Finishing touch for trunk interiors

The doubled battery capacity has made driving a lot nicer by keeping the battery voltages higher under load on these coldening autumn days. Increased driving range also gives new possibilities, such as visiting Tampere city (24 km away from home) without having to find a charging place ;) The functionality of the battery update has now been flawless so I am ready to cover the pack to regain a nice and clean trunk. 

First a simple cover was made from 12mm plywood. It is mounted to the battery pack housing with 4 30mm M8 bolts.

A new removable floor was made from 18mm plywood. A handle was cut in the middle of the plywood so that it can easily be lifted off to gain access to the spare tire space.

The battery pack cover was finished using black felt that was glued on top of the plywood and secured with staples from its sides.

Same felt was used to cover the spare tire space floor.

The spare tire space now works as a place for all the necessary items that I want to keep in the car but hopefully never have to use :)

The new plywood floor covers up the spare tire space with its items.

The original trunk floor felt was cut to fit on its place with the battery pack installed. It was glued to the new floor plywood for easier handling. Now the trunk looks usable again, with still quite a good space left for shopping bags.

 

Corolla eFX's first annual inspection will need to be done soon. I think the car is ready for that now!

Rear battery pack ready for work

Installing the rear battery pack is finally done and it is connected parallel to the front battery pack as shown in the circuit diagram posted earlier. The rear battery pack is electrically a copy of the front battery pack, but mounting it in the trunk is a lot easier environment than the engine room. In the trunk no waterproof encolures were used for the electronics.

This picture shows how the rear pack cable feed through looks from inside the trunk.

The first attempts to make a full charge resulted in a state where the Signalab PCM board blinked two leds next to each other and on the same time it switched its charge protection fets on and off with a frequency of approximately 1Hz. In this state the PCM kept its discharge protection fets off not allowing me to drive. The only way I could find out how this state could be resetted was by disconnecting the PCM from the battery pack. At first I had no clue what was happening and if I could rely on the PCM or not. I could not find a manual or functional description of this Signalab PCM so I did not know if it was some error state or if the PCM was broken.

I decided to double check the wiring if I had done some mistake that would have caused this problem. While checking I noticed that I had missed to install one blade fuse which resulted in a situation that the PCM did not have a connection to one of the cells in the battery pack. To make sure that the problem was linked to this forgotten fuse I charged the battery pack to get the fault state back again. Once the fault was active I installed the missing fuse and the fault disappeared. What a relieve!

Looking back I realized that the fuse was missing between the two cells whose balancing leds were blinking on the PCM. Without any proper manual or schematic I do not know if this was a designed feature of the Signalab PCM or not, but its a good indicator in such cases where connection is lost between a cell and the PCM.

After assembling the missing fuse the Signalab PCM has worked just like the one in the front battery pack. This regained my trust in it and I am hoping for a lot more careless kilometers just like with front battery pack alone.

The rear battery pack cells were not balanced manually in any way before use. The cells had a very consistent 3,3V reading so I decided to give the balancing task to the Signalab PCM board and see if it could handle it without having to help it manually. In the picture above the lit leds tell which of the cells are being bleeded by the balancing circuity at the time when the charger decided that the battery is fully charged and stopped charging. At this same moment the highest cell voltage I measured with my multimeter was 3,8V. I think a few more full charge cycles will be enough to make a good top balancing for the rear battery pack, just like with the front pack where nearly all balancing leds are lit just before the charger ends charging.

Things seem to be working as they are planned and I can enjoy driving with increased power output and efficiency due to lower voltage sag of the cars doubled battery capacity! Next step will be to cover up the rear battery pack nicely.

Installing the second battery pack

The second battery pack installation has been done in very small steps not disturbing the every day driving needs for the car. The pack takes about 1/3 of the space in the trunk which still leaves me with a good enough space for a few shopping bags.

 

The pack is mounted in a housing made from plywood. Each cell is attached to the housing bottom using threaded rods.

 This photo shows how much 24pcs of Winston LYP60AHA takes space from a -87 corolla hatchback.

