About the BEM® सवित्रे™  Savitré MPPT  Solar Charge Controller

The BEM® सवित्रे™  Savitré - 2 Amps MPPT  Solar Charge Controller consists of MPPT digital controller and photovoltaic drivers and is designed to control high efficiency DC/DC conversion used in photovoltaic based Li-Ion battery charging application. It is a 2 Amps (Max.) Solar True Maximum Power Point Tracking (MPPT) algorithm based charger for 37 Volt (Nominal), 42 Volt (Maximum) Li-ion battery. This charger provides you with the ability to extract the maximum possible power out of your Solar panel of rating 12 Volt, 40W, and feed it into the  rechargeable Li-ion battery. This means that the E-Bicycle battery would get fully charged in the shortest possible time with a smaller sized (lower cost) Solar panel.  Recommended size of solar panel is 12V, 40W that can be easily fitted on the rear carrier of a standard bicycle 

Set-up is easy as well. Simply, plug the solar panel into one (input) side of the solar charge controller and the e-bicycle battery into the other (output) side, then Switch ON the charger and the battery would start charging at the fastest rate! Ensure that the solar panel is facing the sun, avoid shadows, and keep the panel surface clean for best performance.   

Installation Procedure of the Solar Charger over the Solar Bicycle

75W, Solar MPPT Charge Controller with OLED Display for E-Bicycle’s 36V Li-Ion Battery 

Features :

1. For Solar Panel of Nominal Voltage: 12V, and upto 75W.

2. Charger Input (solar) voltage range: 10 - 24 V

3. Input (Solar) Current: 4A (Max) 

4. For Li-Ion Battery of Nominal Voltage: 36V

5. Charger Output (Li-Ion Battery) voltage range: 32 - 41V

6. Output (Li-Ion Battery) current: 2 A (Max.)

7. Incorporates a switching mechanism to automatically change the loading on the solar panel, and thereafter operate at Maximum Power Point (MPP). 

8. Hybrid (Analog + Digital (ARM Cortex based Microcontroller with sophisticated MPP tracking algorithm) technology  to control solar panel operating voltage so as to extract maximum power from the panel.

9. Boost mechanism: Non-isolated step-up power conversion

10. Onboard OLED displays Solar and Battery Voltages and Battery Charging Current. 

11. RED and GREEN LEDs show the different operating states of the controller. 

BEM® सवित्रे™  Savitré MPPT  Solar Charge Controller with RED and GREEN LED Indicators 

₹ 1376.00 ₹ 2500.00   (inc GST)

₹ 1,166.10 (+18% GST extra)

BEM® सवित्रे™  Savitré MPPT  Solar Charge Controller with OLED Display  (in addition to RED and GREEN LED Indicators)

₹ 1926.00 ₹ 2500.00   (inc GST)

₹ 1632.20 (+18% GST extra)

Description

This is a Maximum Power Point Tracking (MPPT) solar charge controller for 10-cell (10S), Li-Ion  batteries having nominal voltage of 36 Volts typically used in electric bicycles. (Similar chargers for other battery voltages such as 48 V for EVs are also available). This MPPT solar charger gives you the ability to extract the maximum possible power out of your solar panel or any other photovoltaic device and feed it into a rechargeable Li-Ion battery. 

The MPPT feature gives you the ability to charge a bicycle battery, say of 5 Ah,  from a smaller sized solar panel, say of 40W, in the shortest time, say 4 to 5 hours. The small panel size makes it practical for you to mount it on your bicycle and convert it to an elegant looking solar bicycle.  

Set-up is easy as well. Simply insert the 2.1 x 5.5 mm (male) plug on the end of the cable originating from the solar charger (36V DC) output, into your battery socket. Make sure that your 40W, 12V solar panel has a similar 2.1 x 5.5 mm male plug that can be inserted into the input (female) socket of the solar charger (12V DC solar). Switch ON the power switch of the solar charger,  and you are good to start charging!

The OLED model additionally has a  bright OLED (Organic Light-Emitting Diode) (monochrome or blue) display of resolution  128 x 64, and size 0.96 inch, brightly and boldly displays the solar input voltage, battery voltage as well as the battery charging current.  The OLED display has high brightness, self-emission, high contrast ratio, slim/ thin outline, wide viewing angle, wide temperature range and low power consumption.

MPPT Operation

The MPPT charge controller has a ARM Cortex microcontroller and sophisticated software to detect the Maximum Power Pm point. The software also has the ability to control and limit the charging current to the load (battery), so that the solar panel operation is controlled to a voltage Vm corresponding to the maximum power point Pm, to deliver maximum power. This gives the ability to charge a battery from a smaller (lower cost) solar panel in the shortest possible time. 

(In sharp contrast, a PWM charge controller, that is more popular due to its lower cost, offers very little control action. It is merely a switch that connects the solar panel to the battery and offers no control over the solar voltage. Hence, a PWM controller is unable to extract the maximum power from the solar panel.) 

