Friday, April 17, 2015

EVSE Tester user guide

EVSE Tester on the Geppetto Electronics Tindie store

This page is the permanent home for the EVSE Tester users' guide.

The EVSE Tester allows you to exercise an electric vehicle charging station (EVSE) in various ways, and will display the state of the pilot signal, including the J1772 ampacity indication.

To assemble the quick kit, first install the three through-hole components on the board. Start with the 2x3 pin shrouded DIP header. It goes in the ISP socket. Be sure to mount it with the open side facing pin one, which has the square pad. Next, install the 2 pin screw terminal in the pilot block. Be sure to mount it with the openings for the wires facing outwards. Lastly, install the DIP switch block. It should be mounted with "ON" being down, though this is optional depending on how you want the switches to work.

Once all of the rest of the through-hole components are mounted, it's time to mate the display to the board. Start by laying the display face down on the workbench. Install the 16 pin SIP header, but do not solder it yet. Lay the logic board on top with the pins of the SIP header protruding from the back side to the component side of the board. Again, do not solder the SIP header yet. Next, lift the logic board slightly at each corner and place a spacer. Install a 2-56 nylon bolt into each corner hole so that it passes from the front side of the display, through the display, the spacer and the logic board. Secure each with a nut. Once the display is physically attached to the board completely, make sure the SIP header is positioned so that each pin is all the way in both boards you can solder each pin to both. Assembly is now complete. Apply power and adjust the contrast pot so that the LCD text shows up the best. The correct position will be close to, but not quite at one end of its turning range.

The EVSE Tester requires 6-12 VDC @ 200 mA supplied via a center-positive 2.1mm barrel connector. The power supply is required for the display only. Using the DIP switches to simulate the states of an electric vehicle alone does not require power.

The two pin screw terminal at the bottom center of the back connects to the ground and pilot terminal of a J1772 EVSE plug. The ground terminal is the large connector at the bottom. The pilot is immediately to the right of the ground, when looking into the plug.


Do not attempt to connect anything to the J1772 connector hot lines, which are the two large pins at the top (opposite end from the ground) of the plug. You must assume that 240 VAC power may appear on those pins at any time - possibly as a result of a malfunction. Contact with the hot lines while energized may result in serious injury or death.

Before attempting to connect the EVSE tester to a J1772 plug, switch the four DIP switches to their off position.

Connect the pilot and ground terminals to the EVSE using 22 gauge stranded wire. On the J1772 end, strip about a half inch and twist the strands tightly to avoid frayed endings. Bend the ground wire back on itself where the bare strands emerge from the insulation and insert into the ground pin. Insert the pilot line into its pin without bending. Some electrical tape can be used to secure the leads if necessary.

At this point, the EVSE should be in an idle state, with no indication that a vehicle is present. The tester display should show 0 Hz and a +, indicating that the pilot is pinned to a continuous +12 volts. If the display shows - instead, then it is possible that the EVSE is in an error state (with a -12 volt pilot signal) or is not connected properly.

Flip the "A" DIP switch on. The EVSE should indicate that a vehicle is present, but is not requesting charging. The display should change to show 1000 Hz (possibly +/- 20 Hz) along with a duty cycle and amp rating that corresponds with the expected value from the EVSE in question.

Flip the "B" DIP switch on. The EVSE should indicate that the vehicle is requesting charging, and will energize the hot lines. WARNING - As stated above, the J1772 plug is in a potentially hazardous state when the power is turned on, but the plug is not inserted into a vehicle. Do not attempt this function in inclement weather conditions or with anything inserted into the hot line pins at all. The display should not change.

Flip the "C" DIP switch on. The EVSE should react as appropriate for a ventilation request. What this means will depend on the EVSE. Most will indicate an error. Some will do nothing differently at all (particularly if they're intended to be mounted only outdoors).

Note that it is incorrect to ever have the "C" switch on if "A" and "B" are not also on. Similarly, it is incorrect to have "B" on if "A" is not also on. Always turn on the A-C switches in order and turn them off in reverse order. Doing otherwise won't damage anything, but will expose your EVSE to out-of-spec state transitions.

