Cambell Live - DIY electric car. Inspired?

**Coyote** · 28th November 2007, 18:40

Who else has been inspired into making an electric powered vehicle? I've wanted to make an electric bike for a while after growing up with R/C cars and loving the whine and instant power. Also the videos on youtube of the electric powered drag bike were incredible. Has anyone thought of doing such a project themselves? I'm keen, only I can't even afford to keep my bike running so can't really do anything for a while. Anyone know where you'd get the motor and running gear from?

Was a good article on Cambell Live. Haven't seen the youtube vids yet due to xtra's dial up speed broadband

**JimO** · 28th November 2007, 19:02

12k is a lot of money for something that will only cover 60 ks....but good on him anyway

**Swoop** · 28th November 2007, 19:53

12K less 2.6Kpa saved on benzine!
$2- per 60km...

**davereid** · 29th November 2007, 07:37

Originally Posted by Swoop

12K less 2.6Kpa saved on benzine!
$2- per 60km...

Yeah.. but are those figures really correct ?

Lets take a small jappa car. It would have an engine of about 70-80kw. Maybe we use full power 1% of the time, but an acceptable guess would be that we use about 1/2 of the engines power on average over a normal trip.

So it would be fair to say we need a 80kw engine output to get toyota corolla levels of performance, and we will use about 40kw of energy each hour in our 800kg car.

But our electric car carries 1/2-1 tonne of batteries. So maybe we will need 50-60kw each hour to emulate the performance of the corolla. Or we accept a lower level of performance.

If we are using 50kw/hr of energy, at a rate of $0.20c, our 1 hour of driving will cost $10.

This is comparable to, or more than the small car we were using !
And we will have to budget for battery replacement. We may even be liable for road-user mileage charges, as our fuel is not taxed.

The reality is that a given level of performance will require a certain amount of energy. Regardless of the fuel source.

So when I hear claims that electric vehicles are cheap to run, I am a little skeptical. I am sure they are, but only because they are not being asked to match the performance levels of the vehicles they replace.

**Coyote** · 29th November 2007, 08:24

Power companies are already bastards, I'd half expect them to turn into gas companies and change their prices on the fly.

I'll try get hold of a cheap rolling chassis and see what I can do with the little funds I have. The guy on Cambell live spent so much getting other people to do the work by the sounds of things

**Coyote** · 29th November 2007, 08:30

Originally Posted by davereid

But our electric car carries 1/2-1 tonne of batteries. So maybe we will need 50-60kw each hour to emulate the performance of the corolla. Or we accept a lower level of performance.

If we are using 50kw/hr of energy, at a rate of $0.20c, our 1 hour of driving will cost $10.

0.20c per watt? (pardon the pun)

The guy in the article was using it as a typical car and was able to reach highway speeds, so he was needing similar performance to a standard car. They didn't say how they worked out 60km = $2

**Finn** · 29th November 2007, 08:40

I'm sure a tonne of used batteries will be good for the environment too. Not to mention the energy required to charge his batteries.

The guy should be shot.

**nodrog:Me** · 29th November 2007, 08:43

Originally Posted by Finn

The guy should be shot.

with a tazer.....

**vifferman** · 29th November 2007, 08:44

Originally Posted by Coyote

They didn't say how they worked out 60km = $2

Basically, the batteries needed recharging after 60km, and he reckoned it would cost $2 to charge them. I dunno what the current rate is per kilowatt-hour, but assuming 20c, that's 10 kilowatt-hours (meaning charging up overnight for ten hours using a 1kw charger, or 5 hours using a 2kw charger). The thing is, assuming no losses due to heat etc., that would mean either his car's electric motors are only 10kw, which is unlikely, or he's severely underestimated/understated the cost of charging, which is more likely to be somewhere between $8 and $15. That in itself raises another problem: if his car is actually say 40kw, then it's going to require 20 hours to charge with a 2kw charger, or 10 hours if he's got some super-duper 4kw charger and some special wiring in his house/gargre to power it.

So, we can assume that either his electric car motors don't provide power equivalent to the engine they're replacing, or he's deluded about the cost of running it.

But at least he's saving the baby fursealwhales, preventing globular yawning, and making the Greenies orgasmically happy.

**Pwalo** · 29th November 2007, 08:49

Originally Posted by Finn

I'm sure a tonne of used batteries will be good for the environment too. Not to mention the energy required to charge his batteries.

The guy should be shot.

