Complete Solar Chargers: Frequently Asked Questions
- What is a “Complete Solar Charger Kit”?
AM Solar Complete Solar Charger Kits are designed to include everything needed to charge a battery bank with power from the sun. Different kit variants conform to a variety of applications and degrees of customization. The simplest of these kits are designed to mesh with factory installed pre-wire systems, others extend the wire harness up to the roof, some offer multiple combiner box options, and some offer everything, including panels and mounts.
- What is included in a “Complete Solar Charger Kit”?
Depending on the kit variant, there may be solar panels, mounts, sealant, roof cables, a combiner box, main wire harness, disconnect switch, charge controller, circuit protection, lugs, and heat shrink.
- Why would someone get a “Complete Solar Charger Kit”?
AM Solar simplifies the process of designing and installing a solar array by creating pre-configured kits with properly rated and compatible components that have been proven in our installation bays and on hundreds of RVs across North America. Our kits are a one-stop shop for a pre-engineered solution. If you have a unique application that requires something a little different, let us know, and we’ll customize one of the kits for you.
- What does the charge controller do?
A good charge controller system efficiently draws power from a solar panel, or group of solar panels, and converts the electricity into a form that can safely charge a battery bank.
- What is a combiner box?
A combiner box serves two purposes. The first is to combine the wires coming from each solar panel or string of solar panels in series or parallel (typically parallel) and the second is to cover the roof penetration, feeding wires down to the charge controller.
Learn more: Combiner Box | RV Solar Combing Box
- What is the main wire harness?
This is the cable that goes from the combiner box down to the charge controller, and then to the battery bank. This needs to be thick enough to handle the current over a long distance without creating an excessive voltage drop that will reduce the efficiency of the system.
- What do I need for fuses or breakers in a solar charging system?
First of all you don’t need to be an electrical engineer, kits from AM Solar have all the components properly sized for you and we would be happy to help you design a custom kit. Circuit protection on a mobile solar charging system should be between the positive output of the charge controller and the battery bank. Select a breaker or fuse that is rated just above the current rating of the charge controller. For example, use 20A fuse on a 15A charge controller, or a 40A breaker on a 30A charge controller. As for circuit protection between the panels and the charge controller, we find that fusing individual panels is optional at best; at worst, it’s an unnecessary layer of protection that doesn’t really protect the system from anything it would encounter in the real world.
- Does a solar charge controller stop a battery from overcharging?
Yes, a solar charge controller prevents a battery from overcharging by regulating the voltage and current coming from the solar panels to the battery. After charging a battery, a solar charge controller switches to a maintenance or float mode to keep the battery at full charge without overcharging. It continuously monitors the battery voltage and reduces the charging current to prevent damage and extend the battery’s life.
- How far can a solar charge controller be from the battery?
The distance between a solar charge controller and the battery can vary, but it is generally recommended to keep it as short as possible, ideally within 10 feet (3 meters) to minimize voltage drop and ensure efficient charging. Longer distances can be accommodated with thicker gauge wires to reduce resistance and maintain proper voltage levels. However, it’s crucial to follow the manufacturer’s guidelines for wire size and maximum distance to ensure optimal performance and safety.
- How do I figure out what size Victron charge controller to use?
After you determine what solar panels fit on your roof, and what portable panels you might want to add, sum the wattage, and use that number to select the appropriate charge controller kit.
After you have your solar array planned, now you need to select the appropriate Charge Controller Kit.
An easy way do it is with a Quick Current Approximation:
When you are dealing with small, parallel-connected solar panels that have a Vmp of around 20V, you rarely bump into the input limitations of maximum open circuit voltage (Voc) or maximum short circuit current (Isc), and you can get away with a simple calculation:
Array Wattage / Battery Voltage x 90% Efficiency = Charging Current
If you have four 100W solar panels on a 12V system, the math is 4 x 100 x 90% / 12 = 30A
Learn more: How to select the right charge controller for you array
- Is there a quick reference for what size charge controller and cable should use based on solar wattage?
The list below has wiggle room, but this is generally what we use:
< 230W 15A 8ga
< 300W 20A 8ga
< 450W 30A 6ga
< 700W 50A 4ga
<1000W 70A 2ga
<1250W 85A 2ga
<1600W 100A 2ga
- What’s the difference between PWM and MPPT charge controllers?
PWM type charge controllers are simpler and less expensive than MPPT type charge controllers. MPPT type charge controllers, like the Victron SmartSolar MPPTs have the ability to convert excess panel voltage into higher charging amps, which means that they will produce about 15% more power than PWM type charge controllers.
Learn more: MPPT vs. PWM What does it mean?
- What if you use the wrong size of charge controller?
