Looking for some advice as I prepare to begin

Technical discussion on converting internal combustion to electric
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BigMouse
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Looking for some advice as I prepare to begin

Post by BigMouse » Wed, 24 Oct 2012, 21:44

As I began plans for my conversion, I did quite a bit of research and looked at tons of cars as potential conversion candidates. My main criteria is listed below:

1. Has to look good. The car will be the test bed and demonstration car for what I hope will become an EV component business. I want something eye catching and attractive.

2. Has to be RWD (or have longitudinally mounted engine). This is to simplify the mounting of the engine to the gearbox, as well as preserve the option for direct drive if it proves worth-while.

3. Has to be 2 door. This was because I am considering replacing the back seat with a battery box. Would be silly to do so in a 4-door car.

4. Has to be a car. Not a ute, see point 1.

Looking at the availability and cost of cars on the market, I settled on an e36 BMW coupe, which I purchased and has been my daily driver for quite a while now.
Mine:
Image
Pristine Compact with M3 body kit (for comparison):
Image

I also considered the e36 BMW Compact/Hatch at the time, and would have preferred one, but the coupe was easier to find and the price was right.

With this approaching summer, I'm making plans to actually start my conversion. With luck, the funds should be saved by the end of Autumn and I would like to begin.

My dilemma: Should I stick with the car I have, or should I try to find a compact instead?

Reasons for finding a compact:
-180kg lighter (equates to nearly 0.5sec faster 0-100 time and 10-15km of range)
-A faster car with more range is more attractive and a better demonstration
-Similar look to the coupe, can still be visually appealing with tasteful mods
-The first time I want to go somewhere in the converted coupe and I'm 10-15km short, I'll have major regrets
-ICE-related repairs (radiator, exhaust) I have been putting off on the coupe would need to be done in order to sell it.

Reasons for keeping and converting my coupe:
-Already have it, would lose money in the transition. Money which could go toward more batteries to make up the range difference, but not the acceleration.
-In the time I've owned it, I've done a LOT of work to it (suspension, etc) and I know it's a mechanically sound platform
-Looks marginally better than the compact, to most people
-Avoid the hassle of selling a car.

I've tried to justify the keeping the coupe by making plans to lighten it, but I'd never get 180kg out of it, and any weight reduction I could do to the coupe, I could also do to the compact and get that much more benefit. Also, the most effective weight reduction methods (seats, CFRP bonnet, CFRP boot) are expensive.

I'm leaning toward keeping an eye out for a good deal on a non-running compact and snagging it when I find one. I can swap most of the new suspension parts from the coupe to the compact, and the ICE parts from the compact to the coupe.

I'd love to get some input from folks on here though.

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Johny
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Post by Johny » Wed, 24 Oct 2012, 21:59

If you showed me the coupe and a compact, both electric, and told me that the coupe had slightly less acceleration - I wouldn't care - but that's just me.
The range is a non-event in my book. Anything short of 400km range is not enough - according to just about everyone who hasn't driven an EV. So whether it's 150 or 170km really doesn't matter - again IMO.

The coupe is a REALLY nice looking car - again IMO.

Maybe you should show us a picture of the proposed compact in the same condition.

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Post by BigMouse » Wed, 24 Oct 2012, 22:32

Thanks Johny. The reason 10-15km of range makes a difference for me is because I'm expecting about either 135km or 145km of range. I'd like to be able to drive to car meets in Sydney, which round trip is 140km or so. My estimates (done in excel) don't include regenerated energy, and they only consider range at a sustained average speed. A fair chunk of the trip between here and Sydney is 110kph, that range is based on 80kph average (the rest of the trip would be much less than 80kph). There's also a large hill to climb when leaving Wollongong.

Also, 0.5sec is a significant difference when I'm expecting 0-100 of either 5.5 or 6 seconds. That's quite noticeable and could be important when giving demonstration rides.

The coupe is a REALLY nice looking car, I agree. Even better if I put M3 body parts on it (side skirts, bumper). The compact, as I would have it, would look similar to the second picture I posted, but with the M3 wheels from my coupe, and lowered with the springs from my coupe.

A photo of the compact with those wheels can be found here: http://www.nogripracing.com/gallery/sho ... oto=121087 though I'd want a white one.

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Post by jonescg » Wed, 24 Oct 2012, 23:46

Hey BigMouse, if you don't plan on getting batteries just yet, say more like 6-9 months from now, I plan on doing an epic purchase of EIGs cells, the ones with 175 Wh/kg. I know you were concerned about their life cycle, but hopefully by the time we can place a big order the price will have gone down making the initial cost a bit more palatable. I think the lifecycle figure of 80% referred to 80% discharged per cycle, as opposed to only retaining 80% of its original capacity. I hope to buy some trial cells soon.

PS Go the coupe. Perfect for style and performance, not so hot for seating capacity Image
AEVA National Secretary, WA branch chair.

