One way to maximize your RV’s solar capabilities is through the use of parallel charging with maximum power point tracking (MPPT) controllers. By wiring two or more MPPT controllers together in parallel, you can significantly increase your solar charging capacity.
Benefits of Using Multiple MPPT Controllers
Using multiple MPPT controllers in parallel offers some nice advantages compared to using just a single controller:
- Increased total charging current – By combining multiple controllers, you can multiply the amount of current available to charge your batteries. For example, two 60 amp MPPT controllers wired in parallel will provide 120 amps of combined charging capacity.
- Charging capacity scales up – It’s easy to add more controllers down the road to increase charging capacity as your power needs grow. Just wire additional controllers in parallel as needed.
- Redundancy – If one controller fails, you still have the other(s) to keep charging your batteries. This prevents a single point of failure.
- Flexible array configurations – You can position solar arrays in multiple locations on your RV, wire each one to its own controller, and combine the outputs for greater total power.
- Mix and match controllers – No need for all parallel controllers to be the same model. You can combine different brands/models as long as key specs align.
- Better shading tolerance – Separate solar arrays mean if one array is partly shaded, the other(s) can still operate at full output.
- Improved high voltage capability – Some larger RV solar arrays operate at over 150V DC open circuit voltage. Parallel MPPT controllers can split the total voltage for safety and improved performance.
Clearly, parallel charging setups offer some compelling benefits. The ability to scale up charging capacity over time is particularly nice for RVers looking to gradually increase their solar system size to meet growing power demands from new appliances or changes in usage patterns.
How to Wire Multiple MPPT Controllers in Parallel
Wiring multiple MPPT controllers in parallel is straightforward:
Here are the steps to follow:
- Install separate solar arrays – Each MPPT controller should have its own dedicated PV array. The arrays can be different sizes, brands, wattages, etc.
- Connect array to controller – Connect each solar array to its own controller according to the manufacturer’s instructions.
- Connect controllers to battery bank – Use suitably sized copper cables to connect the positive and negative terminals of each controller to the appropriate terminals on the battery bank. Use the thickest cables your controller can accommodate.
- Adjust controller settings – Program each controller for the same battery voltage (12V, 24V etc) and charging profile if possible. It’s fine if controllers are different models.
- Power up and test – Turn on each controller and verify normal operation when the solar panels are exposed to sunlight. Make sure batteries are charging properly.
And that’s all there is to it! The controllers will now work together to charge your battery bank from the combined power of the multiple solar arrays.
It’s worth noting that the battery bank must be sized appropriately to handle the total combined charging current from all controllers safely. Always check your battery specifications and ensure the parallel controller setup stays within recommended charging current limits.
Also be sure to use appropriately sized fuses or breakers on the battery connection from each controller to prevent overcurrent conditions. With proper circuit protection and an adequately sized battery bank, parallel MPPT controllers can dramatically increase your total solar charging capacity.
Key Voltage Offset Considerations
When wiring MPPT controllers in parallel, there is one technical consideration to note. Each MPPT controller may have a slightly different battery voltage setpoint.
For example, Controller A may start absorption charging at 14.4V, while Controller B enters absorption charging at 14.3V. This 0.1V difference is called a “voltage offset”.
Small voltage offsets are normal from controller to controller and are not usually a problem. However, best practice is to minimize voltage offsets when paralleling controllers. Here are two ways to do this:
- Match controllers – Use multiple units of the same make and model of MPPT controller. Identical controllers will have little or no voltage offset.
- Adjust settings – Program controllers to have identical battery voltage setpoints if possible via the manual settings. Reference manual for instructions.
Voltage offsets primarily impact the transition between charging stages, namely from bulk to absorption. With larger offsets, one controller may shift stages slightly sooner than the others, reducing overall charging coordination.
To optimize parallel charging, aim to reduce voltage offsets to 0.05V or less if possible. This keeps the controllers maximally in sync for seamless charging handed off between units.
With matched controllers or aligned voltage settings, you can connect multiple MPPT units in parallel with full confidence!
RV Owner Upgrades to Dual MPPT System
This couple I met on the road, Steve and Karen have been enjoying the RV lifestyle for 5 years now. Recently they upgraded to a new 40 foot Class A motorhome, complete with residential refrigerator, washer/dryer, dishwasher, and more.
They love spending weeks at a time off-grid, relying on solar to keep the batteries charged. However, their existing single MPPT controller setup wasn’t quite cutting it for their new power demands. After multiple cloudy periods they would have to rely on the generator to avoid draining their batteries too low.
Upon researching ways to increase charging capacity, Steve decided to add a second MPPT controller and solar array to their RV. “… by wiring two 60 amp controllers in parallel, I could double the total charging current to 120 amps,” Steve explained. “This gave our 400 amp-hour battery bank the boost it needed to keep up with the new appliances even during less than ideal solar conditions.”
Steve mounted a new 300W solar panel kit on the other side of his RV roof, wired it to a second MPPT controller, and connected the output in parallel with the existing controller’s battery connections. An electrician friend helped size the fuses and battery cables properly.
The improved charging capacity has paid off. “Even after 3 cloudy days we haven’t had to fire up the generator nearly as much,” Karen said. “It feels great knowing our batteries can recharge faster to keep up with our modern RV lifestyle. Parallel MPPT controllers gave our solar system the upgrade it needed!”
Recommended MPPT Controller Models
If you’re looking to setup or expand a parallel charging MPPT system, here are some top controller models to consider from leading brands like Victron, Renogy, and Midnite Solar:
Victron BlueSolar MPPT Controllers
Victron makes an excellent line of BlueSolar MPPT Controllers that work great for parallel applications. Key options include:
- Victron 150/35 MPPT – 35A output, great mid-range capacity controller.
- Victron 150/60 MPPT – Higher 60A output for more charging current.
- Victron 150/100 MPPT – Largest 100A model, very robust for parallel connections.
Victron controllers offer advanced MPPT technology, Bluetooth connectivity, and a 5 year warranty. The units feature robust DC connections and convenient mounting options.
Renogy Rover MPPT Controllers
Renogy’s Rover line are popular portable MPPT Controllers well suited for RV applications:
- Renogy Rover 20 – 20A model for smaller loads or parallel setups.
- Renogy Rover 40 – 40A capacity for increased charging current.
- Renogy Rover 60 – Top 60A model, combine multiples for over 100A.
Renogy’s MPPT controllers provide very efficient solar charging in a compact, lightweight chassis. The built-in LCD screen shows system performance data and battery status.
Midnite Solar Classic MPPT Controllers
Midnite Solar’s Classic MPPT line offers robust performance and Made in USA quality:
- Midnite Classic 150 – 150V / 35A rating, optimized for 48V systems.
- Midnite Classic 200 – Same 35A output, but higher 200V for more panels in series.
- Midnite Classic 250 – Upgraded to 60A charging capacity.
Midnite Solar controllers feature advanced MPPT technology, a 10 year warranty, and very solid power handling capabilities under harsh conditions.
This covers a few top models, but there are lots of good MPPT options out there from brands like Outback Power, EPEver, Rich Solar, and more. The key is to match the controllers’ specs and wire in parallel for increased charging capacity.
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