A while back, I had gotten a PowerWheels Jeep, but it didn't have a battery or charger. And it always seems that these toy cars end up getting left outside anyways, AND it's a little bit of a pain to pull out the battery to recharge.
Since I already built a full-size electric car AND I am interested in renewable energy, this was the perfect chance for me to build my own low-voltage SOLAR-POWERED ELECTRIC CAR!
The project integrates the PowerWheels with a battery, PV Solar Panels on a custom rack, and a solar charge controller, to design a child's solar-electric car.
Let's get started!
Step 1: Tools and Materials
Here's the Materials:
- Fisher-Price POWER WHEELS ride-on toy or similar
- 20AH, 12V sealed lead-acid battery
- 2 ten-foot sections of 1/2" electrical conduit (for the solar rack)
- Harbor Freight 45 watt Solar Panel kit or equivalent ( http://www.harborfreight.com/45-watt-solar-panel-kit-68751.html )
- 8 x 1.5" stainless steel 1/4-20 machine screws, with matching washers and lock-nuts
- 2 x 5/16" x 5" bolts with matching fender washers and lock-nuts
- 2'x1' of plexiglass, plastic, or other sturdy, waterproof material
- Scrap tubing to make spacers
- Self-tapping sheet-metal screws
- 4 x mending plates
- Assorted electrical connectors, ring and spade terminals
- 30-amp in-line fuse
- Spray paint
- Tape measure
- Drill & assorted bits, including screw-driving bit
- Pipe cutter
- Angle grinder and vise
- Wire strippers and crimpers
- Wrenches and Sockets (7/16" and 1/2")
- Typical safety equipment and PPE (work gloves, safety glasses, hearing projecting, etc.)
Step 2: Get a POWER WHEELS
The one I am using is the JEEP COMMANDO. It's a simple, boxy vehicle with a steel frame under the plastic body.
Instead of spending good money to buy a POWER WHEELS, first check at rummage sales, classified ads, and Craigslist. Used POWER WHEELS usually go for about $50, and it you really look around, you can get them for free.
For example, I got mine for free by placing an ad on Craigslist for "WANTED: POWER WHEELS, working or not..." I originally intended to modify it for use for adult POWER WHEELS Racing, but ended up helping out on a friend's entry instead. (The Jeep DID get used as a pace-car!)
Often, chargers get lost, and batteries are not taken care of and go bad. At that point, many owners are happy just to get rid of the car for free. So, look around, you might now even have to spend any more than the legwork to get your base vehicle!
Not all these cars are the same. Some have more or less structure under the plastic body. Look for one with a good steel frame, that will be easy to attach an overhead rack to.
Chances are that it's been sitting around getting dirty. Help your child take ownership of the project by having him or her wash the car. You may just end up getting more wet than anything, but kids can do more than you think they can - at least let them try!
Step 3: Solar Components
Harbor Freight sells a solar panel kit which is a good set-up for learning about and experimenting with solar power. The solar kit can be purchased for as little as $150 when it's on sale, or you have a good coupon. Knowing that I wanted to learn more about solar by using it, I bought one of these sets when there was a good price on it.
Included in the kit is 3 15-watt amorphous PV panels, a solar charge controller, and two 12V compact fluorescent light bulbs and sockets. The kit is designed for you to supply your own battery and have a small "off-grid" setup, handy for adding electric lights to a remote shed for example.
The solar panels produce electric current, which will be used to recharge the toy car's battery. You simply need to make sure the panels face the sun, and are solidly bolted down to whatever you mount them to.
The charge controller regulates power from the PV panels to the battery, to prevent overcharging. It also has a built-in volt-meter display, and connections for 12V power, including plugging in the 12V bulbs that come with the kit.
I already had a 12V 20 amp-hour battery around. This battery is small enough to fit in the POWER WHEELS battery compartment without modifying the car. Also, each of the solar panels can output one amp. So, if both are in parallel, that's 2 amps of output. Most common batteries shouldn't be charged at a rate faster than 1/10th of their capacity. For example, a 10 amp-hour battery shouldn't usually be charged at more than about an amp. The output of the two solar panels is about the right rate for charging the 20AH battery.
