Frequently Asked Questions
Why do I need an MPPT Charge Controller between the Solar Panel & Battery?
There are 2 very important reasons:
1) To Extract the maximum power out of the panel and transfer that energy into the battery (PWM controllers do not do this).
2) To STOP charging when the battery is full and go into a standby mode to prevent battery damage.
Connecting a panel directly will waste lots of available power and damage the battery if left connected when full. It can become a safety risk overcharging a battery by exceeding its maximum voltage during charge.
Why would I need a Buck Boost Charge Controller?
1) A Buck Boost Controller will produce power in lower light where a standard Buck only controller can not operate since it is not able to boost the voltage.
2) If the battery voltage is HIGHER than the panel MPPT voltage then boost function is needed. This is common with 60 cell panels and a 24 volt battery system - a standard controller will not extract all of the available power.
3) During partial shading of solar panels the MPPT point can drop BELOW the battery voltage so a voltage BOOST function is needed.
Our Buck Boost Controllers transition between Buck and Boost modes automatically and seamlessly to provide power under all possible conditions. On a higher power, 24 volt system this becomes a huge advantage over traditional Buck only controllers.
Why would I use multiple smaller controllers versus one large one?
There are 4 key reasons:
1) Single point of failure would take down the ENTIRE system in the case of one large controller and a series high voltage string of panels. Using multiple smaller controllers increases system reliability.
2) If one panel has a shadow in a large series string that panel will produce little or no power due to bypass diodes in the panel. By using multiple controllers tied to individual panels or a parallel pair the system output power is increased as that partially shaded panel can still produce significant power with our controllers.
3) Multiple controllers increase system power output - each operates as a panel power optimizer and has higher power conversion efficiency than would a single large controller. System Output can be 5% to 10% more in this configuration.
4) You are not dealing with very dangerous and potentially fatal high voltages with our multiple-controller approach.
Why does my solar panel not output the rated power?
Solar Panels are rated at Standard Test Conditions or STC, which is not a real world operating condition. STC is a panel cell temperature of 25°C / 77°F and full sunlight. Solar panels heat up from sunlight and as they do the power drops about 0.45% per °C. Typical temperature rise in full sun is about 40°C / 72°F or a power loss of about 18% from the STC Rating. So, a “245 Watt Panel” will actually produce about 82% of that or 200.9 Watts in Full Sun on a typical Summer Day at 25°C / 77°F.
What does the NOCT Solar Panel Rating mean?
NOCT stands for Nominal Operating Cell Temperature and is 45°C / 113°F with 80% Sunlight intensity. This is usually about 75% of the STC Rating and would be a typical operating condition. The Same “245 Watt” Panel mentioned above has a NOCT rating of 185 watts. Not all panels have this rating but it is more of a real world condition.
How can I tell if my battery is fully charged?
When the Output Voltage reaches 14.4 volts and the current drops to a low value without system load then the battery is Full. The LCD Display will indicate “Bat” “Full” and the voltage. The Power Stage will shutdown. When the Battery drops below 13.5 volts the Charger will resume operation automatically. On a 24 volt system those numbers are 28.8 and 27.0 volts.
What is MPPT and how does it work?
MPPT is an acronym for Maximum Power Point Tracking. Our Solar Charger has this feature and will even extract power out of a partially shaded panel where other charge controllers will not. The Charge Controller is constantly adjusting to this optimum operating point and maintains >99.9% of Maximum Power down to below 1 Watt Output. It does this by monitoring the voltage and current to determine where the optimum operating point is and adjusts this about 6000 times every second.
What is the difference between a “PWM” Controller and Our Charge Controller?
PWM stands for “Pulse Width Modulation”. A PWM controller is only a ON/OFF switch that uses a relay or transistor to switch the solar panel directly to the battery on and off without power conversion of any kind. This wastes a lot of power because you are never operating at the maximum power point. Our Charge Controller is a True DC to DC Power Converter which transfers more than 99% of the Solar Panel’s power to the system battery and doing this while tracking the optimum power point to >99.9% at all times. See our Performance Comparison on the home page for more details.
