Living the RV lifestyle provides a great sense of freedom and adventure. However, boondocking off-grid comes with the challenge of limited access to shore power. Installing solar panels and using MPPT controllers allows RVers to harness the sun’s energy for running appliances, lights, and electronics on the road.
While a single MPPT controller setup works well for basic needs, connecting controllers in parallel can enhance your solar system’s performance. Read on to learn how parallel charging enables higher solar input and faster battery charging. We’ll cover the benefits, considerations, components, and steps for setting up parallel MPPT controllers in your RV.
Why Choose Parallel Charging?
RV solar panels typically feed into a single MPPT controller, which tracks and converts the solar input into battery charging current.
MPPT stands for Maximum Power Point Tracking. These controllers optimize energy yield by operating the solar panels at their highest efficiency point.
Most MPPTs have a maximum solar wattage input capacity. Exceeding this capacity would overload the controller and cause it to shut down.
For example, the popular Victron BlueSolar MPPT 100/30 can handle up to 100V and 30A, or 3000W of solar input. Connecting a 3500W solar array would surpass its limits.
Using parallel charging allows you to combine multiple smaller MPPTs to handle larger solar arrays. Each controller takes a portion of the total solar input up to its rated capacity. The outputs combine to charge your battery bank.
Let’s examine the key benefits of using parallel MPPT charging:
Accept Higher Solar Input
A single MPPT limits the size of solar array you can install. In parallel, the controllers share the wattage across the units.
For example, paralleling two Victron MPPT 100/30 units enables up to 6000W of solar input capacity.
Larger solar arrays generate more power, especially when boondocking in low sunlight areas. Parallel MPPTs allow your system to grow over time.
Faster Battery Charging
MPPTs have a maximum output charge current. One MPPT splits its output across multiple batteries.
This limits the maximum charging speed, especially for large battery banks.
Wiring MPPTs in parallel adds up each unit’s charging capacity. Two 30A MPPTs in parallel could deliver 60A combined.
Your batteries receive concentrated current from each controller, enabling faster charging. This gives you full power faster each day.
Redundancy Against Failure
When camping off-grid, a solar controller failure could leave you powerless.
Having parallel units provides redundancy in case an MPPT stops working. The remaining units continue charging the battery bank.
This redundancy reduces downtime if a unit needs replacement. You can still run appliances using solar power.
Flexible System Expansion
Expanding a standalone MPPT requires replacing it with a larger unit. This means added costs and time rewiring your system.
Adding parallel MPPTs lets you gradually increase capacity over time. Buy controllers as needed to meet your growing energy needs.
You avoid the hassle of swapping out a single MPPT when upgrading solar array size. The system stays online during upgrades.
Load Balancing Across Units
A single MPPT handles the full brunt of solar input fluctuations. Rapid voltage or load spikes can damage the controller.
Wiring MPPTs in parallel distributes the electrical load across multiple units. The controllers share transient spikes rather than absorbing the full impact.
This load balancing protects the MPPTs from overload damage. It extends the lifespan of each unit.
Potential to Save on Costs
Large 80A+ MPPT units cost substantially more than smaller controllers.
Combining multiple 30-60A units in parallel may cost less overall than buying one oversized MPPT controller.
The flexibility of parallel MPPTs also ensures you won’t need to replace an undersized unit later. This saves upgrade costs down the road.
Considerations for Running Parallel Charging
While parallel charging has clear benefits, there are some important factors to consider:
- Output voltages must match – MPPTs in parallel must have identical output voltage ratings to prevent backfeeding between units.
- Batteries see combined current – Your battery bank must be rated to handle the total possible charge current from the parallel MPPTs.
- Careful wiring required – Separate solar input connections, synchronized output wiring, and proper use of fuses and blockers is crucial.
- May need charge controllers – Managing multiple incoming currents may require dedicated charge controllers to prevent battery overcharging.
- Single point of failure remains – If the output wiring fails, the whole system would go down until it’s fixed.
- Higher system cost – Multiple MPPT units plus wiring and installation labor adds up. The investment may not make sense for smaller systems.
Properly designing your parallel MPPT system with the right components and installation techniques can help overcome these limitations.
