Geo EV Performance Issues
Published March 4, 2013: Updated Sunday June 1, 2014
Geo Metro EV Performance Issues So Far
In the last 2 1/2 months, I have driven this electric Geo Metro over 2500 miles. I absolutely love the long range that I get with lithium batteries. For my daily, 40 mile commute, range is no longer an issue. It isn't even in the back of my mind. I just get in and drive where I need to go.
100% Solar Powered:
Recently I hit my 1-year mark of being net-zero with the power company in my home and vehicle. To mark the occasion, I am no longer charging up at work. I don't need to. I have the battery range and enough solar capacity to charge up all from home.
I can now truly say that my commuter vehicle runs on 100% clean energy, that I generated in my own backyard. It is completely solar powered.
Electric Car Charging Stigma:
While I am extremely grateful that my employer provides a 120 volt outlet for trickle charging, there is also a stigma that comes with it, as if they are giving me a free 5-gallons of gas each day. In reality it is the equivalent energy to only about 1 3/4 cups of gasoline, but drivers of F-350's king cabs and DuraMax diesels don't understand this.
The charging station is a pretty good parking spot for other drivers too. Sometimes I run an errand during lunch. Upon my return, some gas car has parked there, even though it is clearly marked "Electric Vehicles Only". If I am depending on the charging spot (like when I drove my pickup truck), it is very stressful to find it unavailable. I would rather just plan on it not being available and make other arrangements.
The charging spot isn't really that convenient for me anyway. I would rather park in a spot closer to the building in which I work. In the winter time, I prefer parking in a spot that is not perpetually shady so the interior of the cab can be warmed up by the sun.
There are more and more electric car drivers at my work. I would rather not tie up an EV parking the spot and let someone else use it.
Range:
There was one time last week that I got a little nervous. I had some extra places to go that day. Upon mapping it out, it was about 70 miles total. I didn't give it another thought because I have driven 80 miles on a single charge several times before.
Only this time, it was very cold and there was a nasty headwind for 1/2 of my journey. I admit I was a little nervous for the last 20 miles but in true, explorer style, I pushed on. I made it to my house with no performance issues and with 0% remaining on the SOC (state of charge) meter. I love the SOC meter. It has proved reliable, dependable and accurate.
Driving in the winter time, the cab can get kind of cool. But I just tell myself, "Suck it up and take it like a man, with an afghan blanket on his lap." My garage is very well insulated and it rarely drops below 40 °F, even in the dead of winter. That 40 degree head start takes the edge off of the -5 °F temperatures outside while driving to work. On these very cold mornings, by the end of a 20 mile drive in to work, my fingers and toes are a little chilly. It's not that bad though, really!
Batteries:
I love the on-board smart battery charger. When I get home, I plug in and forget about it. Just like you might treat your smart phone. You just plug it in and when you need it, it's ready for you.
These lithium batteries are specified to last over 5000 charge cycles when being discharged down to 70% DOD each time. For my 40 mile commute I use about 1/2 of the battery pack (or 50% DOD). By not discharging as much, I should be able to get more than 5000 charge cycles on this set of batteries. But let's assume that I only get 5000 charge cycles out of these batteries. In that case, with less than 300 charge cycles per year, they should last me 15+ years. This works out to about $1 (in battery replacement cost) per charge cycle.
Between the electricity cost of 2 cents per mile (assuming 10 cents per kWh and 200 watt-hours per mile) plus $1 per charge, my daily commute (including battery life costs) is $1.80 per commute. Of course all my electricity is created for free by the solar panels on the house. Therefore, my daily commute cost comes exclusively from the replacement battery costs of $1.00 per commute. Not too bad at all.
At the rate that lithium batteries are dropping in price, while simultaneously increasing in capacity, replacement packs will cost much less and allow me to drive farther than they do now.
Charging:
The charger on my truck is a dumb, inexpensive charger. I built it myself and it works great. It also has a horrible power factor and I never did incorporate any timer or cut-off circuit into its design. It was always up to me to remember to disconnect it. This wasn't too much of a safety issue with flooded lead-acid batteries because any overcharging just desulfates the batteries and boils off a little water. I would regularly maintain them by topping them off with more distilled water every month or so. But accidentally overcharging wastes electricity, something that I abhorred, as I was trying to make my home net-zero for the year.
The Lithium battery charger in the Geo EV is smart and power factor friendly (0.99 pf) but to my disappointment is only 90% efficient.
90% is still pretty good as far as smart battery chargers go but I don't like going through all the hassle of designing a super efficient vehicle, only to then throw away 10% efficiency (and hard earned solar energy), just like that. But what's a green guy to do?
This battery charger is small (as far as EV chargers go). Using a regular 120V outlet in my garage and after driving 40 miles, it takes 7 hours and 8 kWh to charge back up to 100%. That works out to an energy usage of 5 miles per kWh or 200 watt-hours per mile. It restores the battery pack's charge at the rate of ~6 miles worth of range per hour of charging.
Current Leakage:
I work a 4-10 schedule. If I don't drive the car or charge it all weekend, it will sit idle for up to 3 1/2 days before I need to go back to work, I have noticed that the battery pack looses almost 1.5 kWh of its energy during this time.
