Impatience...

As you may have noticed, the blog entries have dropped off rather abruptly in recent weeks. I've sent three e-mails and one phone call to Electro Automotive asking about the status of the battery racks/boxes and received no reply. As you might imagine, I'm a bit frustrated with this and don't really know what to do next.

I should be getting the 18 8-volt golf-cart batteries from American Battery Company early next week. This will allow me to at least connect the batteries to the AC controller and see if I can get the rear axle to spin. Napa Auto Parts is willing to sell me battery grounding straps of any length with eyelets on each end so I can hook everything together. With some 2/0 battery cable and some lugs, I can attach the batteries to the controller. For those of you are thinking "That sounds kinda dangerous," you're probably right. I like to remind myself of Murphy's Law that says "Experience varies proportionately with equipment ruined."

I'm going to ask the EV community if anything funny is going on with Electro Auto these days. I'll keep y'all posted.

(Grrr, it's sunny out and I want my 914 targa top EV! :)

Potbox and Backup Switch

I went back to Parkrose hardware today to pick up stainless steel bolts to attach the motor cables to the controller. In the process, I got some two-conductor wire to make the connections to the potbox switch and backup-light switch cleaner.


Here's the somewhat finished potbox. Note the added accelerator cable and extra pullback spring on the potbox arm. I found I could simply use the original accelerator cable barrell connector if I screwed it in from the backside of the potbox arm. I'll add some loctite to make sure it stays there.

The blue wire has two conductors in it and replaces the two dangling black wires that I originally installed. Note that the pink quick-disconnects are tied to the right two terminals and not the far left and far right terminals as in the original DC design. This switch prevents the motor controller from engaging when the accelerator pedal is pressed.


Here are some "bullet" type crimp terminals I got from Parkrose hardware that just fit into the sockets for the reverse switch on the side of the transmission. These are a bit tough to find and I was lucky that they fit.


Here's the side of the transmission with the two-conductor cable installed on the backup-light switch. I'm a bit concerned because the nearby spinning CV joint could entangle with the wire if I don't tie it down correctly. Without the saddle boxes that came in the original 914 DC design, there are few places to tie this cable to.

On a more dangerous note, I ordered my 18 USBatt 8-v golf-cart batteries from American Battery company in California. The batteries with shipping came out to about $1900, which was slightly cheaper than I expected, given the rising costs of lead and shipping these days.

I plan to purchase several grounding straps to tie the batteries together while they sit on the floor and use welding cable to attach them to the motor controller until the battery boxes arrive from ElectroAuto.

If I ever do drag-race this machine at NEDRA, I might opt for much smaller batteries to save weight. The effective range of the car might only be ten miles, but that's not a problem when drag racing since we can recharge between runs and reduced weight is more important.

Chatting with other EV folks

Last night was the monthly OEVA meeting. There were many electric vehicles there to ponder and I got a chance to chat with a bunch of people. I'm kicking myself a bit for not bringing my digital camera, but that's life.

Victor Tikhonov of Metric Mind and I talked about his new EVision system and how I might get involved with the embedded programming for his latest BMS (battery management system). I'll be visiting his company later today to talk more. John Benson (aka JRAB) brought his functioning 914 DC EV conversion (originally from Electro Automotive) too. Brad Hippert, the president of Porteon (www.porteon.net), and I chatted about production of NEVs (neighborhood electric vehicles) in Portland soon. He seemed interested in the Kalman filtering algorithm I recently researched with regards to SOC (state-of-charge) and SOH (state-of-health) in battery packs.

I had only intended to go for 30-40 minutes to see all the electric vehicles, but ended up being one of the last people there at 10:30pm talking with all these great EV pioneers. With significant lack of sleep from this past week, I think I'll go take a nap now...

Dear Customer...

I received a package from Azure Dynamics yesterday with a field upgrade to the bolts on the AC24 motor for the EV kit. Apparently, the nylon washers weren't good enough to hold the bolts in under all conditions and some of them may get loose. I'm happy that Azure sent these before I started driving the vehicle around, although no major field failures have been reported.


Update: DOH! With the electric motor mounted in the car, I can't perform the upgrade because the bolts won't slide out. Taking out the motor would involved taking off the CV joints and lowering the whole motor/tranny assembly. I think I'm just going to risk this one or apply loads of locktite to the head end of the bolt... Rats.

There are many paths to the same goal...

My 914ev partner-in-crime Randy (who purchased the very first 914 AC kit from ElectroAuto) e-mailed me some photographs of how he's wiring up his terminal blocks and relays. Here are some pictures and descriptions from his 914 AC conversion. (Thanks, Randy!)

