Learning Center

Get the answers you need to purchase and operate your Blue Sky Energy and Genasun controllers.

Frequently Asked Questions

A properly functioning system requires that solar panels, batteries and system loads be balanced. Selecting batteries that are too small or too large, a solar system that is too small, or loads that are too large will lead to poor system performance.

The charge voltage required by a battery changes with battery temperature. A cooler battery requires a somewhat higher charge voltage whereas a hotter battery requires a somewhat lower charge voltage. The battery temperature sensor allows the Solar Boost charge controller to automatically adjust charge voltage based on actual battery temperature. Applying the proper charge voltage improves battery performance and life, and minimizes battery maintenance.

The controller will throttle back the current to keep the voltage at the specified float voltage, keeping the battery fully charged even if you have some loads drawing from the system.

There are two scenarios here – something is broken or wired incorrectly, or the system is assembled correctly and under-performing compared to customer expectations. Genasun performs 100% testing and inspection on the controllers prior to shipping. Your controller worked when we shipped it. Unless the box got run over by the UPS truck, hit by lightning, or was recovered from the bottom of the ocean, it will work correctly when installed. Please read the manual to ensure it was installed correctly. Here are the most common causes of system output not meeting expectations: Panels are rated at “Standard Test Conditions” which should be viewed as a best case scenario. For example, a 20W panel will produce 20W under bright light, on the equator, pointed directly at the sun in cold weather. If you’re not on the equator with temperatures of 5°C, if the atmosphere isn’t crystal clear, if your panel isn’t pointed perpendicularly to the sun at all points in the day, it will not produce the “rated” power. Power from the panel changes over the course of the day. The panel output is a direct function of how much light is available. The maximum output will be during the middle of the day. The further you get from the equator, the smaller that window for maximum light output.

100% testing. Our controllers include LED indicators which give detailed information about system status. Please read the product manual for detailed instructions about your controller. The manual can be downloaded from the product page that describes your controller.

It’s OK( and common!) to use multiple charging sources, and no special precautions are required. When the battery is low, both chargers will be charging according to their capability. As the battery becomes charged, whichever source is set to charge to a higher voltage will “win”, and the other will cease charging.

Genasun solar charge controllers, can charge from a DC source PROVIDED that the input voltage is within spec and the input power is limited such that the rated output current (input current for the GVB series) of the Genasun controller is not exceeded. For most efficient operation, we recommend a power supply in the 15-18V range for typical 12V applications. The Genasun controller will operate the input power source at its maximum output power, and the power source must be able to sustain this output continuously. Most laptop-style power supplies will not stand this type of operation. For OEM or volume applications requiring charging lead-acid batteries with controllers other than the GV-4 and GV-5, or from input sources that cannot be power-limited (such as batteries), please consult Genasun for custom programming. If the power supply is very stiff, the large inrush current may trip the short circuit protection on the controller. If this happens, add a resistor in series with the input to reduce the stiffness of the power supply.

Blocking diodes are connected in series with panels, are conducting during normal operation, and do introduce a voltage drop. Blocking diodes are not normally built in to panels. Blocking diodes do not provide any performance improvement in partial shading, but will eliminate the possibility of damage from one solar panel feeding into another if they are connected in parallel. Bypass diodes are connected across cells within a panel, are not conducting during normal use, and do not introduce a voltage drop. Typically, 12V nominal panels may include 2 bypass diodes, which can sometimes be seen inside the junction box or within the panel laminate. In principle, bypass diodes can aid in partial shading by allowing current to flow around a shaded cell. In practice, there is no benefit in 12V and 24V systems, as losing 1/2 of a panel will not allow enough voltage to charge the batteries.

Solar Panels are simply energy converters that convert light energy into electrical energy. PV modules produce the most power in bright sun and clear skies. PV modules still produce power in cloudy conditions, but power is reduced because less light energy is available. Light sources other than the sun are not of sufficient intensity to produce significant electrical power.

Temperature sensor cables can be lengthed or shortened as necessary. Note: if the cable is lengthened be sure to observe the + & - (red/blk) polarity.

