Greenpower notes

4QD have supplied motor speed controllers to the Greenpower battery powered electric car competition for many years, our controllers are highly efficient, and many races have been won using our controllers. This page has all the hints and tips we’ve learned to assist competitors get the most out of their cars.

When it comes to choosing a controller, our recommendation for new teams is our Porter-5. For the teams that are chasing that last 1% of performance we have the Porter 10XXX which has been used by many of the top kit and scratch build cars. We have a table at the bottom of the page which compares the different models. As of 2025, some teams are starting to experiment with the Pro-100 and Pro-160, We’ve written this article that describes how these models can be used in a Greenpower car.

We also have a Porter 3 speed board, this allows teams to balance the power available to each of the three drivers, or to implement different “engine modes”.

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Greenpower basics

• Get the gearing right. We’ve seen a number of controllers and motors damaged due to the gearing being too high. By this we mean that the motor has not been able to reach its peak efficiency RPM. It is tempting to gear the car for a high top speed, but if the aero and mechanical loads mean the motor is not reaching at least 2200 rpm then,
  • The available energy in the battery is not being used efficiently.
  • There is a risk of overheating the motor and controller. See “Why getting the gearing right matters” below.
• Pay attention to cooling. Even with the right gearing, you still need to make sure the motor and controller are cooled sufficiently. We have this page on how to keep controllers cool. Most of the heat from a motor is generated in the windings on the armature, the shortest thermal path for this heat to escape along is the motor shaft itself. Fitting a cooler to the shaft is an effective solution, but be aware that a fan with a high blade pitch rotating at 2200 rpm will use a lot of energy in shifting the air. Keep the pitch low and paint it black. Thermal cameras are cheap on ebay and can be really useful for finding hotspots.
• Reduce voltage drops. Fitting battery and motor cables of at least 6mm csa will help prevent losses in the wiring.
• Fit motor noise suppression to protect the controller from voltage spikes. See this page for more information.
• To see how to actually wire up a Porter we have this video.

More Greenpower tips

There is a lot of information including the rules, tips etc at the official Greenpower site which you can find here.

The motor and batteries are fixed, so the challenge is how to make best use of the available energy. This means building an efficient design, then getting the most out of the batteries.

Mechanical efficiency; The competition is all about the mechanical design of an efficient vehicle. This, above everything else, will define the result. The areas you must look at are:

• Aerodynamic efficiency;  Wind resistance increases with the square of the speed. To minimise aero losses the ideal approach is to go as slowly as possible, consistent with just running out of battery power exactly at the end of the race [but try telling the driver that!]. Regarding aerodynamic shapes, a round entry and sharp exit are the main points. Tape over any gaps in the bodywork. Remember the underside of the car.
• Rolling resistance; If the vehicle does not roll freely, it is wasting power. Narrow tyres at high pressure will help, as will high quality, well adjusted and lubricated bearings. Use a spring balance to pull the car up a slight incline, measure the force needed, then set about reducing it. Weight distribution will play a part here, if all the weight is over the rear wheels, the rear tyres will deform more than the fronts and increase the resistance.
• Mechanical drive train efficiency; The motor’s mechanical output has to be transferred to the wheels. Chains must be well adjusted and lubricated. What force does it take to rotate the drive wheel? hang a weight off the outside of the wheel, how heavy must it be to make the wheel just rotate? adjust the chain to find the best setting.

Energy usage;

• Getting the most out of the batteries is crucial. Plot the discharge curves for your batteries. Number and test each battery, use the best for the races and the others for practise. We have a diagram for a simple battery capacity tester here. The Greenpower batteries are nominally rated at 36Ah at a 20 hr rate, this will be reduced to something below 30Ah for the 90 minutes of a Greenpower race which means that using more than 20A will likely drain the batteries before the end.
• Then figure out how you can get that amount of energy to last to the end of the event. Options include;
  • Set your maximum speed appropriately, and hope for the best.
  • Have a monitoring system that lets you monitor your energy use and adjust your speed accordingly. To really understand how much energy is left in the batteries then consider fitting a coulomb counter, these are available quite cheaply on line.

 

Comparison of controllers suitable for Greenpower cars

	Porter 5	Porter 10	Porter 10XX	Porter 10XXX	Pro-100 / 160-S	Pro-160-HC
Reverse polarity protection [protects against most incorrect installation]	Y	Y	N	N	N	N
Total mosfet resistance [mΩ]	8	5.6	1.6	0.8	4.8	3.2
Data logging	N	N	N	N	Y	Y
Feature set	Basic	Basic	Basic	Basic	Advanced	Advanced