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A cleaner way to drive

AC vs DC revisited

So I’ve been rethinking the whole AC vs. DC system question and I am moving towards a DC conversion now. Here’s my reasoning: though AC is more efficient and has regenerative braking, it costs about 3-5k more. The extra efficiency comes out to about 5-10%, which, assuming an average DC conversion with a range of 60miles, equates to an added 3-6 miles on range. The other benefit is regenerative braking. In my daily commute on the freeway, there will be very little time when I need to use my brakes. Since I live on a hill, I will be charging my batteries at the beginning of my commute, while the batteries are already fully charged. So going AC won’t give me that much of a benefit.

It would have been great if we could have made it with Steve’s EV during our test run, which would mean that I could just copy exactly what Steve did. However, it looks like I will definitely need more battery capacity. Here’s some back of the envelope calculations that I did. Steve’s 15 8V battery system is about 20.4 kwh and has a practical freeway range of about 30-40miles, based on our test run. If I can fit 20 6V batteries, each of which has about 40% more capacity (US Battery 125 XC):

  • 20 * 6V * 242 amp-hours = 29.04kwh
  • 29.04 kwh / 250 wh per mile = 116 miles
  • 116 * 50% = 58 miles

Looks like it might work, at least on paper. Just as I was contemplating how to go about getting 20 6V flooded lead acid batteries (dimensions of each battery: 10.25L x 7.125W x 11.25H) in the MR2, I met Doug Coleman at one of our recent EV club meetings in Alameda. He brought his recently converted MR2 with just that configuration. I even got a test ride in it.

Decided on my new path, I will start sourcing parts for a DC system assuming a 120V flooded lead acid battery pack.

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Posted in AC vs DC, Batteries, MR2EV, Range

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