Prius vs small non-hybrid car

In response to my comment and post about the cost of driving to work there was a comment on the blog post I responded to suggesting that a small car is better value for money than a hybrid car.

The claim was made regarding a Nissan Pulsar, but to investigate this I decided to compare the Prius with the Corolla Hatchback, as far as I can tell the Corolla Hatchback is the nearest non-hybrid car to the Prius that Toyota sells (being similar in size, weight, and performance). Comparing cars of different make adds extra variables into the equation. Unfortunately the Toyota web site fails to provide specifications for the Prius and only provides a PDF file with minimal information on the Corolla, but it is enough for some minimal calculations.

A car company run by intelligent people would publish the specs on all their vehicles and provide a search form to compare selected models. The Standard Performance Evaluation Corporation has a good search method that allows easy comparison and ranking of items in their database (here is an example). It would be good if Toyota would permit us to compare models in their car range in a similar manner.

According to the Toyota web site the Prius uses 4.4L/100Km when driving in the city and the manual transmission version of the Corolla Hatchback uses 7.4L/100Km (7.7 for the auto). For the average 16,000Km that an average Prius owner drives that would save 480L of petrol which would save about $700 at current petrol prices.

The Corolla Ascent Hatchback (the cheapest of all Corollas) is $21,000 while the cheapest Prius is $37,400. If you compare the Prius with the cheapest Corolla then it’s a $16,400 price difference. If you save $700 per annum then it won’t cover the interest on a $16,400 loan or match the interest rates earned by a bank term-deposit if the $16,400 was invested. So it seems apparent that at current petrol prices (NB petrol prices are expected to increase) and with average Prius driving patterns a Prius will not be more economical than a cheap Corolla.

Currently the Commonwealth Bank of Australia offers 6.05% interest on term deposits of between $10,000 and $25,000. This means that $700 per annum would be the interest on a term deposit of $11,500. If we compare the Corolla Ultima Sedan at $32,000 with the Prius at $37,400 the difference in price is less than $11,500 – but the cars have incomparable sets of luxury and safety features. The Prius i-tech appears to have a super-set of the luxury and safety features of the Corolla Ultima Sedan but at $46,900 is again going to cost more for the average Prius driver.

The Prius is a very quiet car to drive, there is almost no engine noise (when driving at speeds where the Petrol engine is operating there is usually more noise from other vehicles) and no gear changes (handy if passengers are consuming hot or sticky drinks). It has a good set of safety and luxury features and is also a prestige car (no-one will say “oh wow, you’ve got a Corolla”). If you assign a dollar value to these features then a Prius may be the most economical car that meets your requirements!

Finally, let’s keep in mind the fact that petrol prices are steadily increasing. If you save $700 by driving a Prius this year then you may save $1000 next year. There is also the option of converting a Prius to a plug-in hybrid which will be a useful option if petrol prices hit $10/L! Also the amount of money saved will depend on the use of the car. If you are running a courier or taxi business then a Prius will probably be a lot more economical than a Corolla due to the greater distances travelled and the travel in the slow city traffic that the Prius was designed for.

PS All prices are in Australian dollars and concern products on offer in Australia, I would like to see comments from other people who perform the same calculations for their countries.

Update: If this interests you then you may want to read other posts I filed under the Environment and Cars categories.

39 comments to Prius vs small non-hybrid car

  • 38 MPG on the Corolla is so-so, compared to modern small cars. I drive a Honda Jazz (a comparable car, with a much larger luggage capacity and similar sized engine), which gets me about 45 MPG (6.3 L/100Km). The price in AUD is lower than the Toyota for the mid-range model (and a good AUD5000 less for the entry-level model). In fact, looking at it, the Civic Hybrid is AUD5000 cheaper than a Prius too. How much do you want a Toyota?

  • I agree. The price difference is hard to justify without the green factor. From all reports the Corolla is a much nicer car to drive as well. Still, Toyota has now sold 1 million hybrids (including the Lexus hybrids) worldwide so there is obviously a market for them despite the cost. Let’s hope those than can afford them keep buying so the price comes down and PHEVs become a real option on our roads in the near future.

