Friday, October 7, 2011

Electric Truck: How's it working for ya?

I have been driving my truck to work and back (40 miles) almost every day for the past 3 weeks. On some of those days I even made extra side trips, running errands along the way. I estimate my max range is now upwards of 50 miles. I have driven 46 miles on a single charge, (battery was down to 30%).

I got some fancy vinyl lettering to advertise my affinity for electron propulsion.

Now I get a lot of looks from other drivers on the road. I don’t want to give electric cars a bad rap so I tend to drive faster than I should so they can be impressed with my home-made wonder. This is a mistake though and I end up killing my range to where I am limping home the last 2 miles. 

Work In Progress: 
I am still having problems with excessive vibrations at high RPM. This is due to a slightly bent shaft on the transmission and a flywheel that keeps shifting on its key-way.  I removed the motor (a few times now) in order to re-seat the flywheel.  It fixes the problem initially but 120 miles later the vibration comes back.  I have found that by shifting into 4th gear on the highway, the RPM is lower and the truck runs quiet as can be. While driving 60mph, the loudest noise I hear is the wind and other cars on the road.  Most of the time I drive 50mph (while traveling on the 55mph Legacy Highway) to extend my range.

I added Volt and Amp Gauges to my instrument cluster. They provide valuable feedback to how my driving habits are affecting my battery pack and subsequent range.  

While adding LED back-lights to the instrument cluster, I inadvertently shorted something out.  Now I keep blowing a fuse that feeds the speedometer and tachometer. Arggg!  I am still scratching my head on this one.  In the mean time, I borrowed my wife’s GPS so I can know how fast I am going. I would really like to know at a glance how far I have driven though. 
Even though my battery charger can deliver nearly 19 amps initially, as the battery pack charges, its internal resistance changes.  The current flowing in steadily drops until it is only delivering 7 amps at the end of the cycle. I work a 10-hour day with a 27 minute commute each way. Often times, I work later or run an errand on the way home. I rarely have more than 12 hours from the time I come home to when I have to leave for work again.

A 12 hour period is not enough time to fully charge a depleted battery. At the beginning of the week, (after the battery has had a good weekend charge), I drive to work and back with no problems. After charging all night, the battery is only at 90%. The next day I again drive the 40 mile round trip and back with no incidents. By the last day of the week, my battery is only 80% charged by morning. I make it in to work just fine but on the way home, I run out of energy about 2 miles short. I pull off to the side and wait a few minutes for the battery pack to recover before slowly rolling the rest of the way home. 

A lot of EV drivers will tell you that you can simply plug in and charge up anywhere there is an outlet.  That may be true but I liken this kind of behavior to running out of gasoline near someone's home so you take a cup of gas from their lawn mower to get you back on your way. Who's going to miss 25 cents worth of gas or 3 cents worth of electricity?  Instead of cheating my way home from work, I would rather work toward making my truck go farther, be more reliable, comfortable, convenient and simply take me the distance that I want it to go.

I am working on 2 options for a better battery charger. One that runs on 240V which will give me a full charge in under 5 hours and another that still runs on 120V but switches in more capacitors, increasing the current draw a couple hours into the charging cycle. 

After driving at 55mph continuously on the highway for 15 miles with a 100+ amp draw, the motor speed controller starts to overheat. Even with the cooling fans I installed on it, I have to let off the throttle for about 5 seconds every couple miles to keep it from overheating. I added a plastic rain-gutter downspout as a duct directly to the heat-sink on the controller and it really helped a lot. I really need to mount the controller in a better location that it will receive more airflow and still be protected from the elements. 

After covering up the grill with a piece of sheet metal. I took some crude measurements and my current draw (while driving sustained at 50mph) has dropped from 106 amps down to 100 amps.

Not much, but enough to justify investing more time into aerodynamic modifications. It just occurred to me that a 6 amp reduction is a 720 watt power savings. I could allocate that 720 watts towards cab heating during the winter time.