Open circuit voltage of a battery is a direct function of the specific gravity of the electrolyte at the place in the battery where the chemical reaction occurs. This chemical reaction takes place inside the pores of the active material on the lead plates. If the battery has just been charged, the local electrolyte in the pores of the plates is very rich in sulfuric acid and the battery voltage will be high, perhaps 13 to 14 volts. As the battery rests following charge, voltage slowly drops and stabilizes as the electrolyte mixes. A similar change in battery voltage occurs during discharge. While a fully charged battery may read 12.68 volts open circuit, the voltage will drop and then stabilize at a somewhat lower value as a load is applied to the battery. The change in voltage occurs even though the state of charge of the battery has not significantly changed. This is due to the local electrolyte in the pores of the plates becoming less rich in sulfuric acid as the battery supplies current. As the battery discharges, electrolyte more like sulfuric acid enters the pores while electrolyte more like water exits the pores. As discharge continues, the electrolyte in the pores eventually stabilizes at a specific gravity somewhat lower than the average value in the battery, producing the slightly lower battery voltage.

The primary reason for temperature compensated charging is that the required charging voltage for batteries is based on temperature. With out temperature compensated charging batteries the proper charge voltage can’t be employed. As temperature increases, voltage decreases. Where climate temperatures can be extreme during certain times of the year or in certain parts of the country it is easy to see why temperature compensated charging is necessary.

Inverters are designed to allow you to operate appliances from your 12 volt battery system without shore power or your generator. Inverters are not chargers. Some inverters will have a built in charger to help compensate for what the inverter will draw out of the battery(s) when operating an appliance. An inverter can be handy when you want that pot of coffee and it is before or after generator hours and/or you don’t have a generator. Keep in mind what you take out the battery has to be put back. An investment in a good charging system makes sense if you want to use a large inverter. When selecting an inverter, determine what you want it for as it is easy to get carried away or talked into buying a larger inverter than you really need. You can save yourself money by buying an inverter that meets with your lifestyle choices. WHAT SIZE INVERTER DO YOU NEED? The average RV’er usually only needs one of two types. The first is to operate TV’s, satellite dishes, and laptop computers or similar products. A 500 or 600 watt inverter is great and inexpensive for these tasks. The next step up is for those customers who want to use a microwave, coffeepot or other larger power hungry device. A 1500 to 2500 watt inverter will work for these. Remember a larger bank of batteries will allow you to last longer but still what you take out needs to be put back.

Blue Sky Energy Controllers

The -HV version of the product adds the ability to use “higher voltage” 60 cell solar panels. The product can still process up to 340W of conventional 36 cell 12V solar panels like the previous product, but can also process up to 270W of 60 cell solar panels.

Yes!!! Solar Boost charge controllers can be paralleled for large systems. With paralleled charge controllers the large PV array is divided into sub-arrays with each sub-array connecting to it’s own Solar Boost charge controller. Outputs of the multiple controllers then connect to a common battery.

Yes!!! Absorbed Glass Matt (AGM) batteries are still lead acid chemistry batteries. The default charge voltage settings in Solar Boost charge controllers are typically suitable for AGM batteries. Contact the battery MFG to see if slight adjustments are necessary.

Yes. Some level lightning protection is provided in the form of transient voltage protection on both the PV and battery connections in all Solar Boost charge controllers. If you live in an area prone to lightning you should add additional lightning protection devices. Keep in mind that even with additional lightning protection nothing is 100% lightning proof. Damage due lightning is not covered under warranty.

Yes!! But they must be protected from direct contact with any liquids. All external parts are either powder coated or anodized, while internal electronic components are conformal coated for protection from the elements. However, damage due corrosion is not covered under warranty.

The "Integrated Power Net", or IPN Network is a high-speed digital network that allows Blue Sky energy's IPN compatible charge controllers and displays to communicate with each other and work together. The IPN network allows multiple IPN compatible charge controllers to work together as single unit. Resources can be shared such that a single battery temperature sensor and displays can serve all charge controllers on the IPN network. The IPN network does not require a display or special communication hardware to function.

