A Solar Charge Controller Is What?
In order to prevent batteries from overcharging, a charge controller or charge regulator essentially acts as a voltage and/or current regulator.
It controls the battery’s voltage and current as they go from the solar panels.
If there is no control, the batteries will be overcharged and destroyed, since the majority of “12 volt” panels output between 16 and 20 volts.
The majority of batteries need between 14 and 14.5 volts to completely charge.
Is A Charge Controller Always Necessary?
Usually, but not always.
The modest maintenance, or trickle charge, panels, such as the 1 to 5-watt panels, often do not need a charge controller.
A general guideline is that you don’t need one if the panel outputs 2 watts or less for every 50 battery amp-hours.
For instance, a typical flooded golf car battery has a capacity of around 210 amp-hours.
Therefore, you would need a panel that is around 4.2 watts in order to maintain a series pair of them (12 volts) only for maintenance or storage.
The well-liked 5-watt panels are sufficient and won’t need a controller.
You may utilize a 2 to 2-watt panel if you are maintaining AGM deep cycle batteries, such as the Concorde Sun Xtender.
Why are 12 V panels 17 V?
When this happens, the obvious question “why aren’t panels merely constructed to send out 12 volts” arises.
The panels won’t produce electricity if you do that since they will only do so when it is chilly, the weather is ideal, and there is full sun.
In the majority of areas, you cannot depend on this.
In order to still get any output from the panel when the sun is low in the sky, there is significant haze, cloud cover, or high temperatures*, the panels must provide some additional voltage.
A completely charged “12-volt” battery is around 12.7 volts at rest (approximately 13.6 to 14.4 under charge), therefore in the worst-case scenario, the panel must provide at least that much energy.
*Contrary to belief, solar panels function better at lower temperatures. Roughly, a panel rated at 100 watts at room temperature will be an 83 watt panel at 110 degrees.
The charge controller adjusts the panel’s output of 16 to 20 volts to match the current demands of the battery.
Depending on the battery’s level of charge, its kind, the controller’s mode, and the temperature, this voltage may range from roughly 10.5 to 14.6.
(Our battery section has further information on battery voltages.)
Utilizing Batteries And High Voltage (Grid Tie) Panels
Nearly all PV panels with wattages more than 140 are NOT typical 12-volt panels, and as a result, they cannot, or at the very least, should not, be used with typical charge controllers.
Grid tie panel voltages range widely, often between 21 and 60 volts.
Most are not normal 24-volt panels, however some are.
What Transpires When A Conventional Controller Is Used
If the charge controller’s maximum input voltage is not exceeded, standard charge controllers (all bar the MPPT variants) will often function with high voltage panels.
You will, however, lose a lot of power – somewhere between 20 and 60 percent of what your panel is capable of.
Until the battery is completely charged, which takes typically between 13.6 and 14.4 volts, charge controllers use the output from the panels to deliver current to the battery.
A panel can only produce a certain amount of amps, so even though the voltage is decreased from, say, 33 volts to 13.6 volts, the amps from the panel are limited to the rated amps.
For example, if you have a 175 watt panel rated at 23 volts/7.6 amps, you will only be able to get 7.6 amps at around 12 volts into the battery.
Your 175-watt panel will only deliver roughly 90 watts into the battery because, according to Ohms Law, watts are equal to volts times amps.
Using High-Voltage Panels With An MPPT Controller
The only way to get full power out of high voltage grid tie solar panels is to employ an MPPT controller.
See the link above for further information on MPPT charge restrictions.
You may often connect two or more of the high voltage panels in series to cut down on cable loss or use less wire since the majority of MPPT controllers can withstand up to 150 volts DC (some can go higher, up to 600 VDC) on the solar panel input side.
As an example, if you connected two of the 175-watt panels in series, the MPPT controller would get 46 volts and 7.6 amps, which it would then reduce to around 29 amps at 12 volts.
Types of Charger Controllers
There are many different types, sizes, features, and pricing points for charge controllers.
From the diminutive 4.5 amp (Sunguard) control to the 60 to 80 amp MPPT programmable controllers with computer interface, they are available.
Two or more 40 to 80 amp units are often connected in parallel when currents greater than 60 amps are needed.
All battery-based systems typically employ controllers in the 4 to 60 amp range, although some of the more recent MPPT controls, such the Outback Power FlexMax, may reach 80 amps.
There Are Three Broad Kinds Of Charge Controllers, Some Of Which Overlap.
Simple controllers with one or two stages that regulate the voltage in steps using relays or shunt transistors.
When a certain voltage is achieved, they effectively merely short out or detach the solar panel.
Although they are almost extinct, you may still find some of them on outdated systems and some of the really cheap ones being sold online.
Its sole major strength is their dependability; with so few parts, there isn’t much to go wrong.
such as Morningstar, Xantrex, Blue Sky, Steca, and many more that use 3-stage and/or PWM.
Although they are now essentially industry standards, earlier shunt/relay kinds are still rarely used, such as in the really inexpensive systems sold by mass merchandisers and discounters.
such as those produced by Midnite Solar, Xantrex, Outback Power, Morningstar, and others.