  • etbe

    The Prius is the car that gets the most press, so it’s the first one to compare. The Corolla is also from the same company so to compare technologies it seems best to do it within the same company.

    I will have to investigate what Honda has to offer.

  • The “prestige car” factor is the big one, and the reason the Prius gets so much press – anyone can tell from fifty paces “hey, that guy drives a hybrid, he must be socially responsible and a better person than me”. Honda have had low sales of the Civic hybrid, because it looks like a normal car. Well, normal as much as the current-gen Civic can do. See also!

  • joao prates

    You guys can’t be serious. On what parallel universe of yours is the Corolla in the same size, weight, and performance category of a Prius??? The Corolla is a small size car, (isn’t that the title of this article?) while the Prius has a bit more space for passengers than a VW Passat, you go take your measures again. The weight is also bigger on the Prius Where I live the Corolla hatchback is no longer available, but I doubt it would weight 1400 kg, that’s the weight for the top Corolla 2007 sedan model. I can only laugh at the performance comparison: the Prius has 115 cv of power and 478 Nm of torque, now you tell me what Corolla even gets near that, or what Corolla can go from 60 km/h to 100 km/h in 7.2 seconds if you want real action data? I won’t even comment on the equipment both cars offer, they are a galaxy away from each other. In one sentence: you are comparing apples with oranges. If you just want to save fuel, buy a Smart, buy something just to go around town. If you want space, comfort, equipment and performance, along with MPG to rival a Smart, then you must get a Prius. There are lots of cars with better MPG than a Prius, they are just not in the same category.

  • etbe

    Joao, regarding taking measures, it seems that my best option for doing so would be to visit a Toyota dealership with a tape-measure and a stop-watch – unfortunately weighing a car isn’t really an option for me.

    It’s a pity that Toyota don’t provide the data necessary for a more detailed comparison on their web site. But I will try and discover more about the specs and write another post.

  • Joao Prates

    etbe I definitely recommend you to go to a dealership and sit inside one Prius. Take your time adjust the driver seat to your driving position, and then sit on the back as well, and be amazed at the space available. If you have one Avensis nearby, go look at one and compare :) About the specs, I was at the aussie site just now, they don’t have it all, but they do have a lot of info. Since I never bought one single car from a site, I once again recommend you to have a go at a test drive. Try to keep the car for a couple of days, a weekend if possible, so that you can adapt on your own time (you need time to adapt to driving that space craft). The best I can do to help you is to send some tech documentation and english press release, just give me your email, and I’ll send it to you. Here’s mine, so that you can contact me: joao_prates@netvisao.xpt you just have to remove .xpt and use .pt instead. Take care.

  • etbe

    I plan to compare the Prius, Corolla, Camry, and Avensis in detail when I get some time.

    A 2 day test drive seems unlikely unless I can convince Toyota that my review is important to them (I also help an environmental advocacy organisation with some writing so this is a possibility).

  • Ron Valencia

    @directhex |

    6.3 L/100Km ~= 37.34 MPG

  • PatSparkss

    I own a 2004 Prius (had for 3 weeks) and a 1990 manual Camry Wagon (for sale now). I live in Adelaide’s southern suburbs and work in Adelaide’s northern suburbs. I have a commute across Adelaide of about 35km each way. The best average consumption I got from my 2-litre Camry over several fills was 8.0L/100km, so far I am averaging about 4.2L/100km from my Prius. Both cars are about the same size externally. The Prius seems to have better acceleration and is smoother.

    I drive about 25,000km per year therefore my Prius uses 950 less litres of fuel each year. I anticipate petrol will sell for an average of $1.40 this financial year so I will spend $1330 less on fuel in my Prius than the Camry. I kept the Camry for 14 years so if I keep the Prius for a similar time I will save $18,620 over a similar sized car’s fuel bill, more really as prices rise.

