Monthly Archives: April 2018

Solar Li-ion charger board for sensor nodes

Apr 29

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We got our first batch of 100 machine assembled solar Li-Ion charger boards useful for powering all kinds of outdoor electronics like wireless sensor nodes and associated sensors/actuators etc.

 

li_ion_c_april_29_18_v1

 

 

Here are the specs for the WLIBPSU v4.0

  • Max  input (solar panel) voltage:  10.5 V
  • Max charge current: 2  A
  • Max  battery discharge  current: 4 A
  • Li-Ion battery charged in 3 phases (trickle charge,  pre-charge, constant  current and constant voltage).
  • Battery under-voltage lockout supported as load is not connected directly to battery.
  • Charger IC can power the load and charge the battery simultaneously.
  • NTC thermistor as required by charger IC.
  • Multiple output voltages (On separate headers/connectors)
    • ~3.3V  (Max 1 A)
    • 4.9V (Max 50 mA)
    • Li-Ion battery output (Max 4A). This supply is gated by a load switch which can be controlled by a signal external to the PSU (for example – by an external micro-controller).
  • On PCB current and voltage sensors (two ICs) which measure the parameters listed below. All values reported over a single I2C bus.
    • Solar panel output voltage
    • Solar panel output current
    • Battery voltage
    • Battery current
      • Positive values reported when battery is getting  charged
      • Negative values reported when battery is getting discharged
  • PCB specs
    • Layers: 4
    • Dimensions:  48.5 mm x 48.5 mm
    • Mounting holes:  4
    • Finish:  HASL
    • All terminals are 2.54 mm pitch

Assembled in Bangalore using genuine components (including passives) from USA.

We have tested this PSU with a 3W solar panel and  2600 mAh Li-Ion battery.

Test Panel Specs

  • Peak  power: 3  Watts
  • Voltage output at peak power point (Vpeak): 8.5V
  • Current output at peak power point (Ipeak): 300 mA

Test Battery Specs

  • Chemistry:  Single cell Lithium-Ion Battery
  • Capacity: 2600  mAh
  • Output voltage: 3.7 V  (nominal), 4.2 V (full charge)

 

Here is a pic of a WiSense 866 MHz wireless low power wireless node (WSN1120L) powered by the  WLIBPSU v4.0.

Charger PCB, enclosure and battery are inside the enclosure

solar_psu_pic_1

 

 

Battery Voltage Data

solar_2018_may_graph

In the snapshot above, you can see the Li-Ion battery voltage falling during the evening/night and recovering quickly in the morning. This WSN1120L node is operating in RFD mode in which the node stays in ultra low power sleep mode (< 2 uA consumption) and wakes up periodically (in this case every 10 minutes) to sense and transmit data.

If you want to use this charger in your product, we will provide the driver ( c code) for reading the current and voltage measurements.  Note that the charger IC works in stand alone mode. It does not need any external configuration. The voltage and current measurements are performed by two separate sensor ICs (external to the charger IC).  These sensors can be accessed over I2C. You may choose not to read this data.

If you want to use a solar panel with a different Vpeak, we will change the relevant passives free of cost to suit your panel.

For more information on our products, visit wisense.in.

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