Electric Go Kart Story-Part 8

Doubling The Voltage To The Modified Electric Starter Motor To Increase Speed To The Electric Go Kart

In Electric Go Kart Story – Part 7, I discussed speed controllers and motor controllers. Before getting one, I wanted to know if I could double the voltage to the modified Electric Starter Motor and run on 24 volts. A week after Summernats 2012, the Electric Go Kart of Funky Car Skins – ElectricCarConversionBlog.com was tested to determine if the modified 12 volt Electric Starter Motor could handle two 12 volt batteries being applied in series to deliver 24 volts.

The theory being tested was that if the voltage was doubled, the speed would roughly double, since with Permanent Magnet Electric DC Motors, speed is roughly proportional to voltage and acceleration is roughly proportional to current.  The intention was to just double the voltage.

I first took the Electric Go Kart for a test drive in the 12 Volt configuration which was known to work. I was able to drive it and drift a bit with no dramas.

 

I added another 12 volt battery in series so that the Modified Electric Starter Motor would get 24 volts.  It should be noted that the crude motor controller which I built in 2011 did not have any current limiting circuitry. It only did pulse width modulation (PWM) to control speed. The extra battery also meant extra weight and there was only room just next to the rear axle. With more weight on the rear axle, it would theoretically have been harder to drift.

When I took the Electric Go Kart for a drive with the new configuration of 24 volts, it had quite a bit of pick up, was noticeably faster and I was able to do a nice drift when doing a U turn. The person filming the above video did not expect this Electric Go Kart to take off as quick as it did. As you can see, by the time he made it to the corner of the building, I had already turned around (more like drifted around doing a 180) was starting to move in the opposite direction until I lost power.  The Modified Electric Starter Motor ended up smoking up. Within seconds of driving it with 24 volts, the kart went from being a nice and fast with the ability to drift to a motor that was cooked. I cooled the motor by pouring water over it which seemed to cool the modified Electric Starter Motor fairly rapidly.

Later on, I did try driving the Electric Go Kart, but this time on 12 volts, but the modified Electric Starter Motor was not the same.

What are some of the lessons learned:

For starters, it should be noted that Electric Starter Motors are designed to run for only a short time, typically up to 10 seconds before needing a rest for around 1 minute. With the way I use the Electric Starter Motor, I’m exceeding it’s designed and intended capability, so no warranty there.

Starter Motors don’t have any cooling features. Notice how there are no cooling fins, cooling fans or liquid cooling features on them. It is no surprise then that the modified Electric Starter Motor used to power my Electric Go Kart often gets very hot after a few minutes of driving.

Commercially available Electric Motors for Electric Vehicles typically have a cooling fan or have liquid jackets for liquid cooling capabilities.

A number of people including some at Summernats 2012 and the 2011 Canberra International Electric Vehicle Festival have made various suggestions on how I could cool the Electric Starter Motor. Here are some of the suggestions:

• Put some cooling fins (imagine a large washer that fits over the cylindrical casing of the modified Electric Starter Motor) around the circumference of the modified Electric Starter Motor;
• Wrap the modified Electric Starter Motor with copper tubing and have heat sink compound smeared between the copper tubing and casing of the modified Electric Starter Motor. Then have water circulate through the tubing. This would require a little pump and a small radiator to ensure a supply of cool water to the modified Electric Starter Motor;
• Fabricate a water jacket around the Electric Starter Motor;

My new sponsor, Goulburn Mechanical and Performance Centre is in the process of sourcing a bigger Electric Starter Motor for me to modify and attach to the Electric Go Kart.

This is Crazy Al Signing Out.

P.S. I would be interested in your thoughts about which way you think I should go with Electric Starter Motor on the Electric Go Kart which you can add in the comments section below.

Check out the other parts to the Electric Go Kart Story:

Part 1 – What Inspired Me To Do An Electric Go Kart Conversion

Part 2 – Taking Action – Modifying An Electric Starter Motor

Part 3 – When The Rubber Hits The Ground

Part 4 -Extra Parts Added To Electric Go Kart – Adding A Touch Of Professionalism

Part 5 – Replacing Electrical Switches & Electric Motor

Part 6 – Building A Motor Controller For Electric Go Kart

Part 7 – What I’m Looking For When Upgrading The Motor Controller On The Electric Go Kart

Part 8 – Doubling The Voltage To The Modified Electric Starter Motor To Increase Speed To The Electric Go Kart

 

Tweet

Tags: 24 volts, Electric Go Kart, Electric Starter Motor, go kart story
2 Comments »