FAQs - 4QD - Electric Motor Control

FAQs

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Installation questions

Electric motors are electrically noisy, the sparks commonly seen at the brushes are a source of radio frequency interference [RFI] that can cause problems with both the host controller and other systems [have a look at this video of brush arcing]. Historical fact; Marconi used an arc to transmit the first radio signal across the Atlantic.

A new motor and a properly designed motor controller may go on working for years without suffering problems, but over time the arcing and RFI will get worse, and there is a statistical probability of an energy spike of just the right parameters to blow a MOSFET.

Fitting motor noise suppression components, and following these installation guidelines will significantly improve the long term system reliability by reducing the chance of MOSFET latch up and failure.

Have a look at this short video to see examples of a motor with and without noise suppression…..

 

 


Yes. All 4QD controllers can be controlled by a voltage input.

You can use a DAC to provide a voltage output, or use a PWM output directly. We have tested 4QD controllers with PWM inputs between 10Hz and 10kHz.


Yes but be aware that with the high currents that our controllers can switch, come some constraints on mains power supplies. All our controllers use use 20kHz chopping and a transformer fed full wave rectified mains power supply will have a 100Hz or (120Hz in USA) output so you will need to have very good smoothing. Except at relatively low currents, a suitable transformer, rectifier and reservoir capacitor can prove very expensive, so a small battery with a suitable charger is a good [and often cheaper] alternative.

If you use a switch-mode mains supply, you should consider its operating frequency and how it will perform under full motor current chopped at 20kHz.

The main capacitor on the controllers is intended to be sufficient when used from a battery – which itself acts like a large capacitance. For high current use of a power supply you are probably going to require a lot of (expensive) extra capacitance here.

One other issue to be aware of is the voltages developed by regenerative braking. Many of our controllers feed power back into the battery during braking. If there is no battery then the regenerated energy can pump up the power supply voltage to a high level if the motor is stopped too quickly. Although our controllers are protected against such over-voltage, it may damage your power supply.


Yes,it is possible to have two or more controllers driving multiple motors. In the Loco worls it is called “double heading” and we have a number of diagrams in our knowledge base that show how this can be done.

 


Yes, our controllers don’t care how many motors they are connected to, so long as the maximum current rating is not exceeded. The current record is eight.


Ammeters

Fitting an ammeter is a much debated subject, from our perspective we see the following;

Pros

  • Can be interesting to see what you are using.
  • Can indicate mechanical faults.

Cons

  • Needs a shunt [adds losses], or hall effect sensor [expensive].
  • What exactly is it measuring? [battery and motor current are usually different].
  • Most meters are not calibrated for measuring square wave PWM currents.

Voltmeters

A battery voltmeter is more useful Рwe would even say essential  since, as the battery discharges, its voltage drops, so this will tell you the charge state of the battery. Also, under heavy load, the battery voltage dips. If the voltage dips too far then either the load has increased or the battery is getting old.

The built-in approach

Our new Pro-160 controller has been designed with a built in low loss hall effect current sensor. This allows us to display both the battery and motor current as well as battery voltage and controller temperature. Additionally the built-in approach lets us set accurate limits to the drive and regen currents, and also to implement more advanced battery protection measures.

 

 

 

 

 


We often get asked what voltage should be used to give the best performance? To answer this question we need to have a quick look at power, what it is, and where it goes.

To give a vehicle a certain performance takes a particular level of power. This power level depends on the mass of the vehicle, the top speed of the vehicle, the acceleration rate you require and the gradients it must climb.

In an electric vehicle the power comes from the battery. Electrical power is volts multiplied by amps so that 40 amps from a 12v battery is 480 watts. But 480 watts is also given from a 24v battery by a current of only 20 amps. For a particular power, the higher the voltage, the lower the current.

Now electrical current causes heating. The motor, wiring and controller will all get hot and waste power. The heat wasted is proportional to the square of the current multiplied by the resistance. Moving from 12V to 24V halves the current but halving the current reduces the heating losses to a quarter.

It is clear from this that a 24V system is always better than a 12V system – provided you can physically fit two batteries. By the same token 36V or 48V would be even better, heavy duty systems such as fork lift trucks often use 96V, electric cars are now using 600V!

The amount of energy in the batteries is amps X hours X volts. Consider a 12V 60 Ampere Hour battery. Clearly this is exactly the same as two smaller 12V 30 AH batteries in parallel. But the total amount of energy in these two will not change whether we connect them in parallel or in series. So a 12v 60 AH battery can store exactly the same energy as a 24v 30 AH battery.

There is another factor against 12V operation, except at low currents: MOSFETs need a good voltage to fully turn them on, almost all of 4QD’s controllers use an internal 9v supply rail, which is adequate to ensure proper turn-on. However, there is not much difference between 9V and 12V. It does not take much current to be drawn from the battery before it drops 2V at its terminals. A small mount of extra drop in the wiring and the internal 9V supply drops. After that, the available current from the controller drops quite quickly! Remember that the battery current is actually a chopped version of the motor current, see our circuits archive for more detail, so the inductance and resistance of the batteries and battery wiring all contribute to any voltage drop.

For this reason, we would generally not advise 12v operation if the peak motor current is likely to be more than around 30-50 amps.


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