Yes, but it depends on the battery and its own BMS (Battery Management System). Blue Sky Energy charge controllers are primarily designed to charge lead-acid chemistry batteries which include Flooded, GEL & AGM, and are charged by a multi-stage constant voltage charge algorithm. Lithium batteries require close monitoring of individual cell voltage, current and temperature during both charge and discharge. As such most Lithium batteries are not provided simply as raw cells but rather as a complete battery system which typically includes an accompanying Battery Management System (BMS) to monitor and control both charge and discharge. Blue Sky Energy controllers do not include a lithium BMS since the BMS must be closely matched the particulars of the lithium cells it is managing. Whether Blue Sky Energy charge controllers may be used with a particular lithium battery and its BMS depends on the exact needs of the BMS. Some BMS simply require a constant charge voltage of perhaps 14.6V which all Blue Sky Energy charge controllers can provide. Other BMS may require the charge controller to deliver a higher charge voltage or lower float voltage as requested by the BMS. This can typically be done in several different ways based on the particular charge controller, needs of the BMS, and the means the BMS has available to interface with the charge controller.

Our controllers are sold worldwide. Our master distributors can provide you with a retailer in your area.

The Solar Boost charge controller required by a particular application is determined primarily by battery voltage and total Photovoltaic (PV) power.

Genasun Controllers

Yes. All Genasun controllers prevent reverse current to the panels. This keeps the battery from running current through the panels at night.

All Genasun controllers protect against reverse current (the battery sending power through the panel at night, or during a shaded condition). If you have one controller per panel, you should omit the blocking diodes from the system to achieve better efficiency. With multiple panels in parallel running through one controller, blocking diodes are generally recommended to prevent panel damage, unless the panel manufacturer recommends otherwise.

MPPT Technology

MPPT is short for Maximum Power Point Tracking. MPPT does not physically move the PV modules to make them point more directly at the sun. MPPT is an electronic system that operates the modules in a manner that can extract more PV power and deliver higher charge current than conventional PWM charge controllers. Under optimal conditions Solar Boost MPPT charge controllers can increase charge current up 30% or more.

We were confused too. There are a number of golf-cart boost controllers that are advertised as MPPT controllers . . . until you read the fine print. Some clever marketers or lazy engineers came up with the idea that you can “passively” track the Maximum Power Point by operating at a fixed voltage. This is a joke. Tracking is the essential part of Maximum Power Point Tracking. Why? The Maximum Power Point changes. Tracking is the way you adapt to that change, and collect more power. “Passive” turns out the mean that the controller manufacturer took a guess and picked a voltage that will provide the maximum power for one specific panel, at one specific angle, in one specific lighting condition, at one latitude, at one specific time of the year. With this type of controller, you’ll be lucky to get the the maximum potential power a few times a year. The rest of the time, you’ll be loosing a lot of the panel power you paid for. In our own tests in with a competitor’s buck controller advertising “Nominal MPPT”, we found that the performance was often significantly worse than even a PWM controller.

Yes, technically speaking they do, but that’s about where the similarities end. A PWM controller is 100% on (panel directly connected to battery) during normal charging. Once the batteries are full, it reduces the charging current by pulsing the panel between on and off at a low frequency, often ~300Hz. The pulses are observable on the panel input. The current coming out of a PWM controller when the batteries are not full is always a little less (due to control losses) than the current a panel would deliver when directly connected to the battery. The ONLY charging functions of a PWM controller are to prevent overcharging, and to prevent reverse current flow from battery to panel at night. In contrast, while an MPPT controller uses a PWM-type power conversion technique internally, this function is active all the time, whether the battery is full or not. The frequency is typically much higher, 20kHz and up, and is not directly observable outside the controller; the panel input is a steady DC voltage. Most importantly, the power conversion technique used in MPPT controllers can INCREASE the power delivered to the battery compared to a direct connection to the panel, in addition to preventing overcharge and reverse current flow. The function is analogous the the ability of an automotive transmission to maximize the power delivered by an engine by allowing the engine and wheels to turn at different speed ratios. By contrast, the function of a PWM controller is similar to regulating vehicle speed by leaving the transmission in 5th and quickly pulsing the clutch from fully engaged to fully disengaged.