    I purchased my Prius second hand for $24,900 on the road, if I had bought a cheaper car it would most likely have been a Lancer wagon as Toyota don’t make a 2 litre wagon any more. The Lancer would have been new and would have cost a similar price to the Prius once on road costs were paid anyway. If I had bought a similar age car with the same performance and features as the Prius but conventional drive my only option would be a Corolla wagon which is smaller inside, noisier, has less power and less of everything or a PT Cruiser. A PT Cruiser would have cost about the same as the Prius anyway. I wanted a car that wasn’t like everyone else’s, was economical, better for the planet and preferably made by Toyota, I got a Prius.

    I think I made the right choice.

  • etbe

    PatSparkss: You make some good points and the results from people who have made the switch to a hybrid vehicle are valuable.

    One thing that I have to note however is that a 2004 Camry would be quite a bit bigger than a 1990 Camry. You are naturally happy to get a car of the same size that you are used to with more luxury and safety features, better performance, and significantly less fuel use. But someone who switched from a more modern Camry might not be quite as impressed – the recent Camry is getting quite large. The Prius is of course more luxurious and extremely quiet – so there are compelling reasons to consider a Prius instead of a Camry even if fuel use isn’t a criteria.

  • PatSparkss

    Thanks etbe.

    FOr me the size of the old 1990 camry wagon was spot on, I didn’t want to be wheeling a bigger car around, particularly as I spend my working day in a Holden Commodore. When I finish work I want to get in something small and relax while I make my way home. If I had 3 kids I might want a bigger car but I have 1 kid so I don’t need anything bigger.

    The Prius is cheaper than a photo voltaic array and a Corolla, and it probably reduces green house emissions and running cost by more than a PVA. What a great buy.

  • PatSparkss

    Oh another thing, as you have said, the 2004 camry is a much bigger car than the 1990 or the prius, it also uses more fuel than either, so my calculation with a 2004 Camry would have mean’t the Prius will almost pay for its self over the life of the car in fuel savings.

    Try the fuel saving calculator on Toyota Australia’s site,

  • Col

    Has anyone factored in the battery issue on a Prius. Don’t get me wrong, we run a fleet of them and I love driving them. But a battery lasts 8-10 years and costs around $8000, and needs to be installed by a specialist as the voltage is too high for even an electrician to handle. And to make it worse, there’s dangerous ingredients in a Prius battery and no way (YET) of recycling them. Can you see the wrecking yards full of Prius’s in the future because the 2nd or 3rd owners paid too much for them just before the battery died and now they are landfill? And the issue of comparison, remember that they are really a luxury car. I doubt there’s a corolla that compares. Maybe an Accord, not a Corolla.

  • etbe

    According to the above URL the Prius has a 500V battery pack.

    In Australia any electrician can work on two-phase mains power (415V effective), I find it difficult to imagine that the difference between 415V and 500V would prevent an electrician from working on it.

    60,000V is apparently used in some spark plugs. While I believe that 20,000V is more common (sorry I don’t have a reference). Given that every mechanic can work on spark plugs they should be able to work on 500V power.

    Toyota recycles the batteries.

    The batteries apparently cost $3000 and Toyota claims that they are not going to wear out for the life of the vehicle (Prius taxis have clocked up over 200,000 miles), and that it’s the distance travelled not the age that’s the issue (so 200,000 miles would be about 60 years driving for me). But if a battery has a problem one thing that’s worth noting is that it’s below the rear seat – the least likely spot to be damaged in a crash. I expect that it’s not uncommon for a Prius to be written off in a crash but to still have a perfectly functional battery, a forum post I saw some time ago suggested that you should expect to pay less than $1000US for such a battery.

    Col: The above is all from the best data I could find on the net. If you have some evidence to the contrary then please cite references.

  • Marco

    I own a Prius, and my sister a Corolla, from the inside the Prius is a lot bigger, widder and longer. On the back seats the space is huge. On the back the corolla (Sedan) has a little more space for luggage.

