Electric Porsche – A bunch of little updates

I haven’t completed any major milestones lately, however I’ve been working on a lot of little projects.

I temporarily mounted the main battery voltage and current gauges in the center console below the very stylish Sony CASSETTE deck.  Just to see how visible they were at different angles for both the driver and passenger.  They are pretty bright, so I will have to do something about that on the actual install.  Right now I simply have them powered off a 24v wall wart, so it’s shows the voltage and current draw at the meters.  The meters obviously match, but they are also configurable and have two built in alarms that could be used for just about anything.  Since I will be relying on the Soliton1 for low pack warning and limp mode I don’t need that, but it might be useful to have a high/low current LED as a reminder when I’m at or below 1C on the pack (some sort of GREEN LED) or above 500A (some sort of RED warning LED).

The gauges below the stereo are the only “out of place” gauges that I was willing to add to the car, and they will be individually switched so that when I don’t need specifics I can run without them and they will be turned off.  Since I’m behind schedule and hope to get the car on the road this summer/fall I had to skip some of the custom projects to have a hope of finishing.  The Arduino based battery monitor/SOC meter will be on hold for awhile.  So I need some sort of off the shelf SOC/AH meter so that I have a way of monitoring the pack.  (I also want it to drive the stock fuel gauge as a SOC meter)  To do that there are basically two choices, one is the Ziva Plus from Australia, or the EV display from Florida.  Total cost of the two meters is similar so it comes down to features, the EV display wins there so it’s probably going to be the meter of choice.  The one problem is the lack of extra gauge locations in the 944 and as mentioned before, I’m not willing to just mount it anywhere.  The new stereo (whatever that might be) should have a clock, so the stock 944 clock should become redundant, it also happens to be a similar shape and size to the EV display without the housing.

I still have to confirm the dimensions, however it looks like it might be workable with minor modifications.

Since I’m keeping the A/C in the car I need a way to power the stock compressor.  For simplicity I decided to run it off of the tail shaft of the motor (at least to get me started).  This requires a 7/8″ keyed serpentine pulley, I couldn’t find one anywhere, so the best choice was to adapt the stock Porsche crank pulley to the 7/8″ keyed shaft.  The easiest way was to use some off the shelf parts and weld an adapter to bolt on the stock pulley.

I’ll get a better photo of the pulley soon, but the whole adapter including key stock was less than $10.  Also visible in the above photo is the tach sensor made by Recharge Car.  I had planned on making my own tach sensor, however it’s hard to resist the simple bolt on version, especially when it’s not a bad price either.  This feeds into the Soliton1 and the Soliton1 outputs a modified signal to drive the stock tach in the car.

I also started crimping some of the main cables, along with the very short A2-S2 cable on the motor.  I am using 4/0 awg wire in the motor loop, and 2/0 for the batteries.  I was able to get the cables printed at no extra charge, so of course they say electricporsche.ca

I’ve been trying to decide how to mount the commutator end of the motor for awhile now, and after laying under the car for awhile scoping out the options I came up with a plan.  There is a plate on the end of the motor that attaches on the bottom to a Bosch Rexroth extrusion that will be mounted to the stock strut brace as well as two larger tapped holes in the frame.  Above the motor the same plate will hold the bracket for the Soliton1 and throttle.  This is also the first time I’ve fired up the CNC router to make a part for this project.  Everything worked very well and the plate turned out as expected.  There are quite a few extra holes, but that is simply because it was recycled from a larger plate meant for an LCD tv mount.

And of course I can’t make something on the CNC machine without a little engraving.

Due to the thickness of the plate and the proximity to the tach sensor I had to make a small pocket for the body of the sensor to sit in.  This allows the sensor to mount in the stock location on the tail shaft.  I will need to get some allen head cap screws to re-install the sensor since the stock bolts interfere with the plate.

The DC/DC converter charging board never seems to be finished.  Once I got the previous design finished I did some more testing with the A123 20AH cell and the due to the low impedance of the battery, the current output went through the roof.  This is fine for charging one cell, but when I have a string of 96 in series I simply wouldn’t be able to supply enough power to the dc/dc converters.

The solution?

A feedback loop on the trim adjustment of the dc/dc converter that lowers the voltage output to maintain the preset current, and as the cells charge the voltage goes up to maintain current until it hits the CV portion of the charge and then it tops out at the preset voltage.  Like one of the previous versions of the charger it will have two stages or settings so that when I plug into 240V the dc/dc converter portion will automatically increase the current output to make use of the extra power.  The other change in design was removal of the voltage monitoring system due to the large amount of programing work.  This project will be put off until the car is on the road and essentially finished and I have some time to work on it again.  Since I still need some sort of LVC monitoring and I’d like to see how the cells are doing I’ve decided to incorporate 2 cell log 8’s onto each charging board.  This is made easier by the fact my design is already based on 16 dc/dc converters per PCB which means I just need two cell log 8’s per board to monitor the cells.

The cell log 8’s can easily be removed from their plastic casings leaving a fairly small light weight PCB that just begs to be plug into something other than a wiring harness.  (ya I know my picture shows it plugged into a wiring harness, the PCB’s aren’t done yet!)

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