# Planning long-rang EV conversion: Audi A3



## whelmed (Jun 29, 2009)

This is my first post here, so hiya all! I'm looking at doing a conversion which will let me get some long-range mileage out of an EV car (need to do a long trip twice a week). So as the guide says, here are some details:

Your skill level with auto mechanics and fabrication: Good with a wrench, am an electrical engineer, but not done any fabrication.
The range you are hoping to get (how many miles/charge): Ideally, 400km
What level of performance you are hoping to get: want to cruise at 110km/h
How much money you are willing to put into your project: 12k GBP
What parts you've already considered, if any: Audi A3 / VW Golf

Based on a few calculations, it would seem that I'll need roughly 24-26kW of power to sustain that speed, or ~90kWh which is 630Ah at 144V. That's given a weight of around 1400kg, a 0.33 CD, 0.035 rolling resistance, and a drag area of 2.5m^2. 

First thing: I know that's far to much Ah needed, so what I was wondering is if anyone here had experience of coupling EV cars with an electric generator? I've seen a few that can put out 6-10KVA of juice at a low cost, and a few 10-20KVA ones which are quite expensive.

Next: realistically, how much Ah using LiFePo4 can you reasonably stuff into a car? It seems that HiPower has a 144V 200Ah battery rig and according to one of the FAQ's it's only $0.50/Ah (could I get a verification). I'm guessing that it'd weigh about 200kg or so? Any info on this? Would it be crazy to buy two sets of these batteries and run them in parallel?

Finally, are there any other ways that one can extend distance? Are solar panels even worth considering if one lives in Britain?


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## rillip3 (Jun 19, 2009)

whelmed said:


> This is my first post here, so hiya all! I'm looking at doing a conversion which will let me get some long-range mileage out of an EV car (need to do a long trip twice a week). So as the guide says, here are some details:
> 
> Your skill level with auto mechanics and fabrication: Good with a wrench, am an electrical engineer, but not done any fabrication.
> The range you are hoping to get (how many miles/charge): Ideally, 400km
> ...


Solar panels are not worth considering. Their weight and aerodynamic drag are considerable, and they only produce about 200 W when you get one the size of what you see on a house. Even if you car sits in full sun for eight hours a day somehow while you're driving, you're looking at maybe 5 miles, and for the weight you could just add more batteries. If you want solar power, put it on your house to offset your electric bill for charging those extra batteries.

I think 400km is almost certainly out of the question. I hate to be a Negative Nancy, but the number of batteries you would have to haul would be so massive I don't think you could fit it in any reasonably sized car. I haven't looked up an Audi A3, but I'd be suprised if a Hummer could fit the batteries needed to push a regular car 400km. I've heard some folks can get up to 200km with extremely impressive lithium packs. There's just no way to get that range with all electric.

As for the generator, you cannot realistically take a stationary generator and connect it to the car to get that range. Even if you could, there are lots of good reasons why you should not; they're not made for all that jostling and vibration, they're not made to have clean emissions and as such, it's doubtful that it's legal. What you are trying to make is a PHEV (plug-in hybrid/electric vehicle). If you want a phev, you should use a car engine; they are engineered to go in cars and reduce emissions, as well as for workload and duration running time. 

A hybrid is now reaching beyond my mechanical experience, but you're probably looking at putting in an electric motor like an EV, but you need to drop some weight to do so, which may mean putting in a smaller gasoline engine. The mating of these two systems is beyod my ken, so I'll let someone with more experience address that issue further. 

But I will say you're going to have a hard time dropping weight to put the batteries and motor on unless there's already a good spread between the curb weight and gwvr. I'm guessing that being an Audi, it's more of a sports car, which usually have a very narrow spread between those two. I'm not saying this is impossible, but it is going to be EXTREMELY challenging.

AC is also often chosen for these applications due to the ease of setting up regeneration. I'm not familiar with AC very much either, except that it's significantly more expensive. These people spent aout 30k on an AC VW Beetle 2.0, and it's got a 50 mi range.

http://www.cameronsoftware.com/ev/EV_Costs.html

200 Ah Lithium batteries are available, but of course, expensive. You're typically looking at $1.10/Ah, and that's at a good bulk discount through other enthusists like Dave on this board (look at page two or three, he's putting together a bulk order). Buying commerically you're looking at more like $1.15-1.18/Ah. Yes you can put them together in parallel, but if you go with AC, voltages of 300v are normal, so you could put those in series.

I hope that didn't sound too harsh, but 400km is really well beyond the range of even commerically produced EVs, and far beyond anything a DIY'er has accomplished (other than, for example, electric car races where the bodies are custom built, speeds are like 15 mph, they don't have any sort of crash rating because they're not made for roads, etc).