Using this type of PCM causes a lot of wiring inside the batterypack. In here the cells are connected in series and the PCM's cell voltage monitoring wires are connected.

A 50mm diameter PVC tube was mounted under the car to the place where the exhaust pipe and gas tank used to be. The tube acts as a conduit for the rear battery pack cables.

Power and control cables to the rear pack are fed to the spare tire space under the rear battery pack enclosure. Now all the hard work is done for the second battery pack installation. A few more late evenings will be needed to finish up the connections and to prepare for functional tests!

Circuit diagram update 8.8.2014

Adding a second 76,8V 60Ah battery pack to the trunk means changes also to the circuit diagram. The low cost LiFePo4 PCM (Protection Circuit Module) that I am using is not designed for parallel connected battery packs, so I got to design how they could be used in this case.

The schematic above shows how I am going to connect the batteries. The circuit is designed so that it fills the following simple rules:

1. Stop charging if overvoltage is noticed in any cell of either of the battery packs
2. Stop discharging if undervoltage is noticed in any cell of either of the battery packs

Once I have installed the new batteries to Corolla's trunk, tests will show if the two rules will be filled or if more changes are needed. Once the rules are filled I am expecting many more carefree kilometers just like it has been so far.

Corolla eFX will get double range

I decided to build a similar battery pack into Corolla's trunk as there is under its hood. Due to a temporary www.ev-power.eu stock shortage 24pcs of Winston LYP60AHA were ordered in a format of 6pcs LP12V60AH.

The LP12V60AH contains 4 LYP60AHA batteries, and as I want to have access into each cell I need to dismantle the LP12V60AH pack's. It sure felt weird to start cracking open these brand new finely packed 12V batteries! The picture shows all of the tools I used to open the case.

Here is a picture of the LP12V60AH with its cover removed. I think its a quite nice assembly:

To compensate the weight of the battery pack to be installed, I removed the gas tank (13kg) and spare wheel (14kg). This way the Corolla will gain about 30kg weight after the new battery pack is installed, but it will still weight about 20kg less than original.

Cycle Analyst installed

I found the Cycle Analyst while reading these great finnish EV-builders blogs:

http://kwsaki.blogspot.fi
http://electricfinn.wordpress.com

Thank you guys for sharing!

Having got positive recommendations of the Cycle Analyst, I was expecting for a nice product. However it still managed to exceed my expectations. I had reserved a lot more time to install the than what was really needed, and the useability is excellent.

The biggest reason for replacing my old led panel meters was to get an Ah measurement, but all the other statistics that the Cycle Analyst can give are also very nice to have. It is really fun and enlightening to see the Ah reading run while pedaling. Its even more fun when the reading runs backwards while braking!

Bad contact in ME1003 motor brush holder

One day when I arrived at work I noticed an unfamiliar smell coming under the hood. I thought the smell was originated from some insulation material that was overheated, so I looked through all battery terminal connections which seemed ok and did not smell at all. The smell wanished pretty fast after the car was stopped so it was not easy to find its source.

After one short drive when I once again tried to find the source of the smell I noticed that one of the motor terminals was very hot while the other one was cool. The terminal connections looked tight and identical so I realized that I'll have to search for the problem inside the ME1003 motor.

First thing to do was to remove the brush holder cover:

Quite a lot of sand can be seen on the brush holder. At this point no faults could yet be seen.

Next the brush holder was removed for closer examination. It was far easier than I thought, this motor is clearly made for easy maintainance.

Once I got the brush holder on a table the problem could be seen:

The terminal on the left had blackened due to a bad contact caused by a loose bolt. By smelling it from a close distance it could be confirmed that this is the source of the smell. The terminal on the right looks healthy and its bolt connections were tight.

I also noticed that the brush springs were all not identical. One of them was significantly weaker than the majority:

In the picture above two spring on the left represent healthy springs in my opinion. The one on far right had loosed its form possibly due to overhating due to the loose contact as that spring was located on the brush closest to the overheated terminal. I tried to give back its original form but not with a very good result. As my brushes are still quite new the sping force on their current position is quite good also with the damaged brush spring. But as the brushes get smaller the damaged spring will not be able to deliver the designed amount of force, so I'll have to keep an eye on this.

