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Photo voltaic fan with dynamic battery backup for fixed velocity of operation


The best approach of constructing a photo voltaic fan is to attach the photo voltaic PV panel to a DC fan of an identical voltage and energy score. This straightforward association does work, however has few critical drawbacks:

  1. The system doesn’t function at most energy level, leading to a poor utilization of the PV panel.
  2. When the daylight depth varies, the fan velocity fluctuates very broadly. This isn’t acceptable for the person.
  3. The system can’t be used at night time.

There are different designs accessible available in the market. These techniques use a photo voltaic panel and a battery. The photo voltaic panel prices the battery. The person can run the fan on battery energy each time desired. Regardless that this works high-quality, there are limitations. The person can run the fan for just a few hours till the battery drains. Since all the ability is routed by way of the battery the battery experiences a lot of cost/discharge cycles. This limits the lifetime of the battery. Along with this, there are losses within the battery throughout charging and discharging.

A brand new design is proposed right here which runs the fan at fixed velocity. The idea behind this strategy is to make the most of all the ability generated by the PV panel to run the fan. Then inject simply sufficient energy from the battery for the fan to run at near-constant velocity. In the course of the daytime, we’re drawing solely fraction of energy from the battery. If it’s a sunny day, virtually zero energy could also be drawn from the battery. This will increase the lifetime of the battery. Additionally, cost/discharge losses within the battery are diminished. One other advantage of this strategy is the PV panel operates close to most energy level, thus maximizing the PV energy generated. This goal has been achieved with out utilizing complicated switching circuits. Observe that the ability draw from battery is dynamically altering primarily based on the instantaneous PV energy.

Format of the proposed answer

Determine 1 reveals the block diagram of proposed photo voltaic fan. It consists of a photo voltaic PV panel, which is linked to a present limiter. The present limiter output is linked to the LED. The present flows by way of LED then to the FAN+ terminal. The present limiter ensures that the fan present doesn’t exceed the rated worth. The battery can also be linked to the FAN+ terminal by way of resistor (R) and Diode (D). The under-voltage journey circuit is used to show off the FAN when the battery is absolutely discharged.

Determine 1 Block diagram of photo voltaic fan with dynamic battery backup system.

A two-pole two-way change (SW1-SW2) is used to show off the fan when not wanted. Within the fan’s off state, the change connects the battery to the PV panel by way of the photo voltaic cost controller. The photo voltaic cost controller prices the battery and prevents overcharging. Such controllers can be found as off-the-shelf options.

Please notice that the LED has been launched for voltage matching functions, particularly for the design offered on this article. For a photo voltaic fan, this LED will not be important. An evidence on how you can eradicate this LED is supplied within the design part.

As proven within the block diagram, there are two sources that are feeding energy to the fan. One is the battery which provides energy at a reasonably fixed voltage by way of the diode (D). This diode stops the PV present from getting into the battery terminal. The opposite one is the PV panel, which provides energy with a broadly various voltage.

A PV panel really acts as a present supply. Therefore, if the PV present doesn’t discover a path, then the panel voltage goes on growing till the present will get injected into the circuit. Right here on this design, it has to beat the battery voltage on the FAN+ terminal. Because the panel present enters the FAN+ terminal, the battery present will get diminished by that a lot magnitude. Thus, all of the accessible PV energy is provided to the FAN. Nonetheless, if the fan velocity is under the design worth, then some present is drawn from the battery to realize the designed velocity. Resistance (R) helps in pushing again the battery present by growing the entire battery circuit resistance (battery inside resistance + R).

Design of the proposed answer

Determine 2 reveals the circuit diagram of the photo voltaic fan.

Determine 2 Circuit diagram of photo voltaic fan with dynamic battery backup system.

