[tom3141]

Hi all.

I’ve been lurking on these forums for quite a while but I have finally begun a conversion.

The donor is a 1994 Suzuki Cappuccino. For those who don’t know it’s a tiny Japanese kei sports car weighing around 725kg stock. It comes with a 660cc 3 cylinder twin cam turbo engine as standard in front engine RWD layout. Great fun to drive even with its 64hp power output.

I have begun work on the car to get it ready for the conversion. They all have a problem with rusty floors and although mine is a good example it needs some welding before I can go any further.

I have one of the Enova 90kW AC induction motors which I have been able to get turning on the bench using Damien’s combi control PCB controlling the original Enova power electronics. The plan is to connect the motor directly to the prop-shaft for direct drive (diff ratio is 5.125:1). I believe this should give me pretty good performance considering the motor has around twice the power of the stock ICE.

Recently, I obtained some Boston Power Swing 4400 batteries. They have been used but seem to be in pretty good condition. I have around 20kWh in total but I’m unsure whether I will be able to fit them all in! I will be using the car for my commute which is 19 miles each way. I can charge at work but would like to be able to get there and back comfortably on one charge so I’m aiming for a 50 mile range.

The biggest unknowns at the moment are the charger and BMS options. I need to do some research on this as this is the area I know the least about and seems to be the biggest minefield!

I’ll try to keep you updated with progress and I’m sure I will have plenty of questions!


Tom

 

[tom3141]

Hi Malcolm.

Thanks for the charger/BMS suggestions - I will have a look into those.

The cells I have bought are actually already assembled into packs of 8 cells in parallel so the assembly shouldn't be too bad. I'm planning on pairing these up to get 16 cells in parallel and then connecting around 80 of these in series. This will give me around 300V and 70aH.

Cheers,

Tom

 

[tom3141]

Thanks for your interest.

Progress has been slow over the winter, hence the lack of updates. The rust was worse than I first thought but I'm now about ready to weld in the repair patches. The floor had practically detached itself from the sill along the driver's side of the car.

I've removed quite a lot of the engine ancillaries so once the rust is sorted I'm hoping that I can progress a bit quicker and get the engine and fuel tank out.

Unfortunately, I don't have many photos at the moment. Mainly because they would just be photos of rust! I have attached a couple. Hopefully I'll have some more interesting photos soon.

Tom

 

[tom3141]

This is the motor and inverter that I have:

https://evpartssale.co.uk/ev_motors_and_controllers.html

 

[tom3141]

Yeah, I’m going to run it without the reduction gearbox. Just direct drive to the prop shaft. With the 5.25:1 reduction in the rear diff it should still have enough torque.

I don’t know how much torque the motor produces. The stock engine only produces 64lbft and feels quick. I’m expecting double if not triple that from the motor.

 

[tom3141]

No problem, nice to know that you’re thinking along exactly the same lines that I am.

Unfortunately I don’t think the motor will tuck very far up into the transmission tunnel as it is so narrow. The stock gearbox is very long and thin.

The full battery pack weighs around 150kg (bare with no connections/cables/casing). I think I might struggle to fit the whole pack in as it’s such a small car. Once I have the engine and fuel tank out I will have a better idea. The fuel tank area looks quite big (relatively!) but it is difficult to access as the entire rear subframe must be removed to get to it.

Weight wise I think the car will end up heavier than stock but hopefully not by much. It’s 725kg as standard so I’m hoping to stay under 850kg at a guess.

 

[tom3141]

Thanks for all the input guys. It's getting me motivated to get this rust sorted and get cracking on the conversion!

My current plan is to split the battery pack between the fuel tank area and the engine bay. With the charger and some other electrical gizmos in the boot and the inverter above the motor at the rear of the engine bay.

What are the disadvantages to splitting the battery pack? Power losses in the long cables? It seems that whichever way it is done (split the battery or put the inverter at the back) the same problem is going to be present.