Technical Tips

There are several different ways to rate batteries, one of which is amp-hours. Simply defined, amp-hours is current multiplied by time. One amp-hour is equal to one amp of current for a period of one hour. In other words, a 105 amp-hour group 27 battery can deliver 5.25 amps for 20 hours before the battery voltage drops to 10.50 volts, at which point the battery is dead. The same battery will also deliver approximately 10.5 amps for 10 hours, and so on. For typical RV batteries, the amp-hour rating is determined at what is termed a 20 hour rate. That is, a constant current is consumed from the battery that will cause battery voltage to drop to 10.50 volts in 20 hours. The actual available amp-hours from a particular battery will be somewhat more if less current is delivered over a longer period, and somewhat less if more current is delivered over a shorter period. The typical amp-hour ratings of batteries used in RVs is shown in Table 1. Note that golf cart batteries are 6 volt. Two golf cart batteries are connected in series to produce the 12 volts required by RVs. Placing batteries in series increases the total voltage to the sum of the batteries (6V+6V=12V), but does not increase amp-hour capacity. Two golf cart batteries still deliver 220 amp-hours. Placing batteries in parallel increases the total amp-hour capacity to the sum of the batteries, but does not increase voltage. For example, a popular combination is two Group 27 batteries in parallel which will deliver a total capacity of 210 amp-hours (2x105AH=210AH).

Battery Size Typical AMP-hours
Group 24 85 Amp-Hours
Group 27 105 Amp-Hours
4D 160 Amp-Hours
8D 220 Amp-Hours
6 Volt Golf Cart 220 Amp Hours

There are two possible ways to determine the remaining capacity of a battery, specific gravity of the electrolyte, and battery voltage. Since access to the electrolyte in a gel type battery is not possible, the voltage method must be used. If the battery is not being charged or discharged, battery voltage will be open circuit voltage, and remaining capacity can be determined from Table 2. If this method is used, the readings should be taken after the battery voltage has stabilized for a period of at least 24 hours after charge or discharge.

Battery Type
Remaining Liquid Electrolyte Gel Electrolyte
Battery Capacity Open Circuit Voltage Specific Gravity Open Circuit Voltage Specific Gravity
100% ≥ 12.68 V 1.265 ≥ 12.95 V N/A
75% 12.44 V 1.225 12.71 V N/A
50% 12.23 V 1.190 12.50 V N/A
25% 12.02 V 1.155 12.29 V N/A
0% 11.80 V 1.120 12.07 V N/A

The electrolyte of a liquid type battery consists of 36% sulfuric acid by weight in water. As the battery is discharged, sulfate in the electrolyte combines with the lead plates of the battery to form lead sulfate. As the plates take up sulfate, the electrolyte becomes more like water and less like sulfuric acid. As the electrolyte becomes more like water, its specific gravity also gets closer to that of water (SG of water =1), as shown in Table 2. The reverse occurs as the battery is charged. As charging current flows through the battery, the battery plates revert back to their original condition and the electrolyte reverts back to its original sulfuric acid content. Batteries are not 100% efficient at converting charging amp-hours back onto stored amp-hours. Replacing 100 amp-hours of consumed capacity will take approximately 110 amp-hours of charge.

All batteries have a maximum current at which they can be safely charged. Charging a battery at a current greater than this maximum value will shorten battery life, and in cases of extreme over current could result in a hazardous condition due to battery overheating. Our model 6210 has a fully adjustable charge current limit feature which is used to provide the maximum charging current possible yet stay within the limits of your particular battery. Consult the battery manufacturer to determine the maximum suitable charging current for your battery bank. Maximum charging current generally varies based on the battery type (liquid or gel electrolyte) and the total amp-hour rating of the battery bank. Maximum charging values are expressed in terms of "C", where "C" is the total amp-hour rating at a 20 hour rate. Typical maximum charging current values are C÷ 3 for a flooded liquid electrolyte battery, or C÷ 5 for a gel battery. For example, the maximum charging current for one 8D liquid electrolyte battery rated at 220 amp-hours would be 220÷ 3 ˜ 73 amps. Using these charge current limit values, the typical maximum charging current limit for various batteries is shown in Table 3.