Yep, that's the down side for all the petrol/electric hybrid cars as well.

They're no more ecologically sound (if there is such a thing), as anything else on the road.

Still I kind of like the idea of a remote controlled R34. (Sorry officer I wasn't behind the wheel?)

**Fooman** · 29th November 2007, 09:24

Originally Posted by davereid

Yeah.. but are those figures really correct ?

So it would be fair to say we need a 80kw engine output to get toyota corolla levels of performance, and we will use about 40kw of energy each hour in our 800kg car.

Checking my trusty Bosch Automotive Handbook, that's a bit high - for a blocky sedan, with a frontal area of 2 square metres (average), the drag power (~80% of the total resistance needed to be overcome by the motor) is 6.3 kW at 80 km/h or 21 kW at 120 km/h.

For a normal car with aerodynamic features, those figures are 4.6 kW at 80 km/h or 16 kW at 120 km/h. For a fully streamlined car (e.g. the solar powered racers), the figures are 2.3 kW and 7.8 kW.

So for a modern toyota corolla, we're looking at between 6 and 20 kW to maintain (legal) open road speeds (drag + frictional resistance in drivetrain).

Of course, more power is needed for acceleration or going up hill (or turning on AC and other ancillaries), but they are short term transients.

Cheers,
FM

**Badjelly** · 29th November 2007, 09:33

Originally Posted by davereid

If we are using 50kw/hr of energy, at a rate of $0.20c, our 1 hour of driving will cost $10.

This is comparable to, or more than the small car we were using !
And we will have to budget for battery replacement. We may even be liable for road-user mileage charges, as our fuel is not taxed.

The reality is that a given level of performance will require a certain amount of energy. Regardless of the fuel source.

Sorry, but I don't trust your figures. I don't think a small car on a "normal trip" has an average power consumption anywhere near 50 KW.

You're right that the energy the electric car is using isn't free. The potential advantage of electricity over petrol is that the in-car efficiency (electricity -> motive power) is high and the generating efficiency can be substantially higher than a mobile engine can achieve (eg > 50% for a combined-cycle gas power station or ~ 30% for a coal-fired power station vs [what?] for a petrol engine). Then there's regenerative braking, though not for our DIY bloke.

I'm not denying there are several disadvantages of electricity in cars, too, mostly to do with those heavy, expensive, not very environmentally friendly batteries.

**Hoon** · 29th November 2007, 09:54

Originally Posted by Finn

I'm sure a tonne of used batteries will be good for the environment too. Not to mention the energy required to charge his batteries.

Not really. He is using 12 car batteries which are recyclable. The footprint left from these will still be way less than years of petrol fumes.

Even if you factor in the pollution caused by the generation of the power to charge the batteries, in comparison energy produced from a power station is still way more efficient (and therefore green) than that produced from a petrol engine.

I saw the Campbell piece last night too and was quite impressed. The article was very vague but instead of making my judgement based on that I took a look at the guys website instead. The motor specs and battery info are all up there. He uses 12 x 3.4amp battery chargers bought from SuperCheapAuto.

He epitomizes the typical kiwi bloke that could acheive anything in his shed if he puts his mind to it.

**Badjelly** · 29th November 2007, 09:55

Originally Posted by Coyote

The guy in the article was using it as a typical car and was able to reach highway speeds, so he was needing similar performance to a standard car.

Not really. Most cars these days have *much* more power than the bare minimum they need to reach highway speeds.

The top speed of cars and bikes is determined by a contest between power and aerodynamic drag. There are other sources of drag, but at a high enough speed, aerodynamic drag dominates. What is this "high enough speed"? Well, for a car with a reasonably aerodynamic shape, maybe 100 km/h, for a naked bike probably 70 km/h, and for a cyclist maybe 30 km/h.

I happened to read a review of a small car in a random motoring magazine the other day. The car in question was a Citroen something-or-other, it had a 1600 cc engine generating 90 kW (a bit more than a 600 cc sport bike?) and this would push it along at a maximum of 200 km/h. OK, aerodynamic drag increases as the square of the speed, so if you double your speed you increase your drag by a factor of 4 and you increase the power by a factor of 8, yes 8. So at 100 km/h this Citroen should need 12.5 kW (a bit less than my Scorpio's maximum).

So: you don't really need all that much power to mooch around in a car on level roads; the fact that our DIY bloke's car could reach highway speeds doesn't mean its performance is anything like an ordinary petrol-engine car.