I could split the battery into two equal voltage packs but I seem to remember reading that it is best to put the cells together in parallel to get the amp hours that are needed and then connect these all in one series string.

I would also rather keep the inverter near the motor as it has a nice 1m cable with connectors that I would rather not mess around with. I have thought about trying to put the motor directly onto the rear diff but there is just not enough room.

The discussion on the transmission tunnel is interesting. I hadn't really considered this, mainly because I'm not sure if there are extra legal hoops that have to be jumped through in the UK if you start cutting into structural parts. Also, the footwell is already extremely small. I'm 6'3" and, although I find it very comfortable to drive (once I'm in!), there isn't much room for manouvre. I will have a look next time I'm working on the car.

I'm hoping to get the rust work finished over Easter and from there it shouldn't take too long to get the engine out. I think I'll need to get the cardboard out after that to make some models for test fitting! It's definitely going to be a puzzle.

 

[tom3141]

Attached are some photos of the batteries. Each of these contains 48 cells.

 

[tom3141]

I'm hoping to keep them in the original blocks. The busbars can be swapped around within it to change the cell configuration to whatever I need.

I'm not convinced splitting into two equal packs is worth it. Other than the extra redundancy in case of failure, what are the advantages? It seems to me that it would introduce issues with the two packs charging and discharging unevenly. I was planning to connect 16 cells togther in parallel and then 80 of these batteries together in series. If I do what you are suggesting I will need to monitor twice as many cell voltages. I would have to connect 8 cells together in parallel and then 80 of these batteries in series for each pack. I'm open to doing this if it's the best way but I can't see what the advantage is at the moment.

 

[tom3141]

Made some progress today.

I'm now ready to weld the floor repair patches in. Hopefully this will be done next weekend if everything goes well. The engine is also now ready to remove. Everything is disconnected apart from the mounts. I may need to remove some more of the exhaust downpipe but I will wait and see if I can lift it out as it is first.

I also got some photos of the transmission tunnel. They are not the best as the car is on axle stands so I was a bit close to get a decent photo.

The main body of the motor is around 280mm diameter by 330mm long. It is around the same diameter as the gearbox bell housing at its largest. Without any modifciation to the structure I should be able to tuck the motor in so that the front face is around 5-6 inches further back than the engine/gearbox interface.

One nice feature of the transmission tunnel is that it is pretty tall. Originally the exhaust ran down the transmission tunnel underneath the propshaft and was completley hidden as it was above the floor line of the car. It will be tight but I think that I may be able to squeeze some of the battery blocks in underneath the propshaft. If they fit in the width and height then I guess I could probably fit 5 or 6 along the length of the tunnel.

When I'm looking at battery packaging how much thought needs to go into cooling/heating? I believe most OEM EVs have the ability to cool their batteries. Is this generally done amongst DIYers as well? I'm just thinking about whether I need insulation and space for cooling around the batteries. I'm not planning to use the car in sub zero temperatures (celsius) as my commute is quite rural and I'm going to keep my 4x4 for icy/snowy days. The Cappuccino was also pretty tailhappy with the stock engine so I think it would be terryfying in slippery conditions with twice the power! Summer temperatures very occasionally reach 25C but are generally high teens. My current plan is not to worry about heating or cooling but obviously just to make sure they are protected from water and dirt.

 

[tom3141]

Yes, you've understood correctly about the motor position. I think I will be happy with that, especially if I can get some of the batteries in the tunnel.

It's a lovely little engine but would need to be put in a car with a similar diff ratio (5.25:1) otherwise it would be really sluggish. Feels genuinely quick in a car this light but a lot of that is due to the ridiculous gearing. You sit at something like 4500rpm at 70mph in 5th. Redline is at 8500rpm!

