BMW Isetta Conversion

[baronofbloomsburyuk]

Hi everyone. Your help would be most appreciated. I can barely fit an electric socket on a lamp cord, but still read and want to engage

To summarize, a BMW Isetta "bubble" car from 1960, 4 wheel version, to be converted for inner city use. I prefer a minimal/reversible conversion, so only swapping out the ICE but keeping the Trans (not interested in hub motor). With only a 13hp engine currently (single cylinder motorcycle engine), it would seem that I need a very modest motor, and battery -- a used e-motorbike should be good for most parts; Alternatively, a new e-motor but also, low powered (but less cost effective).
A unique challenge is a real lack of space for batteries. If I re-position the original 12v small battery from it's under seat location, there would be enough clearance for a single Tesla model S dimension battery, but at 5.3kwh, not much capacity (also, I assume Tesla batteries are meant to be used for applications with more power needs). I'm just mentioning Tesla to give a feel for available space based on the battery form factor/dimensions. There could potentially be space for another Tesla model S dimension battery in the engine bay.

Details below:
Project: BMW Isetta, 4 wheel version
Current Layout: ICE, Transmission, and a chaincase with integrated rear axle (no differential as rear wheels very near to each other).
Car Weight: 350kg minus approx 50kg in ICE related parts (engine, filter, exhaust, muffler, carb, etc)

Design (I think): Swap out ICE for e-motor and use existing transmission, chaincase,etc. (Not in-hub motor).
- Power: Same or slightly more power than original engine (ICE: 13hp
- Range: Inner city use, I'm sure 50miles is great. Assume 8 or 10kwh would be enough.
- Special challenge: Very little space for batteries, and probably shouldn't add more than 50-70kg in extra weight.
(space available for charger, controller, controller radiator if needed, junction box)

Any suggestions? Parts or motors to look at? Battery is a BIG question...
Thanks. Baron (London, UK)

[baronofbloomsburyuk]

Pic of an Isetta

[Kevin Sharpe]

Any suggestions?

Welcome to the forum

I'd start by mapping out exactly what space you have before spending any time thinking about the hardware. It would also be useful to provide details of the existing drive system.

[Isaac96]

First of all, welcome to the forum! And what an excellent conversion idea!

Now in terms of parts you'll need:
13hp is very little. Let's say a 10kw continuous drive system; that's about the same horsepower, and a 10kw continuous rating means you can use 20kw for acceleration if needed.

Since you don't need the highest power then a lower voltage setup would work well. 48v or 96v would be sensible; it also helps keep battery size and potential electrocution hazards down.

How about a motor like this: https://www.voltsport.co.uk/voltsport-m ... rgy-me1114
Weight of 35lbs, voltages up to 72v. Torque maximum is 65Nm.

And this might be a good controller to pair with it: https://www.voltsport.co.uk/voltsport-m ... duct_id=57

This was the result of 20 minutes of googling by the way. Salvaging an electric motorbike sounds even better; I haven't seen any where I am in the States, but maybe you all have more of those. Of course you'd need to figure out how to control the motor etc, either by use of a OpenInverter board or using the original system. It might be difficult to connect a motorbike motor to a transmission, also the RPM range might not match well.

In terms of batteries, the Tesla modules ~24V each. So if you want to use those probably go for 3 of them. Tesla modules have a good power to weight ratio.
I have no idea how much capacity you'll need to get 50 miles of range; the Isetta is rather a special case (I saw one at a car show, wow it is tiny!)

Best of luck!
-Isaac

[arber333]

For parts i think Isetta falls in category of Renault Twizzy vehicle, therefore i recommend you go and get that motor. Then you use Prius/Auris/Yaris inverter with Johannes brain. For battery i suggest VW hybrid battery 9kWh folded in halfh for 180Vdc and SimpBMS.
Charger... well you could use Prius inverter from single phase rectified.
DCDC is also inside Prius/Auris/Yaris inverter.

