Tuesday, January 31, 2017

PorschEV Charge Monitor

It's been a while since there has been news to report on the PorschEV. We had another mechanical challenge just before Christmas. Motoring merrily down a street in my neighborhood, there was a clattering noise, then the motor spun up to redline and the car slowed to a crawl. After a flatbed ride over to Pro Automotive, Robert Juarez opened the access panel for the motor coupler and found the driveshaft spline had separated from the coupler flange. The good news is they were able to extract it from the rear by dropping the transaxle so I wouldn't need to disassemble the entire motor bay. The weld held just fine, but the metal just outside the weld let go. Robert fabricated a new flange from thicker higher strength steel so I'm hopeful that we'll get more than a year out of it. Unfortunately there are no photos of the new piece, but here's what the old one looked like. That jagged hole used to be the drive shaft spline fitting. Once again the electric stuff is no problem, it's the mechanical bits that bite you.

While the PorschEV was out of commission, I spent some of my holiday planning for the charging monitor I mentioned in the last post. Not surprisingly, just the right electronic bit turned up on eBay. This Dual LED Digital DC600V 100A Voltmeter Ammeter Voltage Amps Meter+SHUNT ships from Hong Kong and arrived shortly after New Year's about the same time the PorschEV came home. No free shipping this time, but $5.99 from the other side of the world is remarkable! 

As usual, the documentation is in pretty sketchy Chinglish, but I found this wiring diagram that helped (not sure where). I learned later that I needed to reverse the leads on the shunt to get it to display the Amps.

The shunt is rated for 100A and 75mV, so I couldn't just wire it into the existing traction pack wiring. I had a spare contactor and I used that to control a parallel
negative charging line so the shunt is out of play when the car is running.

With so much more going on in the rear compartment, I added another charge control relay in the same housing as the meter. It looks a bit messy since I used spade taps to attach multiple lines to the relay connections, but the function is pretty simple.

It is switched on by the relay in the AVC2 module when the charge cable is plugged in. It then passes 12 volts to close the negative line contactor and power the meter. It also energises the charge control relay in the front that closes the mid-pack contactor and powers the charger, DC/DC converter, and forward coolant pump.

It sounds complicated, and I should put together a wiring schematic so I'll remember all of it if something goes astray in several years. But for now, I'm delighted to have a means of checking the progress of a charge.

With the wiring and shunt tidied up, this area may look crowded,

but since most of it is black, it will disappear in use. The normal view of the charge monitor will be through the rear hatch glass.

I watched one charge cycle last night and it works perfectly. The voltage display increased through the constant current phase until it reached the 400 volt target, then held as the amp display moved down during the constant voltage phase until it reached zero. Checking the controller output with the laptop at that point indicated the charge was complete. Unplugging the charge cable removes power from the entire charging circuit including the charge controller, so it is reset and ready to start the next time the charge cable is plugged in.


  1. Why do you do this, Fred?
    Is it just gee-whiz or do you do something with the information?

    1. Hi Bill,

      I outlined the justification for this exercise in an earlier blog post (http://adventuresinevland.blogspot.com/2016/10/revamped-charging-for-porschev.html), but looking back I should have kept the explanation simpler.

      It's all about user feedback. You'll appreciate this when you get to the point of charging the Better Place Pack in the Doka (if Jack doesn't have you replace it with a Tesla pack). The Volt charger/EVTV controller combination has no blinky lights or status display to give you a progress check while the charge is under way. There is also no way to know when the charge is finished unless you have a computer plugged in. That's not practical at a public charging station and a nuisance at home.

      The voltage display on the meter tells me at a glance how far the charge has to go to reach its target voltage. Then when the amp display runs down to zero I know the charge is finished. The charger stops (and posts a message to the computer terminal display), but the coolant pump, fans, and charging station keep running until I unplug the J1772.

      The net is I've been spoiled by the Leaf and evTD, and wanted the same level of practical feedback for the Porsche.

      So gee whiz, that's what I do with the information! Call me if you'd like to discuss.