Electronic Challenges

There were many challenges of all different sizes for our electronics system. There was first trying to figure out how to make a solar car run only on solar power, and then how to run the motor. We'll start at how the car gets all of its power - the solar panels.

How much solar power do we need?

Solar panels on top of vechile

As much as we can get. The more solar power our car can get, the more it can run. If we had the surface area to put more solar panels, we could essentially put enough solar panels to have the car run directly off of them. But this isn't the case, and we were limited to mounting only 2x 200 watt panels. So we have to deal with only 400 watts of power. There are a couple more locations we could have stuck solar panels, like on our front bumper and on the dashboard, but this didn't get done in time. We also contemplated having butterfly doors that would have solar panels on them, so when we were parked the doors could open up and the vehicle could charge faster.

How will this energy be stored?

D Batteries

There are many different kinds of batteries out there, such as Lead Acid and Lithium-ion. We chose Nickel Metal Hydride batteries (Ni-MH). One of the cheapest sizes these batteries come in is your standard D size battery. So we ordered 60 of these to try and test them out on our 72v motor (see mechanical). They are 1.2v and 10 amp hours each, so 60 batteries would produce 72v and 10AH in series.

Tubes Closeall tubes

We weren't sure on how these batteries would be stored, having hundreds of D sized batteries and having to wire them together is a big challenge. The batteries with standard terminals are ~$8 each, and the ones with solder terminals are ~$9. We decided to get batteries with standard terminals and put them into PVC tubes which hold them quite securely. We then had to figure out how to hold the terminals together since they were going in a moving vehicle and could shift around in the tube if there wasn't any pressure on them. We decided to drill holes into the PVC caps and to put a spring on the negative side of the battery terminal so they would stay together. The positive cap was cemented to the PVC tube, and the negative was secured using Velcro. Fifteen batteries were put into each tube, and four tubes where hooked together. We used 300 batteries in total, which are 20 tubes. The image on the right shows how these tubes were wired together.

Later on research told us that we are loosing up to 50% efficiency by having so many small cells. Woops. The alternative was using much heavier Lead-Acid, or the extremely expensive Lithium-ion.

From solar panels to batteries

Canadian Charge Controller

The solar panel doesn't directly plug into the battery packs, it has to be regulated and conditioned by something known as a "charge controller." The charge controller takes the input of the solar panels at ~24v, and outputs enough power to charge the Ni-MH batteries (at 84v). We had a very hard problem in the beginning trying to find a charge controller that took 24v input, and outputted 72v to Ni-MH batteries. Every charge controller on the market is meant for solar installations that use large Lead-Acid batteries, and even the ones we found for Ni-MH would only charge up to 60v. So we looked north to Canada, where a small company called Solar Converters Inc makes custom solar charge controllers. We called them up, gave them the details of what we needed, and to them our order was "standard." We got our controller 3 weeks later and it is as solid as can be.

Controlling the motor

Alltrax mountedAlltrax on top of motor

Unlike certain solar car teams last year, the solar car 2008 needs to have a unit called a "speed controller" to regulate the speed. The speed controller takes power inputs from the batteries and decides how much power will go to the motor which is controlled by the food pedal. Initially, the electronics person who caused 3 fires by building bad speed controllers wanted to build the controller himself. We gave him a deadline of 4 weeks to finish this controller and demonstrate it, or we would buy a controller from a company who we used in the past.

He failed to meet the deadline, and we went and bought a speed controller. But in the process of inquiring about the controller, the generous company Alltrax Inc decided they'd like to donate one to us. Our would-be $800 controller was now donated! The winning solar car team in 2007 used an Alltrax controller and never had a problem, so we were sure this thing would work for our much bigger car. When we first received the controller we wired it up outside of the vehicle, and when we pushed the pedal down it was so beautiful - the motor turned with great response to the pedal. Because of the extremely high voltage throughout the system, we used heavy wires which were 4 gauge. We tried to mount everything close together to reduce resistance, so the controller is mounted above the motor (picture above). Thanks once again to Alltrax for the awesome controller!