Car chosen

Here's my next conversion. It's a 1997 Citroën Xsara. The latest model you can easily convert here in Finland I believe (but I'm not sure). It may not look like much now, but I'm hoping to spruce it up quite a bit. After all it's just a chassis, a base for the conversion. The front might get a big makeover and a new coat of paint is not far fetched at all. Other than that it's a suitable 5 door hatchback with a front wheel drive and it drives suprisingly well.

And yes, it's called the kWsara.

In a magazine

There's a story about the bike in the latest WattiViesti, a customer magazine of the local electric company Pori Energia. There is an online version available. You can find the article on page six. It is naturally in Finnish and the online version unfortunately requires Flash as well.

Bottom balancing to the rescue

Last night I rode my battery pack half empty and today added the 25th cell that arrived yesterday. I then proceeded to drive the pack completely empty so I could bottom balance the new cell as well. I dropped off some badges my S.O. had made, located a gas station not to fill up but to check tire pressure, picked up two salads from the local market and ran out of juice before getting home. Yes, I thought the pack would have 5 Ah more left, but alas it did not. I kept pushing against the 50 volt limit I had set in the controller, that's only 2 volts per cell, but couldn't get home without pushing for real.

I was more than a little worried that I had incorrectly estimated the state of charge of the new cell and now ruined it straight away, but it was not so. It was happily resting at 3.2 volts while the rest of the pack was around 2.5 volts per cell. I didn't take very long to go from very worried to very happy about how well bottom balancing had protected my precious cells. I hadn't been able to break them even by pushing them down to 2 volts. And I tried. The bike would just stop going as the cells refused to give more than a few amps and floated back from their lower limits with no problems whatsoever. I can therefore testify that bottom balanced cells will protect each other and not let you kill their colleagues.

I then turned my attention to the newcomer and drained it down to about 2.5 volts where the older cells were waiting, connected my 2 kW charger and let it do it's thing. About 40 Ah went in as expected. For the bottom balancing I used the electric motor of the bike itself.

Missing cell: Arrived

Finally got my last cell today from faktor.de. It arrived at about 3.276 V. Perhaps a little less than half charged then. I'll now have to drain the main pack before I can add the newcomer into it. It will also need to be drained to 2.7 V initially. I might want to improve upon my earlier bottom balancing on all of the old cells as well. When I did it for the first time I eventually ran out of patience. That's not to say bottom balancing hasn't been working perfectly. It has.

If I converted a car

I've been researching my ideal kit for a car conversion. AKL (Finnish Central Organisation for Motor Trades and Repairs) has set some rules for working on electric vehicles. The rules define that working with over 50 VAC or 120 VDC requires you to notify the Finnish Safety and Chemicals Agency (Tukes) and the personnel needs to be formally qualified for the work. These are also the same voltage limits set by law in Finland for electrical work. Therefore I have concluded that to avoid any problems one should stay below 120 VDC in private conversions as well. That way nobody should have a problem with these vehicles and it kind of makes me feel a little bit safer and more confident as well since there are set limits to work with.

120 VDC might not seem like much, but since the arrival of the new grey CA-series CALB cells which seem to sag a lot less than anything seen before (except possibly the A123 pouches which are quite hard to work with) you wouldn't need to oversize your pack to account for the voltage sag. They are capable of over 10 C discharge which means you can get decent performance at below 120 VDC and cell sizes as small as 60 Ah (10 C at 60 Ah cell is 600 amps). At a floating 100 volts and 500 amps you're looking at 50 kW in power which should be quite enough for a small car.

This brings me to my kit. It's not a kit really, but a selection components I'd use if I'd start the project today.

Charger

I've been using a couple of KP chargers from evassemble.com for a while now and although both of them have arrived with a broken fan, they are quite affordable and seem to do the actual charging fine. On the smaller one I got first the fan itself was broken and/or mounted the wrong way. The 2kW charger I got later had been slightly damaged in transport which prevented the second fan from spinning. These were easily fixable though. Therefore I'd get the KP-L 3kW 116.8 VDC 22 A charger from evassemble.com.

You might think it's a bit silly to start building a kit with the charger, but a good charger is very important and not as easy to come by, especially if you don't want to break the bank. Charge voltage will also determine your pack voltage and number of cells which in turn will define your motor and controller choices. The other option would be to get the biggest charger you can find with charge voltage over 120 VDC and use a relay to cut charging at exactly 120 VDC. You'd only get one more 3.5 volt (charging voltage) cell in though and you'd loose the CV part of the charge. Remember that usually we're first charging with Constant Current (as much as the charger can do) and then we taper the charge by holding the desired voltage (Constant Voltage) while reducing the amps going in until we're at 3.5 volts per cell. The charger will then cut off the charge when a set low current limit is reached.