Although the Harbor Freight kit includes 3 solar panels, that's more power than needed for this project, and two panels is the right size for the roof of the car. Save that third panel for some other awesome DIY project.
Step 4: Building the Solar Rack
The top of the rack needs to be a size to match the solar panels, while the bottom of the rack needs to line up with solid points on the frame of the vehicle.
To start with measure the frame of the vehicle. You may need to remove the plastic body, or at least disconnect it and pull it partially up to get access to the frame. The Jeep has easily accessible push-nuts that hold the body on.
Once you have identified the length and width of where the solar rack with attach to the vehicle frame, write it down.
Drill holes through the plastic body (5/8" spade blade worked well) directly above where the rack will connect.
Next, measure the size of the solar panels, particularly noting any holes or slots that are used as attachment points. You will want the conduit to line up with those points so that the rack holds up the PV panels, but also allows for a bolt or screw from the panels, through the frame to secure it in place.
Depending on your car and solar panels, your rack may be an odd shape, like an old-fashioned football goal-post, a ladder, or some shape other than a rectangle. That's OK, as long as the top fits the solar panels, and the bottom fits the POWER WHEELS.
Cut 1/2" electric conduit to the correct length to build the top portion, which will fit the solar panels. I found that a plumbing pipe-cutter works really well to cut 1/2" conduit. It's safer and quieter than power tools, and leaves a very clean cut that really doesn't require any other filing or finishing.
Weld the conduit together, and lay your solar panels on top to confirm that they fit correctly.
Now you will want to measure how TALL your rack is. You may want to get your little tyke out to the car and see how much room they need to get in and out of the car, allowing plenty of room so they don't bump their head. Remember to leave room for them to grow taller!
Cut four pieces of conduit to the height you chose.
Weld the conduit to solar rack, with the rack laying on the ground, and the "uprights" straight up from it. Flip the rack over and it should look roughly like a pickup truck ladder rack.
Grind down any bad welds, fill in any holes, and then paint the rack. I like Rustoleum Gloss Black spray paint. It always looks nice, seems to hide bad welds, and in this case, matches the trim and tires on the Jeep.
Step 5: Attaching the rack and solar panels
Line up the four uprights of the rack with the four holes, and insert it through the plastic body of the car. You might need an assistant to help you with this - it's hard to hold the rack and line up all the holes at the same time.
The bottom of the rack uprights SHOULD line up with the steel frame of the vehicle, and rest right on them.
Now, hold the rack in place, and FLIP the entire vehicle and rack UPSIDE-DOWN. This puts it at an ergonomic working height and makes it nice and stable, similar to flipping a bicycle upside-down to change a tire or fix the chain.
Use your drill, drill-driver, self-tapping screws, and metal mending plates to attach the PV rack to the car frame. It works best to drill a small pilot hole (1/8") through both the mending plate and the frame or rack and then drive in the metal screw. Once you have attached all four points, you should feel that the rack is very rigidly attached.
Alternatively, for a more permanent attachment, you COULD weld the rack to the frame, but it is a little tight to get a welder in there, and all plastic components must be protected from the welding heat and sparks. (*If not completely covered and protected with welding-proof material, the body WILL melt!*)
Flip the entire car back over onto its wheels.
Now you are ready to attach the solar panels.
The panels that I used do NOT have a particularly good means of attaching them to a rack. The extruded aluminum frames do have a slot and a lip that a tee-shaped fastener could be hooked into.
I searched the hardware store for an appropriate fastener, but couldn't find any. So, I made my own.
I used 1/4-20 machine screws that had a larger-size head on them. The head was about the right size for inside the aluminum extrusion, but was a little too big to fit directly in. By grinding off a bit of one side of the head, I was able to insert the screw head into the frame.
Once inside, the screw is ROTATED clockwise, so that the full width of the head contacts the inside of lip of the extrusion. (See illustration, it makes it a bit more clear.)
