Wiring

Since I'm an Electrical Engineer I expected the wiring of the electric truck to be a little easier than the mechanical parts of the project. I didn't run into any unexpected problems but it was a lot of work.

This is the schematic of my truck conversion. It is not up-to-date (as of 4/13/03) but I'm working on it. Click to link to bigger drawing.

There is no one schematic for each electric vehicle conversion. I had to take in bits and pieces from many different sources to come up with my final wiring diagram. For a good overall view of the EV electrical system I would recommend Convert It, by Mike Brown even though it is a little dated. The wiring diagram that came with my controller (DCP-600) was basically the complete schematic for wiring the high power system.

For wiring the 12v systems I got the Chilton's and Hayne's shop manuals for my Toyota truck but they weren't really specific enough on the wiring to be very helpful. Luckily I found a place online called books4cars.com where I was able to get the actual wiring manual from Toyota for my truck (Toyota Truck Electrical Wiring Diagram 1990 Model). If they don't show the wiring manual for your car send them an email, they were very helpful and were able to find the right manual for me. I found the Wiring Diagram manual to indespensible for connecting the trucks electrical system up to the wiring that I put in, it would have been much harder to do the wiring in my conversion without this manual.

The wiring is divided into two categories, the high power wiring for the electric drive and the low power 12v wiring for all the accessories:

High Power Wiring

The high power wiring needs to be designed to handle the eletricity that drives the truck. This can be up to 186v (when charging) and over 500A (when accellerating) of DC electricity. The wiring and the safety devices obviously have to be designed to handle these voltages and currents.

The batteries are wired together in series string using 1" x 1/16" copper bus bars and 2/0 welding cable. I purchased the copper from Online Metals already cut into 1" strips. I then drilled them, bent them and dipped the ends in solder (using a solder pot) to keep them from corroding. I also covered the copper bus bars in plastic heat shrink tubing to make them a little safer from shorting out during matainence. You'll notice that the shrink tubing is both black and red which unfortunately doesn't indicate polarity of the bus bars, I just ran out of black. The bus bars are bolted to the battery posts using belville washers which make it harder for the nuts to work loose. I also tighten all the connections every time I add water to the batteries. If any of the battery posts was loose it could heat up enough to melt down the lead post so it's a good idea to check them regularily. I think that the 1/16" copper is a little undersized for this application. When I check the bus bars after drivining the truck for a while they are warm to the touch. This means they are dropping some voltage and limiting the current to the motor. I have two choice to upgrade them, either add more copper (1/8" bus bars or double up on the 1/16" bars) or change over to 2/0 welding cable interconnect. The 2/0 welding cable does not seem to get very warm so there must be less current loss. The welding cable is terminated with lugs from EVParts. I used a very large crimper from work with dies for 2/0 cable. Each lug had some NoAlox antioxidant gooped in it before crimping to keep the crimps from corroding (I got it at MSC Industrial Supply). As you can see in the photo there is an inline fuse in one of the bus bars. This is a 500A/250V safety fuse from EVParts just in case something get shorted back in the battery box. The power from the battery box is routed to the front of truck using 2/0 cable again running through 1.5" PVC Hose to protect the cables under the truck.

The plastic hose with the power cables runs all the way up into the engine compartment in the front of the truck. The negative leg goes to the front battery box to complete the series string of 24 batteries. The positive leg goes to a 1000A circuit breaker mounted in the cab down by the clutch pedal where I can get at it while driving. I think it is important to have access to this breaker while driving in case anything goes wrong you can shut off the power from the batteries.

The power from the 144v series string of 24 batteries is routed to a large red Anderson connector before continuing on to the rest of high power circuit. This allows me to easily disconnect the high power electricity before working on the rest of the system which makes it much safer to work on. I feel that if it is easy to take this safety precaution then you are much more likely to do it.

After the main disconnect the high power from the battery is routed through a current shunt on the ground leg and then both the ground and positive legs are connected to high current contactors. These contactors are relays that disconect the 144v of the batteries from the rest of system when the truck is turned off (or connect the batteries when the truck is turned on). You can see that the contactors are only rated for 250A continous and the truck will draw more than that when its accelarating but it says that the contactor can break 2000A at 320V which is the important safety condition. Also contacts tend to get damaged when they arc which occurs when they open or close while carrying current. These contactors only open/close when the truck is turned on/off which is when they are carrying no current. You'll also notice that I used two contactors, on for the positive and one for the ground of the 144v. You really just need one contactor in the positive leg to break the circuit but from what I've read in the mailing list it is safer to have them in both the positive and negative leg because it cuts down on the possibility of a shock hazards when the truck is shut off. The main contactors are turned on by the motor speed controller the DCP-600. When the key is turned on the controller turns on and charges the main capacitors with 144v and then 1.5 seconds later it turns on the main contactors and 144v is connected through the controller to the motor. The reason for this sequence is that if the controller just turned the contactors on the capacitors in the controller would pull a large pulse of current to charge up and draw and arc across the contactor's contacts and cause them to wear down and pit over time. So by charging the capacitors first the controller avoids damaging the contactors. The current shunt in the ground leg is used for the Emeter which measures the state of charge of the batteries. I'll talk more about the Emeter in the instruments section.