Our Charge Controller’s are the most efficient on the market and will give every last watt of power the solar panel can produce. Most other Charge Controllers use Heat Sinks that take wasted power and warm the air - We do NOT need them because less than 4 watts are lost at 250 watts output at 12 volts and 500 watts output at 24 volts.
Can Solar work on Cloudy days or in Northern Latitudes / Colder Climates?
YES... Solar Panels still produce power when cloudy. The amount depends on the conditions but varies from about 5% to 40% of full sun output. Solar Panels LOVE cold weather and produce MORE power when cold. A cold winter day can approach the STC rating on a panel if there is some wind and / or the air temperature is well below freezing. The shorter winter days are partially offset by the colder temperatures. A large battery bank also helps out on cloudy days to augment the system power needs.
What angle is best for my panels?
North of the Equator Solar panels should face due South if possible and be tilted at the mid point between the sun angle on December 21 and June 21. As a guide take your latitude in degrees and add 3. For Example Detroit Michigan is 42° North so the panel tilt would be optimal at 45°. People in the Southern Hemisphere would face their panels North. This gives the best year around power production. The tilt angle can be adjusted up for more Summer Power or down for more winter power at the sacrifice of the other. Near the Equator facing nearly straight up is best with a slight tilt for water drainage. Keep in mind that a panel angle error of 25 degrees from perpendicular is still 90% power.
What Size Solar Panel can I use with the Charge Controller?
The Apollo model Charge Controller will work with panels as small as 10 watts and as large as 280 Watts on 12 volts and 560 Watts on 24 volts. The open circuit voltage must be between 20 and 50 volts for 12 volts and 30 to 50 for 24 volts. Smaller Panels can be connected in series / parallel to make an array as long as it meets the above voltage and power requirements. Panels in series MUST have the same current rating (matched type and size). Parallel Panels must have same number of solar cells or voltage rating but can be different wattage. Our Sol Buck Boost can use up to 350 watts STC on a 12 volt system and 700 watts STC on a 24 volt system. Ra is 12 volt only and 3.5 amps can use up to a 60 watt solar panel.
How many Charge Controller Outputs can be connected in Parallel?
There is no limit to how many can be connected to a system. Each one should go through a 20 amp Circuit Breaker or Fuse to the main DC System Buss and Battery Bank. Systems of many thousands of watts can easily be built by adding panels and charge controllers. Only parallel the output—do NOT parallel inputs as each controller should have ONE panel or array of up to 280 / 560 Watts connected. Our 20 Amp Buck Boost handles 350 / 700 Watts STC Rating for Solar input on 12 and 24 volts respectively.
What types of Batteries can I use?
Any standard Deep Cycle 12 volt Battery can be used however for best performance a 4 or 8 cell Lithium Iron Phosphate Battery will give far superior performance. When using the Lithium cells it is STRONGLY Recommended to use some form of cell balancing and over discharge protection. Most DC-AC inverters shut down at 10.5 volts which is highly desirable. The Full Charge Voltage for Lithium Iron Phosphate is 14.4 / 28.8 volts and is the same for the Deep Cycle Batteries. DO NOT USE A CAR BATTERY— cycle life will be very short. Also of importance is depth of discharge when using Deep Cycle Batteries do not discharge over 50% otherwise the life will be much shorter. Lithium Iron Phosphate does not have this limitation and gives a far superior cycle life. See more information about batteries on the “Solar Components” page.
Another important consideration is charge efficiency... Deep Cycle Batteries only return about 65% of the energy used to charge them because the remainder is lost in heat and out-gassing. Lithium Iron Phosphate is >99% energy return. We have 8 year old Lithium Iron Phosphate Batteries in service at our Solar Research Facility that still deliver 100% of their rated capacity after more than 2000 charge and discharge cycles.
