Microwave Oven Transformer Spot Welder Part 1

Recently while I was at the solar cup event (which we placed 5th overall and 1st in Endurance) I talked with someone about their electric bike. He had used a hub motor from goldenmotors and built the battery himself from the cells inside laptop batteries. We talked for a while about it and I was surprised to find out it had a top speed of around 45 mph (but not on public roads) and a range of over 100 miles. I was really impressed and spent a lot of time researching about different motors, how to build different batteries. I even researched velomobiles, thinking it would be awesome to build a electric powered trike velomobile because of the comfort and range.

I decided to take it one step at a time though. I had already taken apart and salvaged parts from an old microwave so I had all of the parts I needed to build a spot welder. A spot welder is used to connect all of the 18650 cells together to form the larger packs needed to run vehicles.

I started trying to take the second transformer out by hacksawing it directly out of the transformer. I do not recommend this way. I ended up just cutting the weld on the transformer and prying and hammering out the coin coils.

I then used nail polish to cover the places on the primary that I had scratched off so that it would not short.

For my secondary, I did not have thick enough wire and so I made due with 6 strands of 14 gauge wire.

The main parts of the spot welder.

February 28th Mounted the Log

During the week we worked on mounting the log in the boat. The log is where the drive shaft passes through the hull of the boat. We did our best to mount it perfectly straight by having the drive shaft in place and measuring from it to get the log centered. We then traced the log onto the hull and removed the driveshaft since we needed to epoxy the log in place and did not want to risk getting epoxy on the drive shaft.

Here is our dry fit of the log

We then used some quick set JB weld to secure the log to the boat. While this provided a quick setting solution, we feared it might be too weak, so we reinforced it with some two-part marine putty epoxy. This served the benefit sealing and securing the log in place as well as making it look nicer.

Log with marine epoxy applied

View through the strut, log, and bearing

I have also continued working on the parts for our steering system. We are planning on using a rack and pinion arrangement for the steering wheel which I will design and print. To reduce friction we are using heelys wheels as bearings.

Electrical System Done, Motor Mount almost Done

Over the past few weeks we have worked on the electrical system and the motor mount and are nearing the end on both. We went to a workshop where we assembled all of the components for the system. We were able to assemble it and get it to run but not consistently, often having to 'gun' the throttle in order to get the motor to start spinning.

The motors we are using are upwards of $1000 and we did not have that enough to replace it. However, when we were talking to some other people, they suggested we test the throttle potentiometer and switch, as well as potentially the solenoid and even the speed controller. They believed that the problem was probably because of a faulty switch in the throttle. When we got back to the school, we were able to test the parts and when we bypassed the switch it worked perfectly. Instead of a $1300 repair, it turned into a $10 switch repair.

The motor mount is almost in place as well. We are just waiting to finish mounting it so that we can mount both the motor mount and log at the same time so that they line up perfectly. We also have mounted the rudder tube in place.

We also applied a final coat of epoxy to the underside of the boat. We used squeegees to apply the epoxy so as to have a thin, smooth coat across the boat.

Continuing Work on Drivetrain and starting Planning for Solar Panels

This Saturday we continued work on the boat, we made the hole for the drive shaft and started planning on how we will layout all of the components. We are planning to put everything as far forward as possible to keep our center of gravity balanced. We will be placing the motor so it is as close to the bulkhead as possible. The batteries will sit along the sides of the boat, next to the motor with the speed controller below the motor.

The strut and drive shaft mounted loosely why finding where to put the motor mount.

In order to mount the motor, we are planning on using a hinge to connect the motor mount to the boat, that way we will be able to adjust the angle so that it is perfect, and we will be able to lower the motor to access the wiring behind it.

We also started work on laying out the solar cells for our panels. We order two boxes of 40, 6x6 inch cells to use for our panels. We are planning on using corrugated plastic as the backing of the panels to save weight yet remain strong. We plan to use multiple layers laminated together 90 degrees from each other to prevent buckling. Home depot has a box of 10, 4ft x 8ft x 4mm thick corrugated plastic for $110. Here is a link to the description.

The layout for our panels using 6x6 pieces of paper to represent cells.

Underneath our plan is the solar panels from a few years ago. Those panels were too powerful and over the 320 watt limit by over 150 watts. The panels had an extra 19 cells and, by removing them, we reduce weight and make it easier for the driver to see where over them.