The motor speed controller controls the speed of the motor and so controls the speed of the truck when you press down on the accellerator. It does this by regulating the amount of power that flows from the batteries to the motor. The DCP-600 was specifically designed for EV conversions and has a lot of nice features. I've already mentioned the capacitor precharge feature. It includes a throttle position sensor and a tachometer sensor with built in rev limiting. The rev limiting cuts power to the motor if it's revolutions get too high. This is good safety feature because the ADC motor that I'm using can destroy itself if it over revs. This is fairly easy to do if the motor has no load (the clutch is in) and full power applied (the throttle is fully depressed). The tach sensor is optical so I painted the tailshaft of the motor white and black and used that for the tach sensor pickup. I ran into problems because I mounted the tach sensor to the truck frame. It turns out that the motor moved around enough on it rubber mounts that it actually knocks into the tach sensor. This caused wrong tach readings which cause the motor controler to cut out because it thought the motor was over reving. To fix this I need to mount the tach sensor to the motor but to get to it I would need to remove the front battery box so its on my list of things to do. I just disconnected the tach sensor for now. Another possible problem I ran into has to with the contactors that I'm using. I read in the mailing list that the contactors use PWM to cut back on their coil current (they call it economizer). This creates electrical noise that could interfere with the tach sensor and/or the throttle sensor. So I used and EMI noise suppression core on both the throttle sensor cable and the tach sensor cable. I just wrapped the extra cable through the core and I don't seem to have any noise problems.

I used the application schematic from the controller documentation as the basis for wiring design. The controller needs 12v to power up when the ignition key is turned to start the truck. I was able to use the Toyota Truck Electrical Wiring Manual to find an unused wire that was energized to 12v when the ignition key was turned on. I highly recommend getting the wiring manual for your conversion. I pulled out hundreds of wires from the truck when I took the engine out. There is no way I would have been able to find a circuit to energize the controller with the ignition key without the wiring manual.

The throttle sensor is is mounted to the main electronics plate. The throttle cable is attached to a bracket I made and then connected to the throttle sensor arm. Don't worry if the throttle sensor doesn't have compete travel when you depress the accelerator, there is an adjustment on the motor controller for maximum throttle travel. There is also a safety cutoff if the throttle sensor is not in its lowest positition (the throttle is completely let off). This keeps the controller from sending any power to motor if you are inadvertantly stepping on the throttle pedal when you turn the controller on. This caused me a problem in that I orginally only had one return spring on the throttle sensor that wasn't strong enough to pull the sensor all the way off. So a couple of times I couldn't start the truck until I opened the hood and manually pulled the sensor all the way off so that the controller would start. I fixed that problem by adding another spring. Two springs are also a good idea in case one breaks.

The 144v from the contactors is connected to the motor controller through another current shunt. This is used to measure the motor current and is displayed on an anolog meter in the cab. The motor controller is uses 2/0 cables to connect to the motor directly below the electronics mounting plate (see the electric motor section).

The charger I used is the the PFC-20 from Manzanita Micro. The charger in an EV conversion is used to charge the 144v DC battery pack from 120v or 240v AC residential power. The PFC-20 is a great charger, it can charge EV battery packs from 12v to 360v and it can do it from either 120v or 240v AC. It's really nice to be able to charge from both 120v and 240v, you can almost always find a 120v outlet and get over 2000 watts of charging but at home I can connect to the 240v outlet in my garage and get over 3000 watts of charging. (The PFC-20 limits the charging current to 20A on the input or the output whichever is higher so in pratical terms at 120v AC charging the input current is limited to 20A, so 20A x 120v = 2400 watts maxim, on 240v AC charging the output current is limited to 20A to the battery pack charging at 150v, 20A x 150v = 3000 watts). The PFC-20 also has a knob to control the charging current so you can turn it down to avoid tripping breakers or overheating power cords. This charger can also draw more power out of a standard AC outlet than some other chargers because it is power factor corrected. Power factor is the term that describes smoothly the charger draws the AC current out of the outlet. Most less expensive chargers tend to draw the current out in gulps which means they have a bad power factor. This tends to heat up the circuit breakers and causes them to trip at lower currents than their rating, so if you're charging your car you can't get the full 20A from a 20A breaker. Power factor correction smooths out the current draw from the AC outlet so you get the full 20A out from 20A breaker. The AC input connector is on the front left bumper of my truck. A lot of people put the AC input behind the old gas filler door but the way I park in my garage it's easier to get to the front bumper. I used a 30A 125v marine power inlet with a watertight door for my AC charging port. After a year I've been having some trouble with the contacts overheating at high currents. I talked to the guys at work and they said that I need to retighten all the wires in the plugs every year because the copper wire can cold flow and not make good contact. If you don't have good contact the resistance of the connection goes up and the metal contacts will overheat.

To run the rest of the 12v system on the truck (lights, radio etc) I installed a 12v deep cycle battery in the former starting battery position on the left side of the engine compartment. To keep this battery charged I installed two DC-DC converters from Peak to Peak Power in a plastic Hoffman box. These converters drop the 144v DC from the batteries down to 12v at 12A to keep the 12v battery charged. One stays on all the time and is set to 13.5v to keep the 12v battery charged. The converter is switched on when the truck is turned on. It's set to 14.5v to boost the 12v system up to voltage that a normal car shows when its running.

The plastic box has a fan for cooling and also holds four relays. One relay turns on the 12v fans in the battery boxes whenever 120/240 AC is plugged in for charging. Another relay is the charger interlock, it keeps the truck from being turned on and driven away with the AC cord still plugged in. The other two relays are designed to switch high voltage DC(Tyco/Potter & Brumfield PRD-11DY0-12). They have a magnet to keep an arc from forming while switching. One of these relays switches the 144v DC to the DC-DC converter when the truck is turned on. The other relay switches the high voltage DC to the heating element for the truck heater.