Excerpt from Randy's e-mail:

I've also started on the wiring kit. I looked at the instructions
and decided to rearrange things (typical). I put an aluminum project
box next to the controller so that most of the connections and the
relays would be better protected. I also fabricated a plate and a
box to replace the original relay board and am putting connected
there for tying into the harness. To bring the wires into the trunk,
I was able to take advantage of a slot I cut for the Camp 914 rear
trunk shock kit. I've attached a few pictures...


This is where the original relay board went. Inside this box are
connectors to bring the wiring harness and the potbox back to the
relay/terminal blocks in the rear trunk. Still need to try back the
extra length of wires.


This shows the wires between the boxes coming into the rear trunk.
The slot was cut when I installed the Camp 914 shock kit. I may have
to enlarge it a little bit. Note that I was able to bring the plug
between the motor and controller around here with enough length to
make it. That means the only cables coming through the trunk floor
will be the the big motor controller and the battery wires. The two
lower wires are actually loose strands that I put through clear
shrink wrap to make my own harnessed.



This is my rear trunk. The small aluminum box has the terminal
blocks and relays. You can also see that I had gobs of extra cable
length between the motor and the controller - so much so that I would
like to think about cutting them short and replacing the connectors.



Inside of the aluminum box. I've run all the wires I can (until I
get more instructions from ElectroAuto). Note the shrink wrap on the
connectors - something I always do with crimped connectors.


Here are some pictures of the shunt (including one showing where I
am thinking about installing it).


The shunt is a very, very low resistance plate with two bolts on
either end. The large bolts are for the battery wires while the
small bolts all the current meter to measure the voltage drop over
this tiny resistance (and thus the current).

Closing up more loose ends...

I'm still waiting on the battery racks/boxes from ElectroAuto, so I took care of a bunch of little things that have been neglected so far.


Here's the battery tray that the directions said to remove. It came out surprisingly easily with a hammer and mini-crowbar since there were only a few spot welds holding it in. One of the other 914 kit converters questioned why the accessory battery couldn't stay in the original tray, but I decided to remove it anyway and have the accessory battery up in the front trunk near the DC/DC converter.


Taking out the hood latch was a bit tougher. First, I tried a large hammer and a mini-crowbar but that just seemed to mangle the metal. Then, I tried the sawzall and that just sawed the thing off like a hot knife through butter. Live and learn...


Here's the sawed off hood latch. I saved the latch cable tube and latch mechanism to give to Craig at camp914 as parts for someone else. It's a pity that we have to remove this, but the size of the golf-cart batteries clearly interfere with the latch.


In the process of cleaning out the fuel compartment, I removed the washer solution tank. The 914 uses pressure from the spare tire (??!!) to power the washer solution sprayer. The hoses were leaky and the system didn't work. The technical articles at Pelican Parts describe how to replace the pressure-based solution with an electric pump from a fish tank. I find it boggling how the fluid tube actually goes all the way to the steering wheel controls to a mechanical valve attached to the wiper lever and then back out to the washer nozzles. Having that possibly conducting solution away from the steering column wires will be good.


The three-phase AC cable from the motor was too short to actually pass through the 2-inch hole I drilled as suggested in the directions (barely shown at the bottom edge of the above picture). So I drilled a new hole (near middle of picture) and will route the tri-cable through that hole instead. Home Depot sells 2-inch caps that should plug the previous hole nicely.


This is picture inside the fuel compartment on the drivers' side. I've removed the heater hose that came up through the passenger compartment going to the duct on the left (just above the brake fluid reservoir). Since heat no longer comes from the heat exchangers over the exhaust system, we're going to thread the high-current battery cables through the heater ducts to connect the front and rear components.

That, of course, leaves us with the problem of heating the passenger cabin. John Benson, who lives a 20-minute walk away converted a 914 with the DC kit from ElectroAuto and he simply attached two hair dryers to the ducts that originally received the heater ducts from the engine. This is another reason why I removed the washer fluid tank earlier: to get at the passenger side heater duct and make room for the second hair dryer. Apparently, many hair dryers can run off of DC or AC voltage of a wide range which works well for a pack voltage of 144V (nominal).


After vacuuming out the fuel tank compartment and cleaning everything else up, I had some more time. I wanted to test to see if the 12V electrical system still worked. It turns out that the positive wire to the horn is also tied directly to the positive terminal of the 12-volt system. When the driver presses the horn button, it actually connects the ground terminal to the horn. Given this knowledge, I took a 12V UPS battery (12Ahr sealed-lead-acid) and tied the positive terminal to the positive terminal on the horn and the negative terminal to ground. Before I attached the battery, I used a multimeter to make sure that +12V wasn't accidentally shorted to ground.

Somewhat to my surprise, the clock started running and when I turned on the ignition key, the CD player fired up and the relay inside the AC motor controller closed. This will give me an opportunity to hook my laptop up to the AC controller through the RS-232 (serial) port and see if I can communicate with it. Just for grins, I also shorted out the two terminals on the lower terminal block tied to the rear lights and (voila!) they turned on just fine. Given the small size of the test battery, I decided not to push my luck and disconnected it after turning off the key.