If you graph the wattage output of a solar array over time from morning to night, you will see a bell curve distribution, with a peak at mid-day. If you have a solar array that doesn’t exceed the Voc or Isc limit of the charge controller, but is capable of producing more power than the charge controller can pass, you will get output clipping. This doesn’t harm the charge controller, it just gives you a bell curve with a flat peak.
An example of this would be eight 100W panels on a 100/50 charge controller. On a very bright day, an 800W array might be able to feed 60A onto a 12V battery bank, but if you use the 100/50 charge controller, it will be limited to 50A. The 10A that could be, with a larger charge controller, isn’t dissipated as heat, it just doesn’t exist, because the charge controller draws power at a less efficient point along the IV curve in order to keep from overloading. If you don’t know what I’m talking about in terms of the “IV curve” I have a video on that.
Along similar lines, if you have an undersized solar array, or oversized charge controller, this is perfectly reasonable. We design many of our systems this way, to give our clients room to expand if they want to enlarge their solar array. Or to incorporate un-regualted portabel panels into the main solar charging system. But, if you exceed the input voltage limit, or input current limit of a charge controller, you may damage that controller. It’s easy to avoid this expensive mistake, just read the specifications and be comfortable doing addition.
Learn more: AM Solar Education: Solar Panel Specs and IV Curve
- Do you need to size the solar array based on the size of the battery bank?
If you have a lead-acid battery bank, you need to make sure you are topping your batteries off at least once per week to keep them healthy. This establishes a lower limit. While you can’t have too much solar, if your batteries are fully charged most of the time, your solar isn’t doing anything, and you likely spent too much on solar. Because of this, we recommend a ratio of 50W-200W of solar per 100Ah of lead-acid battery capacity. With lithium batteries, you do not need a regular charge, and there is no correlation between solar wattage and battery bank capacity.
- How should I configure my solar panels if I have a 24V battery bank?
With a 12V battery bank, you can series panels and have an array with a higher voltage, like 36V, and the charge controller will step it down. With a 24V battery bank, you NEED to have that higher voltage in order to feed current onto your battery bank. This higher voltage is frequently accomplished by series connected solar panels, or specialty panels with a VMP of 36V.
- What should I watch out for when using old solar panels?
This comes up very infrequently with 12V systems, but you’ll want to make sure your Vmp (Voltage at maximum power) exceeds your nominal battery bank voltage by at least 50%. A voltage that is too low won’t damage anything, but it also won’t result in any charging current. For example, we have had success with 17.7Vmpp panels on a 12V battery bank, but I prefer to keep the array over 18V.
- What could go wrong?
Improperly designed systems might not be able to handle all of the power from the solar array. Undersized components may result in inefficiencies or even fires. Poor-quality components may not last very long and could damage your RV. Over-engineered systems may not be as economically efficient as some electrically sound alternatives.
- Where do you start designing your system, is it solar first? What’s the first step in designing a solar charging system?
You need to figure out how many watts of solar you may want, and in order to do that, you need to consider your constraints. Solar charging systems are typically limited by physical space, budget, and energy requirements. Since a system can be expanded over time, the most important constraint is the physical space where you can mount solar panels. If you’re pretty sure maxing out your available roof space is going to be cost-prohibitive, factor in a budget constraint. If you are only going to power some small loads, and don’t see that need changing in the foreseeable future, then you’ll likely want to do some production calculations and establish an energy production goal.
- What’s a good way to see what solar panels will fit on your roof?
Some simple ways to see what solar panels fit on your roof would be to make cardboard rectangles the size of the solar panels and place them on your actual roof. You can also use painter’s tape to make a scaled version of your roof on a floor. Don’t forget to take into account space for mounting hardware, a path to walk on or access the roof, and any obstructions like vents, antennas, etc. Panel dimensions are clearly listed on our website.
- About how much energy will get from a solar panel?
In Eugene, Oregon (near our headquarters) a tilted 100W solar panel will produce an average throughout the entire year, of 295Wh per day. Since we are in a somewhat overcast climate, at a latitude further north of most of our customers, we feel confident using a 3x multiplier for keeping the math simple and approximating daily solar productions in terms of watt-hours based on a known solar array wattage. This means that if you have 300W of solar panels you’ll get about 900Wh of energy production per day. Of course, you get more than this in the summer, less than this in the winter, and none if you park in the shade.
- How do I know which panels are best for my application?
There are a wide variety of panels. You can base your selection on fit, aesthetics, brand preferences, etc. As long the panel does not violate your aesthetic plans and brand preferences, we recommend mounting the largest panels (as long as they are mobile solar panels, not residential solar) that will fit, because the cost of mounting a 200W panel is the same as the cost to mount a 100W panel.
- Why don’t you have higher-wattage panels?
