in SERIES. To INCREASE CURRENT capacity (amps) you connect batteries in PARALLEL.

BUT there are other precautions needed.

If you look at the schematic of the Big Easy < http://dlnmh9ip6v2uc.cloudfront.net/dat ... er_v12.pdf > in the lower, left-hand corner you will see that the two sets of power connectors. There are no 'protective' devices (diodes or resistors).

SERIES-PARALLEL CONNECTIONS



Here is another example.

BUT don't go connecting them YET!

ADDING A SERIES DIODE TO SERIES BATTERIES
You will need to add a DIODE (1N4004) in series at one end of each pair of series batteries. Then you can connect the series batteries in parallel, The diodes prevent the strings of batteries from interacting with each other.

ADDING RESISTORS TO PARALLELED BATTERIES
When you connect batteries in parallel, there are small variations in voltages, which can end up in them discharging each other. An extreme of this can actually cause certain batteries to catch fire (the Boeing effect). To limit this effect but not eliminate it is good practice to put a 1 to 5 ohm resistor in series with each battery then connect all the free ends of the resistors together.

A rule: IF IN DOUBT, DON'T!

Remember, batteries aren't 'just' batteries, telephone companies employ battery technicians who do nothing other than look after batteries.

The USB chargers should NOT be used. (1) They will only supply 500mA per USB outlet (not all USB connectors are 'power' feeds). (2) If you charge cross connected batteries (series or parallel) in circuit they will likely destroy something in the feed.

Better to either charge the batteries OUT OF CIRCUIT (NO connections) or get properly sized, mains fed, chargers (voltage and current ratings).