Alternatively Rebbl sells an Elcon 2500W charger that you can probably program to your needs.

Battery pack

Now that we know our charging voltage which on the KP-L set for 96 volts nominal is 116.8 volts we can calculate that to get about 3.5 V per cell we need 33 CALB cells. It's actually 3.54 V per cell to be exact, but close enough. 34 cells would put us below 3.5 and 32 above 3.6 V, so 33 is the number for us. The reason we are so careful to choose and match our charger with our battery pack is that we will be bottom balancing the pack and just simply charging to full voltage with no BMS. If you were using a BMS you could be a bit more careless, but you'd end up with a mess of wires each a potential fire hazard and we really don't want to go there. Bottom balancing is the way to go and it really does work.

The number of cells is 33 and the rest depends on the size of your car and probably even more on the size of your wallet. I'd say 60 Ah cells are the minimum to get a 40 km range (or 6 kWh and 3000€) and going up to 180 Ah should give you 120 km range in a 200 kg pile of batteries (or 18 kWh and 9000€). If was to order batteries now, I'd order from ev-power.eu.

Controller

This one's easy. Or hard. Depends on if you just go with EVnetics Soliton Jr. or decide to find some other alternative. You can order one from Rebbl. They also ship them EMC certified to fulfill all EU regulations. 600 amps should be plenty and if you like more you can always opt for it's bigger brother, the Soliton 1.

Motor

This is going fast. Also from Rebbl, or wherever you want to order, the Kostov 10". According to it's spec sheet 115 volts, 270 amps continous at 4500 rpm should give you around 26.2 kW. We don't quite have 115 volts, but close enough to get a ballpark figure. Around 25 kW is very realistic. For peak throughput with the Soliton Jr. at about 100 volts we are looking at double that at 50 kW. Enough for a compact car I think.

Conclusion

There you have it. The main components of a possible future "kWkasi". Pronounced "koo-vee-kasi" in Finnish. Get it? No? Don't worry. Here's the shopping list with quick specs for each component.

Kostov 10" motor (25kW continuous, 50kW peak in our setup, 69 kg)

Soliton Jr. controller (450-500 A continuous, 600 A peak, up to 340 V, 7 kg)

33pcs CALB CA180FI cells (96 V nominal, about 110 V charged, 19 kWh, 185 kg)

KP-L 3kW charger (22 amps at 116.8 volts for 8 hour recharge from empty, 9 kg)

Disclaimer

Please note that although I've mentioned Rebbl webshop quite a few times I have not ordered from them anything yet. Which just means I can't vouch for them. They seem respectable though. evassemble.com and ev-power.eu have come through for me just fine on my previous orders.

Finally shipping

My 25th cell is finally on it's way from Germany. I put the order in at faktor.de a couple of weeks ago and they were kind enough to fill the order last Thursday after claiming they had done it on Wednesday. Tracking says otherwise. Now I do realise it's just a single SE40AHA cell and they make no money from it whatsoever, but the lack of customer service pretty much guarantees I will not order a big number of CA cells from them either. ev-power.eu did their job much better and with no hassle so that's still the place to go for me. Unfortunately they don't even list other than CA180FI size cells, but I'm sure they'll have others by the time I have another project going. Which might as well be never, but I'm hoping otherwise as always.

Other than that I hope the weather stays comfortable to ride for a while longer. Having said that I did end up driving the bike in quite a bit of rain as well. I was at a friend's place helping out with some Linux details and it starter pouring while we were at it. Had to get home so I just decided to give it a go and got home with zero problems. There was quite a bit of water everywhere, but it didn't cause any issues. Actually I think I made my mpg record too. Wet weather makes one gentle on the throttle.

I did get into a talk about swapping my older bike, the Z500 I had planned to convert first, for a VW Beetle, but it sort of dried up. I'd like to get a well restored specimen with a broken down engine. Preferably free as well. Not likely to happen. More likely one of our cars to suffer an engine malfunction. And they're not too likely to be break either. The other one being a Honda VTEC and the other a diesel. Among the list of cars I should have kept for future conversion is a VW Golf that needed to have it's engine replaced. The car I really feel bad about losing though was my first, a 1977 Honda Civic 1200. Now if I could travel back in time to get that beauty back in the condition it was... Oh boy oh boy. It would have made a beautiful electric vehicle.