Grind down four bolts each for both of the two panels.
Next mark where you want the PV mounting holes to go in the top of the rack, Drill straight through the center of the conduit with a 1/4" bit.
Insert the heads of the four bolts into the solar panel so that they hang down from it. Lower the panel onto the rack, and have your assistant help you line up all the bolts. Lower the panel while pushing the bolts through the holes in the conduit.
Add a washer and nylock nut to the bottom of the bolt and tighten. The solar panel will snug down to the conduit rack. You should be able to torque-down this bolt fairly hard. Repeat with the second panel.
Now you are ready to wire-up the vehicle.
Step 6: Wire it up
*Another important note*
On the Power Wheels brand of battery the FUSES for the car are built into the battery. If you use a regular battery, you need to add a fuse. I used a typical inline fuse holder from the auto parts store. (30 amp, 12V automotive fuse.)
The wiring is pretty simple. The solar panels go to the charge controller, and the solar charge controller goes to the battery. Make sure to observe proper polarity. Red goes to the + Positive on the battery and charge controller, and black goes to the - Negative.
The battery is also connected to the existing wiring harness of the car. Since it uses proprietary quick disconnects, you can either cut those off, and convert them to something more common, or you can leave the harness intact and find the matching connector. I didn't touch the wire harness of the car. Instead, I got an old (dead) Power Wheels battery from a friend who has young children with these toys. I cut the special plug off the old battery, and added terminals to it to connect it to a standard battery.
Step 7: Cover it up - New Hood and Stand-offs
A clear cover over the battery and charge controller serve multiple purposes of holding down the components, protecting them from rain, and keeping little children's fingers out.
For the wires from the solar panels, simply route them down the solar rack, and zip-tie them in place.
I made the clear cover from some scrap plexiglass. The area to cover is about 2'x1', but it needs notches taken out to allow for where the front uprights connect to the frame. While I could have used a jigsaw or other basic cutting tool, I happened to be at the Milwaukee Makerspace, where they have a laser cutter. Although a laser-cutter is NOT required, it is a tool that I'm learning, and I thought I would make use of it.
On the computer, I made a simple outline of my 2'x1' rectangle and added the notches that would allow for the solar rack. Once the laser is cut out the plexiglass, I laid it over the top of the battery and charge controller to see how high the plexiglass needed to be mounted. I then made spacers which were that length.
The spacers are simply scrap aluminum tube of a diameter that a bolt will slide right into. I cut two pieces of tube (with my trusty tubing cutter!) to about 4.5" long.
Next, long bolts go through a fender washer, the clear plastic cover, the aluminum spacer tube, a washer, the plastic body, another washer, and a nylock nut.
Once tightened-down, the cover holds and protects the battery and charge controller securely in place. Since it's clear, you can still see the voltage display on the solar charge controller.
In other safety for the project, you could also add pipe insulation to the edges of the solar panels. This is more to protect the head of the parent, as the panels are at about fore-head-wacking-height when leaned over to help the child steer, get in and out of the vehicle, etc.
I also zip-tied the rear "roll-bar" on the Jeep to the solar rack. This gives some cross-bracing and turns that bar into a great "grab-point" for the car. Since it is rear-wheel-drive, by lifting the back of the Jeep with that bar, you can STOP a child from driving forward, and you can also "re-aim" the car if the child needs to spin the vehicle around.
Step 8: Go Play!
Of course, make sure to supervise your child while playing. When both of you are done, DON'T go put the Power Wheels in the garage! Instead, just leave it right out in your backyard! The vehicle will AUTOMATICALLY RECHARGE FROM THE SUN!
Should your child park it under a shade-tree, simply move it over a bit to a sunny spot.
So that's it! Now go enjoy your SOLAR-POWERED Power Wheels - fossil-fuel-free, renewably-powered backyard fun!
For more clean transportation projects, swing by 300MPG.org
For more eco-friendly back-yard and home projects, check out EcoProjecteer.net