At any time (other than when all of the A-C switches are off), you may flip on the "D" switch to simulate a "missing" pilot diode. The pilot diode is a safety feature that allows the EVSE to distinguish between a vehicle and simply dropping the plug into a bucket of salt water. Flipping the "D" switch on should result in an immediate error condition on the EVSE. If it was supplying power, it will stop.


If the display is dim, adjust the contrast knob with a small screwdriver. The correct setting should be near, but just short of one end of its rotational range. If that doesn't fix it, check that the input DC voltage is between 6 and 12 volts. While the EVSE tester runs internally on 5 volts, the power supply is dropped to that level by an LDO on the input which requires 6 volts or more to function properly.

Theory of operation

The pilot terminal is connected to the A-C DIP switches and then to the three state resistors. The three state resistors are then connected to a diode and then to ground. The D switch connects across the diode, to short it out, removing it from the circuit.

The incoming pilot signal also is fed through a second diode with a 100K pull-down resistor into a LM393 comparator. The diode is necessary to protect the comparator from the negative excursions of the pilot signal. The incoming pilot signal is compared to a 1 volt reference from a voltage divider. The comparator output is fed into the controller.

The controller is an ATTiny84 clocked at 16 MHz (it is crystal controlled not because it needs to be fast, but for maximum measurement accuracy). It is connected up to 6 pins of the LCD display and the comparator. Three of the display pins are shared with the AVR ISP programming interface. There are 1K protection resistors in front of the display to insure it cannot interfere with programming.


Wednesday, April 15, 2015

See you at Bay Area Maker Faire

I'll have a table at the Bay Area Maker Faire May 15-17. I'll be giving live demos of hobbyist reflow with my own Toast-R-Reflow oven. I'll be making little 1" round earring/pendants with blinking LEDs in your choice of color (red, green, blue or white). If you wish, you'll be able to take those over to the SteamyTech booth and get a laser-cut enclosure for them. I'll also be making and selling Toast-R-Reflow controllers and power board kits and will have crazy clock and USB ┬ÁISPs and Pi Powers on hand for sale as well.

I've got Square, so credit cards and cash will be accepted.

Wednesday, April 8, 2015

OpenEVSE II / Hydra developments

It looks like the pilot generator that I've been using for OpenEVSE II and the Hydra isn't always 100% reliable. My guess is that the biasing I am doing is too near the edge of the tolerances of the parts and some transistors work and some don't.

To fix this, I'm going to change out some of the parts. To follow along, look at sheet 2 of whatever schematic you like.

The pilot generator has two pairs of transistors, an output pair that switch +12 or -12 to the output, and an input pair that switch the output pair on and off depending on the state of the logic level output from the controller.

The resistors from the emitter to base of each of the output pair will change from 1k to 47k. The resistors from the base of the output pair to the collector of the input pair will remain at 10k. The resistors from the base of the input pair to the pull-up will change to 10k, and the pull-up will change to 1k.

This will result in a decrease in the collector current of the input pair coupled with an increase in the base current. The hoped-for result will be a more solid, assured entry into saturation for the input pair. My thinking is that the problems some folks are having are centered around incomplete turn-on of the input pair, which results in nothing on the output pair for either + or - 12, which winds up causing diode check errors or invalid states, or cars being upset with the pilot or what-not.

Additionally, I have a new design which will replace the four transistors and their bias resistors with two pre-biased complementary pair transistor modules. The whole thing will shrink down to 2 TSSOP-6 packages and a single pull-up resistor.

Also, another revision I've decided to make is to go back to the 20k (instead of 16k) resistor value for the low side of the voltage divider for the GFI comparator. But I'm also going to add a 10k bleed resistor in parallel with the peak-hold cap so that the self-test settles much faster after completion. I'm going to remove the peak-hold cap entirely. Since the GFI signal simply interrupts the controller anyway, there's really no reason to hold onto the peak value. The downside is additional interrupts, but those extra interrupts effectively do no harm, since all they'll do is turn the relays off again. I'm also removing the diode and pull-down from the output of the comparator. Since the LM358 is being fed with the 5 volt (and ground) supply, there's no need to protect the controller from negative excursions.