The battery I have is made up of Boston Power Swing 4400 cells. They did come from a prototype EV but I'm not sure whether they had any heating or cooling. Just checked the data sheet for them (http://liionbms.com/pdf/bostonpower/swing4400.pdf) and the discharge operating temperature is -40C to +70C, charge is -10C to +60C. From the temperature performance graph it looks as though ideally they want to be kept between 30C and 60C. What I don't know is how much heat they will generate themselves under charging/discharging.

 

[tom3141]

I've managed to get hold of a Brusa charger. It arrived yesterday so I now have nearly all the parts I need. The only big thing left is to decide on the BMS options. I'm still thinking of going down the route of a simple overvoltage and undervoltage cut off (no balancing). I'm looking at something like the CellLogs or Zeva 8-cell battery monitor module.

I also noticed something on the motor spec plate yesterday. It has the base frequency listed as 121Hz (3630 rpm). From my research online it appears that this is the frequency at which peak power is available. So, correct me if I'm wrong, I have a peak torque at the motor of (9.5488*90000W)/3630rpm = 237Nm. This gives a wheel torque of 237Nm*5.125 = 1214 Nm. I think I'm right in saying that this is constant between 0 and 3630rpm. 3630rpm equates to around 45mph with the 5.125 diff ratio.

The original engine makes a peak torque of 85Nm at the engine (at 4000rpm), which is 1515Nm at the wheels in 1st gear (3.478 gear ratio x 5.125 diff ratio) or 880Nm at the wheels in 2nd gear (2.021 gear ratio x 5.125 diff ratio).

Looks like I will have plenty of grunt . I'm hoping for a 0-62mph time of around 6 seconds which seems reasonable.

I've borrowed an engine hoist for the weekend so I'm hoping to get the engine out in the next few days. I'll keep you posted.

 

[tom3141]

The Cappuccino has been de-ICEd! Got the engine and gearbox out this morning. That leaves the fuel tank as the only part left that needs removing.

I also began the process of welding the sills. Not the most fun job but it's got to be done!

Photos of the empty engine bay are attached. I'm going to make some mock-ups of the motor and batteries so that I can play around with the layout without having to lug the motor around. I'd love to create a Solidworks model of the engine bay to make this easier but without a 3D scanner it would probably take far more time than it's worth and not be very accurate. I think I'll have to resort to Cardboard Aided Design!

 

[tom3141]

They’re actually in a 6 x 8 array currently connected 6s8p so I just need to reconfigure to get 3s16p within each module. Although they are almost identical in size to two 18650 cells apparently they are actually one oval shaped cell. Someone on a forum (I can’t remember which one) took a cell apart to find this out.

The external dimensions of each module with the plastic casing included is 285mm x 180mm x 80mm.

I have 28 modules in total but I’m just going to have to see how many I can fit in. I only need a range of 40 miles but I want to put as many in as I can so that I can use as little of the capacity as possible in normal use.

The motor is rated at 208V AC which would be a 293V DC battery pack voltage. That’s why I thought 27 modules giving 300V nominal would be the maximum I would want. A slightly lower pack voltage wouldn’t be the end of the world. I think even 24 modules would be ok at 266V nominal (and around 18.5 kWh) if space is an issue.

 

[tom3141]

I had a lot of trouble trying to weld up the sills and floor at the weekend. It may just be my lack of skill with a welder but the steel is so thin on the Cappuccino that I'm finding it impossible to weld. I'm going to reassess it at the weekend but I have even started to conisder whether this is the right car. I don't want to patch it up badly now and put all the work into a conversion only for it to rust to bits in a couple of years. Cappuccinos are terrible for it, mine isn't too bad compared to some but it's not as good as it first seemed. I'm going to try to take the rear subframe out at the weekend so that I can double check for rust on the bodyshell above it. If there is any serious rust there that I haven't already spotted it might be game over for the shell.