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Post by polo-ev » Tue, 13 Nov 2012, 14:06

I converted a VW Polo last year, I drive it every day & now have about 18000 electric km clocked up so from my experience, here are a few things to think about.
To get the range you want you will need 210Ah Lithium cells at the very least & you will be working them pretty hard. Even bigger would be better.
The Bulli hill out of Woollongong would suck a fair bit out of the batteries even before you got on the freeway. You will be pulling 75-100% capacity of your controller up this hill.
Driving at 110km will use almost double the current than driving at 80km.
On a flat road, my little car (1000kg) can cruise at 80km using about 70-80A. Driving at 110km will easily use 135-160A.
I'm in a pretty flat rural area so a lot of my driving is at 90km. A bit of a hill will make the current go up to 180-260A quite easily.
Hard acceleration really sucks juice out of the batteries so don't expect to get good range when you demonstrate how fast the car can do 0-100.

Lastly but the most important.
DO THIS BEFORE YOU SPEND ANY MONEY OR START RIPPING PARTS OUT.
Find one of the RMS VSCCS certifiers and go and talk to them first about what they will require regarding testing & how much the new certification will cost you.

I got mine certified just before the engineering signatory system shut down last year & the new VSCCS system started. The engineer said the new scheme would make it much more difficult & much more expensive to get certification.

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Post by BigMouse » Tue, 13 Nov 2012, 17:18

210Ah cells using what voltage pack? I'm looking at 20-24kWh (60-70Ah cells with 110 in series). That calculation also takes in to account overall efficiency and 80% DOD.

That big climb does worry me a bit, but it's a short part of the overall trip to Sydney from here. I also get to come back down on my way home (after some opportunity charging at my destination).

Of course I'm not expecting to do a day of demonstration and still get nominal range.

I've heard mixed reports about the outcome of the VSCCS.

Some people say it's a lot worse and that on-track testing with professional drivers and all kinds of ridiculous requirements are now in effect.

Others say that it's up to the individual engineer, NCOP14 is still the relevant checklist, and now there are now more engineers to choose from. I suppose I won't find out for sure until I talk to one though. I'll wait until I have my money saved and am ready to start buying things before I ask for an engineer's time.

Also, as an engineering student (4th year) myself, I'll be able to present all my calculations and drawings for the modifications done, which should make the signatory's job a bit easier, and hopefully cheaper.

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Post by polo-ev » Thu, 15 Nov 2012, 14:29

Sorry, I didn't mention the voltage. I was assuming a DC motor at 144V nominal. Looks like you're going down the more efficient AC route.
Don't under estimate the big hill. I know it is only a short part of the trip but it is steep with no let up from the bottom to the top.
You then straight away have the long 110km/h stretch with those up & down sections until you get onto the flat road.
Go for the biggest batteries you get in your car without going over weight.

There is one hill like that out here that goes to an outlying village. 6km from the bottom to the top & uphill all the way. When I went up that one it was a 2nd gear 60km/h job so I didn't suck the batteries dry and/or overheat the controller (my controller has thermo fans too).
You would be going up the hill with fully charged batteries (which is a plus) & the sag would not be as great. Lithiums are great batteries but they certainly sag a lot more once you get past about 50% DOD.

I would suggest that you sound out your employer about opportunity charging given the cost of commercial electricity now. My car gets charged at home on off-peak at about 12.5 cents kw/h & our business gets charged about 37 cents kw/h. 3 times the cost for the same electricity.

Really check out the VSCCS requirements. Find out what the certifier may want & need so you don't get a really unpleasant "by the way, we will have to do an XYZ test at a cost of big $$$$" as you are almost finished.
The engineer I used retired & didn't continue into the VSCCS but he was talking about new brake tests & the like and having to hire race tracks for the day, paying engineers & certifiers for the whole day & such.

I haven't heard of any electric cars being converted in NSW since the the scheme came into play.

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Post by BigMouse » Thu, 15 Nov 2012, 16:41

Thanks for the advice Polo. Once I'm done with Uni, I expect I'll live close to my employer and charge only at home on a daily basis. I'd like the option to be able to go to Sydney without needing a second car, but I'm expecting I'll get a Prius or something as well for the longer trips anyway.

I've emailed two local engineers the other day. Heard back from one today with a very brief reply that didn't really answer my questions. He did seem knowledgeable about EV conversion though, bringing up vacuum brakes, power steering, HV protection, battery restraint, etc. No mention of any testing. I'll try to get some more info from him.

I'm not too worried about VSCCS, mainly because I know several people going through the process now who are getting engine swapped and turbo-charged cars certified. These are large power gains and the only "testing" their engineers are asking for is emissions. The brakes aren't being modified and the weight of the car isn't going to exceed the rated gross weight, so there should be no reason for any track testing. Reading up elsewhere on the internet seems to suggest it's up to the individual engineers what level of testing they require before signing off on the mods.

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Post by Stiive » Thu, 15 Nov 2012, 20:18

BigMouse wrote:
Also, 0.5sec is a significant difference when I'm expecting 0-100 of either 5.5 or 6 seconds. That's quite noticeable and could be important when giving demonstration rides.


What's the motor your going to be using?
Rgds,
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Post by BigMouse » Fri, 16 Nov 2012, 03:37

Custom wound 48vac 132 frame 4 pole motor from Catavolt. I already have it.
My batteries will supply constant V/Hz up to about 250Hz, so it should be a real beast.

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