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Old 02-01-2014, 12:06 PM   #1 (permalink)
Electric MG Midget
 
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Checking Back In (update: MG Midget conversion with 5 year old Li Ion cells)

I wanted to check back into this forum so people new to the electric car scene realize that these cars do last for more than a year or so. My car is now 2 and half years old and still being driven almost daily. I used lion cells that were manufactured in 2009. They are still working fine without a hint of any cell going bad. My cells (Thundersky) were used by a university first, and then after a limited number a charge cycles they were deemed not large enough capacity for them. I got them at a discount, but I was more interested in them because they had already been checked out. I think my hunch was correct because my BMS finishes with a top balance, and I havenít seen any indication that it is struggling to get any single cell up to being balanced. I have over 8,000 miles on it so far. I only have a 10 mile round trip commute so it is hard for me to put on more miles in a year. I havenít seen any indication that my 100 mile range has decreased, but lately I havenít tested it more than 60 miles on a single charge. Iím happy with my choice to use a BMS because for charging, I just plug it in at night and the BMS shuts it all off before the morning. It also senses low voltage cells, so I havenít checked my batteries since I installed them, other than look at the readout from the BMS once in a while. The only issues so far are related to the cold weather since I drive the car year round. The BMS de-rates the maximum current draw based on the battery temperatures. When the temperature drops below 0, I have to be careful not to accelerate too hard, or Iíll trip the fault for exceeding the maximum current.
My recommendation for people wanting to build an electric car that is more than an experiment is to use lion batteries, a properly set up BMS, and keep the transmission and clutch. Size your motor and controller to produce a peak torque that is close to the original engine, and youíll have a very drivable car when youíre done with minimal structural modifications to the original chassis. I hope this helps others considering an electric car build.

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Old 02-01-2014, 03:05 PM   #2 (permalink)
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I have lithium batteries in my motorcycle and I of course don't use it year round but those batteries have been awesome! when I compared them to lead acid batteries they were about twice the cost but 1/4 of the weight and 4 to 10 times the expected life depending on who's figures you look at for each, say you compare the best case of lead with the worse case lithium then lithium are only 4 times as good.

My BMS tells the charger not to top off the batteries when they are below 32F, right now at peek heat of the day it's 5F out and my garage is not heated so I have a 3 foot, 21 watt heat tape glued to the bottom, outside of the battery box that has a thermostat to turn it off at 45F, it does a decent job of keeping the batteries about 30 to 40F warmer then the out door temp without any insulation other then a card board box around the batteries.

My electric car is 33 years old this year, it still has lead acid batteries (when they wear out it's getting lithium) and I've done up grades on it, but most of the work it's needed is breaks, suspension and regular vehicle up keep.
I rebuilt the motor a while back at a cost of about $120 for parts and labor.
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Old 02-02-2014, 12:54 AM   #3 (permalink)
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Ryland,

I'm impressed with a 33 year old EV. That is great. I'm glad to hear you've had good luck with the Lithium cells too. I wanted to convert my midget 10 years ago, but the reports about lithium cells were bad then. I've heard that it wasn't true, just people who didn't realize how to charge them properly speaking up. My garage is insulated and never drops below 40 degrees at night so I haven't had issues charging in the winter. If you're in a cold environment, insulated battery packs and heaters are probably required. I only run into issues when I'm at work all day and the temperature is below 25 degF when I leave. I've now learned to be careful when accelerating under those conditions. The BMS throws a fault, and to clear it I need to turn off the car and then turn it back on all while coasting.

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