Wood is good!

This weekend was more thinking and drawing than building. I designed a caliper adapter plate for the rear brakes and made a mockup in wood. The mockup made me realize that I had measured 7mm wrong. Wood is good!
Later this week I will try to find someone who can manufacture the adapter in steel for me. When I get the steel adapters I will know for sure if I have measured everything right.

The wooden caliper holder adapter mockup mouted on the stub axle together with the wheel hub, brake rotor, caliper holder and caliper

Progress!

At last some progress!
The Skoda Fabia spindles fit perfectly on the A2! Including suspension strut, drive shaft, steering knuckle, spindle joint and ABS sensor. Now I'm going to return the extra A2 spindles and Golf caliper holders I ordered and insted get some calipers and brake discs for these spindles.

The Skoda spindle mounted in th A2. Note that there are no caliper holders. They will be bolted onto the spindle.

Fits great!

Yet another dust bite

I tried my Plan C for front brakes this weekend. It wasn't at all like I imagined it would be. It turns out that in order to fit brake caliper holders on to the wheel spindle of the A2 some serious welding of the spindles is required. My contact at SFRO advice me not to weld in these parts of the car. In order to pass approval I would then have to perform and document weld tests with the spindle and do strength tests of the test welds. Naa, maybe not my cup of tea.

The spindle to the right and the caliper holder in my hand

Instead I turn to plan D!
So, what is plan D?
My friend Björn at the Audi A2 EV Facebook Group showed me a forum where people discuss upgrading the brakes on their A2:s to larger discs. In turns out there is another chassis component used in some VW Polos, Seat Ibizas and others.
I managed to find the same spindle from a Skoda Fabia so my new plan D is to use the spindles from a 2004 Skoda Fabia and the orignial caliper holders, discs and calipers from it. Wish me luck!

I did some dismantling of the rear wheel in order to measure for the adapter plate for the rear disc plates. I will probably do a mockup in wood first. It's tricky to measure right in 3D!

The stub axle between the old drum brake pads and the rear axle behind (just in front of the spring). Between the rear axle and and stub axle is where the adapter plate goes.

Below are som skethes of the original drum brakes and the planned convertion to disc brakes

Swedish to English translation

bakaxel = rear axle

axeltapp = stub axle

nav med hjullager = hub with wheel bearing

bromstrumma = brake drum

adapterplatta = adapter plate

okhållare = caliper holder

bromsskiva = brake disc (rotor)

Peter - Audi A2 : 0-1

So, I lost the first round with the A2.
I took a chance that the spindle housing (wheel bearing husing) from the 2004 Golf IV, made for 280mm rotors would fit on the A2. Well, it didn't :-(
Actually the spindle housing itself fits on the car, but the drive shaft did not fit in the spindle. And, the Golf has a different system for the ABS sensor. The A2 has magnetic type whereas the Golf seems, well different.

The Golf spindle with hub to the left and the A2 spindle to the right. Very similar...

The A2 hub (left). The Golf hub with a separate rotor for the ABS sensor (right)

I was also considering taking the hub and the bearing from the A2 and put it into the Golf housing, which was my Plan B. But I realized that 1), the manual says that the bearing and hub on the A2 is destroyed when pulled out of the housing so I would have to purchase a new one, and 2) which is worse, the fitting of the bearing in the housing does not work the same way on the Golf as on the Audi, so the bearing would not fit anyway.
Well, I gambled and I lost.
This means I have tested Plan A and Plan B so I will have to resort to Plan C.
Plan C means doing the same thing in the front as for the rear brakes. That is to manufacture an adapter that will fit on the spindle housing and allow a brake caliper from a brake system with a larger rotor to be fitted on the housing. Since the spindle housings on the A2 has built in caliper holders that prevent fitting larger rotors (which was the reason for changing the spindles in the first place) I will have to saw those holders off.
Stay tuned and I will tell you about this when I get there. As for now, I will lick my wounds...

The Audi A2

The Audi A2 is a compact MPV, or supermini, built by Audi during 1999 and 2005. The A2 was no big success to Audi. It didn't sell so good mainly due to its rather high price and the A2 program was shut down in 2005.
The reason for me to chose the A2 are several.
It is a cult car that was manufactured during a rather short time period and they are not so common.
The body is built from aluminium using the Audi Space Frame technology, which is the same as is used in the Audi A8. The aluminium makes the car light, which is good if you build an electric car, and resistant to corrosion, which is good when building on a car that has seen some miles on the road.
The A2 is a four seater with plenty of leg room in the back seat thanks to its height and just enough room for a couple of dogs in the rear. Actually the trunk space is the same as the VW Golf which looks like a larger car.

