I'm not sure I understand Battery powered cars

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dargles
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Re: Newbie Questions

Postby dargles » Wed Jan 30, 2008 1:09 am

Hmm... plenty to think about.
And qdos - you are doing a *very* good job of arousing interest!

ChrisBarron wrote:
...There is a weight premium to pay, in particular for lead acid, and that impacts acceleration power requirements more than it does the power required to run at speed, but ultimately lighter is better...


OK... I guess I can see that.

Our daily driver is a Golf with an on-board travel computer, which does tend to make you think about driving habits. I've been a little surprised at some outcomes:

1) The rate at which I accelerate isn't as important as I thought. Just put your foot down (within reason) and get to the speed you want to go at and it saves spending ages accelerating up to speed.

2) Overrun and especially coasting (probably illegal... :roll: ) are big-time savers.

3) I'm not convinced that 56mph is the most economic speed; I think it might be slower, around 40mph or so. Speeding up through to 70mph sends the consumption sky-high. I dread to think what the 80/90mph-ers get to the gallon!

4) It doesn't seem to be as important to be in top gear as it is to keep the revs around 2000rpm

5) Braking is a no-no. Well, it's better than hitting the car in front, I suppose, but driving in a way that avoids braking saves loads.

To bring this back to EVs, I guess a number of these issues relate to "facts of life" and simple dynamics/entropy issues. So I guess that, the faster an EV goes, the more electricity it will consume on a per mile basis, for example?

I also guess 4 is completely irrelevant in an EV, because of the linear (more or less?) torque graph?

Ah... I nearly forgot. And of course there's the issue of accessories...
To protect the batteries, I would have thought that air con (ok, I can do without that) and heaters (in winter?? demisting the screen??) were no-nos. How do you handle that? Warm woolly socks and plenty of de-icer, or is it not as bad as I think?

Regards, David

ChrisBarron
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Re: Newbie Questions

Postby ChrisBarron » Wed Jan 30, 2008 9:15 am

dargles wrote:Hmm... plenty to think about.
And qdos - you are doing a *very* good job of arousing interest!

ChrisBarron wrote:
...There is a weight premium to pay, in particular for lead acid, and that impacts acceleration power requirements more than it does the power required to run at speed, but ultimately lighter is better...


OK... I guess I can see that.

Our daily driver is a Golf with an on-board travel computer, which does tend to make you think about driving habits. I've been a little surprised at some outcomes:

1) The rate at which I accelerate isn't as important as I thought. Just put your foot down (within reason) and get to the speed you want to go at and it saves spending ages accelerating up to speed.


I really shouldn't comment on that without knowing the way that the computer operates, but I think the reason you're seeing hard accelertation impact fuel consumption only so slightly is due to the way in which the sensors are calculating your consumption. Hard acceeleration is the single biggest contributor to poor fuel consumption

Most consumption devices don't measure true fuel flow, because instead of doing the job properly and fitting an expensive fuel flow measurement device you can get a roughly accurate method for measuring fuel consumption by doing load calculations based on throttle pedal position whilst at the same time measuring the level of unburnt hydrocarbons at the exhaust gas sensor.

The actual methods used differ slightly between petrol and diesel models but they're on a par in terms of them not being totally accurate. The second and more important reason it won't be accurate is that it might be updated only once per second, so you could accelerate hard for 1.9 seconds but the software will only measure one point in the acceleration phase and use that measurement, now with approximately 50% error, to calculate the average. The programmers roughly calculate that you will spend only a small ammount of your time accelerating compared to the ammount of time you will be running under much lighter loads so they don't consider the acceleration to be anywhere near as important.


5) Braking is a no-no. Well, it's better than hitting the car in front, I suppose, but driving in a way that avoids braking saves loads.


Yes, because you would have to waste a lot of fuel having to accelerate again. Much better than your computer can measure at the moment, this is the best indicator of how much fuel is wasted in acceleration cycles.

Cordially,
Chris

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aminorjourney
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Postby aminorjourney » Wed Jan 30, 2008 9:48 am

Hi David,

Accessories will make an impact to range, but as with many things surrounding electric vehicles there's a huge range of what will and won't affect your range.

My car uses a 2.5kW continuous rated motor. It uses about 60 A at 36V and a crusing speed of 30 mph (about 10-15 mph less than my top speed). Using my car's 400W heater (draining about 10 A by my reckoning) would affect my car's range quite a lot.

However,

On a larger vehicle with a larger battery pack and a more powerful motor that same 400W heater probably won't make much of an impact to the overall range.

Does that make sense? I'm full of cold so not entirely with it!

Nikki.
Nikki Gordon-Bloomfield

EVangelist and Media Relations Coordinator, www.ZeroCarbonWorld.org
Host, www.transportevolved.com

http://about.me/aminorjourney/bio

marktime
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Postby marktime » Wed Jan 30, 2008 1:42 pm

1) The rate at which I accelerate isn't as important as I thought. Just put your foot down (within reason) and get to the speed you want to go at and it saves spending ages accelerating up to speed.

2) Overrun and especially coasting (probably illegal... ) are big-time savers.

3) I'm not convinced that 56mph is the most economic speed; I think it might be slower, around 40mph or so. Speeding up through to 70mph sends the consumption sky-high. I dread to think what the 80/90mph-ers get to the gallon!

