Who Killed the Electric Car?

Date By joe Category misc Comments 2

I just finished watching this movie.  It doesn't make you feel good (unless you work for the oil companies I suppose).  I was already aware of a lot of the bits and pieces of this story.  I had read about key battery patents being held by oil companies. I was aware that most of the electric vehicles developed by auto manufacturers around the turn of the century were taken back by said auto companies and destroyed.  I was aware that the auto companies felt that there was not enough demand to support an electric car market.

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Building the controller power board

Warning: long post. During February and March we were building the power board. Credit for the mechanical design goes to Brian. I'll detail our experience in making this power board, but first here is a picture of the finished item:

Assembled controller power board
Assembled controller power board

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Decommissioning the Truck

Date By joe Category Truck Comments 0

Today I drove the truck in what I think is the last trip with the internal combustion engine (ICE).  I drove it from my house to the shop where we will be doing the work.  I noticed a few weeks ago that I had a radiator leak and so I pretty much stopped driving it.

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Attempting to sell the engine

Date By joe Category ICE Comments 2

UPDATE: the engine has been sold

I need to get rid of the internal combustion engine (ICE) and was hoping to get at least a little cash for it.  It is in working order and has low miles for its age.  I put a listing on craigslist and I also ...

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Parts Decisions

It's been a while since the last update, but a lot has been happening.  I made decisions about most of the major components and have placed some orders.  In fact, I have already received the motor - here is is:

New ADC FB1-4001A received from Cloud Electric
New ADC FB1-4001A received from Cloud Electric

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Still here, just haven't updated in a while

Date By joe Category misc Comments 0

I realize I have not updated this site with any new information or video of MOSFETs blowing up lately. Despite the lack of posts, we are still working on this project. In November we were experimenting with another battery balancing scheme that involves using inductors to transfer charge between adjacent cells. I got the idea from a TI application note. While I was able to make it work on a small scale, it was very inefficient and was going to prove to be a lot of trouble to get working in a useful way. Sorry I don't have any circuits or scope photos to show you for this. more ...

Battery Experimentation Part 2

Overdischarging Oops

I've had a chance to experiment some more with the small Lithium Iron Phosphate (LiFePO4) cells that I purchased from batteryspace.com.  I originally purchased 4 of these 1300 mAh cells.  I've since learned what happens when you over-discharge a cell.  I was discharging the 4-cell pack using a stepper motor as I described in this earlier post.  I was periodically recording the cell voltages, with the goal of spotting the knee when the cell becomes fully discharged.  This was going okay but at some point I ended up in a hallway conversation (this was at work), and when I got back to check, one of the cells had a negative voltage (about -0.6 volts).  Interestingly the motor was still running and the other cells were still delivering current.  I disconnected the cells and let them sit for a while.  The reversed cell eventually became positive again, about 0.2 volts.  I attempted to charge it, and when I did the cell voltage pretty quickly came back into a normal range.  But when I stopped charging, the voltage eventually dropped back to about 0.6 volts.  Clearly this cell is no longer good. more ...

Prototype Controller Testing Part 3

This week we modified the power circuit, replacing the freewheeling diodes with another MOSFET, and replaced the original MOSFET driver with a half-bridge driver.  Here is the original motor drive circuit, per the ReVolt design (specific part names/values not shown):

Original Motor Driver Design
Original Motor Driver Design

And here is how we modified it: more ...

Prototype Controller Testing Part 2

Last week we tried out the "ReVolt" open-source controller for the first time.  At the time, we only had one MOSFET and diode installed.  We were able to spin the small motor at 12V, but when we tried the kart motor at 48V, something popped so we stopped for the evening. This week, with some modifications and a more cautious approach, we were ready to try it again.

Cause of Last Week's "Failure"

First, some commentary on what went wrong last week.  When Bill took apart the power section, he really could not find anything wrong.  At the time we thought that perhaps there was a current spike through the diode as we applied power to the big motor.  But now we think that maybe it was the silver epoxy.  Perhaps there was a high resistance path somewhere that overheated when we started to flow some real current through it. more ...

Battery Experimentation Part 1

We want to better understand how these LiFePO4 batteries work, so I ordered 4 small hobby cells.  These are the same chemistry and cell voltage as the big battery cells that will make up the truck battery pack, so I think it is reasonable to study these to learn how the big battery will work.

I ordered 4 1300 mAh cells.  These are not expensive at all.  I also ordered a 4-cell charger which was a little pricey but I want to get straight to studying the battery characteristics, more ...