My 5c

[damian.lo]

Hi,

If I'm looking at this small car also I will put next 5c to Your garden
Don't get me wrong but for me it's really loss to get this almost antique to make EV. I know how it's great to make this, since I did also the same with my car (2006 production year) and how this world of DIY EV is fascinating, but my heart is bleeding at this.
So: maybe to do some conversion better will be to get something minor and put Isetta to garage and open after next 20 years?
I don't know why, but the older I get the more I'm more romantic
Like I said: only 5c maybe less. Don't get this too much serious.

[baronofbloomsburyuk]

Any suggestions?

Welcome to the forum

I'd start by mapping out exactly what space you have before spending any time thinking about the hardware. It would also be useful to provide details of the existing drive system.

Yes, you're right about the space consideration. I hoped to find a 3d model (accurate) for cabin and engine bay, but no such luck. I'll get out and measure, etc. Thanks.

[baronofbloomsburyuk]

First of all, welcome to the forum! And what an excellent conversion idea!

In terms of batteries, the Tesla modules ~24V each. So if you want to use those probably go for 3 of them. Tesla modules have a good power to weight ratio.
I have no idea how much capacity you'll need to get 50 miles of range; the Isetta is rather a special case (I saw one at a car show, wow it is tiny!)

Best of luck!
-Isaac

Thanks Isaac96: Your motor idea is good, along with controller. It's the location of the batteries, which I'm figuring out. I would think that 10kwh, max 15kwh would be enough for a 350kg vehicle. Thanks for your feedback.

[baronofbloomsburyuk]

For parts i think Isetta falls in category of Renault Twizzy vehicle, therefore i recommend you go and get that motor. Then you use Prius/Auris/Yaris inverter with Johannes brain. For battery i suggest VW hybrid battery 9kWh folded in halfh for 180Vdc and SimpBMS.
Charger... well you could use Prius inverter from single phase rectified.
DCDC is also inside Prius/Auris/Yaris inverter.

My 5c

This is cool -- except I can't find any details on the 9kwh "folded in half" battery. Is there a name for it? can it be found on ebay or elsewhere? I'm trying to get a feel for the dimensions. Thanks.

[baronofbloomsburyuk]

Hi,

If I'm looking at this small car also I will put next 5c to Your garden
Don't get me wrong but for me it's really loss to get this almost antique to make EV. I know how it's great to make this, since I did also the same with my car (2006 production year) and how this world of DIY EV is fascinating, but my heart is bleeding at this.
So: maybe to do some conversion better will be to get something minor and put Isetta to garage and open after next 20 years?
I don't know why, but the older I get the more I'm more romantic
Like I said: only 5c maybe less. Don't get this too much serious.

OMG, this was the best I totally understand and accept your 5cents. They did make 160,000 of these cars, so surely many will survive.. but also, I sooooo don't want to "keep" anything for the future, locked in the back of a storage garage. Use, abuse, enjoy it. I will use it in it's gas engine form first, and if I can afford to convert to electric, then I will do it.

[baronofbloomsburyuk]

By the way, I watched the film "Gattacca" when I was in university, and I have dreamed of vintage cars that make electric engine sounds ever since... sooooo sexy.

[Isaac96]

For parts i think Isetta falls in category of Renault Twizzy vehicle, therefore i recommend you go and get that motor. Then you use Prius/Auris/Yaris inverter with Johannes brain. For battery i suggest VW hybrid battery 9kWh folded in halfh for 180Vdc and SimpBMS.
Charger... well you could use Prius inverter from single phase rectified.
DCDC is also inside Prius/Auris/Yaris inverter.

My 5c

This is cool -- except I can't find any details on the 9kwh "folded in half" battery. Is there a name for it? can it be found on ebay or elsewhere? I'm trying to get a feel for the dimensions. Thanks.

