Gavin Shoebridge – an electric vehicle nut, a keen environmentalist

                Electric Car Conversion Blog By Gavin Shoebridge

March 28th, 2012 at 12:42 pm

Can you add a generator to an electric car for more range?

For example, a generator like this one could charge your pack in just 4 hours.

For example, a generator like this one could charge your pack in just 4 hours.

Can you simply add a generator to your electric car for more range? Well, yes… and no.

If you’re talking about adding a wind generator, or some kind of power recovery system attached to a wheel to recover electricity while driving along – no. That just won’t work, no matter who tells you it will. Trust me, I’ve done the math and written the article.

If however, you’re thinking of installing a gasoline generator in the boot (or trunk as my American readers call it) then yes, you can boost your range when you’re idling or cruising at a low & constant speed.

What size gasoline generator will you need to achieve this? Well, that depends on how big your battery pack is. If you’re not in a hurry and your car is stopped while you’re shopping/at work etc, then we’ll run through some really simple figures.

First of all, let’s assume you have a small and cheap generator that puts out around 2000 watts. If your car is stopped for an hour, and your charger is plugged into your generator, then you’re going to generate 2000 watt-hours, or “2 kWh” in fancy speak (though in reality we’d probably lose about 15% of that power through inefficiencies).

If your battery pack is 20 kWh in size, and it’s at half-full (10 kWh) then that one hour of recharging will have brought it back up to 12 kWh capacity – or in really useful terms that we can all understand – you’ve replaced around 6 miles of range (assuming your EV used 0.3 kWh per mile, which is a fairly average economy for a home conversion).

Now, if you were actually driving at the time, would it be beneficial at all? Well, realistically, unfortunately not. This is because driving your home converted EV for about an hour would probably use around 15 kWh of electricity, and in that same hour, your little generator will have only replaced about 2 kWh.

So the secret to reliable range extension with a generator is to find the right output. I would recommend for a typical EV, somewhere around 10 kWh output. Unfortunately, this means a pretty large and heavy (and very expensive) generator which realistically will need to go on a trailer.

Then there’s the problem of matching the output voltage from the generator to the same voltage your car is using. For example, attaching a 24 volt DC generator to your 144 volt DC battery pack is not going to end well. The generator will probably sizzle its circuitry before you can say, “Where’s that smoke coming from?”.

If the cost isn’t an issue, and if you can adjust your generator’s voltage to match your EV’s pack – and if your car can handle towing a generator trailer – then it might just be an option for you. If done well, the positives to such a system are immense if long distance driving in your EV appeals to you.

There’s also the option of having the generator controllable from the comfort of the driver’s seat, so you can start, stop, and monitor what the generator’s doing (and shut it off in an emergency) without having to leave your seat.

Ultimately it comes down to practicality for your situation and cost. Let’s face it, when it comes to EVs it’s always about cost – that’s often the motivating factor behind breaking your “oil addiction” in the first place!

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  • George Wilson
    4:35 pm on March 28th, 2012 1

    Form the committee commissar.  Be the chairman and electrify them. 
    Advertise in paper, on radio and on line. 
    If you lead they will come. 
    Be the magnifying glass that focuses the light to start the fire. 
    Don’t follow the rules – make the rules. 
    Set the standard.
    Gather world conversion rules, regulations and laws.
    There is a world engineering body that does this.
    An automotive engineer I know here in Perth is on it.
    I will try to get info for you. 
    NCAP 14 I believe is the Australian standard and theAEVA has representative engineers on their safety committee.

  • John
    5:33 pm on April 3rd, 2012 2

    Actually the wind turbine idea does have some theoretical merit but is entirely impractical. Wind turbines need to be quite large to generate useful amounts of electricity. We’re talking about 3 meter diameter to power a car sort of size. Power is proportional to diameter squared. The turbine would only do anything useful if there was wind velocity over and above the car velocity. Imagine your compact car (electric land yacht) with its 3 meter articulated (so as to always face the prevailing wind) turbine strapped to the roof sitting in a typical Wellington breeze, a ridiculous thought I know. While the vehicle is sitting stationary facing into the wind the turbine will be generating a useful amount of electric power. Put the car in drive and release the brake and with sufficient gearing the car should be able to move forward despite the enormous push back of the turbine. Power = Force x Speed, so if the force is enormous the speed must be low for moderate power consumption. For a given power lowering the speed increases the available force which in essence is what gearing down is. The forward velocity of the car adds to the wind speed and increases the power generated by the turbine but also increases the push back force generated by the turbine. At some speed (probably very slow) the power generated and the power used to overcome the considerable drag will reach equilibrium and the car won’t be able to travel any faster. If the wind turned to be behind the car the turbine push back would become a push forward assisting forward motion but the cars forward velocity would subtract from the wind speed. Once the cars velocity reached wind speed the turbine would completely cease to function and would also no longer provide any push forward force. Due to inefficiencies in reality equilibrium would be reached at some velocity considerably slower than wind speed. If the wind was to the side of the car it would experience no push back or push forward force and the vehicles forward velocity would change the winds vector rearward. Note the energy harvested has to come from the static wind speed not the vehicles forward velocity and the practical limitations are imposed by the size of the turbine that could reasonably be used and the available wind speed. It might make an impractical car but would make an interesting land yacht as long as it didn’t flip over every time the wind changed direction.

  • John
    10:23 pm on April 4th, 2012 3

    If you Google the spirit of Amsterdam you can find a wind turbine powered \"car\" that can travel at 6.6 m/s in a 10 m/s wind, heading directly into the wind, using nothing but the wind to propel the vehicle. There is also a vehicle that can travel down wind at 2.4 times the speed of the wind using nothing but the power of the wind (DDWFTTW). It is basically the reverse of the turbine car with the wheels driving a propeller instead of the turbine driving the wheels. While that seems like perpetual motion at work it’s not. The propeller produces more thrust when blowing against the wind than when not but consumes no more power than when not. If you think about it when the vehicle reaches wind speed air movement relative to the vehicle stops (and consequently aero drag becomes nothing) but the ground is still moving at wind speed driving the wheels which is driving the propeller and providing thrust to propell the car to higher speeds (faster than the wind). As such the vehicle won’t move without the wind blowing. I should point out that both of these vehicles have more in common with a tricycle than a real car. Both of these vehicles don’t use electricity as a medium but are direct drive via a gearbox.

  • Angel
    9:07 pm on April 21st, 2012 4

    I have had mine for 2 years now. I have started my bcuakp generator about 2 dozen times. I have 91 hours on my bcuakp which was installed at the same time as my wind and solar. Solar PV cells are estimated to last 50 years unless they get to hot which is over 160F for long periods of time. Wind generators will last for 20 years unless they get destroyed for high winds (over 55mph) so it is recommended that their is a brake on it that automatically stops or slows down your wind generator at high speeds.

 

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