Zach’s Electric Diablo

Last night, I soldered up the first section of the BMS board.  On the top side of the PCB there’s a processor, an FTDI USB bridge chip, a bunch of fuses and a handful of passive components:

On the bottom of the board, I soldered on four (out of the 50) shunt resistors:

I am mounting the shunt resistors away from the board to allow for better air flow.  They get pretty warm with 2.5amps flowing through them.

So far, the initial tests look good.  I am able to program the processor, flash LEDs and send data over USB.  Next, I need to test communications to the LTC6802.  In order to do this, I need to wire it up to some batteries.  I’ve got some nice connectors on order to make this job easier and more fool-proof.  They should be here in a few days.

I also spent a little time welding up some brackets to hold the roll cage in place.  I’ll snap some pics of these next time I am down in the shop.

Here it is:

Not bad for $100.  I had http://goldphoenixpcb.biz/ fab it.  I’ll start soldering it together soon.

Tonight, I spent some time writing code to decode the serial output of the multimeter.  The serial stream represents a map of the 7-segment LCD elements on the display instead of just a simple reading.  So, it took a little work to map out the characters.  However, it now works and can now start work on my fuel gauge code.  This code will eventually go onto the “creature comforts” circuit board that I am designing.  This board will:

1. Act as a fuel gauge
2. Be an interface to the heating/air
3. It will monitor door sensors (and will drive the dash lights)
4. In will produce a “bing” if turn the ignition off and leave the lights on or leave the keys in the ignition and open a door.

Additionally, I bought a handful of parts this week:

1. LED backup lights from ebay.  This is sort of a test.  If they work, I will buy similar lights for turn signals, brake lights, and markers.
2. 500amp 50mV shunt (my 1000amp 100mv shunt isn’t giving me good readings)
3. Meter to read the current shunt (I got the $60 radio shack special and it works great)
4. Fiero windshield wiper motor and controller board

Last but not least, I cut out a small bracket for mounting the fire extinguisher:

As I type this, the printed circuit board for BMS version 2 is being fabricated in china. I should get it back next week.

I tested my heater tonight. With all the heating elements wired up I got an air temperature of 190deg F. It was pulling about 23 amps. I tried disconnecting one element from each of the heaters (there are four elements per heater) and the temperature dropped to 112deg F pulling around 8amps.

I’ll probably stick with the 190deg as I am sure that will feel good on a cold morning. However, 112deg might work as well, just a little more frugal. Maybe I’ll wire up a switch.

I replaced my slave clutch cylinder. A coworker let me borrow his “Power Bleeder”. It worked very well and made the job of bleeding the clutch very easy to do with just one person. Hopefully, this one doesn’t leak.

I spent some time testing an old board I had made to monitor the amount current flowing through the main shunt. This board was supposed to be a fuel gauge, keeping track of how much energy goes in to and out of the battery pack. Unfortunately, it’s not working. The second I touch the throttle the circuit gets overwhelmed with electrical noise. I tried a number of things to filter this noise, but there is just so much. Nothing I do seams to make a difference. The interesting thing is that if I use my multimeter to measure the shunt, the readings are nice and clean. I think the meter has decent filtering and is doing a ton of averaging (as it seams to update about once a second). I’m thinking I might take the easy way out and just permanently mount the meter in the car and use it’s RS232 to read the current. I could then just build a simple microcontroller board that reads this data and keeps track of the pack’s charge. It’s not the most elegant or the most accurate (as it will miss short current spikes), but it’s simple and it works. Sometimes “works” is better than “elegant”.

Today, I put a little more work into the heater setup. I found (what other EV’ers have used) a couple inexpensive ceramic heaters.

I’ve mounted two of the elements, in parallel, across the face of the modified heater core.

I’ve glued them in place using high temperature RTV gasket compound. I’ll test it out once the RTV fully cures.

This week I also got a new keyboard for the car (typing on the touch screen is a pain), a fire extinguisher (safety FIRST!), a new slave clutch cylinder (my old one was leaking) and an ultrasonic parking sensor kit which I will mount in the rear bumper.

Last, but not least, I put the finishing touches on BMS V2.0. I’ll send it off for fab this week.

Last night, I took apart the my heater/AC unit. I was hoping the AC coils and the heater coils would be easy to separate. I wasn’t so lucky. They are wrapped around each other in one monolithic block.

It would be trivial to take out the whole core and replace it with a ceramic heater, but then I would lose AC (which I really want to keep). Another option is to use an external system to heat water and pump it through the system. Neither option sounds all that great. I think I am going to try and find some ceramic heater elements that will fit into the core (with a little modification).

Today, I put up some new shelves in my container to try and organize it a little better. With winter on its way, I need room in there for epoxied and filled parts to cure.

I also realized that it’s getting dark much earlier and I often find myself driving the car at night. Holding a flashlight while driving is a little tough. So, I went ahead and installed the headlights. I did a test fit of the body to see how much the lights need to be raised. Looks like somewhere around an inch and a half will do.

At the end of the day I spent a little time trying to figure out why my water pump (used to cool the zilla motor controller) keeps cycling on and off. I didn’t figure this one out…

My current Battery Monitoring System works pretty well, but there are some issues that need to be fixed.  I’ve decided to build version 2. This time I’m going with a completely different topology, a single board to monitor and balance all the batteries.  This will be much simpler, much cheaper and hopefully easier to troubleshoot. I will be using a new battery monitoring chip from Linear Technologies, the LTC6802, which is designed specifically to monitor big series lithium battery packs.  This means I only need a single microcontroller to monitor the entire pack.  I’ll use a second controller as a watchdog (can’t be too careful).  The general schematic is done and I’ve started the layout.

After some jumper settings and a secret configuration menu, my Mac Mini and Lilliput screen come on when I start the car and automatically shutdown (cleanly) when I turn off the key. The main trick was to use a “smart” power supply. The one I used was a Carnetix CNX-P1900. It takes in 12v and a signal from the ignition switch. It outputs 18v for the Mini and has a controlled 12v output to power the screen. It has a special plug which attaches to the Mini’s motherboard and lets the power supply virtually press the power button on the Mini. It is fun to turn the key and hear the Mac bootup sound (even though it boots to windows XP).