What Arber means is that the 9Kwh VW battery, which is 360v, will be split in half and then connected in parallel. Thus the voltage will be 180Vdc. That would be a good capacity for such a light car, and also help keep the total weight down. Arber, do you have a link to this battery? I'm not familiar with it.

It would be good for you to decide what voltage range to use; either the 72v system, or a higher power 180v system. Any higher voltage is probably overkill; you don't need very much power.
The low voltage systems are usually more or less turnkey (all the components can be bought off the shelf). All you need from there is a battery and some wiring.
A system like Arber is suggesting, with the 180v battery, is lots more fun. It would involve getting a used inverter and retrofitting a board from Johannes, then finding a motor and learning how to connect it to the inverter. Then you must tune the inverter to work well with the motor and with the battery. Also it tends to end up costing less (depending on how many things you blow up; trust me, it's fun )

-Isaac

[arber333]

I have one 9kW WV Passat hybrid battery here in my workshop. I use it as a test piece. It has BMS installed, it has contactors and precharge relay and main fuse. It is liquid cooled and it assembles like lego .

https://www.diyelectriccar.com/forums/s ... Golf+cells
viewtopic.php?f=9&t=620&hilit=VW+Golf+GTE

[SciroccoEV]

I have a 1994 Solectria Force sitting outside my house, which was a conversion (from new) of the American (Geo Metro) version of the Suzuki Swift. It's looking like the car itself may require too much work to save, so I might have a motor, single speed gearbox and controller well suited to something like the Isetta.

[baronofbloomsburyuk]

I have one 9kW WV Passat hybrid battery here in my workshop. I use it as a test piece. It has BMS installed, it has contactors and precharge relay and main fuse. It is liquid cooled and it assembles like lego .

https://www.diyelectriccar.com/forums/s ... Golf+cells
viewtopic.php?f=9&t=620&hilit=VW+Golf+GTE

Thanks for the message -- I clicked the link and truthfully, the diagram is scary to me One of those moments when I realize that I'm not an electrical engineer, and just being in love with an EV conversion is not enough Hmm... Additionally, how large is that battery park, if you were to ballpark the length/width/depth. Please don't go to great effort, just wondering if it would fit. Thank you.

[baronofbloomsburyuk]

For parts i think Isetta falls in category of Renault Twizzy vehicle, therefore i recommend you go and get that motor. Then you use Prius/Auris/Yaris inverter with Johannes brain. For battery i suggest VW hybrid battery 9kWh folded in halfh for 180Vdc and SimpBMS.
Charger... well you could use Prius inverter from single phase rectified.
DCDC is also inside Prius/Auris/Yaris inverter.

My 5c

This is cool -- except I can't find any details on the 9kwh "folded in half" battery. Is there a name for it? can it be found on ebay or elsewhere? I'm trying to get a feel for the dimensions. Thanks.

What Arber means is that the 9Kwh VW battery, which is 360v, will be split in half and then connected in parallel. Thus the voltage will be 180Vdc. That would be a good capacity for such a light car, and also help keep the total weight down. Arber, do you have a link to this battery? I'm not familiar with it.

It would be good for you to decide what voltage range to use; either the 72v system, or a higher power 180v system. Any higher voltage is probably overkill; you don't need very much power.
The low voltage systems are usually more or less turnkey (all the components can be bought off the shelf). All you need from there is a battery and some wiring.
A system like Arber is suggesting, with the 180v battery, is lots more fun. It would involve getting a used inverter and retrofitting a board from Johannes, then finding a motor and learning how to connect it to the inverter. Then you must tune the inverter to work well with the motor and with the battery. Also it tends to end up costing less (depending on how many things you blow up; trust me, it's fun )

-Isaac

Thanks for explaining in such detail... I am not proficient so I do go and google every 2nd sentence I only want to replace a 13hp combustion engine, so let's say max 20hp equiv motor would be more than enough I think... I mention this b/c when I looked at an Electric Classic Car example of a Fiat 500, that was a 550 kg car, and they added an AC 20 HPEVS motor with 3 Tesla batteries of 5.3kwh each and I'm..... pretty... sure that it was a 72volt system (and i think a 50mile range, based on their youtube video). So, with an Isetta at 350kg, a less powerful motor, I would think 72volt would be max. I'm not into speeding, etc, note that this is not exactly a super 'stable' car.