The specs of the primary parts are as follows:

  • Photo voltaic PV panel energy score = 10 Wp
  • Voltage at most energy (Vmp) = 17.5 V
  • Open circuit voltage of the panel (Voc) = 21.2 V
  • Present at most energy (Imp) = 0.58 A
  • Voltage score of the BLDC fan = 12 V
  • Present score of the fan = 0.2 A
  • Variety of followers linked in parallel = 0.58/0.2 = 2.9 (Rounded off to three)
  • Nominal Voltage of SLA battery = 12 V
  • Battery capability = 7 Ah
  • Ahead voltage of 1 W white LED = 3 V
  • Max present score of White LED = 1W/ 3V = 0.33 A
  • Magnitude of present restrict = Vbe/R1 = 0.6/1Ω = 0.6 A

As proven within the circuit diagram, the PV+ terminal is linked to the present limiter circuit by way of change SW1. The present limiter consists of two PNP transistors: T1 (BC556) and T2 (TIP32). T2 is ahead biased utilizing resistor R2 (2.2 kΩ). When the drop throughout resistor R1 exceeds 0.6 V, T1 turns ON and limits the present in T2. Observe that the orange LED4 in collection with R2 is used for indicating the presence of PV voltage.

Wow the engineering world together with your distinctive design: Design Concepts Submission Information

The output of the present limiter is linked to the followers by way of three white LEDs (LED1 to LED3) linked in parallel. These LEDs are used right here for voltage matching functions. The fan and the battery each are rated for 12 V. Nevertheless, the voltage on the collector of T2 is held at about 15 V underneath all daylight situations. The LEDs drop 3 volts and subsequently the fan will get about 12 V from the PV panel. The rated present of every fan is 0.2 A. Therefore, to match the utmost present of PV panel (0.58 A), the three followers are linked in parallel. If now we have a fan with a 0.6 A present score, then single fan is enough.

Please notice that the proposed circuit has been designed utilizing simply accessible parts. If we needed to eradicate the collection LED, then we might have had to make use of a 15 V battery (e.g., Li-ion battery with 14.8 V score is on the market). Additionally, now we have to make use of a fan designed to function at 15 V. Followers with 18 V rankings can be found. These may very well be operated at 15 V, with barely diminished air circulation. Alternately, three 5 V followers may very well be linked in collection.

The battery can also be linked to FAN+ terminal by way of the fuse (1A), schottky diode D1 (1N5822) and resistance R3 (1Ω). The p-channel MOSFET T3 (IRF9540) can also be included in collection. This MOSFET (T3) together with the comparator circuit is used for disconnecting the fan when the battery is absolutely discharged.

The aim of R3 is to extend the supply resistance of the battery circuit. This may permit the PV facet to push again the battery energy extra successfully which helps in maximizing the utilization of PV energy. The worth of R3 must be as small as doable to scale back energy losses.

The opposite terminals of SW1 and SW2 are used to attach a photo voltaic cost controller to the battery when fan is turned OFF. Photo voltaic cost controllers cost the battery whereas monitoring the utmost energy level. When the battery is absolutely charged, the charging is stopped.

The circuit diagram of the battery’s undervoltage safety circuit is proven in Determine 3. It makes use of the comparator IC1 (LM311). A reference voltage of 5.1 V is linked to the non-inverting enter (Pin2). On the inverting enter (Pin3), the potential divider circuit consisting of R12 (47 kΩ), R13 POT (50 kΩ) and R14 (47 kΩ) are linked. The POT is used to set the tripping voltage at inverting enter.

On the output pin 7 of the comparator, resistors R15 (2.2 kΩ), R16 (1 kΩ) and a inexperienced LED5 are linked. The terminals of R15 are linked to supply and gate terminals of T3. Resistor R17 (100 kΩ) is used for introducing hysteresis.

Determine 3 Circuit diagram of comparator circuit used for battery underneath voltage journey.

When the battery is charged, the output of comparator is low. The drop throughout R15 is larger than the gate supply threshold voltage of MOSFET. Therefore T3 is ON. When the battery voltage drops under the journey voltage, the comparator output goes excessive. The drop throughout R15 turns into zero and the MOSFET turns OFF. The LED5 additionally turns OFF to point battery is discharged.

Testing the circuit

First, the circuit was examined with battery OFF situation by eradicating the fuse. At numerous daylight intensities, the PV voltage (Vpv), PV present and fan voltage are famous down. Determine 4 reveals the plot of fan energy versus Vpv. It’s noticed that the PV voltage varies from about 8 volts to 19 volts. Beneath 8 volts, the followers cease rotating. The fan energy varies from 1 W to six W. This produces a really giant variation within the circulation of air from the followers.

