My Electric Lawn Mower named Frankenstein:

NPS has got to be one of my favorite places to find deals. Any store that sells nuts and bolts by weight is alright in my book. The other day, I happened across a bunch of small 6-volt rechargeable AGM batteries. Most of them were priced at $1.08 each. I have walked by this isle many times before but for some reason, today, I got an epiphany!
“Why not buy 20 of these little guys and string them all together into a 120 volt battery pack?”

Not only would it be a useful test bed for repairing the controller in my electric truck, but I could also modify my electric lawn mower to run on this battery pack instead of the heavy 12 volt deep cycle battery it currently uses. 

My electric lawn mower runs great, but it is really heavy and a huge workout pushing it around my ½ acre yard each week. It has a large 115Amp-Hour, 12 volt battery that powers an inverter, that converts the 12 volt DC up to 120 volts AC, which is then rectified to high voltage DC, which then powers a DC motor. Each conversion has some efficiency loss.

In order to provide enough power to cut a thick green lawn, the 12 Volt battery has to be able to deliver 80 Amps continuously. There is a phenomenon in all batteries called “The Peukert effect” which causes a large battery delivering a lot of amps to act like a lower capacity battery.

For example, If you have a 100 Amp-hour battery, it will provide 1 amp continuously for 100 hours. But if that same battery tried to deliver 100 amps for 1 hour, it wouldn't last for 1 hour like we had hoped. Because of the Peukert effect, it may only last 40 minutes or so depending on the battery chemistry and age of the battery.  CURSE YOU PEUKERT EFFECT!!! 

A power inverter is a marvelous invention that converts 12 volts DC to 120 volts AC.  Like everything else in the universe, work comes at a price. The inverter used on my lawn mower has about a 5-15% efficiency loss involved in the conversion. When the battery is ½ discharged, and while under load, the voltage drops below 10.5 volts and the inverter goes into a low voltage alarm state, shutting itself down. I can still have enough capacity to mow my lawn using this battery, but it bothers me that I am pushing around an extra 20 lbs of lead with no way of extracting the energy out of it.

In addition to the small losses of the bridge rectifier, at 157 Volts, the rectified DC doesn't run the motor at it's top speed either.

By using a 120 Volt DC battery pack, the current draw from the battery will be in the 2 to 5 Amp range, not 60-90 Amps like with a 12 volt battery. Also, because the 120 Volt DC is true DC, and not rectified, unfiltered DC, the motor will run at its full speed.
When the pack starts to discharge, instead of shutting off completely, the motor just spins a little bit slower.

A few months ago, I discussed how reducing resistive losses in the battery-inverter wiring allowed an extra 15 minutes of run-time before the inverter would shut down.  That worked great but it's time I take it a step further.

Before:
12 Volt 115Amp-Hour deep-cycle battery. 50.2 lbs (plus inverter and wire 3.4 lbs).
12 X 115 = 1380 Watt-hours, or about 13 cents worth of electricity.   

After:
Twenty 6 Volt 4.5Amp-Hour AGM batteries. 32.4 lbs
20 X 6 X 4.5 = 540 Watt-hours, or about 5 cents worth of electricity.

Both designs mow the lawn just fine, but for a manually propelled lawn mower, the 21.2 pound weight loss is a night and day difference.  By pushing around less weight, it takes me less time to mow my lawn.  1 hour 5 minutes down to ~52 minutes.

EV Conversion Part 3 – Installing the Electric Motor:

It’s amazing to me how simple a job can become when you have the right tools, good lighting and room to work.

Mandatory tools for an EV conversion job:

• A place to perform the EV conversion, (for 200 hours or 2-6 months).

• Impact wrench with deep walled sockets

• Engine lift or cherry picker

• Arc welder

• Angle grinder

• Chop Saw with metal blade

• Drill press

• Paint sprayer

• Neoprene gloves x100 pair or more if you have OCD like me.

I bought a large DC electric motor and a generic adapter plate for connecting the motor to the transmission bell housing.  I tested out the DC motor with a 12 volt battery to verify it works. 

 I lined up the motor with the adapter plate and clamped it in place. 

 

Yeah, that kind of looks like blood but its spray paint from my first attempt at matching up the holes on the transmission bell housing.   I drilled holes that matched my specific transmission.

I also had a shaft coupler machined that would match the shaft of the electric motor to the existing fly-wheel from the old engine. I still want the clutch intact for this EV conversion.

By grinding down a raspy metal file, I made a key for the motor shaft to lock into the coupler.

I used a couple extra hunks of metal from the old engine to secure the motor in place. I welded them to the motor and bolted them to the frame of the truck.

Wow! I now have a truck with an electric motor. I have to drive this around the block.

I connected up two 12-volt batteries in series and connected them to the motor with jumper cables. Using one end of a jumper cable for an instant on/off throttle control, ZAP, the truck came to life!

I drove it down the street a few of times at the screaming speed of 10mph.  Check out this video clip of me test driving it here.

I really need to get more batteries and install the motor controller. Eventually this truck will drive at freeway speeds. 

EV Conversion Part 2 – Making it look nice:

After I pulled out all the parts from the internal combustion engine, I took a good look at the truck carcass that remained. It was dirty, rusty and kind of ugly. Since I was making such a large investment in a vehicle that I will be driving for the next 5-10 years, I decided to spend some extra time and make it look nice.

I washed off all the grease, pulled off the bed, sanded down the frame and primed all bare and rusty metal.

After that, I painted the frame a shiny black color. Once that paint had cured, I taped off all the glass and painted the truck with an air sprayer. It took 2 hours to tape everything off and only 15 minutes to spray the paint on.

I’m no expert in auto body paint but the paint job turned out very nice.

It was so easy, (relatively) that I now want to re-paint my 1992 Honda Accord.

They have so many wonderful hues and colors of paint now days. I believe the color of my car is called, “Fading, cracking vomit.” I’m going to re-paint it “Tree Hugger” green.

Electric Car Conversion Part 1 – The Donor Vehicle and The ICE Removal:

In 2008, I bought an old Geo Metro for $1 for the purpose of converting it to an all electric car. I calculated it would have a 40 mile range and only cost me $3000 in parts. It would be the perfect commuter car, requiring only $0.67 cents in electric fuel to get me back and forth to work each day.

Unfortunately, my enthusiasm for the project faded when we moved to another house out of the range of the car's design.

Fast Forward 3 years:

My desire for an Electric Vehicle was rekindled by the announcement of the Nissan Leaf.  But after nearly a year sitting on the waiting list, I opted to roll my own, again.

I have read that the an electric vehicle will have greater range if it can carry more batteries.  It makes sense.  More fuel = more range. 

A Geo Metro has a light frame but has little room for extra weight. A pickup truck is relatively lightweight but has a stronger frame that can handle additional battery weight.

In June 2011, I acquired a 1992 Toyota Pickup Truck. Although the mileage was high, it was in good cosmetic condition.

I ripped out all the “unnecessary” parts. The internal combustion engine, radiator, gas tank and the exhaust system. 

This lightened the truck weight by 500 lbs and freed up a lot of room in the engine compartment for an electric motor and batteries.