Maximum power point tracking (MPPT).
These are the top controllers available, and their prices reflect that.
However, with efficiency in the 94 to 98 percent range, they may significantly reduce costs on bigger systems since they provide the battery with an additional 10 to 30 percent of power.
See our page on MPPT for additional details.
Most controllers come with some kind of indicator, either a simple LED, a series of LED’s, or digital meters.
There are several more recent models with built-in computer interfaces for monitoring and control, like the Outback Power, Midnite Classic, Morningstar MPPT, and others.
The most basic often merely contain a few of tiny LED bulbs, which indicate that you have power and are receiving some kind of charge.
The majority of people who have meters will display the voltage, current, and battery voltage coming from the panels.
Some further display the amount of current being drawn from the LOAD terminals.
We have only three-stage PWM and MPPT charge controllers in our inventory.
(In truth, “4-stage” is something of a marketing buzzword; it was once known as equalization, but someone felt that 4 stage was superior than 3).
And now we even see one that is advertised as “5-stage”….
What Exactly Is Equating?
The term “equalization” refers to the process of making an effort to equalize, or bring all of the cells in a battery or battery bank to precisely the same charge.
In essence, it is a time of overcharge, often between 15 and 15.5 volts.
It will bring all of the cells in the string up to capacity, even if some of them are lower than others.
It also performs the crucial task of churning the battery liquid by generating gas bubbles in flooded batteries.
Of course, unless you have been parked for months, this normally does not help you much in an RV or boat since regular movement will achieve the same result.
Additionally, you may not obtain enough current in systems with tiny panels or huge battery packs to actually accomplish much bubbling.
Batteries may also be balanced with a generator and charger in many off-grid installations.
A “PWM” mode is available on a lot of charging controllers.
Pulse Width Modulation Is Referred To As PWM.
One approach of float charge that is frequently utilized is PWM.
A sequence of brief charging pulses are sent to the battery by the controller instead of a constant output, acting as an extremely quick “on-off” switch.
The controller continuously assesses the battery’s condition to decide how quickly and how long (wide) to emit pulses.
It may just “tick” and transmit a brief pulse to the battery every few seconds in a fully charged battery with no load.
The pulses in a drained battery would be very lengthy and almost continuous, or the controller would switch to “full on” mode.
Between pulses, the controller assesses the battery’s level of charge and makes an adjustment.
Due to the strong pulses that PWM produces, it may also cause interference in radios and televisions.
Check out this page if your controller is making noises.
What Does A “Low Voltage Disconnect” Or “Load” Output Mean?
Additionally, some controllers have a “LOAD” or LVD output that can be used for smaller loads like lights and appliances.
The advantage is that because the load terminals have a low voltage disconnect, anything connected to them will be turned off and the battery won’t be discharged too far.
For modest, non-critical loads like lights, the LOAD output is often employed.
A few, such as the Schneider Electric C12, may also be used as a lighting controller, to switch lights on at dark, however the Morningstar SLC lighting controller is typically a better option for that.
Do not use the LOAD output to operate any but extremely modest inverters.
Inverters may blow the controller because of their extremely high surge currents.
Since it can only drive smaller loads, most systems do not require the LVD function.
Depending on the rating of the controller, this may range between 6 to 60 amps.
Only the smallest inverter may be operated from the LOAD output.
For load control, gen start, etc., certain controllers, like the Morningstar SS series, allow the load output to drive a heavy duty relay.
When the load is low and the location is unattended, RV & remote systems like camera, monitor, and mobile phone sites most often utilize the LOAD or LVD output.
What Do My Controller’s “Sense” Terminals Do?
A pair of “sense” connections are included on certain charge controllers.
There is no voltage drop because the sense terminals only carry a very little amount of current—up to a tenth of a milliamp.
It “looks” at the battery voltage and contrasts it with the voltage the controller is producing.
The charge controller will slightly increase its output to make up for any voltage loss between the battery and it.
These are solely used when the cable between the controller and the battery is lengthy.
These wires, which may range in size from #20 to #16 AWG, carry no current.
Because it is difficult to unintentionally cut or squash, we like to use #16.
They connect to the controller’s SENSE terminals as well as the two charging wires’ respective terminals at the battery end.
“Battery System Monitor”: What Is It?
Controllers are different from battery system monitors, like the Bogart Engineering TriMetric 2025A.
Instead, they keep track of your battery system and provide you with a fairly accurate picture of its state, as well as what you are consuming and producing.
They record data such as the total amp-hours going into and coming out of the batteries, their charge level, and other things.
For medium to big systems, they may be quite helpful in measuring precisely how your system is doing while using different charging sources.
They are a bit excessive for small systems, but they make for a fun toy if you want to monitor each amp’s activity.
A computer interface and several additional capabilities are included in the new PentaMetric model from TriMetric.
Visit our Charge Controller page on our website for a comprehensive list of all of our charge controllers, pricing information, and online ordering.
For battery monitors, meters, and shunts visit our Meters & Monitors page there.