Determine 4 Plot of PV energy to fan with out battery backup.

Determine 5 reveals the plot of fan energy when the battery is ON. It’s noticed that the Vpv variation is restricted inside the vary from 14.7 V to 18.7 V. This means that the circuit tracks the utmost energy level of the PV panel fairly intently. The blue hint is the ability provided by the PV panel to the fan. The fan PV energy at 14.7 V is about 2.5 W. That is important enchancment over the bottom energy of 1 W when the battery was OFF (see Determine 4). Thus, the presence of the battery improves the ability generated by the panel.

The orange hint in Determine 5 is the sum of the PV energy provided to the fan and the ability drawn from the battery. This curve is sort of flat with a variation of about 1 W within the full vary. Thus, the followers run at virtually fixed velocity even when Vpv varies from 14.7 V to 18.7 V.

Determine 5 Plot of PV energy and complete energy to the fan with dynamic battery backup.

Determine 6 reveals the ability provided by the battery to the fan. When the PV energy is at a minimal, the battery provides most energy. Because the PV energy to the fan will increase, the ability draw from the battery reduces. At full PV energy output, the ability drawn from the battery may be very small.

Determine 6 Energy draw from the battery with variation in PV voltage.

Fabrication

Determine 7 reveals the present limiter circuit and the under-voltage journey circuit assembled on a PCB. Transistor T2 and MOSFET T3 are mounted on warmth sinks. T2 operates within the lively area subsequently, the warmth dissipation from T2 is greater. Therefore, an even bigger warmth sink has been used. When T3 is ON, it has small quantity of conduction losses. Due to this fact, a small warmth sink is enough.

Determine 7 PCB with a present restrict circuit and battery undervoltage journey circuit.

Determine 8 reveals the absolutely assembled proposed photo voltaic fan system. LED1 to LED3 are mounted on a steel clad PCB. This MCPCB is mounted on a small aluminum channel. The aluminum channel acts as warmth sink. The LEDs, photo voltaic cost controller, change, fuse and the SLA battery are mounted on a Bakelite panel.

The three followers and the controller PCB are mounted on two small aluminum channels. The interconnections are made to the PCB by way of the terminal strip soldered on the PCB.

Determine 8 Totally built-in photo voltaic fan system together with the photo voltaic cost controller.

Functions

The proposed system can be utilized for off-grid functions. The advantages of off-grid techniques are as follows:

  • Unaffected by grid failures
  • Decrease transmission losses
  • Decrease wiring prices.
  • Helpful throughout emergencies when there are extended grid failures
  • Lowered burden on the grid

Lastly, the system has been designed for a fan load for example. Nevertheless, the identical strategy can be utilized for different kinds of masses (e.g. lamp masses, heater masses, cell and EV chargers and so forth.)

Conclusion

From the outcomes proven within the graphs, it’s doable to inject energy from two totally different sources to the fan. The PV panel acts as a present supply and dynamically controls the ability drawn from the battery. Thus, with out utilizing complicated switching circuits we are able to run the followers at fixed velocity when the output from the PV panel is very fluctuating. All of the accessible PV energy at any given immediate of time is fed on to the followers. Solely steadiness energy is drawn from the battery, thus bettering the battery life. Additionally, the vitality misplaced within the charging and discharging of battery is diminished to some extent.

The proposed design could be simply scaled up for greater energy techniques. These days, BLDC ceiling followers can be found. The proposed circuit could be a good match for a BLDC ceiling fan in installations the place a battery backup is required.

For higher efficiency, the ability losses within the circuit must be stored as little as feasibly doable. Particularly within the resistor R3 and diode D1. If needed, a number of diodes may very well be linked in parallel to scale back the present in a person diode. This may scale back the ahead voltage drop to some extent.

References:

[1] Photo voltaic day lamp designs use passive and lively current-limiting circuits – https://www.edn.com/solar-day-lamp-designs-use-passive-and-active-current-limiting-circuits/

Vijay Deshpande labored as an electronics {hardware} engineer for greater than 30 years in numerous industries. After retirement primarily engaged on low price, Off-Grid, photo voltaic lighting techniques.

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