How many Amp Hours should my Batteries have?
The answer depends on your usage...how much power you need and for how long determines the number. For an off-grid application you should have at least 3 days worth of battery capacity to support the average power load… this allows for 3 consecutive cloudy days and still have power. As a rough guide for every 100 watt-hours of load you should have 30 amp hours of battery with Deep Cycle and 10 amp hours with Lithium Iron Phosphate cells. The difference is because you should not discharge Deep Cycle more than 30% so you need 3x the battery capacity for longest cycle life. Lithium Iron Phosphate does not have this limitation.
How many Solar Panels do I need?
The answer depends on power needs and how much average sunlight you get per day. Typically you want your batteries to fully re-charge with as little as 4 hours of sunlight and at the same time support your AVERAGE power load. So using a 60 amp hour battery and 4 hour charge time you need 15 amps of charge current or 1 charger board hooked to a 250 watt panel as a minimum. If you get a lot less of sun you need to use more panels and boards to compensate for the cloudy days. When doing an off grid system its better to size the solar array for the MINIMUM sunlight to meet electrical needs so you never run short of power. This would occur during the winter solstice or shortest day of the year.
Cloudy climates should be 5x to 10x the average load to ensure you don't run out of power. Better to have extra than not enough. A backup generator is a good idea for times its cloudy for a week straight.
What happens if I connect too much solar to the Board?
The answer somewhat depends on if its too much voltage or too much power— Too much Voltage can damage the unit. Over 50 volt for Apollo and 54 volts for Sól but less than 60 volts the board will display “Err” then “001” or “O.L.” depending on which version you have.
Above 60 volts will cause PERMANENT DAMAGE and is not covered under warranty.
Hooking up too much power (Over the STC Rating) can cause either the current limit to activate or an over temperature “Hot” shutdown. This will not damage the charge controller but you will not be getting the full available power of your panel at that point during peak conditions around solar noon.
So its important to stay within the Charge Controller specification limits.
Apollo = 280 / 560 Watts STC for 12 / 24 volts respectively V2.xx version
Sól = 350 / 700 Watts STC for 12 / 24 volts respectively on the 20 amp V1.04 version or later
What Happens if I hook up the Solar Panel reverse Polarity?
The Protection will activate and the board will sit in power down mode (OFF) until the fault is corrected as long as the voltage is less than 60 volts. Above that permanent damage will occur and that is not covered under warranty.
What Happens if I hook up the Battery reverse Polarity?
The Protection will activate and the board will sit in power down mode (OFF) until the fault is corrected as long as the voltage is less than 30 volts. Above that permanent damage will occur and that is not covered under warranty.
Is the unit protected from Water or liquid Spills?
No—and that is not covered under warranty. Keep it dry.
What Happens if the Air Temperature is OVER 114F (45C)?
The Thermal Protection may activate if the average Board Temperature reaches 165F / 170F and limit the Power Output. “Hot” will display on the LCD during thermal shutdown. This will not damage the unit however you no longer will get the full output of your panel. It is therefore important to allow natural convection cooling when using the controller with larger panels. Best to use the charge controller indoors in a temperature controlled environment so this never happens. The controller is designed for open air panel mounting or wall mounting.
How long can my wires be?
Keep in mind that long wires loose power especially at higher currents. Use #12 wire for BOTH input and output. Solid THHN wire is easier to work with. For Best Performance keep them as short as possible— less than 50 feet on the Panel side and less than 5 Feet on the battery side. Power loss can be calculated as follows: (Current in Amps)^2 * Resistance in ohms. #12 wire is about 0.003 ohms per foot at room temperature (both sides added) so a 5 foot cable at 16 amps will have losses of about 3.84 watts (16*16*.015=3.84).
Panel wires can be longer than 50 feet just keep in mind the power loss in the wire when sizing a system. #10 AWG wire can be used to reduce this loss on longer runs.
If there are any additional questions you think should be added please let us know at www.diysolarforu.com and fill out the “contact us” section.