DC to DC Boost Controller

The MPPT charge controller is a DC to DC transformer that is designed as a step-up transformer (boost controller).  The step-up transformer is highly efficient - the output power delivered to the battery is only marginally lower than the power extracted from the solar panel. The loss in the transformation process is small, typically less than 8%. 

Figure 4 shows the characteristics of a boost MPPT charge controller where Pbat = Pm while Vbat > Vm . Figures 5 to 7 show the block diagram of the MPPT charge controller at different hierarchical levels.   

The DC to DC step-up (boost) transformer converts 10 - 24 V solar input to 31 - 42 V output to charge the battery. The boost converter is designed with a huge toroidal inductor and two large heatsinks so that it can handle and boost 100W of solar power. 

Protection

Please note there is no reverse polarity protection. Check the polarity of the solar panel before plugging in. 

All other protections, such as over-voltage protection, over-current protection,  are incorporated in the design and are monitored by the sophisticated software residing in the ARM controller.

Operating Modes 

Table 1. LED and OLED States when the Charger is Switched ON

Sr. No. MODE/OLED Display RED LED GREEN LED STATE NOTES

1. NO DISPLAY   OFF OFF NO SOLAR INPUT     All indicators and OLED  in OFF State; Solar Panel disconnected /
Inadequate solar power fed to charger / Inactive state
2. STANDBY OFF-P OFF-P INITIALISATION In transition; for a short period after Switch ON

3. CHARGING ON OFF-P CHARGING Battery in Charge Mode. 

4. FULL OFF-P ON FULLY CHARGED Battery is Fully Charged. 

5. ERROR 1/2 ON ON ERROR/CHARGED Battery disconnected, or BMS activated indicating FULL charge

*Error State means Battery Management System (BMS) may be refusing further Charge though the FULL Battery Voltage has not been reached. 

Note:

1. When a particular LED is In the OFF-P state, faint glitches / pulses / flashes can be observed at regular 2 second intervals. This is introduced to distinguish the ‘operating’ states from the ‘Solar Panel Disconnected’ state, or to check if the controller is dead.

2. Since the charger draws power for its own operation from the solar panel, in the ‘Solar Panel Disconnected’ state, or at night, the charger is non-operational and hence the display and LEDs are completely OFF (no flashes can be observed). 

3. For higher efficiency, the charger is designed to not draw power from the battery for its own operation. This also helps retain battery power for a longer period of time. Hence, if the solar panel is disconnected, or at night, the charger is non-active/ non-operational.

Installation and Operating Sequence  

1. Insert the solar charger output power male plug (2.1 x 5.5 mm) into the battery charging  (36V DC) input socket. Place the solar panel facing the sun. Insert the solar panel (12V DC) output (male) plug into the solar charger input socket. 

2. Switch ON the power switch provided on the charger. It would enter the ‘Standby’ state with both LEDs in the OFF-P state (see Table 1 above). 

3. Within 5 seconds from power ON, the OLED will light up and display the following in the four rows (actual voltage values may differ):

   1. Battery Voltage: BAT V 36.5

   2. Battery Current: BAT I  0.00

   3. Solar Voltage: SLR V 21.5

   4. Status: STANDBY  

4. In the next few seconds, the charge controller starts to load the solar panel. You will observe that the Solar Voltage will drop from its no load value (say 21.5V) down to approx. 14V. At the same time the battery current will increase from 0 Amps, to say 0.65 Amps (for a 40W panel), in steps. 

5. Over the next few seconds, the controller will run further checks to ensure that it is loading the solar panel in the most optimum manner, so as to extract maximum power from it. On completion of these checks, the status of the OLED changes as follows:   

   1. Battery Voltage: BAT V 36.5

   2. Battery Current: BAT I  0.65

   3. Solar Voltage: SLR V 18.3

   4. Status: CHARGING

The status of the LEDs changes to Red LED: ON and Green LED: OFF-P.

Depending on the amount of solar energy available the charge controller would stay in this CHARGING state from 2 to 5 hours. On a bright sunny day, the charging current would be higher and hence the time taken for charging would be less.   

6.  After the charging process gets completed, the status of the OLED changes as follows: 

   1. Battery Voltage: BAT V 40.5

   2. Battery Current: BAT I  0.00

   3. Solar Voltage: SLR V 21.5

   4. Status: FULL

The status of the LEDs also changes. The Red LED goes to the OFF-P state and the Green LED goes ON. In the state, the charge controller stops the charging process. The solar panel is no longer loaded; however a negligibly small amount of power is still drawn to supply the controller circuits: the ARM controller, the OLED display and the boost controller.
The solar panel is no longer required and this is the right time to switch OFF the power switch of the charge controller to cut off the solar panel. 

It is a good practice to keep the switch OFF the power switch at night, and switch it ON the next day after there is sufficient daylight to power up the charge controller. In case you forget to switch OFF the power switch the previous night, it does not harm or damage the controller. However, there may be instances when the OLED fails to display due to absence of proper power-on reset the next morning when the sun rises slowly and gradually.  See Fault diagnosis below for further details and workaround for this known issue.    