    Referring to bats, Toyota says the wound wear out so fast as we may think, even so the first Prius was release 10 years ago, and is still working with the same bats (the first version has almost half of the capacity and worked with less volts). Even so if someone have batts probles, the only thing they have to do is press the start button for 3 seconds, and the Hybrid system stops and Prius works like a regular car. Only Toyota has this option.

    My father has a Hybrid Honda, I must tell that on highway the MPG is almost the same, but in the city a full hybrid makes all the diference.

  • Benslimane

    Comparing a a brand new Prius with a brand new non hybrib car of its category (Toyota Corolla), doesn’t justify the added cost unless it is used as a taxi, courrier, or other driving jobs that use the car to its limits. For normal every day communting I think it is economically wise and environmentally friendly to buy an old Toyota prius (year 2000 or 2001). They are sold as used cars in many sites at very affordable prices. By doing this way you can have the best of both worlds, affordability, fuel economy, space, and extra features that the prius offers. I don’t understand why people go for brand new cars. It is ok if they are rich and can afford to buy outright, it’s not ok if they have to borrow the money and slave for years to pay it out.
    Buy an old car and help the environment by recycling old goods and putting them to good use. Forget the prestige of owning a new car, it only lasts few months and the car joins the old car club with a heavy devaluation bill and probably few mechanical problems and some scratches to the body work.

  • I had a test drive in a Prius last week a brand new 07 model; I had the instant fuel usage on screen. I tried as hard as could to be Mr economical and I achieved up to 12 ltr /100 and only once 0/100 only managed to average 9ltr/ 100km avg at the end of the 10m km trip. I only managed to activate the electric motor once. I was on flat ground and in city speed zones.
    Until they make it more electric than petrol I will stay with my current vehicle, it just isn’t worth the extra cost.

  • etbe

    disapointed: The Prius design has always been based around using electricity only for speeds <20Km/h. So when starting a Prius you will only have the Petrol engine running if the batteries are low. One thing to note is that car dealers spend a disproportionate amount of time driving at low speed (they often arrange cars such that a test-drive in a model that is not selling well requires moving two or three other cars first). Also in the car dealership a car spends some time with devices such as the air-conditioner running when it's not moving. When I test-drove a Prius the battery was entirely flat from such things and the petrol motor started before I even started moving the car!

    If you were driving a car that had an entirely flat battery then you might experience significantly less reported efficiency as a result (due to the battery being charged).

  • Cynical

    Toyota says the battery in a Prius will last from 8 to 10 years. The real test on how long a battery will last is the Toyota Warranty period. If they won’t guarantee a battery for more than 1, 2 or 3 years, then that is the life of the battery.

  • Ron3KL

    I agree with some of the previous comments about the comparison with a Corolla being inappropriate. I have read claims by Toyota that interior space is similar to a Camry. This is confirmed by vehicle dimensions listed on the US Federal EPA web site.

    I don’t own a Prius but recently rented one to go on holiday with my family. As I use a folding wheelchair, we were worried about fitting into the Prius. I was amazed to find that there was more interior space than my Volvo V70 wagon. There is easily room for 5 adults, with tall teenage boys in the back seat. As for the boot, we were able to fit my wheelchair, a folding bicycle, 3 large duffel bags, 2 day packs, a briefcase and a cooler bag into to the Prius boot without difficulty. The load came up to the top of rear seat headrests and I could still see out with the drivers mirror.

    As for the price comparision, the cheapest Corolla and the cheapest Prius is not a fair comparision. The base Prius has significantly more inclusions than a base Corolla. At the very least the Prius should be compared with an auto Corolla which costs $2000 more. That would still leave out VSC, alloy wheels, rear spoiler, fog lights etc.

    So for the space reasons and the equipment included, the price comparison that seems more vaild would be with a Camry.