The cockpit

The cockpit feels almost like a bigger Audi from the time. The main difference compared to an Audi A6 is the smaller distance between the driver's and front passenger's shoulders.

 

The trunk

 

The trunk

The back seats fold up and reviel a pretty large space.

Underneath the back seats is the gas tank today. A battery box will go there instead.

Beneath the trunk is the muffler and the 12V battery and tools box. Another battery box will go there.

I'm sure I won't get a job as a 3D artist after this ;-) but I tried to show the two rear batttery boxes in a 3D drawing (Jörgen, forgive me ;-). The exact space is still to be measured, but I think they will both hold one layer of standing CALB CA100FI (100 Ah LiFePO4 cells) which are 22cm tall.

The original 12V battery will be replaced with a smaller one, maybe located in the double floor in the front.

The rear batttery boxes

 

The rear battery boxes from underneath.

In the front I plan to put another batttery box, right where the radiator is today. I'm hoping to get enough height to have two layers of cells on top of eachother there.

 

The front battery box. Note that the hood is taken off.

You don't open the hood on the A2, you take it away! Instead theres is a small service hatch that is used to check oil and fill up windshield washer fluid and coolant. I might put a charger inlet there instead :-)

The service hatch.

The double floors in the front seat

 

The double floors in the front are great places for putting stuff away since the engine compartment is quite small. The depth is about 15cm. Today there is the ECU (Engine Control Unit) that I might try to get rid of. It won't have an engine to control, but it might be involved in other activities as well.
In the back seat there is no double floor.

The back seats passengers have a much more upright position thanks to the deep floor. Behind the back seat passengers foot box is where the space for batteries start (which is now gas tank, rear axle, muffler, tools box and 12V battery).

Other Audi A2 conversions

Maybe the best known conversion of an Audi A2 is Simon Kay's conversion the he published as a series on Youtube.
The German company L.E. Mobile have converted quite a few Audi A2:s.
Please comment if you know of other A2 conversions!

The plan

The overall plan of this project is to get rid the ICE (Internal Combustion Engine), the fuel and exhaust systems and istead put in an electric motor, a bunch of lithium ion batteries, a controller for the motor and lots of other stuff thats needed to get the car working. I have a pretty detailed plan right now, but the actual components might change depending on what prices I can obtain.

Brakes

I have already mentioned the brake system in earlier posts, and this is only to circumvent (follow?) the Swedish regulations for converting cars. It has nothing to do with the electric conversion.
There is one more thing to the brakes though. Most modern cars have vacuum assisted brake servo and so does my A2. However, when the ICE is removed there is no source for vacuum so I will need a separate electric vacuum pump.

Motor and controller

The motor I plan to use is a Kostov K9" 220V. Kostov is a Bulgarian company who manufacture motors for fork lifts and now for DIY (Do It Yourself) electric cars. The motor develops 32 kW sustained and 78 kW peak. The peak power is only available during short accelerations for  couple of seconds, but this is usually what you want power to. If you use the max power for much longer the motor and/or controller will overheat and shut down. The motor is rated for a voltage of 220V DC and at peak power the current will be 500A! It is not very big, only 22cm diameter, 46cm long and weighs 45kg!
To control the speed of the motor I need a motor controller. The controller applies voltage in shorts bursts thereby limiting the average voltage and the speed. I am planning to use an Evnetics Soliton Jr which can handle up to 340V battery voltage and up to 600A motor current. This will be just right for the motor. I nice feature with the Soliton is that it is configurable via a standard Ethernet connection and a web browser.

Transmission

Transmision? Do you really need a transmission in an electric car? Well, it seems that the easiest way to convert a car to electric is actually to keep the transmission and the clutch. The available (affordable) electric motors have a torque curve that is usually flat up to around 3000rpm and then torque decreases down to the max rpm which is usually around 6000rpm. This means that if you go only one gear you either have to use a high gear to obtain a decent top speed. This means sluggish acceleration and high currents at low speed. Or you chose a low gear that gives you good low speed acceleration, but low top speed. An easier way is to keep the transmission and use two gears; second gear for city driving and fourth gear for highway, for example.