There are 2 very important reasons:
1) To Extract the maximum power out of the panel and transfer that energy into the battery (PWM controllers do not do this).
2) To STOP charging when the battery is full and go into a standby mode to prevent battery damage.
Connecting a panel directly will waste lots of available power and damage the battery if left connected when full. It can become a safety risk overcharging a battery by exceeding its maximum voltage during charge.
Why would I need a Buck Boost Charge Controller?
1) A Buck Boost Controller will produce power in lower light where a standard Buck only controller can not operate since it is not able to boost the voltage.
2) If the battery voltage is HIGHER than the panel MPPT voltage then boost function is needed. This is common with 60 cell panels and a 24 volt battery system - a standard controller will not extract all of the available power.
3) During partial shading of solar panels the MPPT point can drop BELOW the battery voltage so a voltage BOOST function is needed.
Our Buck Boost Controllers transition between Buck and Boost modes automatically and seamlessly to provide power under all possible conditions. On a higher power, 24 volt system this becomes a huge advantage over traditional Buck only controllers.
Why would I use multiple smaller controllers versus one large one?
There are 4 key reasons:
1) Single point of failure would take down the ENTIRE system in the case of one large controller and a series high voltage string of panels. Using multiple smaller controllers increases system reliability.
2) If one panel has a shadow in a large series string that panel will produce little or no power due to bypass diodes in the panel. By using multiple controllers tied to individual panels or a parallel pair the system output power is increased as that partially shaded panel can still produce significant power with our controllers.
3) Multiple controllers increase system power output - each operates as a panel power optimizer and has higher power conversion efficiency than would a single large controller. System Output can be 5% to 10% more in this configuration.
4) You are not dealing with very dangerous and potentially fatal high voltages with our multiple-controller approach.
Why does my solar panel not output the rated power?
Solar Panels are rated at Standard Test Conditions or STC, which is not a real world operating condition. STC is a panel cell temperature of 25°C / 77°F and full sunlight. Solar panels heat up from sunlight and as they do the power drops about 0.45% per °C. Typical temperature rise in full sun is about 40°C / 72°F or a power loss of about 18% from the STC Rating. So, a “245 Watt Panel” will actually produce about 82% of that or 200.9 Watts in Full Sun on a typical Summer Day at 25°C / 77°F.
What does the NOCT Solar Panel Rating mean?
NOCT stands for Nominal Operating Cell Temperature and is 45°C / 113°F with 80% Sunlight intensity. This is usually about 75% of the STC Rating and would be a typical operating condition. The Same “245 Watt” Panel mentioned above has a NOCT rating of 185 watts. Not all panels have this rating but it is more of a real world condition.
How can I tell if my battery is fully charged?
When the Output Voltage reaches 14.4 volts and the current drops to a low value without system load then the battery is Full. The LCD Display will indicate “Bat” “Full” and the voltage. The Power Stage will shutdown. When the Battery drops below 13.5 volts the Charger will resume operation automatically. On a 24 volt system those numbers are 28.8 and 27.0 volts.
What is MPPT and how does it work?
MPPT is an acronym for Maximum Power Point Tracking. Our Solar Charger has this feature and will even extract power out of a partially shaded panel where other charge controllers will not. The Charge Controller is constantly adjusting to this optimum operating point and maintains >99.9% of Maximum Power down to below 1 Watt Output. It does this by monitoring the voltage and current to determine where the optimum operating point is and adjusts this about 6000 times every second.
What is the difference between a “PWM” Controller and Our Charge Controller?
PWM stands for “Pulse Width Modulation”. A PWM controller is only a ON/OFF switch that uses a relay or transistor to switch the solar panel directly to the battery on and off without power conversion of any kind. This wastes a lot of power because you are never operating at the maximum power point. Our Charge Controller is a True DC to DC Power Converter which transfers more than 99% of the Solar Panel’s power to the system battery and doing this while tracking the optimum power point to >99.9% at all times. See our Performance Comparison on the home page for more details.