    By the way, Ron Valenica wrote:
    | @directhex |
    | 6.3 L/100Km ~= 37.34 MPG

    Incorrect. 6.3 L/100KM – 44.8 MPG!

    Shouldn’t use US conversion sites as their gallons are different to the rest of the world.

    The simple conversion between L/100KM and (Imperial)MPG is:

    282.481 / L/100Km = (Imp)MPG OR 282.481 / (Imp)MPG = L/100Km

    On holiday we did 514km of mixed driving. Some CBD, some highway (not the Prius’ strength), some small town meandering, some sightseeing. Overall economy was 5.2L/100km (54.3 inperial MPG).

  • etbe
    Cynical: The above web page says that the battery warranty is “8 years/100,000 miles”, see section 17. It was the first result from my google search, it’s a good idea to consult google for the answers to such questions.

    Firstly please direct me to any public information from Toyota about the sizes of those cars. The Australian Toyota web site is a joke, has minimal information and the PDF brochures that they will sent you via email (after some delay) are not very informative either. My todo list includes an item of visiting a Toyota dealer with a tape measure and a ruler. The only formal information I have had from a Toyota representative is from a dealer who claims that a Prius is best compared to a Corolla (but that was a while ago and things may have changed).

    As for the price comparison, there are many features in the Prius which are (IMHO) useless. I don’t want leather seats, alloy wheels, a spoiler (I don’t drive fast enough for it to do much good), fog lights (there is almost never any fog where I live), and lots of other “features”.

    As for MPG/L/100Km conversions, AFAIK the US is the only country still selling petrol in gallons so the US version of the measure is what counts. If you disagree with me on this issue then please cite some web sites that use MPG to measure fuel efficiency for cars which use a gallon other than the US gallon.

  • Paul

    I’m an owner of 2006 Prius. I’d like to share my experience with everyone.

    1. Fuel economy

    The driving habit is a big factor for fuel economy. I prefer smooth driving, ie. I try to avoid hard brake and hard acceleration. So far, I have fuel economy about 4.6 L/KM (actual usage, not reading on the display) on 14,000 KM.

    2. Price

    The price for Prius in Australia is quite expensive compared with USA which is the biggest market for Prius. Plus, USA government provides tax incentive for hybrid car buyer. I don’t see any meaningful encouragement from Australian government for the hybrid car.

    If not counting the low emission and other merits (quietness, high tech, big space, etc.), buying Prius in Australia seems to be a more expensive option (ie. purely based on fuel consumption calculation).

    Please note that if your calculation is based on the USA price, the result might give you a different idea.

    3. Comparison and critics

    There are plenty of criticism and praise for Prius you can easily find on the internet. I think it is fair to say Prius is not for everyone. But if anyone wants to write an article about Prius, I’d recommend the person to drive Prius for at least a few days before picking up the pen. My own experience is that the more you drive it, the more you like it. Of course, with today’s busy life pace, that is a big ask.

    There is a Prius forum web site,, where you can find plenty of Prius information. On this web site, you can find topics about fuel economy and comparison with other type of cars.

    I think this is enough for me to say for now, otherwise, you’d thought I’m a Toyota sales person.

  • Paul

    Sorry, one mistake in my previous post: my current fuel economy should be 4.6 L/100KM, not 4.6 L/KM.

  • ummmmmmm…….. i hate hybrid cars becaus you cant costomize the engine. If you put a superharger on the hybrid sewing machin engine the little thing will blow

  • etbe

    gordon: It seems that in the future all performance vehicles will use hybrid technology. For example consider the Lexus hybrid with a V6 engine which outperforms the non-hybrid V8 version of the same vehicle.

    People who try to customise their cars always amuse me. Such customised cars generally can’t compare to the performance of cars which were designed for performance. Cars that were designed for performance often cost less than the hotted up cars too, even before you consider the insurance premiums (which are extremely high for customised cars as the owners of such vehicles are likely to crash them).

    If you want a cheap performance car then get a second-hand European saloon in the performance variant. It’ll cost less than a typical “rice boy” car, give better acceleration, better handling on wet or icy roads, and be much more comfortable too.