Before purchasing the Cappuccino I had considered a kit car or scratch built. I'm half considering this again using everything out the Cappuccino other than the bodyshell. However, reading through the IVA (Individual Vehicle Approval) manual has scared me off a bit. The section on EVs is worrying. Have any of you UK based builders got an EV through the IVA? It seems that it has to be tested against the ECE R100.01 standard which sounds pricey. Also, on this note, for a normal EV conversion in the UK, is it still the case that you just have to send the V5 off with a change of fuel/engine and then get it MOT'd? Or is there an EV test/inspection that it must pass?

I'll probably end up sticking with the Cappuccino, I think it was just an overeaction to laying under the car all day attempting to weld and not getting anywhere! The other option is getting a professional in to do the welding. However, I think it would need to go to a proper car restorers rather than a local garage/bodyshop. They are going to want to strip it right down to a shell to dip or blast it before repairing properly. I don't think replacement floor or sills are available so it would need repair panels making from scratch. I don't know if it's going to be worth the cost.

 

[tom3141]

It's a small car and you are stripping it down - have you thought about making a "rotisserie" for the shell so that you can weld across and down rather than up

Yes, I've considered that - it might be the way to go if I decide to stick with the Cappuccino.

Since it's unlikely there's a kit in existence designed to use Cappuccino components, this would presumably be a scratch-built

Yes. I've always fancied designing a car from scratch. I do a lot of design using Solidworks for my job so have the tools to do it. I might even have a go at a design just for fun even if I don't proceed with it. Another reason I'm tempted by the scratch built route is that I can design it around my components. I wouldn't have all the issues trying to cram the motor and batteries into spaces where they don't fit.

Are the Cappuccino components really what you want in a scratch-built (maybe they are, as they would be light, have a sophisticated design, and use modern parts), and is that the best way to get value out of the car you have?

This is bascially what I'm weighing up at the moment. As I said I want to have a proper check over the entire bodyshell once the subframes are out. Then I'll have to decide how I get the most value out of the car. If the rust I have already found is all there is, then it would probably be silly to scrap the shell. However, the components would be really nice for a scratch built car. All the important bits are bolted to the subframes so it would be relatively easy to build.

It's essential to cut back to clean metal, or at least metal that can be ground back to a clean surface without becoming too thin. Grind back paint or rust at least a centimetre from the edges to be welded.

Don't try to make continuous seam welds. Make a series of overlapping "spot" welds.

If the existing metal is so thin that it still keeps burning back, it helps to use lap joints where possible. Make patches that lap underneath the existing metal. That way the new metal will draw some of the heat away and prevent burning through. The easiest way to make these patches is with a joggling tool – you can find them for as little as £20 on ebay.

Thanks for your tips Malcolm. I think one of the problems I've had is that I haven't cut enough metal out. I cut out all the actual rust but the edge of the floor I'm trying to weld to is too thin. It's ridiculously thin metal from the factory so any rust at all makes it paper thin.

I have made up the patches already. I'm doing lap joints as well but still burning through the floor on my MIG's lowest setting. I've also had trouble getting the two overlapping pieces of metal clamped up nicely, any little gaps and it is impossible to weld.

Part of the problem is that I was not expecting to have to do this welding when I bought the car and I'm desperate to get cracking with the conversion. If I decide to stick with it and do the repair then I'm going to have to accept that it's going to take a while to do properly.

 

[tom3141]

So I've decided to stick with the Cappuccino. It seems currently the regulations are fairly straightforward for a scratch built EV but they are expected to change in the near future. If I started a scratch built and didn't finish before any new regs come in it would cost a fortune to make road legal.

I've found someone who can do the welding for me so I'm going to pay him to do it. It will mean that I can get cracking on the conversion which I'm desperate to do. He can't fit me in for a few weeks so in the meantime I'm planning to confirm the mounting points for the motor and battery boxes.

I did some measuring up at the weekend and I think I can fit 12 battery modules in the engine bay in front of the motor, 10 modules in the boot, and 3 modules in the fuel tank area. This will give me 25 modules which should be enough. I'm going to design some battery boxes and double check these fit in the space available.

