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EV Schematic · 28 October 05
In the last episode of Electronics for Dogs they covered the high voltage section of a typical EV schematic. It was missing a few things and, of course, didn’t cover any of the low voltage controls. Time to bring all of that together.
The last EV schematic I drew was in early 1996. Back in 1996 people were starting to think this internet thing might actually go somewhere and, what-the-heck, let’s buy some of this Yahoo! stock.
Well, I didn’t buy any Yahoo! stock but I visited them a number of times, sat in their giant purple and yellow chairs, and even wrote the software that served up Yahoo! maps and yellow pages for the first few years.
Those were the days.
The schematic from ‘96 was for the EV’s first controller, a Zapi. It was a really nice controller. Powerful, programmable, serving up to 800amps. But I had the regen lust. When I finally worked up the nerve and wiring to try out the Zapi’s regenerative braking the controller self-destructed. After a few customs mix-ups, countries going on vacation, and other comedy routines I ended up swapping it for a Curtis controller.
Curtis controllers have been around for quite awhile and are still sold today. It’s not the most powerful controller on the market, but it does a good job at an ok price.
If I were to buy a new controller today I’d give serious thought to the Zilla. C’mon who doesn’t want an electric car controller that requires a Hairball Interface? But seriously, the Zilla is built and supported by folks who’ve been making and driving EVs for a long time. They are also active on the EVList.
For now let’s concentrate on the wiring for the Curtis. I’ve reworked the old schematic and I think everything is more or less in place. There’s an extra high voltage relay which I can’t remember if I used before or not.
When you are making an EV the more safety cut-offs the better. Ditto with fuses. Since you never know what is going break you try to have enough redundancy in the circuit to cover your butt. Things like: what if the accelerator pedal gets stuck under the shag carpet AND a relay sticks on?
Solid Purple lines (top) are the high voltage positive, Solid Blue lines (bottom) the high voltage negative. Red for the normal car 12v line and the 12v ground is separate from the high voltage ground. The cool red symbol is an inertia switch. It’s an impact triggered shut-off switch, removing the control voltage from everything in the case of an accident.
Note that the Charger and EMeter are to the left of a relay. They are always hooked to the battery pack so we can charge them (of course) and monitor the charge state. No reason to have any of the other equipment hooked up when the vehicle is off.
There’s another addition to the circuit that I’d like to make but haven’t designed yet. Essentially I want to make it so that none of the relays get energized if you turn on the ignition while the accelerator is down. There’s a micro-switch hooked to the potbox (which is hooked to the “gas” pedal) as you can see, so either I repurpose that switch or add another.
Other electrical items not shown on this schematic would include the electric vacuum pump and probably some sort of magnetic or optical pickup to drive the tachometer.
I haven’t decided yet if I’ll go with a new heating system or not, so here’s the ceramic heater circuit. Ceramic heaters can be purchased pretty cheap from your local *mart. They have inverse resistance, which means the hotter they get the higher the resistance, keeping it from overheating. Still, it gets pretty hot and you don’t want to run it without a fan. If you look close at the schematic you’ll see that I added a wire to the car’s normal fan circuit, which forces the fan to at least low speed whenever the heater is on.
The heater worked pretty well, but on the wicked cold days after being in the office parking lot for eight hours it could take awhile to get the window defrosted.
The EMeter, which is now called a Link-10 and made by Xantrex, would be wired like this. The purpose of the DC-DC converter is to maintain the isolation between the 12vdc circuits and the high voltage pack.
I like the meter, although a bigger display showing volts and amps at the same time would be sweet. There’s a few new meters out that do this, notably the Batman II, but I don’t know much about them.
The EMeter started having problems towards the end of the last EV, which I’m suspecting were caused by corrosion and/or a bad DC-DC converter. It would register phantom current draw, even if I disconnected (and shorted) the wires from the shunt. Since current flow is used to track amp hours I would get into the car some mornings and find the meter in the red, even when I knew the batteries were fully charged.
Hopefully a new DC-DC and clean install will straighten it out.