  • David

    I read with some amusement that Toyota Landcruisers are selling in higher volumes even with fuel predicted to reach $2.00 a litre by christmas and simultaneously the article was stating Toyota are dissappointed with the Prius sales in Australia compared to the US.

    Curious I worked google to get a price for a Prius in the US. I found the drive away price in the US was between $20k and $21k, our dollar is more or less equalto the US dollar so at $37k plus I wonder why Prius sales in Australia aren’t as high as in the US? I wonder if price has anything to do with it?

  • etbe

    David: My impression is that pretty much all cars are cheaper in the US. I believe that they have lower taxes, and the larger market also provides economies of scale.

    From TV adverts etc it seems that 4WD vehicles are being sold with some significant discounts at the moment. I have not been tracking Toyota prices so I’m not sure if this applies to them. If they are discounting Landcruisers then a bunch of people who wanted them for years but couldn’t afford them might be buying now, if so it’ll be a short-term thing.

  • Geddy

    The problem is that everything in Australia is double the price of most of the rest of the world. I moved to Hong Kong 7 years ago and even HK is cheaper than OZ.

  • Colin

    etbe said:

    “60,000V is apparently used in some spark plugs. While I believe that 20,000V is more common (sorry I don’t have a reference). Given that every mechanic can work on spark plugs they should be able to work on 500V power.”

    My apologies, but Australian laws make no concession to logic! In Australian law, only an electrican is permitted to work on mains power wiring, even an electrical engineer (far more qualified) cannot work on mains wiring – does that seem a bit odd to you? It is odd. The electrician’s peak groups have pushed job protecting laws onto us that are laughable. In New Zealand, with short training, a householder can wire his own house. It still has to meet independant inspection and testing. In NZ, there are fewer electrocution deaths per capita than in Australia! In Australia, the reality is that most people with any experience, do their own mains wiring work and tell no-one. My conclusion, low levels of electrical knowledge lead to more electrocution deaths. My prescription – train more people through TAFE colleges so they can follow their hobbies and increase the general skill level of the whole population. Less emphasis on certificates and far more real knowledge in the general community. The law simply makes intelligent good citizens into criminals without any good reason other than the desire of public service administrators to control everything.

    Cars are not regulated by the same rules. As yet, there are no laws prohibiting anyone from dealing with spark plugs.

    The energy behind an electrical system is what defines the risk factor. High voltages in spark plugs are used to ignite fuel but have low levels of energy. Electric shock from a spark plug hurts, but is rarely life threatening. Electric shock from 240 volt mains, with high current capacity, can be lethal. Careless handling of spark plug leads is not usually dangerous, unless there are inflammibles about. Careless handling of NiMH batteries with 500V and high current capacity leads to unwanted metal welding and exploding wires – similar in risk factors to mains wiring. However, I don’t believe the average electrician knows enough about hybrid cars to work on them. I imagine the factory training for mechanics working on hybrids is adequate. However, until some idiot welds his 3 year old to the floor pan of his Prius, pollies have nothing to gain by making rules about them.

    You’re right about customising cars, however, the human propensity to personalise possessions, even if it’s only putting a few stickers on a laptop is so common, that you have to expect it. It doesn’t make much sense, but it’s human nature. It’s amazing how many car/motorcycle owners know so much more about exhaust systems than factories full of engineers who devote their lives to automotive engineering. Sure there are issues such as cost-performance tradeoffs in factory products, but it’s rare that big improvements are available these days. I’m frequently amused by the dust bin like exhaust outlets under the back of the average rice boy’s dream.

    Modification usually only end up reducing reliability, and unreliable cars are horrid. I’d rather have slightly less performance and have the damn thing start every time. Please remember that my comments are moulded by maturity – that just means I’ve got white hair. *laughs*

  • etbe
    According to the above URL as little as 300mA of DC can cause ventricular fibrillation. How does that compare to a spark plug?

