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101 Renewable - Charge Controllers

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Last Updated
20th of March, 2020

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How PV Controller works

Solar Charge Controllers - Presentation:-

A charge controller, or battery charge controller limits the rate at which electric current is added to or drawn from electric batteries. Charge Controllers are used in Off-Grid Installations and they support functions like: prevent overcharging, protect against overvoltage, prevent completely draining ("deep discharging") of a battery, perform controlled discharges, maintain the battery state of charge. Here is a list of the main types of charge controllers used in a PV installation based on technology they use and the supported functions.

Stand-alone Charge Controllers:

Simple charge controllers stop charging a battery when they exceed a set high voltage level, and re-enable charging when battery voltage drops back below that level. A Charge Controller can be mounted in series or in parallel as a shunt to a battery bank.  A series charge controller or series regulator disables further current flow into batteries when they are full. A shunt charge controller or shunt regulator diverts excess electricity to an auxiliary or "shunt" load, such as an electric water heater, general heater elements, when batteries are full. Here is a list of main Stand-alone Charge Controllers:

M.P.P.T. Charge Controllers:

MPPT Charge Controller is a maximum power point tracker, a DC to DC Converter which takes the DC input from the solar panels and changes it to high AC frequency. That one in turn it is converted back to a different DC current to match with the batteries bank requirements. MPPT Charge Controller operates in the range of 20 to 80 KHz. The MPPT charge controller compares the output of the solar panels with that of the battery bank voltage, then determines the power the panels need to produce to charge the batteries.

P.W.M. Charge Controllers:

PWM is an acronym for Pulse Width Modulation. When the battery is recharged to a regulated voltage, the controller will begin limiting the amount of current into the battery in such the regulated voltage is maintained but not surpassed. The method of current regulation, referred to as PWM, pulses current into the battery with pulses of a varying length. Longer pulses allow a greater percentage of the current to flow into the battery, shorter pulses restrict current to a lower percentage.

Lighting Controllers:

Fully waterproof PV Charge and Lighting Controllers used for area lighting, roadside signs, and warning signs, can be used with 12- or 24-volt systems, 15-amp and 40-amp versions are also available. Controllers have a motion sensor to activate the light or load when motion is sensed. They have temperature compensation and can be used with sealed or flooded batteries. Pulse action reduces sulfating.

Generator Start Controllers:

Generator Start Controller allows your conventional auxiliary generator to automatically start based on low battery voltage and/or high temperature. A generator-starting controller receives start commands from the 12-volt output of an inverter auxiliary relay, a user-supplied switch, an auxiliary relay in an inverter, a voltage controlled relay, a timer or any user-supplied contact closure system.

Relay Controllers as Logic Module Controllers:

The Relays are Logic Modules which provide control functions such as high/low voltage alarm, load control and generator start for 12-, 24- or 48-volt battery systems. It controls up to four independent relay driver outputs by reading digital data inputs or by reading battery voltage. The outputs can be used to operate any of the relays systems presented on this page or any other mechanical or solid state relay with a coil voltage that is the same as the battery voltage used to power the relay driver.

Stand-alone Charge Controllers - Technologies:-

Maximum Power Point Tracking (M.P.P.T.) Controller:

solarcell-ivgraph3

Maximum power point tracking or MPPT is a technique used by grid tie inverters, solar battery chargers and similar devices in order to get the maximum possible output power from the PV array. Solar cells have a complex relationship between solar irradiation, temperature and total resistance that produces. This relation translates into a non-linear output efficiency curve known as the I-V curve. It is the purpose of the MPPT system incorporated into inverters and charge controllers to sample the output of the cells and apply a resistance (load) to obtain maximum power for any given environmental conditions. Essentially this defines the current that the inverter should draw from the PV in order to get the maximum possible power (since power equals voltage times current). And based on this indication from the MPPT system, the inverters or charge controllers are auctioning on the PV array output. Below are some of the MPPT conditional situations to explain how this principle will apply.

At night, an off-grid PV power system uses batteries to supply its loads. The battery bank voltage when fully charged may be close to the point where the PV array's peak power is maxim. This is unlikely to be true at sunrise when the battery is partially discharged. Charging may begin at a voltage considerably below the array peak power point, and a MPPT system can resolve this mismatch indicating the charger to start charging from next closest available value on the MPPT hysteresis.

Pulse With Modulation (P.W.M.) Controller:

state-of-charge

PWM’s Charge Controllers ensure efficient charging of the battery system (the battery bank). PWM helps to regulate the often inconsistent voltage delivered by power sources (solar panels) in order to protect the system batteries from overcharging. When a solar array has the PWM mode activated from the charge controller, that one uniquely handles the job of battery charging by constantly checking the current battery state and self-adjusting accordingly to send only the right amount of charge to the battery.

In essence, this type of charge controller works by reducing the current from the power source according to the battery’s condition and charging requirements, which is in contrast to on/off charge controllers which suddenly cut off power transfer to minimize battery overcharging. The PWM charge controller does this by checking the state of the battery to determine both how wide the pulses should be as well as how fast they should come.

With that information, the PWM charge controller then self-adjusts and sends the appropriate pulse to charge the battery, it will vary the length and speed of the pulses sent to the battery as needed (see graph). This is essentially a rapid on and off switch. When the battery is nearly discharged, the pulses may be long and continuous, and as it becomes charged the pulses become shorter or trickled off. This trickle or finish type charging mode is important for systems that can go days or weeks with excess energy during periods when very little of the solar energy is consumed.

This type of charge controller is ideal for solar arrays where excess energy is a regular occurrence; The PWM charging provides several key benefits: higher charging efficiency, rapid recharging, and healthier batteries operating at full capacity.