4) It doesn't seem to be as important to be in top gear as it is to keep the revs around 2000rpm

5) Braking is a no-no. Well, it's better than hitting the car in front, I suppose, but driving in a way that avoids braking saves loads.



Dargles, all good stuff there:-

1/ Is true as long as you are going to make good use of your momentum, we've all seen nutters go off at full charge to the next roundabout or red traffic light half a mile away.

2/ I used to think of it as changing gear very slowly, I can't do it any more in my Pruis but it paid dividends in my Zaferia.

3/ It's all about drag, it increases exponentially with speed. Go a slow as those around you will tollerate, I love the 40 and 50 mph speed limits on motorway roadworks :D

4/ That's a good rule of thumb.

5/ It's all about planning and anticipation.


Plus one of my own:- Check tyre pressure regularly.


Keep up the good work

MarkTime
Soft as Graphite, Hard as Diamond, Black as Coal & clear as CO2, It's a Carbon thing!

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ChrisB
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Postby ChrisB » Fri Feb 01, 2008 11:39 pm

David why not pop along to my Berlingo day/weekend and see an EV working in real life and see what its like 8)
I see your not far away from me :wink:

Details in the Berlingo section

ChrisB
I reject reality and substitute my own !!!!!!

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dargles
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Postby dargles » Sun Feb 03, 2008 11:49 pm

ChrisB wrote:David why not pop along to my Berlingo day/weekend and see an EV working in real life and see what its like 8)
I see your not far away from me :wink:
ChrisB


Hi, Chris - thanks, that sounds good. That's the weekend of our annual dance (I'm a Scottish Country Dancer if you hadn't guessed from my avatar), but with a bit of luck, I should be able to persuade my better half to join me and pop over earlier in the day on Saturday if that fits in OK. Perhaps I can get in touch nearer the time.

marktime wrote:2/ I used to think of it as changing gear very slowly,


I like it! Well officer, I missed my gear change and... :D

marktime wrote:..
Plus one of my own:- Check tyre pressure regularly.


Good point. I have a pump in the back of the car, but I forget to check because I need to top them up so infrequently. :oops:

Umm... Can I move this on now to follow up Nikki's comments and think about heaters? Where I'm coming from on this one is as a camper. I like camping because it makes you think about everything that you use - every drop of water wasted is another drop of water you've got to carry back from the tap! So I have this sort of hierarchy in my head when it comes to electricity and the drain it's going to put on my leisure battery. It goes something like this:

1) Lighting - no problem. LEDs brilliant, low energy/fluorescent good, old fashioned tungsten OK
2) Laptop/mobile phone/AA rechargeable batteries OK, but not too often.
3) Fridge - no. If you have to have a fridge, it will have to run on gas.
4) Anything that involves heating - cooking, keeping warm, electric kettles etc - absolutely no way. Must be on gas.

Obviously the above assumes you're wild camping; on a hook-up, you can burn away. Well, I don't mean being extravagant is OK of course... :)

You can fit a solar panel, or a wind turbine, but typically, these do no more than keep a battery in a good state of charge; they would have to be very beefy to even keep a fridge powered up, let alone support any form of heating.

So you can probably see where I'm getting to here with EVs. I can see that running a heater on fossil fuel makes sense, as I gather the Berlingo Electriques do, and that this will still be better than running the engine on fossil fuel. So now I'm left with all sorts of questions. It would be nice to have a heater running on diesel rather than petrol; then presumably you could get away with running it on bio diesel or filtered chip oil or whatever - does anyone do this? Also, having this dual fuel system around then means you've got to have a tank for the fuel somewhere - presumably the BE has the original fuel talk left in and the batteries squeezed in around everything else? Then, for camping, a 3kg butane (a 907 for those in the know) seemed to last for about 10/11 days; a 6kg propane seems to last for ever. Is it possible to fit and carry a propane cylinder on a car? There are all sorts of regs, but it can be done on a boat; is it possible to do this legally on a car? Has anyone done this?

Sorry this is a long post!
Regards, David

jonathan jewkes
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Postby jonathan jewkes » Thu Feb 07, 2008 9:00 pm

I think that in the UK a heater is essential to keep the windscreen demisted. I am on my second EV - each has had a different type.
My metro conversion used a Propex heater running on butane gas and producing warm air which was ducted into the original ventilation intake. It was only modestly effective. In daily winter use a 4.5kg butane cylinder lasted 6-8 weeks. My Elcat van has an Eberspacher heater fuelled by petrol which heats the water in the original heater circuit. I have found it much more effective. This winter it has used about 10 litres of petrol every 6 weeks.
Both Propex and Eberspacher make heaters to heat either water or air. The hot air versions are much bulkier. Propex use butane or propane fuel, Eberspacher use petrol or diesel.
I carried a butane cylinder in the back of my metro for several years without any problems, though clearly a gas leak and an electrical fault causing a spark would be a bad combination. I don't know if there are any regs, but it would probably have been more sensible to house the cylinder in some form of enclosure and vent it to the exterior, or else have the cylinder under the bonnet where there is free flow of air.
Jonathan Jewkes
Daily EV user for 10years - an enthusiast and also a realist

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dargles
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Postby dargles » Sun Feb 10, 2008 2:27 am

Thanks, Jonathan, that's most helpful.
Regards, David


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