After loads and loads of searching through online EV forums and watching videos on YouTube, I decided to take a chance on the Manta 2 DC permanent magnet electric motor. I was able to find the motor and an adapter plate on EBay for a cool $463.35 with tax and shipping ($60 above my estimate, but I also purchased a mount). Wohoo!! It’s happening!
Right around this time, I managed to sell the Yanmar for $550 to a friend who is building up his own sailboat, an Islander 30. This is big, as it will offset ~ 1/3 of the cost to repower Cinderella. I could have parted out the engine and probably broken even, but the time and care involved was not something I wanted to take on.
So, I have a motor, but what about the rest? I needed a controller, what’s a controller, how do they work? Back to Google. Let’s simplify controllers, they are a means to “control” power flow into an electric motor to vary the speed of your motor. Otherwise, you have either full speed or no speed. Which, as you can imagine is not ideal when trying to maneuver in tight quarters.
Classically, DC motors were controlled by resistors. Resistors simply take the energy going into a motor and burn it off as heat, therefore reducing the energy going to the motor. Nice, simple, right? Wrong! “Burning off” as heat translates to poor efficiency and also adds heat to electronics which substantially shortens their life.
Enter the controller, the controller plays upon the concept of Pulse Width Modulation or PWM, a fancy acronym for a simple concept. Basically a microprocessor (think computer) controls a series of switches (kind of like really small light switches) which open and close very, very quickly. When this happens the stream of energy going to the motor is stopped, then started, then stopped, then started and so forth from those switches. The end result is a means to speed up and slow down an electric motor without excessive losses.
That’s great, but I still don’t know very much about controllers, which one do I need, what do I need to watch out for? I am after all pretty new to all of this.
More research, more google, and I landed on a company called Kelly Controls LLC. Kelly Controls makes controllers for all sorts of applications, for both AC and DC motors. Kelly Controls have a couple of benefits that set them apart from the others: cost, programmability, reverse, and regen ability.
The controller decision was possibly the most challenging so far. There are a handful of major brands: Alltrax, Curtis, Kelly, Sevcon and a few others. I only know this due to the EV forums, which spoke highly of Alltrax, Sevcon and Curtis, but had mixed reviews of Kelly.
From what I could tell, most of the major EV sailboat kits out there utilize Sevcon controllers. Why did I land on Kelly? Well after speaking with a few of the companies, I was told that their controllers “Don’t do regen” with PM motors. They also don’t reverse internally, I would need to buy another $200 component to make that work. Bummer! The decision was simplified, Kelly Controls it would be.
Controllers are rated by two basic numbers, Amps and Volts, sounds an awful lot like high school physics. Both of these components are defined by the motor and battery bank choice. Amps, or the measure of current through your system is the limiting factor for all things battery.
Batteries are rated in Amp/hrs or the amount of current that they can provide for a set amount of time. Remember I said my electric system in the boat pulled about 20-30 amps at 12V? That probably means little to anyone that hasn’t had a refresher in high school physics, but it simply means I can run my electronics for about 10 hours before I need to charge the batteries. The same concept applies to my electric motor, the only difference is that the motor will use a higher voltage, and the amp draw will vary with how fast I want to go.
After comparing Cinderella’s system with that of other conversions, I will hope to run Cinderella between 20 and 60 amps. That translates to speeds of about 2-4 kts or roughly 2-5 mph for those non-boaters.
Knowing this, I should be able to motor for 1 – 4 hrs on my cheap batteries and 2-8 hrs on the ideal Oasis Firefly’s. But the Fireflies will last a lot longer and can take more abuse between charges, they are the ideal battery. Motoring slowly, I should expect about a 30-40 mile range which is sufficient to allow Cinderella to get through the locks and into the Puget Sound (1.5 mile trip), remember I plan to regen under sail, and will eventually install solar panels. This should allow for plenty of summer sailing fun while I get my funds in order to upgrade before I make the trip around the marble.
Alright back to my controller choice. I will be running Cinderella’s motor at 48V, so I have one of the numbers figured out, what about the Amps? I told you I plan to run the motor at 20-60 amps right? Well the motor is capable of 100 amps, and from what I read, you want at least 50% head room to keep the controller running efficiently (why they don’t rate them practically is beyond me). This narrowed my search down to a 48V 200-300 Amp controller capable of regenerative braking. I also wanted the controller to have the ability to reverse the charge to the motor which will allow me to reverse without buying more components.
With those stipulations, I settled upon the Kelly Controls PM48301, a 300A 48V controller with Regen for $349. Along with the controller I purchased some fuses to protect the wiring, a contactor to allow for an on/off key switch, and a heat sink to help keep the controller cool in the tropics. The total purchase price was $695 with shipping.
This brings my total to $1158.35 if we subtract $550 for the engine I sold, that figure becomes 608.35. Not too bad, I’m still on track with my budget. I still need batteries and a lever that can convert my boats throttle lever into an electrical signal that the controller can recognize.
Follow along on My Experience with EV – Part 4 where I buy more electronics to get Cinderella electric.