This page discusses the onboard charging system for my Toyota MR2 EV.

Russco 24-120 Charger and boost transformer
Russco 24-120 Charger and boost transformer
Russco Charger Installed behind passenger seat
Russco Charger Installed behind passenger seat
boost transformer installed in engine compartment
boost transformer installed in engine compartment
Marine shore-power plug for charging in old gas cap location
Marine shore-power plug for charging in old gas cap location

The onboard charging system allows the car to be plugged directly into grid power for recharging the batteries. Some EV's (including most of the factory built ones) were built to be charged from an external, wall or kiosk-type charger, but these are hard to come by, and that may limit your driving options to within round-trip distance of your home. By having an onboard charger, I can recharge anywhere that has electricity, at the expense of a few pounds of extra weight, but that means that (time permitting) I can recharge at my destination, allowing trips farther from home.

The Charger

The Russco-branded battery charger is about the most economical EV battery charger you can get. It is adjustable to support a variety of battery configurations. I ordered mine with a timed shutoff feature and an external boost transformer, necessary since my pack voltage will be higher than the 110-volt line voltage used for charging. (I will eventually be running a 136-volt traction battery pack)

The charger is mounted behind the driver's seat so that it can be reached for adjustment and monitoring. It doesn't need to be visible when the car is being driven. I had to make some Chassis Modifications to allow space for the charger to be mounted. The boost transformer will be located in the engine compartment, just behind the charger.

The Plug

It was easy to make the old gas filler neck and fuel door into the charging port for the car. I used a marine-style 30A, 110VAC plug (round style, with three prongs, twist lock). A simple plastic sheet cut to size and drilled out mounts the plug to the location of the gas filler neck. I will carry an extension cord with the right style of plug around to allow opportunistic charging. I'll set up some sort of basic charging kiosk as well in my carport, for convenience.

Interlocks and Safety

In addition to simply charging the batteries, the charging system in my car incorporates a couple other functions. There is a light on the dashboard that comes on when the car is charging. A relay closes that will prevent the ignition from being turned on. And, a ventilation fan will run to vent hydrogen gas from the tightly sealed front battery compartment. All these accessories are powered by a wall-wart style power supply, that is wired into the 110VAC supply to the car. It is protected by a GFI and a one amp fuse. The GFI and power supply are located under the driver's seat.

There are laws on the books that say any onboard electric vehicle battery charger must include a ground-fault interruptor. There is one built in to my Russco charger. I have added a second one, along with a small fuse, in the circuit that powers the charging indicator light, ventilation fan, and charge interlock relay

Charging indicator light and interlock relay

The Charging indicator is simply a lamp that lights up on the dashboard whenever the car is plugged in. This gives a quick, visible-from-outside indication that the car is charging. The interlock relay is wired in a normally-closed configuration, so that powering up the charging system will open the relay. When open, the EV Control Electronics that power the main and reversing contactors are disconnected to prevent the car from driving. A better setup would be to have a kill switch on the gas filler door, but that would have been more work.


Parts for creating the ventilation fan: one electrical outlet box and one 12-volt computer cooling fan
Parts for creating the ventilation fan: one electrical outlet box and one 12-volt computer cooling fan
Front compartment ventilation fan, completed and attached to bulkhead.
Front compartment ventilation fan, completed and attached to bulkhead.

Ventilation fan

Charging lead acid batteries can produce hydrogen gas. Hydrogen gas, plus oxygen gas (present in the atmosphere, duh) plus a spark, equals Kaboom. That would be bad. Think Hindenberg. My frontmost and rearmost EV Battery Racks are mounted in compartments of the car that are open to the outside environment, so any hydrogen gas that is generated will dissipate safely. However, the 5-battery rack that is located in the front trunk compartment of the MR2 is fairly well sealed in. Because of this, I decided it would be a good idea to incorporate a ventilation fan to pump out any hydrogen gas that is generated.

I removed two rubber plugs at the bottom of the tub area, below the battery rack. This will let in air at the bottom of the compartment (and also allow me to hose off the battery pack and have the water drain out easily). I installed a small fan (the same type as you find in a computer power supply) at the very top of the trunk compartment (where the hydrogen will collect, since it is less dense than the rest of the atmosphere) to pump out any hydrogen that collects.

The fan is attached to a small cowling (made from a plastic electrical box for a light switch or 110v plug) and this entire assembly is screwed to the back of the trunk wall. I cut a hole in the trunk wall through to the vent cavity where the windshield wiper linkage is, and where the fresh air intake for the cooling system is. The fan is wired such that when the car is charging, or when it is running, this fan will be running to pump out any gases that collect. I suppose I could have just cut a couple vents into the hood as well, but that seemed a bit uncouth.