Fault Diagnosis  

1. For safety reasons:
   Keep the battery always connected to the charger before connecting the solar panel or switching ON the charger. 

2. Charger non-operational when battery is connected:
   Merely connecting the battery and pressing the power switch to the ON position does not power up the charger.  Make sure that a solar panel is connected at the input with correct polarity to feed power to the charger circuits. 

3. Charger non-operational when both battery and solar panel are connected:
   Ensure that the solar panel faces the sun and that the sun rays are incident perpendicularly on the solar panel. Disconnect the solar panel and check its voltage with a voltmeter. The open circuit voltage of a 12 V, 40Wp solar panel should be approx. 21 volts. If the open circuit voltage is less than 18 volts, wait for the sun to rise up adequately. 

4. OLED is OFF but the RED and GREEN LEDs are either ON or OFF-P.
   If both the battery and solar panel are connected, and the controller power switch is in the ON state, and the RED and GREEN LEDs are either ON or OFF-P, it indicates that the charge controller is powered up and the software is running properly. However, the OLED did not get a proper power on reset and hence the display is blank (does not display any characters or values). Such a condition may observed typically in the mornings (if you have forgotten to switch OFF the controller the previous night). In the morning, when the sun rises slowly, the OLED supply voltage rises too slowly, and the OLED may fail to get a proper reset.
   Work-around: To exit the blank OLED display condition, simply switch OFF the power switch, wait for about 5 seconds and then switch it ON again. The OLED will get a proper power ON reset and will start to function normally. 

5. Fails to Charge Battery / ERROR 2:
   Both battery and solar panel are connected. Power switch is pressed ON. Charger LED and OLED appears to light up, However the charger fails to charge the battery and the OLED displays the following: 

   1. Battery Voltage: BAT V 39.2

   2. Battery Current: BAT I  0.00

   3. Solar Voltage: SLR V 21.5

   4. Status: ERROR 2

The BMS (Battery Management System) inside the Battery has activated and this disconnects the battery from the charger. Approach your battery supplier and get the battery problem corrected. Till then, you can use the battery and also get it charged from the charge controller, albeit to a slightly lower value. In other words, you will not be able to use the full (100%) battery capacity but you can use a lower, say 80% of the battery capacity.   

6. ERROR 1:
   Both battery and solar panel are connected. Power switch is pressed ON. Charger LED and OLED appears to light up, However the charger fails to charge the battery and the OLED displays the following: 

   1. Battery Voltage: BAT V 21.5

   2. Battery Current: BAT I  0.00

   3. Solar Voltage: SLR V 21.5

   4. Status: ERROR 1

Though you have connected the battery, there is a break in the connection. When this happens, the OLED shows the battery voltage to match the solar voltage, namely, 21.5 V. The OLED also displays ‘ERROR 1’ which means that the battery is not connected.

Package Includes :

1 x Solar MPPT Charge Controller with OLED Display  for 36V E-Bicycle

1 x Operating Manual (Or Soft Copy can be viewed here).

Specifications

Model: OLED

Input:  Panel Mount DC Power Jack Socket (Female) 2.1 mm x 5.5 mm

Output: Cable with DC Power Jack Plug (Male) 2.1 mm x 5.5 mm

OLED Display with I2C Interface 0.96 inch, BLUE

Input (Solar) Voltage (V) 10 to 24

Max. Input (Solar) Current (A) 4

Output (Battery) Voltage (V) 32 to 41

Max. (Battery Charge) Current (A) 2

Max. (Battery Charging) Power (Watt) 75

Conversion Efficiency (%) 94

Operating Temperature (°C) -40 to 90

Switching Frequency (kHz) 50

Length (mm) 110

Width (mm) 60

Height (mm) 40

Weight (gm) 250

Shipment Weight 0.300 kg

Shipment Dimensions 15 x 10 x 6 cm

Warranty

15 Days Warranty

This item is covered with a standard warranty of 15 days from the time of delivery against manufacturing defects only. This warranty is given for the benefit of customers from any kind of manufacturing defects.  Reimbursement or replacement will be done against manufacturing defects.

What voids warranty:

If the product is subject to misuse, tampering, static discharge, accident, water or fire damage, use of chemicals & soldered or altered in any way.

Figure 1. MPPT Charge Controller with DC Plug (Output)

Figure 2. Location of MPPT Charge Controller from Source (Solar Panel) to Load 

Figure 3. V-I  and Power characteristics of Solar Panel showing Operating Point controlled by MPPT Charge Controller 

Figure 4. Graphical representation showing that power delivered by the MPPT Charge Controller to the battery, Pbat, is equal to the maximum power extracted from the solar panel (Pm) 

Figure 5. Block Diagram (Level 1) of the MPPT Charge Controller

Figure 6. Block Diagram (Level 2) of the MPPT Charge Controller

Figure 7. ARM Cortex Microcontroller used in the MPPT Charge Controller to run a sophisticated software