Key Components for Parallel MPPT Charging
Here are the main items you’ll need to set up parallel solar controllers:
MPPT Controllers
Choose two or more MPPT units with identical voltage specs – normally 12V or 24V nominal.
Ideally select the same make and model. This ensures synchronized charging algorithms between the units.
Aim to combine smaller controllers rather than one oversized unit. Three 30A units can outperform one 90A MPPT.
RV Solar Boost recommend the Smart Battery (SBP) series MPPT controllers for their advanced LBPS technology, compact size, easy parallel capability and mobile app monitoring & control.
Solar Wiring and Breakers
Use an appropriately sized breaker for each MPPT solar input channel. This protects the panels and wiring from overcurrent damage.
Have sufficient cabling to wire the arrays separately into the individual MPPTs. Follow the wire gauge size recommendations.
Fuses or breakers are required for each MPPT output feeding the battery bank. This contains damage in case of controller failure.
Battery Bank
Make sure your battery bank capacity and charge rating meets the total potential output of the parallel MPPTs.
Using multiple battery banks with dedicated controllers can also prevent overcharging from the combined solar input.
Charge Controller (optional)
A separate solar charge controller can be helpful for managing multiple incoming battery charges and preventing overcharging.
Smart Battery offer AC coupled and DC coupled external charge controllers that combine MPPT output and manage battery health.
Remote Monitoring
A remote monitoring system like the Smart Battery mobile app lets you check on each MPPT unit from a central point.
This makes it easier to manage several controllers and ensures the system is charging efficiently.
How to Wire MPPT Units in Parallel
Once you have the needed hardware, you can begin installing the parallel MPPT charging system:
1. Mount the MPPT Controllers
Install each controller close together on a flat surface, wall, or pedestal mount using the mounting holes.
Make sure they are protected from direct sun and rain exposure. Allow sufficient clearance for airflow and wiring room.
2. Connect the Solar Arrays
Run the cabling from each solar array to the PV input of its designated MPPT controller.
Use appropriately sized breakers to protect each set of solar panels and wiring.
3. Wire the Outputs Together
Connect all the MPPT output pairs in parallel to feed the battery bank.
Install fuses on each output to prevent backfeeding if a controller fails.
Match the polarity across each output connection! Mixing positive and negative will severely damage the system.
4. Link to Battery Bank
Connect the combined MPPT outputs to your RV house battery bank or banks.
Make sure the battery capacity and charge rating exceeds the total potential current from the parallel MPPTs.
Having separate battery banks and a charge controller can help manage the multiple incoming charges.
5. Connect Monitoring System
Install any remote monitoring hardware and apps to view system performance and settings.
Smart Battery’s mobile app makes it easy to check the status of each MPPT controller from your phone.
6. Configure the Units
If needed, log into each MPPT controller and synchronize the settings – make sure they have identical output voltage and charging algorithms selected.
Double check that the solar input and output capacities match the ratings of the controllers and batteries.
7. Power Up and Test
Turn on each MPPT unit and verify they start charging the batteries. Check the voltages and charging status using the monitoring app.
Thoroughly test the system and inspect all the wiring connections. Make any needed tweaks before relying on the solar setup for off-grid power.
Get the Most from Your Parallel MPPT Setup
Once installed and tested, a few usage tips will help maximize performance:
- Periodically clean the solar panels to maintain peak input to the MPPTs.
- Check that all controllers are receiving solar power and active each day.
- Inspect wiring connections, fuses, and breakers regularly for faults.
- Monitor battery state of charge and charging status using a smart battery monitor.
- Reduce electrical loads during poor weather to avoid overly draining batteries.
- Consider load balancing across two battery banks to prevent overcharging from combined MPPT output.
- Follow charging and maintenance steps to keep batteries healthy and maximize solar capacity.
Solar Power Anywhere with Parallel Charging
Installing parallel MPPT controllers enables you to capture more power from large solar arrays. Your batteries charge faster, you gain system redundancy, and can easily expand capacity over time.
While wiring multiple controllers requires careful design, the benefits let you harvest ample solar energy anywhere the sun shines.
Smart Battery’s MPPT units and monitoring app make it easy to set up parallel charging right from your phone.
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