Converting petrol to electric
Discussion
Hi all, this is one for the more mechanically minded out there!
I have been considering converting an old boxter with a knackered engine (everything else, chassis breaks etc look good) that I have access to to electric.
I can obviously go down the route of giving the car to a professional to tackle, however in a moment of Christmas sherry trifle induced madness I got to wondering how easy would it be to do it myself (with help from a mechanic friend)?
starting with the basics - what would I need to buy, and what sort of costs would I be looking at?
then onto actually converting - how much fabrication would need to be done? - and is that fabrication possible in a 'domestic' garage?
finally, I imagine that once converted DVLA need to inspect and approve - is that a costly/difficult thing?
look forward to you all telling me I'm a fool
s
I have been considering converting an old boxter with a knackered engine (everything else, chassis breaks etc look good) that I have access to to electric.
I can obviously go down the route of giving the car to a professional to tackle, however in a moment of Christmas sherry trifle induced madness I got to wondering how easy would it be to do it myself (with help from a mechanic friend)?
starting with the basics - what would I need to buy, and what sort of costs would I be looking at?
then onto actually converting - how much fabrication would need to be done? - and is that fabrication possible in a 'domestic' garage?
finally, I imagine that once converted DVLA need to inspect and approve - is that a costly/difficult thing?
look forward to you all telling me I'm a fool
s
The drive train shouldn't be too hard - you ought to be able to source a motor/axle assembly then get some custom fabricated half-shafts to connect it to the Boxster's existing hubs; build and weld some appropriate mounts for it onto the chassis and you're pretty much there. Similarly the inverter you can probably lift from a donor (probably the same one).
The interesting bit is the battery. Most EV battery packs aren't going to fit in a Boxster so you'll either need to modify one or build one from scratch. If you maintain the electrical topology of an existing pack and just rearrange the cells you might make this slightly easier but you still need think very hard about cooling; especially if you want to be able to fast-charge. You need to think about protecting the batteries in the case of a crash too, both in terms of electrical isolation and in terms of impact protection.
Some packs are internally composed of a moderate number of smaller packs each of which is individually cooled, which would make life much easier, but you'd have to find information on which packs were divided up how and then how they would fit into your shell.
You'd also have to think about how to power the various ancillaries which run off the engine. If it's an old Boxster it'll have HPAS with an engine driven pump which you'll need to electrify (or you could remove the PAS completely). Are you expecting the air conditioning to work afterwards? Things like that need thought. You'll also need a way to charge the 12V battery; most donor EVs will have some sort of system you can probably pinch but I think some run their ancillaries off the HV pack these days.
Assuming you can weld, I think the main barrier to doing it at home will be electronic rather than mechanical. Integrating all of the different ECUs and looms will not be trivial. I develop embedded systems for a living (albeit not automotive ones) and the electronics are the bit I'd be worried about.
The interesting bit is the battery. Most EV battery packs aren't going to fit in a Boxster so you'll either need to modify one or build one from scratch. If you maintain the electrical topology of an existing pack and just rearrange the cells you might make this slightly easier but you still need think very hard about cooling; especially if you want to be able to fast-charge. You need to think about protecting the batteries in the case of a crash too, both in terms of electrical isolation and in terms of impact protection.
Some packs are internally composed of a moderate number of smaller packs each of which is individually cooled, which would make life much easier, but you'd have to find information on which packs were divided up how and then how they would fit into your shell.
You'd also have to think about how to power the various ancillaries which run off the engine. If it's an old Boxster it'll have HPAS with an engine driven pump which you'll need to electrify (or you could remove the PAS completely). Are you expecting the air conditioning to work afterwards? Things like that need thought. You'll also need a way to charge the 12V battery; most donor EVs will have some sort of system you can probably pinch but I think some run their ancillaries off the HV pack these days.
Assuming you can weld, I think the main barrier to doing it at home will be electronic rather than mechanical. Integrating all of the different ECUs and looms will not be trivial. I develop embedded systems for a living (albeit not automotive ones) and the electronics are the bit I'd be worried about.
Edited by kambites on Thursday 2nd January 19:35
I think you would need a lot of inside knowledge on all the electronic modules communications so would need to remove all the relevant parts very carefully from the donor vehicle. Cut the body not the wires and keep checking it still boots up and talks at the various stages.
I did a conversion on a small motor bike and the DVLA process was straight forward enough though this was in 2008. They did give it a cursory glance over, then at a convenient sub branch in Bristol, which I trailered it to. Waited an hour and got the new registration document.
I did a conversion on a small motor bike and the DVLA process was straight forward enough though this was in 2008. They did give it a cursory glance over, then at a convenient sub branch in Bristol, which I trailered it to. Waited an hour and got the new registration document.
Major T said:
I think a crashed BMW i3 would be a good donor, i don't know if that's been tried before. Tesla too expensive, leaf too slow.
I doubt it, highly integrated electronics package. Sounds like a fun project on a Boxster. I'd keep it as bare bones as possible, no PAS, no AC, rip out the gearbox and do direct drive, and go for enough range for local hoon runs. I don't know anything about it but I'd start buy researching what batteries and motors and control units you can buy off the shelf. Someone must have done a Boxster before as they seem ideal; relatively fragile engines, MR layout and now very cheap for what you get.
https://www.youtube.com/watch?v=4_SOP86n-PM
Edited by LayZ on Friday 3rd January 15:29
I've no knowledge of the DVSA/change of motive power issue, but if at all possible, DON'T modify the chassis/monocoque - use bolt-in subframes etc. Reason being, as soon as you "modify" the chassis (cut/drill/weld), strictly, it will then be subject to an IVA test, and if you can avoid that, do so, as it's a whole world of joy, and one can't assume that a production car will pass it without work.
Don't get me wrong, nothing magical about passing an IVA, but it you don't have to...why would you want to.
Don't get me wrong, nothing magical about passing an IVA, but it you don't have to...why would you want to.
HKP said:
I saw that they are selling a rear subframe specifically for this on eBay. It takes a Tesla motor. They were recommending a Chevy Volt battery. It might be worth contacting the seller.
Good find - just had a look at what is probably the same thing. Looks well thought out, and while the price might initially make you think twice....there's a lot of work gone into the design there and although it is all very DIYable with the right approach, if the OP wants a bolt-in solution, that looks like a good start to me.(No connection of any kind with seller of that part, not EV conversions!).
LIkely to be a huge undertaking and a minefield but with Evs improving all the while and fossil fueled cars being discouraged it could be an interesting business proposition for a few Eastern European garages or similar to start offering professional standard conversions just as they cornered the LPG market for not dissimilar reasons a few years back. Would improve the reliability and longevity of cars that have a reasonable potential of becoming future classics but for which engine noise isn't the main selling point.
So here's a question. If considering an electric conversion, would it be better to look at fitting a small motor to each wheel and use the space occupied by the internal combustion engine and fuel tanks for the batteries? Or would it be better to fit a single larger motor under the bonnet connected to the existing driveshaft (I assume you wouldn't still need a gearbox in either case)? I thought that's what Jauar did with their e-E type but there the project brief was that the removal of the engine should be reversible.
So here's a question. If considering an electric conversion, would it be better to look at fitting a small motor to each wheel and use the space occupied by the internal combustion engine and fuel tanks for the batteries? Or would it be better to fit a single larger motor under the bonnet connected to the existing driveshaft (I assume you wouldn't still need a gearbox in either case)? I thought that's what Jauar did with their e-E type but there the project brief was that the removal of the engine should be reversible.
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