The DC-DC converter is always on and constantly supplies power to the clock and other electronics in the car. The motor speed controller also has power supplied through a bleeder resistor. On the high side, I can measure a 110mA current draw all the time. At 80 VDC, this is only a 8.8 watt continuous power draw and would account for about 3/4 kWh of energy loss over a 3.5 day period. I don't yet know where the other 3/4 kWh is going. But I do know it is cumulative over time. Maybe it's internal leakage in the battery pack itself?
Motor Issues:
In hind sight, the motor I chose for this design is probably too small. While it is peppy and its performance is perfectly adequate for my freeway driving needs, it does tend to get hot when I push it to hard for too long. While adding aeromods reduced current draw and extended the battery range, they also restricted airflow to the motor, causing it to heat up even more.
In January 2013, after loading up with 350 lbs of wheat, white flour, sugar and oats, I drove 65 mph for 30 miles back to my house. I may have overdone it on that trip because when I got home the motor smelled really really hot; and it was.
I added a duct to keep the motor's air flow and cooling under control.
I also moved one of the BMS temperatures sensors onto the motor so I could better monitor its own temperature. That helped a lot but I soon discovered (6 weeks later), that the damage had already been done.
One day, I was running an errand during my lunch break. I accelerated hard at a light and immediately noticed a jerky loss in performance coming from the motor. It first I thought it was my home-made shaft coupler breaking a weld, (This happened once to me once in my EV pickup truck). But this time, I still had power and was still able to drive the vehicle back to work. The motor was making funny noises and acting really jerky the whole time.
After work, decided it would be safer to drive home on the back roads instead of the freeway. As I was about 2 miles into my commute, the current draw started varying wildly and the motor was now delivering power in brief surges. Then nothing. No spinning, no noise, no movement at all.
I called up my good buddy Austin who was leaving work around the same time. He gave me a 20 mile tow home using his Toyota Camry. Luckily Geo's are super light. Thanks Austin, I owe you big time.
Upon investigation, a cracked brush caused a buss-bar inside the back of the motor to overheat, which in turn, (over time), caused a screw to back out, overheat and eventually melt. When that screw (connecting 2 buss-bars together) melted, it opened the circuit inside the series permanent magnet motor.
I was able to quickly replace the lava screw, bringing the motor back to life.
This temporarily allowed me to continue to commute to work and back for the next 2 weeks.
Not wanting to take any chances, I bought a new brush assembly for $86 and swapped out the old one. No more heating issues for now. Now I have spare parts for the future.
Ice Storms:
On January 24, 2013, Northern Utah had a freezing rain event. This is quite common back East but it is extremely rare in Utah. In fact, there has not been freezing rain here in almost 40 years.
Just as luck would have it, I was driving to work on the morning of this historic occasion.
I use a little 12V, 8 Amp Harbor Freight space heater to keep the windshield from fogging up. It works great but on this day, it did not have enough heat capacity to keep the ice from building up on the windshield. I had to pull over and scrape off the windshield every 1/2 mile. Nobody should ever be driving in these conditions.
After 40 minutes, after traveling only 8-miles, for my own safety, I called off work and went back home.
I initially thought that my washer fluid lines were also icing up but later that day, I discovered the washer fluid nozzles on the hood of the car were plugged up with gunk. Using so much fluid all at once must have kicked up some old sediments in the tank clogging up the nozzles. I took them apart and blew them out.
While my little 100 watt heater didn't cut it, a 3200 watt heater would. I'm still deciding on a solution that will work using only a 72 volt battery pack. Most available EV heaters require at least 120 VDC.
In the mean time, I settled on a heated seat cover. Maybe someday I will actually pull the trigger and get a real heater.
Corrosion and Creature Comforts:
I probably should have gone with a newer year for the donor vehicle. I didn't notice this when I first rescued this car from being crushed but the doors are starting to sag by a few millimeters. It makes them increasingly difficult to open and close. I may have to do some retrofit welding to get them to sit properly on their hinges.
Also I wish I had automatic door locks and windows. At the time, I was very concerned about any extra vehicle weight. But in hindsight, I would have been OK with an extra 100 lbs worth of creature comforts. Oh well, maybe next time.
Conclusion:
As with any new design, there are bugs that will need to be worked out. Overall, I love this EV! It does everything that I had hoped for and more. It is such a great feeling that ultimately comes when you make something great, have some failures along the way, correct the problem and finally succeed. That's what life is all about isn't it? Live your life, make mistakes, don't give up, persevere, learn, grow from your mistakes and finally succeed in the end.
I plan on continuing to drive this vehicle for years to come. As we head into the warmer spring and summer months, I hope that I can continue using the same PM motor. I am concerned about it overheating when the outdoor temperatures reach 90 °F or higher.
I have a backup plan of swapping it out with a larger, more powerful AC motor and controller but that would set me back another $3800. I don't want to do that unless I absolutely have to. But then I could then use the old motor for an electric riding lawn mower project that I want to tackle.
Cheers!