 

[tom3141]

I did a test fit of the motor and inverter at the weekend. Unfortunately I wasn't able to get the motor fully into position as it wouldn't slide underneath on a jack and is too heavy to lift in from above. I'll need to borrow an engine hoist again to do this. It looks like it will fit and will mount quite easily on the subframe though.

The inverter is a really snug fit - I didn't realise how big it was until I put it in the car! A photo is attached. I had forgotten about the water cooling pipe outlets which mean that it sticks further out into the space that I was planning to use for batteries. With the inverter in place I think I'm only going to be able to fit 8 batteries in the front and even that is going to be quite a squeeze. This will bring the number down to 21 (233V nominal, 16.4kWh). I'm not sure that I'm going to be happy with this so I'm considering a few different options.

I could try to reduce the size of the inverter. There is a fair amount of empty space inside but I'm not sure that I will be able to reduce the size enough to gain much/any more space for batteries. It would mean machining a new water cooled base plate so I don't think the slight gain in space would be worth the effort.

Another option I'm considering is removing the passenger seat. I could fit the entire battery pack (28 units, 310V, 21.8kWh) in the passenger space and it would simplify the conversion quite a lot. The main purpose of this car is a fun and cheap car for me to commute in (40 mile round trip) so not having a passsenger seat wouldn't be the end of the world.

The issues with the plan to split the pack between the engine bay, boot, and fuel tank are:

• smaller than ideal pack size
• lots of batteries just behind the front bumper and just in front of the rear bumper worries me from a safety point of view
• weight distribution probably isn't ideal (batteries in front of front axle and behind rear axle)
• radiator would need to be relocated
• no room for spare wheel or roof panels in the boot
• quite a lot of design work needed for three seperate battery boxes
• complex wiring and long cables between different parts of the pack
• not much room left for things like vacuum pump, water pump, contactors and charger

Putting the batteries in the passenger space would solve all of this. The only downside is the loneliness!


I'm still weighing it up at the moment. I don't really need to make a final decision until I've had the welding done so I will see if there is any other way around it over the next few weeks.

 

[tom3141]

So I test fitted the motor today. Thankfully there were no suprises - it actually fits quite nicely! I should be able to use one of the mounts that came with the motor along with a simple bar to support the back of the motor.

What is the general consensus on rubber motor mounts? It will be easier and simpler for me to just bolt/weld the solid mounts directly to the subframe. I've read a few threads giving pros and cons but personally I don't really see the need for rubber mounts.

The attached photo shows the front motor mount roughly in position.

 

[tom3141]

No problem Peter

I've arranged for a guy to do the welding for me as I didn't want to get bogged down with all the rust. It should be getting fixed at some point in the next couple of weeks. I do have access to a TIG welder at work - I've had a few attempts using it but I find it very difficult to have a steady enough hand. The guys on Youtube make it look so easy!

I think I'm going to stick with the inverter at its original size (at least for the time being) but thanks for your offer. I do have acces to a machine shop at work but I'm trying to keep things as simple as possible so that I can get on the road quicker.

The plan for connecting the motor to the propshaft is to use the primary gear from the gearbox as you suggest. I have already stripped the gearbox down but I haven't tried machining the gear yet. I'm hoping to give it a go on the lathe at work this week.

I've ordered a second hand propshaft (from a Bentley!) that should be turning up on Tuesday. The original propshaft is obviously too short and it seemed easier to find a new propshaft the correct legth rather than extending the old one. The first one I found on eBay that was roughly the right length was from a Bentley Turbo R! It was cheap so I thought I may as well give it a go . The plan is to machine an adapter plate for each end so that I can bolt the prop flanges to the diff at one end and to the primary gear at the other.

I put the motor in position today ready for test fitting the propshaft when it arrives. Once I'm happy that the propshaft, adaptor plates, and motor all fit together nicely I will get the motor mounted permanently.

Tom