    Careless handling of the 12V battery used to start a car can also cause welding…

  • A Patten

    Re any hybrid, can anyone advise the cost of the electricity factor. Also how far a hybrid goes on a full battery or kwh of electricity used for a 100% recharge or how many kwh are consumed at a set speed or specific distance.

  • Colin

    Hi etbe,

    OK, an excellent question from someone not familiar with electrical principles.

    There are many analogies between electric circuits and water.

    Any electrical power source has a pressure, electromotive force, described in volts.

    Same as with water, varied sized piping, orifices and pressure may be used. A very high pressure jet of water, a water pistol, is quite harmless. Likewise, a high electrical pressure, with either a limited source or a very small aperture will likewise be harmless.

    You specify 300mA, or 0.3Amps of current. That sort of current through the human body is very likely to be fatal due to the response of the heart to clamp tight when the outside electrical signal over-rides the internally generated pacemaker. Unfortunately, the heart has a tendency to stay clamped unless re-triggered into operation – the paddles of a defibrillator.

    The really important part of this puzzle is Ohm’s Law. I=V/R The voltage, V in any circuit is the independant variable. Voltage causes current to flow. To speak of current without any reference to the voltage that caused it is to only know half the story. Any current that flows is directly proportional to applied voltage and indirectly proportional to electrical resistance. Power supplies have several characteristics. It is possible to build a power supply that can give very high voltages with only limited ability to supply current. A typical 9V miniature battery is a example. If you connected it to a 6V motor car, it wouldn’t even flick the starter motor, the instant that a very low resistance load is applied, the battery terminal voltage would drop suddenly, collapsing to a low voltage. The low voltage would create only a tiny current in the low resistance circuit. It’s bit like trying to run a fire hose pump from a bucket, all you get is only tiny squirt, then nothing.

    This is very much like the spark plug power supply. It has two factors that make it fairly safe for human manipulation. 1. It has a high internal resistance, so as soon as any current starts to flow, IE the spark actually breaks across the plug terminals, the voltage drops to something relatively low. 2. The spark voltage is only there for the very short time of magnetic collapse within the coil feeding the spark plug. The electrical energy in the spark reflects the fact that the closed points have been building, over time, the energy stored in the magnetic circuit of the coil. When the points open, the magnetic energy collapses quickly to produce a high voltage in the thousands of turns secondary winding of the coil. The available current is very limited by the high internal resistance of the thin wire coil and any interference resistors fitted. Typically they are 5000 ohms. End result, while the violent muscle contractions hurt – a lot – they are harmless.

    In a similar way, the 12 volt battery is also quite harmless in terms of human electrocution anyway. V=12, R? Well, typically, a human hand to hand resistance, if gripping something tightly, is about 100,000 ohms. You could get a 300mA current easily from a car battery, but the electrical resistance would have to be 40 ohms. Even the sweatiest hands and best grip possible make such a high resistance, that electrocution with car batteries is impossible. Put maybe 20 of them together in series (voltage adds) and lock your victim into an electric chair, ensure that the victim is wet or sweaty, then throw the switch. Death is then far more likely. Curiously, many electric chair deaths are far from instantaneous. The high power supplied – it cooks human flesh if you don’t die immediately and there were many grizzley examples of this vile form of capital punishment. Fortunately, it is now no longer used.

    Typically, most electronics workers over 50 have worked on valve systems. Typical power supplies were 300 to 800 volts, but as many people, myself included will tell you, rarely fatal, although a bit dangerous. Usually, most people only ever touch this sort of voltage by mischance, and this rarely means taking a tight hold, it’s usually a matter of the back of a hand or finger accidentally brushed up against a live connection. End result is arm flung well back out of harm’s way followed by the obligatory cursing.

