Solar Power for Subs: Panel Connections

In this edition of Franklin AID, we continue our series on solar pumping systems, specifically the configuration and wiring of solar panels. Though this step is relatively straightforward, it is a critical one. A system could have all the right panels, but if they are not wired together correctly, the controller/motor won’t receive the voltage and/or current needed to fulfill the system’s water requirements.

Solar panels are DC devices. That is, just like batteries, they produce a direct current. Also just like batteries, they can be wired together to produce the exact combination of voltage and current required. There are two key points to remember when connecting multiple solar panels:

1)     When panels are connected in series, the total voltage delivered is the sum of the voltage produced by each panel. However, the amount of current (amperage) available will only be the current produced by a single panel. This is very similar to what happens when two or more pumps are connected in series. The total head produced will be the sum of the pressures produced by each pump, but the flow produced will remain equal to the flow of one of the single pumps.

2)     When solar panels are connected in parallel, results are flipped. The currents become cumulative, but not the voltages. Once again, this is very similar to connecting two or more pumps in parallel. If the intakes and discharges of two or more pumps are connected, we produce more flow, but the pressure generated will only be the pressure generated by a single pump.

So how are solar panels connected in series and in parallel? Using our pump analogy again, think about connecting two or more pumps in series. The discharge of the first is connected to the intake of the second and so forth. Likewise, to connect two or more solar panels in series, the positive terminal of one solar panel is connected to the negative terminal of the next. The positive connection of the panel can even be thought of as the “output” and the negative terminal as the “input”. This is shown in the diagram below.

panels in series

To wire two or more solar panels in parallel, all of the positive terminals are simply connected together and the all of the negative terminals are connected as seen below.

panels in parallel

To summarize, when panels are connected in series:

  • Total voltage is the sum of each panel in the series
  • Current (Amps) remains the same as a single panel in the series
  • Power (watts) is the sum of each panel in the series (since power = voltage x current, this makes sense) 

When panels are connected in parallel:

  • Voltage remains the same as a single panel in the parallel connection
  • Current (Amps) is the sum of each panel in the parallel connection
  • Wattage is the sum of each panel in the parallel connection

What about a combination of panels in which some are wired in series and others in parallel? The same rules apply, of course. Voltage will add up for those panels that connected in series and current will add up for those panels connected in parallel. In some installations, a combination of connections may be needed to produce the voltage and current required.

The good news is that Franklin Electric’s SolarPAK Selector provides the needed panel array configuration for any given installation. In that segment of the Selector, note that in the first column of the Panel Array Configuration box, the term “String” denotes how many panels should be wired together in series.  The second column indicates how many strings (groups wired in series) should be wired in parallel. Looking at the example we used in the last post, the SolarPAK Selector tells us that we need ten of the panels we have specified and that they need to be configured in one parallel string (one string of ten wired in series).

 Solar Screenshot-frank

Once again, we’ve only provided three pieces of information – location, water requirements, and the panel characteristics supplied by the manufacturer, and Franklin’s Solar Selector has done the rest, even how to connect our panels.

Solar Power for Subs: Part 1

solar installHarness the power of the sun; over time, that age-old dream has become a reality. With solar technology, we can use the sun’s energy to do work, to move things and drive machines. Today several manufacturers, including Franklin Electric, offer solar pumping systems that harness the power of the sun to get water from the ground—even where there’s no power grid.

Over the next several weeks, Franklin AID will examine in detail how these systems work, their sizing, their proper application and set-up, and their advantages and disadvantages. By the end of this series, you will have a very complete understanding of where solar pumping fits into your product portfolio, along with how to install one of these systems.

Why Solar?

To begin with, why use a solar pumping system? There are two simple answers: 1) because there’s no power where the water well is located, and 2) because the power is free. But there can be other reasons to use a solar pumping system that may be less obvious. Perhaps power is available where you need water, but it’s unreliable. If that location is remote, the end user may not even be aware when the power is off. Couple that with a critical water supply and the simple reliability of solar pumping can make a strong case for it. A prime example here is open range livestock.

In other cases, there may be power nearby, but the well is several hundred feet away from the power source. The cost of trenching and running copper to the wellhead could often outweigh the cost of a solar pumping system. In other areas, electrical power may available but very expensive. Since the sun shines for free, solar simply makes the economic sense.