Now, where are those battery boxes from ElectroAuto.... If I really get impatient, I think I'll line up the 18 8-volt golf cart batteries on the floor and run two battery cables into the controller just to see if I can get the motor to turn. I can attach most of the battery terminals together using bent copper bars and just use cables for the terminals on the end. Since this would just be for light testing, I might even be able to get away with cheaper 2/0 welding cable.

Next up: installing two-wire cable for the backup switch and potbox to keep things looking nice.

More SOC/SOH battery research

I spent all day today going through those hundred technical articles on SOC (state-of-charge) and SOH (state-of-health) algorithms for lead-acid batteries. They were all fascinating, but the one I really liked involved a Kalman filtering algorithm to constantly estimate the internal parameters of the lead-acid battery.

The algorithm models the battery and samples the current draw and voltage across the pack. Based on the current, it estimates the new voltage for the next sample time. It then compares the actual voltage to the sampled voltage and alters the parameters of the model in real time to match the actual voltage. In a short duration of time (on the order of 4-5 minutes with varied driving) the model parameters converge and prediction of the next voltage becomes remarkably accurate.

Throughout the day, the parameters of the battery change as the algorithm tunes itself and we can directly determine the SOC (state-of-charge) based on the modelled parameters. The parameters even drift very slowly over the lifetime of the battery so we can actually determine the SOH (state-of-health) as well. I'm sure there will be issues given that the pack contains many batteries. The computation also requires a rather powerful DSP (digital signal processing) microcontroller to refine the parameters.

Despite the high compute power, I still think this algorithm is worth pursuing because of its accuracy and the possibility of its use in more mainstream electric vehicles for the average user who doesn't want to know all the details of monitoring a complex battery pack for SOC or SOH. ("Just tell me how much battery fuel I have left and when I need to replace a battery...")

I also spent a few hours researching the CAN (controller-area-network) bus that's used for communications in some automotive applications these days. The CAN bus uses differential signalling, which makes it highly noise immune in automotive environment. This will be important for the battery management system in case I end up using a central controller that talks to mini-controllers on each battery for monitoring. It saves on wiring and allows for many measurements (such as voltage, current and temperature). If I have time, I might even write up code for a PIC microcontroller to convert CAN bus traffic to serial port debugging messages.

Measuring State-of-Charge on Lead Acid Batteries

Since I'm still waiting on parts from ElectroAuto, I decided to take the plunge and do some extensive research on Lead-Acid battery technology. The 914 AC kit uses 8V golf cart batteries and I'm wondering if different batteries like Hawkers or Optima Yellow-Top batteries would be better.

After researching different battery types, it looks like the Hawkers and Optimas can put out more amps for more torque and are more rugged, but the golf-cart batteries still rule in terms of capacity per weight and size. With the AC system, I'll probably be pulling less amps and am looking forward to the extended range. Both US-Battery and Trojan have 8-volt golf-cart batteries. The kit was specificially designed for the US-Battery model and the equivalent Trojan battery is just 1/8" of an inch larger in one dimension, so I'm guessing it won't fit in the battery cases provided by ElectroAuto (grrr...).

Given that I'm using lead-acid technology, one of the big challenges is knowing just how much charge is left in the batteries so I don't run them down below 20% SOC (or state-of-charge). This turns out to be a very difficult problem because drawing current from lead-acid batteries, especially at different rates, causes a widely varying voltage at the terminals. The non-linear dynamic nature of the battery makes accurate SOC measurements difficult, if not impossible.

I feel very fortunate in that the company I work for (HP) has a subscription to IEEE Xplore, so I downloaded literally a hundred scientific papers today on battery management and state-of-charge measurement of lead-acid cells.

The simplest method that seems to have the most promise takes the average of voltage and current over the past few minutes and uses that with an interpolated lookup table of discharge curves to determine the approximate state of charge. A more complex method actually forces a small (25mV) AC voltage back into the battery at a variety of frequencies to extract the complex impedance of the battery structure. If you take this measured complex impedance along with some measurements of the battery when no current is drawn for an hour, you can supposedly derive the average concentration of the sulfuric acid in the electrolyte, and thus the current SOC. The electrolyte concentration is one portion of the complex impedance model.

I've been in contact with Victor at Metric Mind here in Portland who is developing the state-of-the-art EVision battery monitoring system. We might possibly work together on a project after chatting at the next OEVA (Oregon Electric Vehicle Association) meeting.

This week is packed, so I might get to hooking up the back-up light wiring on the EV if there's time on Friday. Off to some interesting bedtime reading on lead-acid modelling technology...