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Ben Brown

Electronics and Embedded Systems Engineering

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Contents

LiPro PCB

LiPro Micro

The LiPro Micro provides state of charge monitoring, passive balancing and safety discharge for lithium batteries. The key benefit to utilising the LiPro Micro on your battery pack is the high accuracy balancing of the internal cells, prolonging the life of the battery.

The key features of the LiPro Micro:

  • State of Charge display (Based on cell voltage curve)
  • Cell balancing (to within 5mV total error)
  • Safety discharge after 7 days idle
  • If pack sits at a high voltage for a long period of time the unit will discharge the pack down to a safer voltage level to prevent cell damage
  • Very low power usage. (<100uA)
  • Designed for LiPo and LiFePo4 (LiPo 4.1/4.2/4.3/4.35/4.4V & LiFePo4 3.6v) – Default profile supports most LiPo packs – Different curves can be selected to suit the connected pack – 3-5 Series cells supported (solder bridges on the back to select cell count)

Operation

Connect the small PCB to your battery’s balance plug. The board comes with a JST connector populated, this is normally a 3S but 3,4 or 5 is available on request. This is also very easy to change if you are used to soldering.

Display

The unit features a LED display consisting of 5 green and 1 red. When the unit first activates, it will show a LED pulse animation to test the display. (Starts on the left and moves right.)

Following this, the unit will display the detected cell count. If this does not match the connected battery, check the voltage of the cells to ensure they are okay. If the unit is still not detecting the correct number of cells, the unit may be damaged.

The unit then displays the SOC of the battery on the 6 LEDs.

If the pack SOC < 20% a single red LED will light to indicate this and then the unit will shut down into a very low power state. Otherwise, a green LED will light for every 20% of SOC the battery has. The LEDs will last for around 3 seconds and then go out.

If after this you see a dancing pattern of alternating LEDs, the battery you have connected needs balancing, as it is out by more than 50mV across the cells. We recommend charging the battery so that the unit can begin balancing the battery. The unit will begin balancing the battery once it’s above 80% SOC.

Status

When the unit is running it will check if the battery is above the storage voltage, if the battery is at this higher state of charge it will keep track of how long the battery is in this state. If the battery is in this state for longer than 2 days, the unit will begin discharging the battery pack to the storage voltage. If you wish to cancel the safety discharge, disconnect and reconnect the unit as this will reset the timer. If you do not wish to have this feature enabled, you can select battery profiles without this feature. If the unit is in the middle of the discharge, this is indicated by all the LEDs on the unit flashing on and off. The pattern is the middle two LEDs followed by the outer pairs, alternating.

If while the battery pack is above the set threshold the cells are out of balance by more than the threshold the unit will begin balancing the pack. While this occurs the unit indicates this by blinking the corresponding green led to the battery number that is currently being discharged. The green LED closest to the red LED corresponds to the lowest cell in the pack.

Use Case: Quadcopter batteries

One of the biggest applications for these modules is quadcopter batteries, as these are often charged with chargers of dubious quality and calibration. By using these modules to balance the batteries while charging lower quality chargers can be used without affecting the balance of the batteries. We highly recommend leaving the module plugged into your batteries whenever you can. Removal for flight is entirely your choice and highly depends on how your battery is mounted into your craft.

I personally use these modules on all of my batteries and have it plugged into the battery unless I am charging. This provides all the safety features with very little effort. By having the modules on the batteries when they are charged, if I charge my batteries to go flying and then something happens and I don’t fly, the modules ensure forgotten batteries are not damaged.

Use Case: LiFePo4 12V Battery Bank

I Use one of the 4S modules on my LiFePo4 battery bank to balance the cells when they are charged. While this was slow initially as they came fairly out of whack (around 0.15V error cell to cell), the back now rarely balances. Make sure when using a module for this, to disable the safety discharge.

Safety Discharge

When a lithium cell is sitting at a higher state of charge, the chemistry is not at a stable equilibrium. This imbalance is what leads to capacity loss when a battery sits charged. If you run your batteries down in heavy use cases (Such as quadcopters), when you take the cell off duty the open circuit voltage will slowly rise back up due to the chemistry of the cell stabilising. The unit monitors the battery, and when it has been left for a long period of time it will slowly discharge the battery. This prevents the battery being damaged by the chemistry degrading.

Force Safety Discharge

If you realise your not going to use the battery for a while, or have another need to store the battery, you can force the unit to skip the timeout and go straight to safety discharge mode. To enter this mode, you need to push the button while the unit displays the SOC 5 times. You will know when you reach the count, as the unit will show one cycle of the discharge pattern before the SOC. Note: If your battery requires balancing, this will be performed before the safety discharge will start

Changing cell count

Changing the cell count for the unit is really easy soldering. On the back of the unit is a set of solder jumpers that are used to set the cell count for the unit. These are marked which cell counts they are required for. Make sure all the ones not required for your cell count a disconnected.

You will also need to swap out the connector on the unit to match the desired cell count (depending on connection method).

Setting the chemistry/battery profile

The unit comes pre-programmed with four battery profiles. These are :

  1. Generic LiPo profile (Should work for all)
  2. Li-ion/Li-Poly 4.1V (Lower voltage scale / storage voltage)
  3. 4.3V Li-Poly HV (Higher voltage scale / storage voltage)
  4. LiFePo4 Generic Profile

ID Display

When changing the chemistry the unit displays the battery chemistry id in binary on the LED display. The red LED is fixed on while displaying the value. The green LED closest to the red LED is the lowest ‘bit’. This means the patterns are:

  1. green-red
  2. green-off-red
  3. green-green-red
  4. green-off-off-red

To change the profile:

1. Connect the unit to the battery
2. On the back of the unit, there are two metal pads marked for changing the profile
3. Using a metallic object, join these two pads
4. Press the button on the front of the unit
5. The unit will display the ID of the new profile
6. Press the button repeatedly until the desired id is displayed
7. Remove the link between the pads
8. Press the button again to exit the battery chemistry setting mode

Note:

These modules are entirely designed and produced in Australia, however, the PCBs are produced in china due to lack of local manufacturing options. Currently, these modules are hand assembled and tested. So if your unit arrives DOA or you are having issues, please contact me or the distributer you purchased through.