Finally, some people want to use greener products as much as possible and nothing fits the bill better than solar. Marketing reasons can even enter the picture. For example, organic farm operations that market themselves as such may want to use solar pumping for irrigation in order to be able to promote this to their customer base. In such cases, electricity from the grid may be readily available.

Why Not Solar?

Of course, solar pumping by definition has a big drawback: it needs the sun to operate.  As a result, pumping systems that are strictly solar can’t deliver water 24 hours a day. But irrigation normally isn’t required 24 days a day, and in other applications, a storage tank or cistern may store more than enough water when the sun is down or the weather doesn’t cooperate.

In a residence or business, however, we do want water to be available under pressure 24 hours per day. So although stand-alone solar pumping systems aren’t likely to completely replace conventional residential systems, that doesn’t mean they can’t be combined with battery-powered systems or traditional grid systems. We’ll cover these options later.

In summary, where solar systems really come into their own are in applications such as livestock watering, irrigation, vineyards, and anywhere a grid power is unreliable or nonexistent. That’s a pretty exciting development for our industry.

Stay tuned for the next post in this series, where we’ll cover the starting point of all solar pumping systems: the panels.

SubMonitor: Overheat and Rapid Cycling Protection

In previous posts, we’ve covered the details of how SubMonitor protects a 3-phase installation from high/low voltage and under/overload conditions. This time around, we’ll cover overheat and rapid cycling.

All motors generate heat. In order to ensure proper operation and maximum life, a motor must be able to effectively dissipate the heat it generates. In the case of a submersible motor, that method is the cooling flow of water that is drawn past the motor by the pump above it. If that cooling flow is interrupted for any reason, the motor can overheat and fail.

Franklin Electric submersible 6- and 8-inch motors labeled “Subtrol Equipped” contain a built-in sensor that can detect and report an overheat condition when connected to a SubMonitor. When an overheat condition occurs, the sensor sends a series of continuous electrical pulses up the motor lead and drop cable. SubMonitor recognizes this signal and takes the motor offline to protect it.

No temperature adjustment is required if an overheat condition occurs; the sensor is pre-calibrated, and SubMonitor’s default setting for overheat detection is ON. If SubMonitor detects an overheat condition, it will take the motor offline for 10 minutes and then attempt a restart. If the overheat condition is still present on the restart, SubMonitor will take the motor offline again, repeating the cycle until it reaches a maximum number of attempts.  Both the time-out and restart settings can be adjusted manually. This time-out setting can be adjusted from 5 to 60 minutes in 5 minute increments (default is 10), and the restart setting can be adjusted from 0 to 10 restarts (default is 3).


SubMonitor also protects against rapid cycling conditions that can occur, for example, with chattering contacts. If SubMonitor detects more than 10 starts in 10 seconds, it will take the motor offline one minute. After that minute has elapsed, it will attempt to restart the motor 3 more times before requiring a manual reset. This setting is also adjustable, but the default parameter generally covers the vast majority of installations.


Even though SubMonitor protects against many of the circumstances that can harm a submersible motor, there are certain damaging conditions to which SubMonitor does not apply. We’ll cover those in our next post.

Note: Even if a motor does not contain a Subtrol heat sensor, SubMonitor will still protect it from high/low voltage, under/overload, and rapid cycling conditions.

A Timely Topic – Using a Generator with a Franklin Sub

As a result of the recent weather events on the east coast, Franklin Electric’s Water Systems Technical Hotline has been receiving a high number of calls concerning the use of generators with submersible installations. In order to provide an easy reference for all, it makes sense to review generator sizing here in Franklin AID.

Note: The use of generators must follow all local, state, and national electrical codes. ALWAYS consult these codes before installing a generator. In addition, make sure the generator is properly ventilated and that you are familiar with its operating instructions before putting it into use.

Guidelines specific to using an engine driven generator with a Franklin submersible motor can be found on page 5 of the Franklin Electric AIM (Application, Installation, and Maintenance) Manual.

To determine proper sizing, refer to Table 5 on page 5 of the AIM Manual. (Click the illustration above for a close-up view.)Note that the numbers in the sizing chart apply to both 3-wire and 3-phase motors. If it’s a 2-wire installation, the minimum generator sizing is 50% higher than listed in the chart. This is because of the higher starting current required for 2-wire motors.

Also note that the sizing chart only applies to one submersible motor. If other devices are being powered, they must be identified along with their power consumption. Even though some of these items may not run continuously, they still need to be taken into account, per the generator manufacturer’s recommendations.