We don’t recommend using residential solar panels in mobile applications. These are typically panels rated at 270W or more. Their larger frames make them more difficult to mount and they don’t hold up well to road vibration. The wider spans of glass tend to flex more, which leads to microfractures in the cells, which leads to a decline in performance over time. Additionally, these larger panels typically have a higher voltage which makes it difficult to mix future add-on panels. That being said, many people use them, and the price might be low enough to offset the reduced performance.
- Can panels be mixed or do they all have to be the same?
Panels with a similar (operating voltage) Vmpp (within about 3V) can be connected in parallel. The closer they are in voltage, the more efficient the system will be. If you parallel connect two panels with a different Vmp, or series connect two panels with a different Imp, the combined panels will be forced to operate at a weighted average Vmp (parallel) or Imp (series). This new operating point won’t be optimal, but it will be close. The loses from the sub-optimal configuration will be much smaller than the wattage contribution of the odd panel, so in most cases, we’re fine with it. Just don’t mix something like a 300W residential panel with a 100W off-grid panel. The voltages and currents will be way off and may push a panel outside its rated operating rage.
- What do all the variants within each of your panel models represent?
Each of our solar panels is sold with a number of variants to match the different ways that they can be connected to a system. Raw panels are just panels, with no mounts or wire harnesses. Other options represent unique connection types that might be used with a particular combiner box or wire harness (e.g. MC4, SAE, ATP, or AMS C-box). You can also choose if the panel will be connected in series to an existing panel.
- Should I tilt my solar panels?
Solar panels produce more power when they are pointed toward the sun. Some people like to tilt their panels to increase the cross-sectional surface area exposed to the sun. This makes sense for large rigs like 5th wheels, that are stationary for long periods of time, but tilting is rarely worth the effort on a van. The panels would need to flattened before driving and the increase in energy production would be very small.
- What are the pros and cons of portable panels?
AM Solar sells a wide variety of portable panels that can work along with a roof-mounted solar array.
Pros:
You have the option for more power than what your roof allows.
You can park in the shade without losing your ability to charge.
Cons:
Portables can be prone to theft, bulky and heavy.
You might trip over the cables and you have to move them to keep them in the sun.
When we work with portable panels, we prefer to remove the factory solar charger, and route the portable panel to the same charge controller that the roof array is using. This gives you several advantages: A better quality MPPT charge controller, higher line voltage means less line losses, monitoring of all solar on one system.
Learn more: How to get the most out of your portable solar panel
- What are the pros and cons of flexible solar panels?
Flexible panels are great if durability and a low profile are your biggest concerns. Because of this, we think they make great portable panels. But, we don’t recommend permanently mounting flexible panels to a vehicle’s roof. In all the brands that we have tested, we have seen that flexible panels tend to only last about two years (look at the warranty of a flexible panel and compare it to the standard 25 year warranty of a conventional panel.) Flexible panels also don’t produce as well as conventional panels when exposed to off-angle light. Probably the worst consequence of using flexible panels is that they transfer heat to your roof whereas conventional panels shade your roof. I’ve seen burn marks on roofs.
Learn more: Friends don’t let friends mounts flexible panels directly to their roof
- How are panels mounted?
Most of our solar panel kits come with a two piece stainless steel mounts that are designed to grip the frame of the panel and attach directly to the vehicle’s roof. Our non-penetrating mounts adhere to the roof with 3M VHB tape, which is covered by sealant, and designed to provide a strong hold for the life of the vehicle. By having a two piece mount set, the L-Foot is fasten to the roof and the mount adapter to the panel, all conected by a bolt, it allows for the panels to be removed for servicing or tilting without reapplying the L-foot. If mounting to a rack is preferred, our mounting hardware can be removed, or modified to enable rack mounting. AM Solar has never had a taped panel blow off a roof.
- Should I wire my RV solar panels in series or parallel?
Whether to wire RV solar panels in series or parallel depends on your system’s voltage requirements and shading conditions. Wiring panels in series increases the voltage which can allow for the use of thinner cables, but higher voltages are susceptible to arcing, which can lead to fires. Additionally, series connected arrays don’t perform as well as all-parallel arrays in partial shade conditions. Conversely, wiring panels in parallel increases the current, which requires the use of thicker cable, but compared to solar panel, cable is relatively cheap and because of the improved performance in partial shade conditions, we prefer parallel configurations.
Learn more: Series Solar Panels vs. Parallel Solar Panel Arrays for Your RV, Van or Skoolie
- What if I have other questions?
Fill out our Quote Request form and we’ll be happy to get you answers.
Temperature Sensor for BMV-712
Support from AMSolar is definitely 5 stars. 1st line of support for Victron equipment provided through distributors. AMSolar likely one of the best when it comes to RVs.
Tom B