Saturday, September 3, 2016

evTD Refinements

WARNING! ACHTUNG! Long and involved post ahead. You have been warned!

Truth to tell, the final days of construction on the evTD were pretty frantic. I had a deadline to leave for EVCCON 2012, and I might have taken a few shortcuts. I've also learned a thing or two in the four years since she became roadworthy. This became most apparent several months ago when I had a gentleman from Germany who was very interested in purchasing the car. The deal fell through as we learned that the German Dept of Motor Vehicles was intent on making it impossible to register any imported one-off vehicle. As part of the process I wrote a user's manual to support the sale. Documenting the steps for each simple action it became clear that things weren't so simple:


  1. Pull out the Emergency Stop Switch to close the main contactor
  2. Connect laptop computer to Charger Controller with USB cable
  3. Using an ASCII terminal program as outlined in the TC Charger User Guide, check and reset the charging values if necessary. I generally charge to a Target Voltage of 256 volts (approximately 3.55 volts per cell), a Target Current of 20 Amps, and a Terminating Current of 5 Amps.
  4. If charging from the Alternate NEMA L6-20 Inlet Port, connect both ends of the charge cable before turning the white auxiliary charging switch to “ON”. This prevents arcing at the plugs when applying power.
  5. If charging from the J1772 Inlet Port, open the cap on the inlet and insert the J1772 plug until the catch snaps into place. Ensure that the NEMA L6-20 plug from the J1772 inlet is plugged into the alternate inlet port, then turn on the white auxiliary switch. Finally, turn on the toggle switch on the J1772 Inlet box to begin charging.
  6. When charging is complete, turn off both switches on the inlet boxes and push in the Emergency Stop Switch to open the main contractor before removing the charge cord.
That's a far cry from my ideal scenario - just plug it in.

The Law of Unintended Consequences now comes into play. The AeroVironment TurboCord  made the NEMA connection redundant, so out it came. In its place, I installed a nice sealed 12 volt battery for a Mazda Miata that fit really nicely in that space. I'd been running on the DC/DC Converter only since I had installed the NEMA box, and it seemed that it would reduce wear and tear if the battery supplied the power for those things that run even when the car is off. Those things are called parasitic loads for a good reason - they'll suck the life out of your 12 volt battery in no time at all.  One startup failure showed me it's not good to let your auxiliary battery run down to 3 volts keeping the radio, GPS speedometer,  JLD404 volt/amp meter, and AutoBloc AMP fuel gauge driver powered up. 

Then there's the emergency switch. You may recall an earlier mishap with this thing. At the time I rewired it so it wasn't carrying the full 12 volt load, but it was still an extra step to pull it before turning the ignition switch or charging and push it back in when you're done.

Finally, what's with the charging controller losing its memory settings so the laptop is necessary for each charge? I had wired the positive lead to an unswitched 12 volt and the little computer chip set was apparently subject to some surge issues while the car was running that erased its settings.

So here's the plan: build a little circuit box that takes over the control of the 12 volt battery, the emergency switch, and the charge controller. All of that is predicated on rewiring the emergency switch to a switched circuit so it will automatically energize the main pack contactor when the key is switched on. That eliminates the Soliton1 controller error that causes an annoying error light when I forget.

This all took a great deal of head-scratching time and one important little electronic component.

Found this on Amazon and figured for $15.00 how could I go wrong? It's an XINY Voltage Control Relay. It's one of those amazing Chinese gadgets that does all kinds of magical things with free shipping and absolutely no documentation. A bit of Googling around turned up a few documents in Madarin and this one in English. You're welcome.

The function I use is the voltage triggered relay that engages when the voltage reaches a preset lower value and then disengages at an upper value. I have it set to kick in the main pack contactor when the voltage drops below 12 volts which runs the DC/DC Converter until the voltage reaches 13.4 volts, then removes power from the contactor.

While I was at it, the same thing can be done with the charger, so I added some circuitry to manage that as well. I have a Tucson EV J1772 Adapter Box that I bought back in 2011 for the eBugeye. It has a simple toggle switch controlling the J1772 pilot signals, so I moved that function to a relay so the switch could also control power to the Charge Controller. Since the hood must be raised to charge anyway, one switch didn't seem so bad. I may move to an AVC2 controller in the future, but for now this is fine.

The circuit winds up looking like this:

I know it's not SAE spec, but it works for me figuring out logically what goes where. In real life, the box wound up looking like this:

The black box at the top is the J1772 Pilot Signal relay and the smaller black box below the terminal block is the diode to prevent the charge controller from getting power during other operations.

The XINY voltage control relay is mounted to the lid and wired to the terminal strip inside. I'll build a housing for the XINY that shows only the voltage LED, but for now it's still a pretty tidy installation.