With the motivation from The Future of Transportation Symposium and Car Show I was able to get the car in a complete enough, tidy, safe and drivable state. So being the first day it was above zero I drove it to work. The JLD404 wasn’t quite set up correctly, it was a decimal point off on the Current and AH’s, but it still gave me an idea of energy usage. Since I don’t have the EMW deluxe dashboard hardware set up again I’m using the JLD404 as my only instrumentation. So to implement the auto reset I’m simply using one of the built in relays and a voltage alarm. My pack charges to about 317v (92 x 3.45) so I have set an alarm that when the voltage reaches 317v which is my full charge and the charger terminates very quickly after that point. This will likely give me a small error since it will continue to charge after reaching 317v, to increase accuracy I could set a 2nd alarm for a low current level and put the relay contacts for the two alarms in series. That would mean it would reset the JLD404 when current has dropped to zero AND the voltage is at or above 317v, the only time this happens is at the end of charge. I’ll start with just the voltage alarm and reserve the other for an AH warning or disable function. If this proves unreliable I will revisit using the end of charge signal from the charger.
Since it takes awhile for me to put these blog posts together I actually have had time to run with the auto reset on the JLD404 using only the built in voltage alarm. Typically I have a reading of -0.01 to -0.03Ah on the JLD when I come back to the car, this is actually far more accurate than I had expected and should work very well long term. I may have to see how this plays out at higher and lower temperatures, but it’s currently working perfectly and I am as close to 0Ah as I would hope.
I had my first “break down” this past Friday, but luckily it happened while I was at work, which gave me access to the resources required to patch the problem and allow me to drive home and fix the car. This will mean more to the fellow 944 owners, the rear side panels behind the wheel wells have tubing and drains that allow water to flow through and out of the car. I spent a lot of time ensuring that all of these were clear and the tubing was in good shape and connected correctly on the passenger side of the car. The previous owner had a CD changer installed in the drivers side cubby, and for whatever reason I had assumed that the drains were working because the changer still worked. I installed my DC/DC converter in this cubby and as you might be guessing the main drain was plugged. We had a few days of heavy rain and that side panel filled up with water, well not exactly full but there was 4-5″ of water in it. This meant the bottom 1 – 1.5″ of the DC/DC converter was actually under water. This included the fan and the 300v output rail of the PFC section of the power supply. When I turned on the car there was a very loud POP and the car didn’t turn on. The pack voltage was fine but the 12v dash gauge didn’t read anything. I quickly turned off the car, opened the hatch and turned off the maintenance switch. I confirmed the pack voltage which was fine, but the 12v system read about 3v. My 12v battery is the original battery that came with the car. It’s been drained to zero volts more times than I can count, and it only stays alive because the demand on it is so low. So there is no chance I could use this battery alone to power my 12v system and get home. Fortunately we had a couple of 4P 100Ah thundersky battery modules that were used as a battery backup on one of our products at work. I had checked them and left them at roughly 55% SOC for long term storage a few months earlier so I knew one would have plenty of energy to power the car and get me home. I disconnected the dc/dc converter from the 12v and 300v batteries and temporarily connected the TS pack to my 12v system. The voltage came up quickly as it brought the lead acid back to life. I drove home without issue, though being much more conservative in my driving and use of the wipers/fan etc.
The dc/dc converter that I use is similar in concept the the Vicor Megapac that many people use, it’s a PFC front end that will accept AC or DC input over a wide range with a motherboard style layout that allows you to install a number of different modules for your desired usage. The motherboard was toast (literally) but luckily all of the modules were just fine. I plugged these modules into a spare motherboard I had on hand and the dc/dc converter was back up and running with no downtime. I also took this opportunity to “Fix” the fan in the dc/dc converter that sounded like a small jet turbine and the noise/airflow was driving me crazy, as it was by far the loudest thing in the car. I played with the voltage to the fan and found a nice compromise between airflow and noise. The car is much nicer to drive now. There is a good chance I will be able to repair the motherboard and lowering the fan noise was a big win so all in all this “break down” wasn’t a bad thing.