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Exploring Off-Grid Wind Power with the Marlec Rutland Furlmatic 910-4

In a previous article we explored the use of solar energy in the development of an off-grid electrical system for a sustainable campervan project. This time around, we will be exploring the use of wind power in the interest of building combined renewables to support our fast growing off-grid objectives.

This article will cover the process of assembling the Marlec Rutland Furlmatic 910-4 Windcharger and evaluate the charging potential of miniature wind turbines in the interest of generating useable power for off-grid environments. Our eventual goal will then turn to utilise wind power as part of a larger hybrid solar and wind based renewable energy system mounted to a campervan.

wind turbine

Parts List

  • Marlec Rutland FM910-4 Windcharger (790-3971)
  • Marlec HRDi Charge Controller
  • Deep Cycle Leisure Battery

Assembly and Test

The Rutland 910-4 Windcharger kit comes with everything we need to build our turbine but does require some assembly before we can begin to take advantage of any untapped wind power. This particular model features a three-phase generator with a low-friction slip ring that allows for efficient yield even in low wind speeds, changing wind directions and even turbulent airflow.

The Windcharger kit comes packaged with the main generator head-unit alongside six rotor blades and a nose cone. The turbine also features a mechanically furling tail fin that protects the generator by automatically turning it out of strong winds during adverse weather conditions.

For this experiment, a two-core cable has also been attached to the turbine for testing purposes and to later connect the charge regulator that will be responsible for converting any energy for storage in the leisure batteries.

wind turbine assembly

The Rutland 910-4 Windcharger kit

The kit includes all the fixings required to build the turbine so assembly is simply a matter of following the instruction manual. The first step is to attach the blades to the head-unit using the self-tapping screws provided and a firm hand. Each blade is fitted using four screws, two on each side, and an interference fitting, which means the rotor is incredibly secure and safe, even at high wind speeds. The rotor hub is designed in such a way that it is impossible to insert a blade in the wrong direction thanks to small notches in each blade. The recess in the generator plastic moulding also makes it easy to tighten the screws using a long screwdriver.

wind turbine assembly

Attaching the blades

The furling tail fin is designed to freely pivot between two end stops using a pair of plastic bushes attached to the end of the metal tail assembly. The fin is pitched at fifteen degrees off vertical which stops it from flapping around in lower wind speeds but is designed to push the turbine away once the wind speed rises above an aerodynamic threshold. The tail fin can be easily attached with two nyloc nuts.

wind turbine tail

Attaching the furling tail fin

The final stage of the turbine assembly is to attach the nose cone, in this case by using a short piece of scaffolding pole to mount the generator at an accessible height, while making sure to limit the movement of the blades. Additionally, we can then test the free movement of both the rotor and slip-ring to ensure there are very few friction losses that may impede our overall energy yield.

wind turbine

Attaching the nose cone

With the turbine now fully assembled we can use a longer piece of metal tube to mount the turbine overhead in an area of clean air-flow ready for testing. For this experiment, we will again be using an old piece of scaffolding as a temporary mount while we conduct testing, as it conveniently meets the requirements for inner and outer tube diameter as specified by Marlec. Feeding the extended power cable through the old scaffolding pole will allow us to take measurements from the wind turbine while observing it from the ground.

wind turbine

Full assembly mounted on a steel pole

We can observe the raw voltage output from the turbine using an oscilloscope. The trace allows us to see the rectified three-phase output from the generator, its rotational frequency and the mean voltage which is proportional to the respective wind speed. Once we have confirmed the voltage output from the turbine, we need to start converting this power into a useable format in order to charge our off-grid batteries. To do this, we will be using the Marlec HRDi charge regulator which is designed for the Furlmatic 910-4 turbine.

power charge regulator for wind turbine

Marlec HRDi charge regulator

The HRDi charge regulator can accept two separate battery banks that need to be connected first in order for the device to detect the target battery voltage. Additionally, the battery sensor probe can be placed nearby to provide temperature compensation while charging. With the turbine temporarily restrained, we can then connect the output cable using the screw terminals provided, before letting it spin freely and observing the charging characteristics of the generator.

power graph wind turbine

The claimed yield of the turbine

The charge regulator features an LCD screen that displays some key metrics which include the current generated from the turbine and the charge status of each battery in real-time. However, during testing, I discovered that the turbine output voltage needed to be higher than the battery voltage before any charging could occur. This meant that despite the useable voltages generated from the turbine at moderate wind speeds, the yield from the charge regulator was actually zero!

performance graph wind turbine

The claimed power curve of the turbine

This behaviour suggests a significant compromise in the efficiency and yield of the system, especially where the turbine is designed to start generating power at a very low cut-in windspeed. The power curve graph illustrates this further, where the turbine can be seen to start generating as soon as the windspeed rises above three meters a second, which is accurate, but the regulator may not cut in until around eight!

wind turbine testing

Moderate to higher wind speeds generate 11v with no yield from the regulator

Comparing the performance of the turbine against an equivalent photovoltaic system, a solar panel will generate small currents at a high nominal voltage even during cloudy weather, which by contrast suggests an inefficiency in the way wind power is converted to electrical potential in this case. Testing revealed that the turbine would actually start spinning even when there was no perceivable wind and would generate tens of watts confidently during a moderate breeze. It was therefore very frustrating to observe the lack of power converted into charge for the batteries, despite the otherwise excellent performance of the regulator when the turbine was exposed to strong winds.

wind turbine energy generation

Stronger winds cut in to produce around 20 watts

In conclusion, the Furlmatic 910-4 wind turbine is simple to use, easily assembled and has a lot of potential as an off-grid energy solution but is hindered by the need for optimal environmental and aerodynamic conditions. Ironically, the turbine itself performs exceptionally well in low-wind speeds and turbulent air, as evidenced by my testing setup. However, if the performance of the charge regulator can be used as an accurate benchmark for all miniature wind turbine applications, this inefficiency may affect their widespread feasibility as a sustainable solution for existing and future infrastructure projects.

With this in mind, I am keen to continue testing the Furlmatic Windcharger in more optimal conditions and compare its performance against any equivalent models in the interest of developing a feasible solution for my off-grid campervan project. I am particularly keen to demonstrate an intelligent blend of wind and solar power as part of a more rounded renewable system that is reactive to changing environmental conditions such as day and night running modes.

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A keen maker and electronic engineer with a passion for the environment, renewables, alternative transport and anything off-grid. Man with a van and founder of the Kickstart Kamper sustainable campervan project. Grassroots Education Sustainability Ambassador. Compulsive tea-drinker. BrightSpark 2017. BEng.
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