Our Charge Controller’s are the most efficient on the market and will give every last watt of power the solar panel can produce. Most other Charge Controllers use Heat Sinks that take wasted power and warm the air - We do NOT need them because less than 4 watts are lost at 250 watts output at 12 volts and 500 watts output at 24 volts.
Can Solar work on Cloudy days or in Northern Latitudes / Colder Climates?
YES... Solar Panels still produce power when cloudy. The amount depends on the conditions but varies from about 5% to 40% of full sun output. Solar Panels LOVE cold weather and produce MORE power when cold. A cold winter day can approach the STC rating on a panel if there is some wind and / or the air temperature is well below freezing. The shorter winter days are partially offset by the colder temperatures. A large battery bank also helps out on cloudy days to augment the system power needs.
What angle is best for my panels?
North of the Equator Solar panels should face due South if possible and be tilted at the mid point between the sun angle on December 21 and June 21. As a guide take your latitude in degrees and add 3. For Example Detroit Michigan is 42° North so the panel tilt would be optimal at 45°. People in the Southern Hemisphere would face their panels North. This gives the best year around power production. The tilt angle can be adjusted up for more Summer Power or down for more winter power at the sacrifice of the other. Near the Equator facing nearly straight up is best with a slight tilt for water drainage. Keep in mind that a panel angle error of 25 degrees from perpendicular is still 90% power.
What Size Solar Panel can I use with the Charge Controller?
The Apollo model Charge Controller will work with panels as small as 10 watts and as large as 280 Watts on 12 volts and 560 Watts on 24 volts. The open circuit voltage must be between 20 and 50 volts for 12 volts and 30 to 50 for 24 volts. Smaller Panels can be connected in series / parallel to make an array as long as it meets the above voltage and power requirements. Panels in series MUST have the same current rating (matched type and size). Parallel Panels must have same number of solar cells or voltage rating but can be different wattage. Our Sol Buck Boost can use up to 350 watts STC on a 12 volt system and 700 watts STC on a 24 volt system. Ra is 12 volt only and 3.5 amps can use up to a 60 watt solar panel.
How many Charge Controller Outputs can be connected in Parallel?
There is no limit to how many can be connected to a system. Each one should go through a 20 amp Circuit Breaker or Fuse to the main DC System Buss and Battery Bank. Systems of many thousands of watts can easily be built by adding panels and charge controllers. Only parallel the output—do NOT parallel inputs as each controller should have ONE panel or array of up to 280 / 560 Watts connected. Our 20 Amp Buck Boost handles 350 / 700 Watts STC Rating for Solar input on 12 and 24 volts respectively.
What types of Batteries can I use?
Any standard Deep Cycle 12 volt Battery can be used however for best performance a 4 or 8 cell Lithium Iron Phosphate Battery will give far superior performance. When using the Lithium cells it is STRONGLY Recommended to use some form of cell balancing and over discharge protection. Most DC-AC inverters shut down at 10.5 volts which is highly desirable. The Full Charge Voltage for Lithium Iron Phosphate is 14.4 / 28.8 volts and is the same for the Deep Cycle Batteries. DO NOT USE A CAR BATTERY— cycle life will be very short. Also of importance is depth of discharge when using Deep Cycle Batteries do not discharge over 50% otherwise the life will be much shorter. Lithium Iron Phosphate does not have this limitation and gives a far superior cycle life. See more information about batteries on the “Solar Components” page.
Another important consideration is charge efficiency... Deep Cycle Batteries only return about 65% of the energy used to charge them because the remainder is lost in heat and out-gassing. Lithium Iron Phosphate is >99% energy return. We have 8 year old Lithium Iron Phosphate Batteries in service at our Solar Research Facility that still deliver 100% of their rated capacity after more than 2000 charge and discharge cycles.
How many Amp Hours should my Batteries have?