Lighting System Controller:

Light Controller Schematic

Some of the features of a lighting controller: It is a PWM type of controller with an additional function for day and night detection using the PV array IV information. They have temperature compensation and can be used with sealed or flooded batteries. Pulse action reduces sulfation. This type of controllers are fully waterproof.

(Generator) Start Controller:

The primary job of any generator is to run a load. In our case, the load is represented by the batteries bank The generator is used to charge House, RV's or Boat - Batteries' Banks. Dead or defective batteries (batteries with defective cells) can’t be properly recharged, therefore we need to keep batteries always in good working order to gain maximum efficiency from the generator. The three most common fuel types of generators are Diesel, LP, and Gasoline. All of them have to be made aware of the batteries status and start recharging the batteries and keep them under float voltage values. The generator will trickle recharge in a floating charge process a battery bank, keeping that in the parameters needed to kick in, in case of an outage.

That can be done with the help of an Automatic Generator Start. This feature is designed to automatically start the generator, and keep it running until the batteries are charged. Auto-Gene prevents the batteries from falling below a designated state of charge, even when we are away or to prevent overcharge and in this way to bring battery status under the gassing voltage level which in turn runs down (damage) the batteries. Running down the batteries will shorten their lifespan, making Auto-Gene a welcome battery maintenance tool and a way to improve the life and quality of shore living. (Shore living it is when we rely only on gene power resources for electrical appliances).

Logic Module Controller:

relay driver how it works

The need of logical relay as a robust way to control a PV System it is very much in demand and allows some of the more complex circuits to be correlated, we talk about PV Solar Modules, Start Generators, Battery Banks, Battery Charge Controller, Load Controllers and Alarms (see the picture on the left hand side). These Logical Relays are logic modules which provide control functions such as high/low voltage alarms, load control and generator start for 12-, 24- or 48-volt battery systems. What makes them be in demand is the simple way to connect and correlate all the elements together offering basic monitoring features.

Charge Controller Voltage Set Points:-

relay driver how it works

Low Voltage Disconnect ( L.V.D.):

The deep-cycle batteries used in renewable energy systems are designed to be discharged by about 80 percent. If they are discharged by 100 percent, they are damaged. That is called over discharge. The only way to prevent over discharge when all else fails, is to disconnect loads (appliances, lights, etc.), and then to reconnect them only when the voltage has recovered. All modern inverters have LVD built in, The inverter will turn off to protect itself and your loads as well as the battery bank. Because charge controllers are dealing with DC at battery level some of them have one built in. When you purchase a charge controller with built-in LVD, make sure that one has enough capacity to handle DC loads. For small 12V PV Systems a good value is at 10.8V.

Load Reconnect Voltage (L.R.V.)

Another voltage set-up point is Load Reconnect Voltage or LRV. After the controller disconnects the load from the battery at the LVD set point, the battery voltage rises to its open-circuit voltage. When the PV module connected for charging, the battery voltage rises even more. At some point, the controller senses that the battery voltage and state of charge are high enough to reconnect the load, called the load reconnect voltage set point. LRV should be 0.08 V/cell (or 0.5 V per 12 V) higher than the load-disconnection voltage. That brings the LRV set up point for 12V batteries at 12.5V

Low Voltage Disconnect Hysteresis

Is the voltage difference between the low voltage disconnect set point (Low Voltage Disconnect - LVD) and the voltage at which the load will be reconnected (Hysteresis). For the same considerations for 12V batteries we will have an interval of 1.7V between LVD and LRV. This interval should be as high as possible to prevent frequent disruptions to the connected load.

Voltage Regulation Hysteresis-

On the battery charging  hysteresis the PV Array  will reconnect at Array Reconnect Voltage (ARV) set value which will make sure that sufficient power is supplied from the PV Array. As a rule for 12V PV systems it will be a voltage between 12.5V and 13V. The charging hysteresis interval must be sufficient to ensure the frequency of charging will not damage the battery. Again for a 12V battery system the Voltage Regulation (VR) will be between 14V and 14.4V.  Voltage regulation is the set-up voltage point assigned to stop controller from over charging the battery (bank).

Voltage Temperature Compensation Set Points:

That will affect lead-acid and AGM batteries based on their chemistry. The chemistry in lead-acid batteries causes energy to flow more easily in warm temperatures and less easily in cold temperatures. This affects how much energy a battery can absorb during the recharge process. Most charger voltage set points are set for room temperature, 25°C [77°F]. If set point is not adjusted for temperature then the battery might get overcharged and gas when it’s too warm, or undercharge and sulfate when it’s too cold. The end result of either scenario is a battery with a shortened lifespan, sometimes significantly if exposed to extreme conditions. Here the steps to set voltage for temperature compensation:

We consider a Flooded Deep Cycle Battery having following parameters:
>_28V Charging Voltage @ 25°C [77°F] given by manufacturer
>_-5mV/°C/Cell factor compensation with temperature
>_24V battery (bank) voltage

We want to charge this battery at 40°C ambient temperature:
>_We determine the battery number of cells: 24V/2V(per cell)=12Cells
>_We determine the battery compensation factor: 12*(-5mV/°C/Cell) = -60mV/°C = -0.06V/°C

We determine the voltage set point we need to charge the battery at 40°C ambient value:
>_Differential voltage value: (40°C - 25°C)*(-0.06V/°C) = 15*(-0.06V)=-0.9V,
>_We compensate the charging voltage for temperature increase from 25°C up to 40°C: 28V+(-0.9V) = 27.1V,
>_The compansated charging voltage value is: 27.1V. Charge controller will be set to this value for optimal charge @ 40°C ambient temperature.

 

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