Battery Typical AMP-hours Maximum Current
One Group 24 = Liquid 85 Amp-Hours 28 AMPS
One Group 27 = Liquid 105 Amp-Hours 35 AMPS
One 8D Liquid 160 Amp-Hours 73 AMPS
One 8D Gel 220 Amp-Hours 40 AMPS
Two 6 Volt Golf Cart = Liquid 220 Amp Hours 73 AMPS

There are four key criteria for proper battery charging: Charging current must be no more than C/3 for flooded liquid batteries and C/5 for gel batteries, where "C" is the AH rating @ 20 hour rate. Two Group 27's maximum current = 2x(105AH)/3 = 210AH/3 ? 70A.
The battery must be charged at a temperature compensated acceptance voltage of ??14.2V @ 80°F, temperature compensated at -16.7mV/°F. As temperature increases, voltage decreases. The acceptance voltage must be applied until battery current decreases to the critical value of 1.0A per 100AH of battery capacity. 1A/100AH is the key indicator of full charge without over charge.
Once the battery is charged, voltage must decrease to a temperature compensated float voltage of 13.3 V @ 80°F. A healthy battery that is fully charged will draw a float charge current of 1/500 to 1/1000 of the C rating, or 0.2-0.4A for 2 Group 27's.
DESIRABLE THREE STAGE CHARGE REQUIREMENTS
1. Temperature compensation: Optimizes float and acceptance voltages based on battery temperature.
2. Some units offer user selectable voltage or temperature -- fully automatic is best.
3. Full charge determination based on actual charging current.
4. Charge current is the best indicator, not time.
5. Must be actual "charging current", not charger output current.
6. Changes with battery size (1.0A/100AH) -- selectable current is best.
7. Selectable battery electrolyte type.
8. Selects the proper acceptance and float voltages for liquid or gel electrolyte.
9. Remote sensing and control of battery current and voltage.
- Voltage sensing eliminates the effect of cabling voltage drop.
- Current sensing allows for proper charge termination, and bulk charge limiting.


Open circuit voltage of a battery is a direct function of the specific gravity of the electrolyte at the place in the battery where the chemical reaction occurs. This chemical reaction takes place inside the pores of the active material on the lead plates. If the battery has just been charged, the local electrolyte in the pores of the plates is very rich in sulfuric acid and the battery voltage will be high, perhaps 13 to 14 volts. As the battery rests following charge, voltage slowly drops and stabilizes as the electrolyte mixes.
A similar change in battery voltage occurs during discharge. While a fully charged battery may read 12.68 volts open circuit, the voltage will drop and then stabilize at a somewhat lower value as a load is applied to the battery. The change in voltage occurs even though the state of charge of the battery has not significantly changed. This is due to the local electrolyte in the pores of the plates becoming less rich in sulfuric acid as the battery supplies current. As the battery discharges, electrolyte more like sulfuric acid enters the pores while electrolyte more like water exits the pores. As discharge continues, the electrolyte in the pores eventually stabilizes at a specific gravity somewhat lower than the average value in the battery, producing the slightly lower battery voltage.

Temperature compensation: The primary reason for temperature compensated charging is that the required charging voltage for batteries is based on temperature. With out temperature compensated charging batteries the proper charge voltage can’t be employed. As temperature increases, voltage decreases. Where climate temperatures can be extreme during certain times of the year or in certain parts of the country it is easy to see why temperature compensated charging is necessary.


Inverters are designed to allow you to operate appliances from your 12 volt battery system without shore power or your generator. Inverters are not chargers. Some inverters will have a built in charger to help compensate for what the inverter will draw out of the battery(s) when operating an appliance. An inverter can be handy when you want that pot of coffee and it is before or after generator hours and/or you don’t have a generator. Keep in mind what you take out the battery has to be put back. An investment in a good charging system makes sense if you want to use a large inverter.
When selecting an inverter, determine what you want it for as it is easy to get carried away or talked into buying a larger inverter than you really need. You can save yourself money by buying an inverter that meets with your lifestyle choices.

WHAT SIZE INVERTER DO YOU NEED?
The average RV’er usually only needs one of two types. The first is to operate TV’s, satellite dishes, and laptop computers or similar products. A 500 or 600 watt inverter is great and inexpensive for these tasks. The next step up is for those customers who want to use a microwave, coffeepot or other larger power hungry device. A 1500 to 2500 watt inverter will work for these. Remember a larger bank of batteries will allow you to last longer but still what you take out needs to be put back.