To get back on the road I replaced the overheated bolt and nut and cleaned the contact surfaces:

The picture above shows the result of the repaired contact. I also checked the tightness of all other current carrying bolts and I would consider that 40% of them were too loose! After tightening all of them I reassembled the motor and I've been driving again with no mysterious smells;)

Knowing that I have a weak brush spring and that the current carrying bolt connections can get loose again I searched the internet for others experiences. I was more that happy to find this link:

http://evmc2.wordpress.com/2012/11/17/motenergy-brush-holder-me0804-rev-a-dept-of-a-closer-look/

I am seriously concidering of ordering that improved brush holder version with those welded connections and larger buss bars. It seems like an excellent solution for my brush holder situation!

Time for summer tires

It's been a long wait for the days to warm up as summer gets closer. Hoping for no more freezing days this spring I changed summer tires.

The car has worked great! No brakedowns and the only maintainance has been keeping the tire pressures high to keep the rolling friction low.

Corollaefx has now done 3900 km electrically and it saves me about 100€/month compared to a gasoline driven 2002 Ford Mondeo that I used to drive. These savings are based on calculating gasoline vs. electricity cost and smaller insurance and tax costs.

The co2 emissions have most likely dropped only to a fraction of the Mondeo's 185 g/km as most of the battery charging is done at the moment at home using hydropower purchased from Suomen Energiayhtiö.

Winter came eventually

The temperature has been between -15..-22degC for a week now and I got the cold driving experiences I was waiting for. I installed a simple indoor/outdoor temperature sensor in the middle of my battery pack to see what happens there while driving. I learned that the temperature rise was about 15..20degC so the temperature would climb up just above 0 on a -15degC day.

With such low temperatures the battery pack was struggling to keep up the voltage during uphills and I had to be patient not to give too much throttle or the battery voltage would have dived below 50v and the BMS would have cutted off for sure. As there was less than normal power available from the batteries due to their temperature it was hard to keep up with the traffic at some points.

To improve the situation while the cold weather came here to stay, I decided to seal the engine room and insulate the battery pack as well as I could.

I used bubble wrap to insulate the battery pack. Then I blocked the airflow from the engine room using foamed plastic (the gray sheets in the pictures). I also covered the bottom of the engine room from all bigger holes.

This had a dramatic positive effect for winter driving! Today morning the outside temperature was -22degC and the battery temperature was +4degC when I started my every day work trip from garage. When I got there the battery pack temperature showed +22degC and the battery performance was close to what it was in summertime!

Another positive surprise was that when I went to lunch four hours later the pack's temperature showed still +15degC while the outside temperature was 30 degrees less!

I think the rest of the winter will be easy driving unless any super freezing days will be ahead.

Almost forgot; when I reached work the car's cabin temperature was -12degC.. To fix this I ordered a new warmer hat and a pair of gloves ;)

Cold batteries, weak performance

So far 1400km of driving with electricity has been fun and easy! This winter has been quite warm and the lowest temperature has been -10C while driving. On that temperature the battery performance is weakened remarkably. Their internal resistance is increased lowering power output and efficiency. I assumed that the batteries would heat up internally to a more efficient working temperature level but this has not seemed to happen. For that reason I decided to try to decrease the batteries cooling by blocking the airflow through the battery pack. The pictures above show how the airflow was blocked through the front mask of the car. Also the original motor covers were installed below the batteries which guide the airflow away from the batteries.

I do not yet know if this modification helps to increase the battery pack working temperature as I still do not have temperature sensors  equipped. Also the winter got warmer so I'll have to wait for more cold driving experiences.

A combined ampere-hour / temperature meter is under development using an Arduino and DS18B20 temperature sensors. After all needed components have arrived I am optimistic to get them installed soon as we got a flying start with the application thanks to my brother's Arduino experience!

Corollaefx perfomance specifications

Here is a list of the car's performance specifications learned so far:

Rated motor power: 11,5kW
Weight: 940kg
Nominal traction battery capacity: 4,6 kWh (76,8V 60Ah)
Top speed: 84km/h reached at 5th gear
Operating range: 37km reached at 0 celsius temperature, driver and one passenger, 50km/h average speed.
Energy consumption: ~ 19kWh/100km measured using a energy meter on the charger supply cable.