The answer depends on your usage...how much power you need and for how long determines the number. For an off-grid application you should have at least 3 days worth of battery capacity to support the average power load… this allows for 3 consecutive cloudy days and still have power. As a rough guide for every 100 watt-hours of load you should have 30 amp hours of battery with Deep Cycle and 10 amp hours with Lithium Iron Phosphate cells. The difference is because you should not discharge Deep Cycle more than 30% so you need 3x the battery capacity for longest cycle life. Lithium Iron Phosphate does not have this limitation.
How many Solar Panels do I need?
The answer depends on power needs and how much average sunlight you get per day. Typically you want your batteries to fully re-charge with as little as 4 hours of sunlight and at the same time support your AVERAGE power load. So using a 60 amp hour battery and 4 hour charge time you need 15 amps of charge current or 1 charger board hooked to a 250 watt panel as a minimum. If you get a lot less of sun you need to use more panels and boards to compensate for the cloudy days. When doing an off grid system its better to size the solar array for the MINIMUM sunlight to meet electrical needs so you never run short of power. This would occur during the winter solstice or shortest day of the year.
Cloudy climates should be 5x to 10x the average load to ensure you don't run out of power. Better to have extra than not enough. A backup generator is a good idea for times its cloudy for a week straight.
What happens if I connect too much solar to the Board?
The answer somewhat depends on if its too much voltage or too much power— Too much Voltage can damage the unit. Over 50 volt for Apollo and 54 volts for Sól but less than 60 volts the board will display “Err” then “001” or “O.L.” depending on which version you have.
Above 60 volts will cause PERMANENT DAMAGE and is not covered under warranty.
Hooking up too much power (Over the STC Rating) can cause either the current limit to activate or an over temperature “Hot” shutdown. This will not damage the charge controller but you will not be getting the full available power of your panel at that point during peak conditions around solar noon.
So its important to stay within the Charge Controller specification limits.
Apollo = 280 / 560 Watts STC for 12 / 24 volts respectively V2.xx version
Sól = 350 / 700 Watts STC for 12 / 24 volts respectively on the 20 amp V1.04 version or later
What Happens if I hook up the Solar Panel reverse Polarity?
The Protection will activate and the board will sit in power down mode (OFF) until the fault is corrected as long as the voltage is less than 60 volts. Above that permanent damage will occur and that is not covered under warranty.
What Happens if I hook up the Battery reverse Polarity?
The Protection will activate and the board will sit in power down mode (OFF) until the fault is corrected as long as the voltage is less than 30 volts. Above that permanent damage will occur and that is not covered under warranty.
Is the unit protected from Water or liquid Spills?
No—and that is not covered under warranty. Keep it dry.
What Happens if the Air Temperature is OVER 114F (45C)?
The Thermal Protection may activate if the average Board Temperature reaches 165F / 170F and limit the Power Output. “Hot” will display on the LCD during thermal shutdown. This will not damage the unit however you no longer will get the full output of your panel. It is therefore important to allow natural convection cooling when using the controller with larger panels. Best to use the charge controller indoors in a temperature controlled environment so this never happens. The controller is designed for open air panel mounting or wall mounting.
How long can my wires be?
Keep in mind that long wires loose power especially at higher currents. Use #12 wire for BOTH input and output. Solid THHN wire is easier to work with. For Best Performance keep them as short as possible— less than 50 feet on the Panel side and less than 5 Feet on the battery side. Power loss can be calculated as follows: (Current in Amps)^2 * Resistance in ohms. #12 wire is about 0.003 ohms per foot at room temperature (both sides added) so a 5 foot cable at 16 amps will have losses of about 3.84 watts (16*16*.015=3.84).
Panel wires can be longer than 50 feet just keep in mind the power loss in the wire when sizing a system. #10 AWG wire can be used to reduce this loss on longer runs.
If there are any additional questions you think should be added please let us know at www.diysolarforu.com and fill out the “contact us” section.
Contact us at: DIYSolarForU@gmail.com