The frequency of the voltage delivered by the generator will be a function of the engine’s RPM. Motor speed varies with the frequency of the output voltage, and since pump affinity laws relate power to performance, generator sizing can have significant impact on pump output. For example, if the generator is putting out a voltage at a frequency that is below 60 hertz, the pump will not meet its performance curve. Likewise, if the frequency is above 60 hertz, it may overwork the motor and trip its overloads. The generator manufacturer’s instructions will contain guidance on how to adjust the generator’s frequency. Of course, you’ll also need a voltmeter that measures frequency. Most of today’s digital voltmeters contain this function.

The thrust bearing in a submersible motor requires a minimum speed of 30 hertz (about 1800 RPM), so it is important to start the generator before starting the motor. Likewise, it is equally important to stop the motor before the generator is shut down. Failure to do so may result in damage to the motor’s thrust bearing during start-up and coast down. The installation of a simple transfer switch will allow the motor to be turned on and off independently of the generator. (Note: circuit breakers should NOT be used for this function.)

More critically, a transfer switch also functions as a safety device to isolate the utility electrical supply from the generator. Without a transfer switch, the generator can back feed into the utility lines and, in a worst case scenario, cause serious injury or death. Unfortunately, the transfer switch is one of the more commonly overlooked safety devices required by the National Electrical Code (NEC).

Code also requires that the generator be properly grounded in order to protect against electrical shock in the event of a fault. Like all electrical conductors, the ground wire must be correctly sized for the load it is designed to carry.

Hopefully, you won’t find yourself in a no-power situation that necessitates using an engine-driven generator. In the event that you do, taking appropriate precautions and following this protocol will help make sure you can get your Franklin sub back online.

What makes a submersible motor different?

As a professional water systems contractor, you’ve probably faced situations like this: you’re installing a submersible pump/motor, and the homeowner wants to know why a submersible unit costs “so much”. He may have formed this opinion because he recently replaced a motor in an HVAC unit, a sump pump, or even a jet pump. In any case, chances are good that he is comparing the submersible to an aboveground motor or pump. As you know, this is a classic case of comparing apples to oranges, since submersible motors are very different from aboveground motors. This issue of Franklin AID will review some key aspects of submersible motor construction in order to help professional water systems contractors like you explain to a homeowner why a submersible motor appears to be more expensive, but worth the cost. Continue reading

The Super 90 Submersible Motor

An Exciting New 6” Specialty Product With Many Proven Features

Super 90 submersible motors are available in three-phase ratings of 5 hp through 40 hp

The Super 90 premium grade encapsulated submersible motor is a problem solver for the geothermal market and for other applications that have temperature, cooling flow, or thrust conditions that exceed the design limits of standard submersible motors.


 -Excels in low-flow or no-flow applications such as reservoirs, wet wells, large diameter well casings, and lake or pond installations (typical of golf course and irrigation systems) with ambient water temperatures of up 86°F (30°C).

-Operates in water temperatures up to 195°F when water flow past the motor is at least ½ foot per second. No need to down-rate the motor.

-Franklin Electric’s newly developed high temperature encapsulation technology permits the motor to operate at elevated temperature levels.

-Allows for a 25% increase in the capacity of the down-thrust bearing when compared to standard submersible motors. The design change to an upthrust bearing results in 100% more upthrust capacity than standard motors.

-Lead assembly features 125°C cross-link polyolefin (XPLO) wire and is designed to be field replaceable.

-Available in standard 300 series stainless steel or 316 stainless steel Corrosion Resistant models. Continue reading

Generator Sizing for Submersible Motors

Last issue we discussed alternative energy. This time we would like to help eliminate some of the mystery and confusion that occurs when sizing a portable generator. Obviously Y2K has prompted an influx of power loss concerns, but generators have always been used with submersible motors.

Safety First: If you are adding a generator for Y2K or other emergency power needs to your present power supply, you must follow all local, state, and national electrical code requirements. One of the most commonly overlooked safety devices is a TRANSFER SWITCH. A transfer switch is required by the National Electrical Code (NEC) and is used to isolate the utility electrical supply from your generator. If this is not done, your generator can backfeed into the utility lines causing serious injury or death to you, your neighbors, or utility work crews.

In addition, always read and understand the manufacturer’s instructions. Properly ground your generator per manufacturer’s instructions and local electrical codes. Also remember, generators use fuel to operate. Proper ventilation is required for exhaust fumes, and never re-fuel the generator while running. Continue reading