[baronofbloomsburyuk]

For the people who just responded kindly to my post, here's an overall question:

I may be detailed and interested, so I make detailed notes about componentry, sketches of the vehicle, designs of layout, etc; however, I really have zero electrical engineering background, and I wouldn't trust myself to implement/install, unless I was with a skilled/aware person.
So, what do you think? For someone in my shoes, who is obsessed with all things electric, but who has skills not related to implementation, is it really a dichotomy of paying £20k to a service or just not do it at all? It does seem that many people are willing to afford such investments, but in real terms, it's just not an option. Even if I can find a way to get affordable parts, labour may just be the nail in the coffin.

Queue the sad music..

[Isaac96]

For the people who just responded kindly to my post, here's an overall question:

I may be detailed and interested, so I make detailed notes about componentry, sketches of the vehicle, designs of layout, etc; however, I really have zero electrical engineering background, and I wouldn't trust myself to implement/install, unless I was with a skilled/aware person.
So, what do you think? For someone in my shoes, who is obsessed with all things electric, but who has skills not related to implementation, is it really a dichotomy of paying £20k to a service or just not do it at all? It does seem that many people are willing to afford such investments, but in real terms, it's just not an option. Even if I can find a way to get affordable parts, labour may just be the nail in the coffin.

Queue the sad music..

This is the real question. Some of us here (myself included) are not electrical engineers; however, most have some experience with at least basic electronics.
If you want to work on the car yourself I'd like to suggest starting with something smaller and cheaper than a car; how about building an electric bike? It's entirely possible to make something rudimentary without spending over $300 (I've done it twice). Then you could at least see how you do when building something, and gain good experience without spending lots of money or potentially hurting yourself. And then you can be the skilled (or at least aware) person.

Alternatively, you could find a consultancy service of some sort. Then, even if you don't have someone installing the batteries with you, you can at least have someone to help you make decisions like where to install them, how to avoid damaging them, et cetera.

Either way I think you will find this a very rewarding project. But I hereby officially warn you that it will never be done; you will always be finding ways to make it better.

-Isaac

[baronofbloomsburyuk]

If you want to work on the car yourself I'd like to suggest starting with something smaller and cheaper than a car; how about building an electric bike? It's entirely possible to make something rudimentary without spending over $300 (I've done it twice).
-Isaac

Hi Isaac,

Actually, that's why I'm doing the Isetta -- both b/c it would be useful to have it converted, but also more b/c it's really a motorcycle with a small body on top, and it's practise for a full sized car later, as battery/range prices hopefully reduce in the future. Thanks.

[Kevin Sharpe]

So, what do you think? For someone in my shoes, who is obsessed with all things electric, but who has skills not related to implementation, is it really a dichotomy of paying £20k to a service or just not do it at all?

Post an WTB advert in the classifieds setting out your basic requirements and budget. I doubt you'll get anyone who will help today *but* one third of our course attendees are professional automotive people who intend to offer conversion services (many at low cost). The issue for you is the bespoke nature of your conversion which means lots labour and high costs.

[baronofbloomsburyuk]

So, what do you think? For someone in my shoes, who is obsessed with all things electric, but who has skills not related to implementation, is it really a dichotomy of paying £20k to a service or just not do it at all?

Post an WTB advert in the classifieds setting out your basic requirements and budget. I doubt you'll get anyone who will help today *but* one third of our course attendees are professional automotive people who intend to offer conversion services (many at low cost). The issue for you is the bespoke nature of your conversion which means lots labour and high costs.

Thanks, makes sense. A Fountain of info