You will find articles organized by categories, along with recent comments, along the right hand column of the website. If you are just getting started with the idea of converting a gas car to electric be sure to check out Your First Electric Car
Welcome and enjoy!
Schematic Update · 15 December 05
The rest of life, home and work, has been keeping me busy lately which translates into less tangible work on Eve.
Still working on shoe-horning the electric heater assembly into the old A/C box such that all of the air goes through the heater cores and is safely away from the plastic side-walls. Also, before doing much of the installation and wiring of the heaters I needed to update the schematic.
Being more of a visual thinker I tend to do “what-if” designs first, sketching out schematic ideas on paper or a whiteboard. When that finally looks good it’s much easier to implement the real thing.
After a few experiments and false starts here is the updated schematic for the heater circuitry.
We are using two ceramic heaters this time. Do we turn both on at the same time or provide individual control? Having both is good when you need to blast the defroster, but is probably too much (too much current and heat) when merely trying to take the edge off the cold.
It takes an extra switch and relay to add the additional control, which isn’t that expensive in the grand scheme of things. I’ve wired it such that you can leave the “high” switch on all the time and just turn on/off the main heat switch.
This schematic shows the second ceramic heater with the positive lead going through a separate relay. We use relays because these are high current and voltage lines: 144vdc with up to 15 amps when going full blast. Our 12vdc line is used to control the relays and remains separate from the high voltage.
Also note the addition of a thermal switch. That’s the funky looking thing with “Thermal” next to it. Since a couple of them came with the ceramic heaters it seems a pity not to use them. Not sure yet on the placement, will have to experiment, but the idea is that the switch opens up if the heater mounting area gets too hot.
Since I was updating schematics I’ve gone ahead and added a safety interlock to the main high voltage schematic. Reader, Alvan, was kind enough to send a schematic proposal for the interlock, which I’ve modified a bit and integrated into the design.
For those who have seen the earlier schematics I should note that I’ve updated the colors as follows:
- RED – 12vdc positive
- BLACK – 12vdc ground
- PURPLE – 144vdc positive
- BLUE – 144vdc ground
Let me try to explain the circuit.
When you turn on the ignition the 12vdc goes through a fuse and one or more safety interlocks like the inertia switch shown here. It could also go through a hood latch detect and a relay energized when the charger is plugged in. The idea is that anything which shouldn’t be “true” when you go to start the car is used to inhibit this control line.
The potbox is hooked to the accelerator pedal and when you press on the “gas” the switch closes. The switch has normally closed (NC) and normally open (NO) contact positions. the NC lead to an interlocking relay setup. If you don’t have the pedal pressed the relay will energize via the bottom 12vdc. If the pedal is pressed, then the relay doesn’t turn on and the high voltage line stays disconnected.
Once the interlock relay energizes it provides its own “holding” voltage. You may also notice that the bottom left high voltage relay (I should number these) turns on with the ignition: meaning the DC-DC converter and heater turn on immediately. The other high voltage relay only turns on when the accelerator is engaged.