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## whelmed (Jun 29, 2009)

Thanks for the info rillip3! I figured that was the case with the solar cells. Just had a sit and think about my numbers and if you stack these batteries in series you get 300V @ 200Ah, or 60kWh (280km @ 100km/h). I think the error I've made is in under estimating the weight. If the charts are right then it's 0.1kWh/kg for LiFePo4, which would mean 600kg worth of batteries to get that level of power output. A bit more weight than I was hoping for.

However, the question of the generator still stands. I know it would create emissions, but it would be a small engine (10-20hp) so it would be quite small. I don't think that there would be much to worry about in terms of the design ruggedness of using a stationary diesel engine in a moving vehicle (a petrol, possibly). Plus I could use the existing catalytic converter on the car for clean emissions, and they weigh in at 110-150kg. Would also keep the radiator. Though probably inefficient, they will probably have a 240V plug on them which I could then feed back into the controller so wouldn't have to worry about re-designing much.

As for AC/DC, the regenerative breaking isn't that important to me - most of my driving will be at speeds of 30-70mph on smaller streets with little breaking. If the cost wasn't much more I'd consider it, but I'm not looking to drop 30k on this.


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## PatricioIN (Jun 13, 2008)

honestly, for the money involved in even coming close to the range you require, I would suggest having two cars. An inexpensive EV for the majority of your local driving and a good high mileage regular car for the required long hauls. If two cars are out of the question, then get a good hybrid like an old Insight or a Prius. Hell you could get a used Prius and do the lithium plug in conversion for probably what the batteries alone would cost to go 400km on pure electric. And a plug in Prius could net you somewhere around 100mpg while acting like a EV for shorter, lower speed daily trips.

In the best of all worlds (until battery technology GREATLY improves), we'd all have hybrids capable of driving 50-60 miles as an EV - that would switch over to a "normal" Prius type hybrid mode for any needed trips beyond that range. That way, we'd have EV's and regular ICE vehicles in one car. Capable of all our foreseeable needs.


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## Matthijs (Jun 19, 2009)

When I calculated the drag area (area*Cd=CdA) I discovered the Audi A3 does not have a terrifically good figure on this. Only 26.9*0.33= 8.87 when you look at this list with CdA figures you can get a notion of it's aerodynamic efficiency. It would mean that you loose a considerable part of energy just pushing air out of the way. 

If you want a long range EV I would consider looking at an Audi A2. (At best the A2 1.2 TDI 3L) The A2 has a remarkable interior space for its exterior dimensions, including a boot, at 1,141 litres (40.3 cu ft), which is larger the Audi A3. And it can fit the batteries very easily. 

Here is someone converting an A2: http://www.evalbum.com/2047 and Website/Youtube Channel (He is from the UK living in Italy) He calculates 80 to a 100km with just 16 kWh of HiPower LiFePo4 batteries.


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## liquidferrum (Jun 21, 2009)

been thinking about this for a while... some thoughts:

the generator can run at constant (optimum) rpm, so even thought it doesn't have the emission equipment, it might come out ahead, or not as bad as it seems. 

You can downsize your battery pack based on what your desire for a runtime on your generator. maybe some EDLC? caps instead?

With a diesel generator you could be into wvo, wmo, etc.

i think it seems like a great project, but i was planning on starting small first, to test the principals. 

it must not be too bad of an idea, because Oshkosh truck has a HMMT that runs off a generator to charge a cap bank, and that runs hub motors on the wheels i think. they claim huge fuel efficiency gains, and also have a mobile power plant.


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## ithinkidontknow (May 14, 2009)

Something to think about:

http://www.jstraubel.com/EVpusher/EVpusher2.htm

There are others who have done the same and this would accomplish your goals from what I can tell.


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## whelmed (Jun 29, 2009)

ithinkidontknow said:


> http://www.jstraubel.com/EVpusher/EVpusher2.htm
> 
> That's hideous but brilliant!
> 
> ...


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## liquidferrum (Jun 21, 2009)

you're right. you could really lose out if this didn't work. If you were in it for the EV all the way though, you could reuse the batteries, controller, and motor. i would say the only TOTAL loss might be the adaptor plate. but unless you let them sit around until there defunct technology, the rest of the items should sell.

I was thinking even smaller scale than that though. i.e. gokart. i've seen some people do them with an old starter motor, make a pwm controller, and use an auto alternator coupled to a small briggs and strat. 


i guess if the hybrid didnt work, you could always pull out the genset and replace it with batteries. I wonder about the recharge speed of the batteries. how much can you pump into lead acids? lithium?


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## whelmed (Jun 29, 2009)

Anyone know of small form factor 10-15kW generators? I've found a ton of the massive ones, but that simply won't do for this project.


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## liquidferrum (Jun 21, 2009)

http://polarpowerinc.com/products/generators/index.htm


they have up to 10kw, kinda pricey though


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