Battery and charger

The most important part of the conversion (and the most expensive) is the battery pack. I am planning to use Lithiun Iron Phosfate (LiFePO4) cells which have a good combination of good energy density, life time, and security (they don't go in flames if you overcharge them which I have heard some other LiIon chemistrys do). The newer cells also work pretty well at low temperature which is important if you live in northern Sweden. Each cell has a nominal (the voltage changes during discharge) voltage of 3.2V and the battery pack voltage I am aiming for is 230V nominal. This means I will be using 72 cells. Each cell will hold a charge of 70 or 100Ah. I will decide which when I know the available space for batteries in the car. If I go for the 100Ah cells some math tells us that 72 x 3.2V x 100Ah = 23kWh of energy. The weight of the cells will be around 250kg so the car will probably become around 100-150 kg heavier than before the conversion. The cells I would like to use are manufactured in China by China Aviation Lithium Battery (CALB), but I haven't found a decent price on them yet.
To charge the batteries I obviously need a charger. The standard Swedish power outlet is 230V,10A and a standard three phase outlet is 230V or 400V,16A. I have not decided on charger yet, but I would like it to be able to utilise both of these outlets. It will probably be a 3kW charger (230V,16A) since I haven't seen any reasonably priced 400V chargers.

Battery management and monitoring

Basicly the idea about battery monitoring and management is that you should not overcharge nor overdischarge the individual cells in your battery since this will decrease their life time. So, in order to prevent over discharge and overcharge a battery monitoring system can be used to detect potential over discharges (low cell voltage)  and potential over charge (high cell voltage). Battery management systems then either disconnect a cell from charging using a shunt or shuts down the whole vehicle during discharge. The act of disconnecting a cell from charge results in a more even charge among the cells in the battery. This is called balancing the cells and specifically this is called top-balancing since the balancing is done near the maximum allowed charge of the cells.
There is an ongoing debate in the DIY community about battery management and monitoring (BMS). The agument for not using a BMS is that the most damage to a cell is done when over discharging, not when over charging it. In order to prevent unbalance near the minimum allowed charge bottom balancing can be used onstead of a BMS. This is probably the route I will go and I will likely spend an upcoming post on the topic.

Heating

Heating of the passenger compartment is important in northern Sweden. Without the ICE there is no heat source. I believe I will need at least 3kW and preferably 4kW of heat power. Many DIYers use ceramic air heaters which they put in instead of the heater core that is heated by the cooling fluod from the  engine. Since my A2 has a ACC my idea is to keep the water heater core and put in a thermostat controlled water heater and a water pump instead. I figure the output from the ACC to the temperature flap can be used to control on/off of the water heater and pump so that the heater will no be on in the summer. The battery voltage of 230V means I can use European standard heaters. Still, I haven't decided on which to use. Maybe one or two Calix engine heater. Or a MES DEA heater with bulit-in pump.

Performance

My simulations of the car ends up in a top speed of 140km/h, acceleration 0-100 km/h in 10s and an energy consumption of 16 kWh/100km using the EU drive cycle. The theoretical range would then be  23/16 x 100 = 144km when driving the same speeds and inclinations as the EU cycle. A more realistic computation ends up in a range of 130km when driving 100km/h and discharging the battery to 80%. Since my commute is around 60km/day I believe that a range of 100km is sufficient. That will give me some margin for error and heat in the winter.

Steering

Many modern cars have power assisted steering powered by the ICE. The A2 has hydro electric power steering (powered by an electric motor) so it will hopefully work even without the ICE.

Instrumentation

Some new things will be nice to monitor in the electric car. For example, the charge of the battery,  battery voltage,  motor current, energy consumption. Some new instrumentation will be needed to show all this and I will also try to retain the original instruments as far as possible. For example using the existing tachometer and the fuel gauge to show battery charge. Most of this is controlled via a CAN bus in modern cars so hacking into the CAN will be one fun challange.

Budget

Well, I have already spent SEK 55 000 (EUR 6 100) on the car and my total budget is SEK 200 000 (EUR 22 200). More than half of the 145 000 for the conversion budget is for the Lithium cells. Then comes the motor controller, the motor and the charger as the next most expensive parts in the conversion.