Preparing for winter

The Corolla has been very reliable for the 850km that I have driven so far. During this time I have not had to use my gasoline powered car at all so I took it off from street use. The trips outside corolla's range can still be made by my wife's diesel car, so no problem there.

I'll try to use the corolla on my everyday driving through the whole winter. It will not be easy though. So far -7 degrees celcius is the lowest temperature that the car has faced and that time it survived from work to home. The low temperature increases friction due to gearbox oil which had a remarkable effect on driving. To minimize that effect I searched for the lowest viscosity oil at cold temperatures from local shops filling API-GL4 requirements. After a careful search I decided to use Redline D4 ATF oil that can be used in both automatic and manual gearboxes. After the oil change a good improvement could be noticed at below freezing temperatures while no difference could be noticed on warmer days. I do not know which oil the corolla had before, but most likely it was mineral oil that gets very stiff on cold days.

As the temperature drops so does lifepo4 battery performance as well. The unloaded cell voltage is not affected much, but the internal resistance of the cells is increasing remarkably as temperature decreases. The battery pack is so well cooled in its current location that I am thinking of insulating the battery pack thermally so that their internal losses would increase the cells temperature hopfully to a better working level. Otherwise I am expecting the PCM to shut down the operation at around -20 degree celsius due to too low cell voltage on a long uphill where 200-300 amps are drawn from the batteries for quite a long time.

Despite the very cold driving experience I very much enjoy driving the corollaefx. The 300W windshield heater has been great to keep the windows clear but it definitely does not warm the cabin!

Warning sign on its place

A warning sign was placed on top of the battery pack lid. It also states the nominal voltage of the battery pack (76,8V) to easily tell what voltage level is used in the car.

I have driven 409 km at the moment and no big problems have occured. The weather has been mostly rainy with temperatures around 5 celcius. The 300W heater for the windshield has also been good enough so far, but I am starting to get the feeling that it might be underrated on sub zero temperatures.

When I changed the winter tires I noticed that one front brake made quite a lot of unnecessary friction. I removed the brake pads and cleaned them and their surroundings. As a result both front wheels felt similar to rotate. This brake fix had a very positive effect on driving. The battery current reduced approximately 15A at 60km/h and now also the fourth gear seems to be useable! This increased the useable speed range up to 80km/h on even road. With a low powered vehicle such as this one it is truly advantageous to minimize all losses possible.

First electric driven day at work

As the corolla is not highway capable, I drove my 18 km trip to work through smaller roads. The speed limits on the way were between 40-60 km/h which the corolla handles nicely. Only the 2nd and 3rd gears are needed in normal driving. 2nd gear works well on 0-40 km/h and third gear gives a speed up to 65 km/h.

I found four workmates to join me for lunch and we drove there all five of us packed into the corolla. The car's low power was easily noticeable for the driver as full throttle was often needed for a normal acceleration. It was fun though!!

I am not yet sure if the corolla would make it back home without charging. Until it is sure I'll charge the batteries a bit to make it safely at home for a full charge.

Corolla eFX is now street legal!

The compliance with electrical safety regulations was shown with a commissioning inspection record made by a local qualified electrician. All high voltage cables and their feedthroughs were inspected visually. The charger input cables were tested for proper PE- continuity and insulation resistance. A warning sign to be placed on top of the high voltage enclosures was planned and a proper one will be installed as soon as possible. The approved commissioning inspection record was brought to the vechicle inspection station and then the Corolla was able to be approved for road use.

The picture above shows the car's new changed information after the electrifying project. Drivetrain is changed from gasoline to electricity. All five seats are left in use, new weight is 940kg which is 50kg less than original. The change percentage of this car is now 16%, 14% came from the changed motor and 2% from removing the radiator.

This Corolla made 176202km using gasoline. I hope it will do many more with its new electric propulsion!

