Going to the Portland Better Living Show

Yesterday was a long day. I spent over seven hours on my feet at the Portland Better Living Show displaying the 914. My throat was hoarse at the end of the day from answering the same questions many times. Overall, people were very interested and I'm hoping a few will show up at the next OEVA meeting.

Many thanks to Gary Graunke (who set this whole thing up), Ken (forgot his last name) and Joe Williams (on the left) for hanging out with me during the nine hour show. Joe and Ken will take care of the booth today and I'll finish up the last six hours tomorrow.

On a side note, I purchased a DVD from Bob Bath regarding his CivicWithACord project. He's documented much of the work needed to get a fifth generation ('92-'95) Civic converted to electric. This is one of the prime candidates for the open-source vehicle conversion kit I'd like to work on, so there's lots of information to leverage.

Installing LED Lights and Fixing the LED Flasher

I received a shipment of 3-watt LED lamps and a low-load flasher relay from superbrightleds.com yesterday. The bulb bases were the same, so replacing the bulbs was easy. I ordered the CF13GL-02 LED flasher relay, which is a plug-in replacement for the Porsche 914 relay and responds to the much lower current pulled by the LED lamps.

After installing everything, I found out that the LED flasher was able to detect such a low bulb current, that it was stuck in the "on" mode (relay clicking) all the time. I measured 3 MegaOhms between the bulb output terminal and ground, even with all the lights turned off. I'm guessing this probably comes from leakage through grease or other leaky paths in the system.

Soooooo, I guess it's time to reverse-engineer yet another component that doesn't work...


Here's my dining room table with the test setup. I drew out the schematic of the LED flasher and got the datasheet for the PNP transistor that was activating the circuit.


Here's the modified flasher relay. Without going into too many details, I replaced one resistor and shunted one terminal to 12V with another resistor so that the input ignores loads with a higher resistance than about 200K ohms.

I'm a bit discouraged that people are selling this relay knowing it doesn't shut off in a real automotive environment.

Addendum: Here is the partial schematic for the LED flasher with suggested hack to fix the flashing problem with a leaky terminal.



Ah well, I'm happy with the results, and the flashing LEDs look great.

Cheers,
Tim

2000 miles and counting

I broke 2000 miles with the 914 EV this week. The car has been running smoothly with no complaints. One of the "features" of the 914 is that the turn signals come on (but don't flash) if you leave the turn lever in the "left" or "right" position, even when the ignition is turned off. This presents the dilemma of running down the 12V battery while the main pack is charging. If the 12V battery is dead, you need a small 12V battery (9V would probably work) to activate the DC-DC converter relay to bootstrap the 12V charging process.

The PakTrakr with the series 100 ohm noise-reduction resistor has eliminated all the spurious error alerts. I took a serial log of all the batteries during my commute (graph below) and found battery #11 (the second battery in the front compartment) to be drooping slightly more than the others. I noticed that it tended to have more acid around the battery caps on top of the battery and it's fluid level was lower. The accuracy of the PakTrakr is only 0.1V so the voltage droops look like sharp steps on the graph.


UPDATE: Roger asked me to explain the graph above in a little more detail. The PakTrakr logs voltage for each battery and then dumps it out a serial port in .csv (comma separated) format for MS Excel. I captured the above graph from the chart that MS Excel generated. The batteries are 8 volts apiece and the serial port dumps tenths of a volt (scale on the left edge). This graph displays voltage for all 18 batteries (each is a "series) in the system. As I drove to work with acceleration and regeneration, the voltage on the batteries varied. The batteries with reduced health or capacity will tend to droop lower during heavy acceleration and spike higher during regenerative braking due to higher internal resistance or lower energy capacity. As I mentioned earlier, I found that series #11 on the chart was consistently at the lowest value during heavy acceleration periods, so I suspect that battery will have some issues sooner than the others. I topped off its water to increase its storage capacity a bit. You'll also notice that the "steady-state" voltage at the end of the chart is lower than at the beginning, showing that the pack has gone through some discharge during the 15-mile commute.

I'm getting more involved with the OEVA club. If I don't get elected co-chair next Thursday, I'm going to start an open-source EV conversion kit sub-group within the OEVA. I even have a lawyer friend who is willing to assist with some of the open-source gotchas involved in such a project. Researching my motivations and how much I'm willing to throw myself into this will definitely be important.

Have a great weekend everyone.

Fixing PakTrakr Signal Integrity

Well, I played around tonight and looked at some of the PakTrakr signals on the oscilloscope and found some noise on the data line going between the PakTrakr "remote" modules. It looks like each PakTrakr remote has three wires coming out of them:

Black - zero volts from that module
Red - 11-12 volts from that module
Green - 3.3 volt signal that sends a pulse train every second (pulses to zero volts)

The signal on the green wire had significant over and undershoot on it, so I thought of ways to take the edge off the signal.


Here's my experimental setup. I added series 100-ohm resistor to the green wire going into the PakTrakr module and all the noise cleared up. The messy serial output from the display module cleaned up too. In the picture above, the wire from the rear PakTrakr remote is the gray wire coming up from the lower right corner. I have some alligator clips and an o-scope probe tied into the mess and insulated with masking tape (what hack job). The alligator clips allow me to insert various series resistors with the green wire. Again, 100 ohms seemed to do the trick nicely.

I gave feedback to Ken Hall at PakTrakr.com so hopefully he can incorporate this into his future designs. The only other thing that bugs me about the PakTrakr is that the modules seem to be made of teflon. No tape I've tried will stick to the back of them. I'll probably end up attaching Velcro with epoxy or something.

One more problem (hopefully) solved...

Playing with PakTrakr

Many months ago, I installed a PakTrakr (www.paktrakr.com) to monitor the state of my batteries and it's been acting rather flakey. The PakTrakr consists of several serially connect "remotes" which drive a "display" unit in the driver compartment. The voltage displayed shows the pack voltage and is supposed to monitor the state of each battery and the State-Of-Charge (SOC) for the pack too.

In short, the voltage displayed jumps around quite a bit. The different in voltage jumps correlates closely with the voltage being monitored by an individual "remote" unit, so I'm guessing that the communication link is bad. I contacted Ken Hall at PakTrakr.com and he suggested adding EMI suppression cores to the links between the "remote" units to cut down on electrical noise. So, I collected a bunch of spare EMI cores from a local computer recycling center and wrapped the remote cables around them. I also put dielectric grease on the connections to see if that would help with corrosion and connectivity. The result: The noise problems got far worse and the PakTrakr display doesn't register anything meaningful.

It's possible the dielectric grease messed up the connections, so I'll try removing the EMI cores and see if I still have the problem. This is not a critical part of the car, but it would be nice to measure the state of the batteries. It turns out that the Zivan charger is doing a reasonable job of over-charging the flooded batteries to keep them balanced. I've only had 50 millivolts of difference between the highest and lowest voltages when I get home from work after 16 miles of driving, so I think the pack is still doing okay. I hope this pack lasts 2-3 years while the costs of lithium batteries come down.

On a slightly non-914ev related note, I'm going to be running for a co-chair position within the Oregon Electric Vehicle Association. If I don't get elected, I'd like to start an open-source EV kit that uses all local businesses to manufacture the custom car parts with freely available designs. We'll see what this year has in store...

Cheers,
Tim