    Similar logic applies to 240Vac mains. While there is an occasional electrocution, I would guess that there would be hundreds of thousands of electric shocks each year. While there is some danger, it isn’t often fatal. Rather a lot like driving a car…

    Power, needed to weld with, is given by Watts=Volts X Amps. To weld, you need only a modest voltage, but you need a very low resistance external circuit and a power supply with a very very low internal resistance and lots of current capacity. Given the high starting surge we employ lead acid batteries for, and you have quite a dangerous device, but only if something metallic and thick connects the two terminals. Hands are safe, spanners are not.

    I hope this give some guide the the puzzle of electric shock. One quick rule of thumb for poweer supplies is this, if it is physically small, it’s unlikley to be able to weld or kill, since it takes big components to handle power or high voltage. Look inside a transistor radio, everything is tiny. Thw slightest extra bit of uncontrolled current and internal components would heat up enough to incinerate. Big transformers, like on the power poles are very dangerous. Anything powered by a 9V battery will be safe, although it could use a voltage multiplier circuit to give you a short shock, it would be harmless. Irrespective of how much voltage multiplication is applied to a 9V radio battery, it can never supply enough power to harm someone.

    Back to the water analogy, a domestic hose is essentially harmless. I high pressure fire monitor, like those used to control crowds, can break bones. Umm, like engines, size is everything. *grin*

  • etbe

    Colin: Actually I’m quite familiar with electrical principles. I merely can’t find a reference for the current used in a spark plug and the duration that the current can be sustained (does it compare with the 5ms used in a defibrilator?).

    I’ve just spoken to an electrician about the issues related to 500V @ 100A. The real problem with DC apparently is it’s ability to sustain an arc. With AC there is a period of zero voltage which helps in breaking an arc. Of course this means that you just have to not create the arc in the first place.

    One particular issue is that of switches. A switch that is used for AC is not going to be suitable for DC of the same voltage as the arc can be sustained inside the switch. With some common configurations of solar PV on home roofs the voltage from the array of PV panels is over 300V. I know of one installation where the installer advised the home owner that if the switch connected to the solar panels was turned off while the sun was shining brightly then the switch would probably be destroyed!

    A friend is creating his own electric car (replacing the engine of a small car with an electric motor). He is using a large number of small rechargeable batteries. Presumably removing one 10V battery at a time from the array would not be a great challenge, so that would be one safe way of disassembling it.

  • GregB

    It interests me that so much effort is put into comparing Hybrid versus non-hybrid, based on price.

    If prices were the only factor in purchasing any car, then surely no-one would buy a BMW, or any luxury car?

    I have just purchased an ’05 Prius, and am enjoying it. It was bought for fuel economy and green-factor, knowing that hybrids are merely a stepping stone to much better technology that hasn’t been released yet.


  • GregB

    (So what I was trying to say, which has been alluded to, in previous posts: different cars for different people, for different reasons..)

  • etbe

    GregB: There are many factors which go into the decision of which car to buy, and everyone has their own weight that they assign to those factors. For corporate use price is a major issue. For a courier company, if the car is being driven 100,000km per annum the equation would be much different.

    For luxury cars things are different again, being more expensive can be seen as a good thing.

  • fred

    “A friend is creating his own electric car (replacing the engine of a small car with an electric motor). He is using a large number of small rechargeable batteries. Presumably removing one 10V battery at a time from the array would not be a great challenge, so that would be one safe way of disassembling it.”

    If the rest of the circuit is complete and you disconnect ANY battery, the full voltage minus the individual cell pack (in your case, 10v) will be across the disconnected wires.

    Its still just as dangerous. An understanding of basic electronics, how cars work and most importantly, reading the service manuals is adequate to remove and refit HV components in hybrid vehicles.

  • etbe

    Fred: The design of the car in question is not based around simply putting batteries in series (to increase the Voltage), there are also parallel sets to increase the current capacity. So removing one battery will remove a fraction of the current capacity.

    Also one possible way of removing a cell from a live system (IE not using the isolator switch) would be to put a diode across it. With the diode the voltage across the battery would be about 0.6V, even at 10A that shouldn’t cause too many problems.