Inspection results and new high voltage cables

The car itself was approved as it was and it was weighted to be 50kg lighter than its original weight! However its new electrics need to be proved to comply with safety regulations (link to the applied regulation in finnish: www.finlex.fi/fi/laki/alkup/2011/20111064). Once I have the required documentation available and delivered the Corollaefx should be ready to hit the streets!

Driving the car to the inspection was fun! It was a rainy day so the heating could be tested to see if the windshield stays out of fog and it stayed very clear! The performance was quite like expected; not too much power available. 2nd gear felt as the best choise to get the car moving from a stopped situation. I reached 80km/h with 4th gear but as the needed currents were over continuous current levels I decided to slow down and drive 60-70 km/h using 3rd gear. With this drivetrain and chassis 70km/h looks to be the continuous maximum driving speed at the moment. I can't wait to get the car into everyday driving to get more experince and testing:)

The picture above shows new high voltage cables that were installed. The old welding cables used earlier were removed as they were not in a very good shape and I did not know what type they were. The new cables are 50mm^2 H07V-K type purchased from a local hardware store IKH.

All set for inspection

Shield were made to prevent accidental touching of battery terminals and powered connectors. They were made from clear acryl sheets that were painted black on the bottom side. The shields also block some of the spashing water from reaching the battery terminals.

Also the motor controller assembly got an enclosure which was modified so that it can be opened by a single butterfly nut.

As everything works now I think its time to have the Corolla inspected to make it street legal as an electric car!

Updated main circuit diagram

Quite many changes were done to the initial circuit diagram along the way. The changes were governed by the idea of not needing to alter the original wiring. The circuit diagram shown above shows the current state of the Corolla eFX electrical connections. I am currently happy with it as everything seems to work well.

The biggest change to the original circuit diagram are the six parallel connected power MOSFETs that are located between the 12V battery negative terminal and the chassis. They were added to boost the discharge current capability of the PCM circuit from 20A up to about 100A. The gates of these MOSFETs are controlled by the same gate drive that controls the 12V battery pack PCM discharge MOSFETs. This way when the PCM notices an undervoltage situation the MOSFETs are turned off  protecting the lifepo4 cells from potential damage.

The other major change was the addition of the 72V to 12V isolated power supply. This change made it possible to use a common 12V relay to wake up the motor controller. It also provided an isolated 12V power supply to be used by the panel meters. The 72V to 12V isolated power supply chosen is actually a low cost plug type offline AC/DC power supply that needs only about 50Vdc to start up. Not all of them do, but many of them do start with a lot lower voltages than the typically rated voltage range of 96Vac...250Vac. Of course, if used with a lower than specified input voltage the output current can not be expected to reach rated values.

Electric brake booster mounted

The electric vacuum pump and the vacuum operated microswitch were mounted close to the vacuum brake booster. The pump was mounted using a rubbery tube clamp to damp some of the pump's vibrations. This electric vacuum pump is quite a shaker when it is on.

12V PCM tested

After successful tests with the 72V battery pack's PCM branded as Signalab, I was expecting similar behaviour from the 12V battery pack PCM. I do not know the manufacturer of this board which is shown in the picture, but it is still available in eBay.

When I first connected the batteries to the 12V PCM I had my multimeter connected to measure the resistance between the P- and B- terminals. I was expecting the resistance to drop close to zero when the last cell was connected. To my disappointment the resistance dropped before the last cell was connected to the B+ terminated. My first assumption was that the board was faulty. A new PCM board would take weeks to arrive so I though that I would examine this one a bit more before giving up with it.

I disconnected the PCM and took it to my lab room to examine it with a laboratory power supply. I found out that the PCM worked as it should with the cell over- and under voltages, but what was left undocumented is that if any cell voltage would be less than about 0,7V the under voltage situation is no longer detected and the P- terminal is enabled again (if the other cell's do have a valid voltage between 2.0 to 3.85V). This happened to me during the first test of the PCM when the last cell was disconnected and still the P- was enabled.

Now that I know how this circuit works I decided to install it anyway although the circuit can not be expected to disconnect the load if for example a wire gets disconnected between the PCM and the battery pack.