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LiPo USB Charger Hookup Guide
Introduction
We love LiPo batteries! They pack a walloping, power-supplying punch in a
tiny, flat package. And, they’re incredibly easy to recharge, when that time
comes. If you’re looking to make your project mobile and easily
rechargeable, we can’t recommend this pairing enough: an 850 mAh LiPo
battery and an embeddable USB LiPo charger.
This tutorial will explain how to use the USB LiPo Charger with any of our
single-cell LiPo batteries. We’ll focus on the LiPo Charger and Battery
Retail kit, but this information can be applied to that charger and any
compatible battery.
Required Materials
• USB LiPo Charger
• A single-cell LiPo battery
◦
The charger can be made to work with batteries of any
capacity, including 40mAh, 110mAh, 400mAh, 850mAh,
1000mAh, 2000mAh, and the 6000mAh fatpack.
• A
5V power source,
options include:
◦
A computer USB port with attached mini-B USB cable
◦
A USB Wall Adapter and mini-B cable
◦
A 5V Wallwart Supply
Suggested Reading
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• Battery Technologies – Learn all about the different kinds of batteries
used in portable projects, including the one most applicable to this
tutorial: LiPos.
• How to Power Your Project – LiPo’s are a great power source, but
their not the right choice for every project. This tutorial will help you
figure out which power source is best for you.
• Voltage, Current, Resistance, and Ohm’s Law – There’ll be quite a bit
of talk about current and resistance, so make sure you understand
how they’re related with voltage.
Inputs and Outputs
On this page, we’ll dissect the USB charger, examining all of the inputs,
outputs, and specifications of the board.
Charger Input – Power Supply
First, you’ll need something to supply power to the charger, so it can
regulate power to the battery. Connect your power supply to one of these
two inputs: a
barrel jack
(5mm outer diameter, 2.1mm center pole, center-
positive) or a
mini-B USB
connector.
Your power
supply voltage
should be
between 4.75 and 6V.
A 5V USB
supply – from a mini-B cable connected to either a computer USB port or
wall adapter – makes for a perfect power source. Or, if you want to use the
barrel jack input, we recommend the 5V wall adapter.
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The
current requirements
of the supply will depend on how you’ve set the
charge current on the board. By default, the charge current is set to
500mA,
so make sure your supply can handle that. Computer and laptop
USB ports are most suspect here; 500mA is the defined max a port can
supply, and oftentimes they’re set to have an even lower output than that
(e.g. 100mA).
You can safely attach both a 5V wall-wart and USB supply to the board.
There is some protection (diodes!) on-board to prevent reverse current. The
higher-voltage supply will source power to the chip.
Charger Output – Single-Cell LiPo Battery
Once you’ve connected a power supply to your charger, the next step is to
connect a battery. This board will only charge a very specific battery, make
sure it meets these requirements:
•
Single-Cell Batteries Only
– Your LiPo should have a nominal
voltage output of about 3.7V, and get up to around 4.2V at a full
charge. That means single-cell LiPo’s only. If you have a multi-cell
battery – something with a nominal voltage of 7.4V or more – this
isn’t the charger for you.
•
Battery Chemistry
– The charger will only work with
Lithium-
Polymer or Lithium-Ion
batteries.
•
Capacity Considerations
– To avoid explosions (which are only
very briefly fun), you shouldn’t charge these LiPos at a current over
1C. That means a 500mAh battery shouldn’t be given a charge
current over 500mA, a 100mAh shouldn’t be charged higher than
100mA. This board is designed to charge at 500mA out-of-the-box,
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but it’s easy enough to change that rate. See the next page if your
battery’s capacity is under 500mAh.
All of our compatible batteries are terminated with a white
JST connector,
which you can plug directly into the mating black connector next to the
BATT IN→
label. If your battery is terminated with some, weird, non-JST
connector, you can also use the
un-populated 0.1"-pitch header
directly
behind the JST connector. Wires or other connectors can be soldered to
this header, if desired.
System Output
The LiPo USB Charger is designed to be easily
embeddable inside a
project.
The
←SYS
OUT
connector allows you to connect your battery
output to the remaining parts of your project.
You can use the “SYS OUT” header to power a 3.3V Arduino Pro. All while
leaving your battery connected to the charger.
As with the battery connection, you can use either the JST connector or the
nearby 0.1"-pitch header to connect your project.
The
SYS OUT
output will connect your project directly to your battery. That
means the battery supply voltage (somewhere between 3.6 and 4.2V) will
power your project. Make sure you regulate that as necessary.
Charge Status LED
The on-board red
Charging
LED can be used to get an indication of the
charge status
of your battery.
Charge State
LED status
No Battery
Floating (should be OFF, but may flicker)
Shutdown
Floating (should be OFF, but may flicker)
Charging
ON
Charge Complete
OFF
If you want to add your own, larger LED, there’s an unpopulated footprint
where you can solder either a 3mm or 5mm LED in the tiny (but bright!) red
LED’s stead. Make sure you get the polarity right, though.
Setting the Charge Current
Before you plug a battery into the charger, you should be aware of your
battery’s capacity
and the
charge current
supplied by the charger. To be
safe*, you should keep the charge current
at or below 1C
of your battery.
That means you should charge your 850mAh battery at 850mA or less, and
a 100mAh battery at 100mA or less.
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The charge current controls
how fast your battery will charge.
If you have
a 1000mAh battery, charging at 1000mA will fully charge that battery in 1
hour. Charging it at 500mA will mean a full charge takes twice as long – 2
hours. So more charge current is better…as long as it doesn’t exceed your
battery’s specifications.
The featured component on the LiPo USB Charger board – an MCP73831
– has a
programmable charge current
feature. It can be set to deliver
anywhere
between 15mA and 500mA
to a battery. To program that value,
a resistor is connected from the
PROG
pin to ground. There are already
two resistors on-board, which can set the charge current to either 500mA
and 100mA. A small jumper is used to select between those. You can also
add your own resistor, to set a custom charge current.
Jumper-Selecting
Next to the charge-status LED there are three bare pads that form a
two-
way jumper.
The center pad connects to the MCP73831’s
PROG
pin, and
the outer two pads connect to a pair of resistors. The labels next to those
outer pads indicate the charge current that they set.
If you look
really
closely at that jumper, you may see a small trace
connecting the middle pad to the
500mA-labeled
outer pad. As such, this
board is
configured to deliver a 500mA current by default.
To change the charge current to 100mA, you’ll need to
cut that small trace
between the pads (a hobby knife is recommended), and apply a solder blob
to connect the
100mA-labeled
pin to the center pad.
As an advanced trick, you can short both pads to the center (connecting
both resistors in parallel) to set the charge current to 600mA.
Custom Charge Current
If neither 100mA or 500mA will work for you, there is an unpopulated
resistor footprint to allow you to set a custom charge current.
Before adding the resistor,
disconnect both jumpers
discussed in the
section above. Then use this equation to select your resistor:
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