#kellycontrollers

Now that we’ve talked about how the electrical system is supposed to go together from a power perspective, I wanted to touch on my specific system and how the control signals for the throttle and motor are connected to my motor controller.

I started out building the system on my workbench. Below, you can see the contactor (black box on the white paper) hooked up to the batteries (yellow) with a keyed ignition switch. Attached to one of the terminals of the contactor is a fuse (white cylinder). Here, I was purely testing out the functionality of the contactor along with the ignition switch.

In addition to all of the main electrical power setup that I detailed in my previous post, the control signals need to be hooked up to the motor controller as well. For my Kelly KEB72601 controller, everything connects using a “J2″ plug. From the Kelly manual, the pinout for the connector is:

The wiring diagram for how to use these pins from the manual is below:

Interpreting the wiring diagram above, the important pins for base level functionality (no regenerative breaking) are: 

1 (power from the battery, mentioned in previous post)

2 (ground, used for the throttle)

5 (0-5V signal coming from the throttle)

7 (5V output for the throttle and the motor sensors)

11, 12, and 13 (Hall effect sensors from the motor)

14 (ground for the motor sensors)

Below is a beautiful blurry photo of the J2 connector (metal cylinder below the socket wrench with a mess of wires coming out from it) as I crimped on some small connectors to the end of the wires noted above for quick connect/disconnect to the motor sensors and to the throttle.

Connecting the Throttle

The throttle I selected was a 3-wire potentiometer throttle. The idea here is that you send a ground (0V) and high (5V) signal on two wires, and the output wire will sweep from 0-5V based on the throttle position. At rest, the throttle will output 0V, and at wide-open throttle (WOT), the throttle will output 5V. So, pin 7 connects to the max throttle wire (5V), pin 2 connects to the resting voltage wire (0V), and pin 5 connects to the sweeping output voltage wire of the throttle.

For my specific throttle, I purchased a Magura throttle from Electric Motorsport. You shouldn’t. Their “documentation” was not super clear, but more importantly the throttle I received simply didn’t work. I thought I had made a mistake wiring the system when it didn’t work, but in fact the maximum voltage the throttle out out was so low that the motor controller didn’t even register it. Fortunately, I had another throttle from the XM Chinese scooter I had dismantled earlier and was able to use to that instead. Below is a video of me trying out the Magura throttle and nothing happening :(

Once I wired of the functional throttle, I was able to test out the wiring of my motor sensors...

Connecting the Motor Sensors

For brushless motors, there are Hall effect sensors in the motor that detect the current position of the rotor (spinning part). This provides the motor controller with the information it needs such that in can send the right power signals at the right time to the electromagnets on the stator (stationary part). These 3 Hall effect sensors will have output wires running from the motor to be connected to the controller, in this case pins 11, 12, and 13 of the J2 connector. You will also need to run power (pin 7) and ground (pin 14) to the appropriate wires coming from the motor. In the case of my motor, there was a diagram that indicated the different pins on a connector coming from the motor -- 3 Hall sensors, power, and ground. The diagram for my motor wasn’t super clear on the order (A, B, C) of the Hall effect sensors, and the diagram Kelly had for my motor confused the issue some more. I actually ended up trying all combinations of Hall sensor inputs to my controller in order to determine what setup actually worked. Below is a shot of the white board in my garage. In the bottom right corner, you can see the table I made for each combination of wires (letters indicated the color of wires I was connecting to one another). The starred line is was the one that worked best and that I went with going forward.

So far we’ve gone over all the major pieces involved in the electrical system for the moped: the motor, the motor controller, and the batteries. Now, it’s time to talk about how all these pieces connect and what other components are necessary to tie the whole system together!

First off, we need a fuse for the high-power (up to 48V, 300A) circuit. The specific fuse to get depends on your system -- I got a 400A fuse myself.

The next new component we need to talk about is called a contactor. A contactor is pretty much just a fancy heavy-duty relay -- an electrically controlled switch. The idea here is that we have a comparatively high-powered circuit that we want to safely open and close. A contactor is placed in between the batteries and the motor controller on the high-powered circuit. In its default state, the contactor is disengaged and thus does not connect the batteries to the motor controller. The contactor is controlled by a separate signal -- you can either use your full system voltage (provided your contactor’s “coil voltage” supports that high of a voltage) or a 12V accessory voltage. When you apply that voltage across the control terminals, the contactor closes and physically connects the high-power circuit, supplying power to the motor controller.

That brings up another piece of the electrical system -- we need a 12V circuit too! Although a lot of old mopeds used 6V systems for their accessories (lights, horn), 12V is the modern standard. Now that we don’t have an engine with an alternator/magneto, we don’t have anything to charge a 12V battery like a traditional gas vehicle would. For this we need a DC-DC converter -- a device that takes one input voltage and creates an output voltage. I mentioned previously that I got a DC-DC converter that accepts an input voltage of 24-72V and produces an output of 12V -- perfect for my system. (If you have a bit of an electrical engineering background and are interested in reading more, a buck converter is a good place to start.)

Now let’s first talk about connecting the 48V system: the batteries, the motor controller, the fuse, and the contactor (the motor connects directly to the controller, so we’ll touch on that later). To connect these components, we need to use adequately sized cables to handle the current. I used this tool to guide my decision on what type of cable to buy: http://www.solar-wind.co.uk/cable-sizing-DC-cables.html. I ended up using 4 gauge cables, as I had access to them already. A point of recommendation: make sure you get flexible welding cable for this. I picked up some 4 AWG at Home Depot, and it was very stiff and not useful for this project. I’m downgrading to 6 AWG on my next rewire (details to come later) and would recommend this or the equivalent gauge for your project. You’ll want to grab some appropriately sized lugs to crimp on too.

Once you’ve got your cables, the 48V system is pretty easy to hook up once you’ve got the order to connect everything right. My main point of reference is from the manual for my Kelly motor controller:

The 48V circuit here is along the dark lines around the border: the B- terminal on the motor controller connects to the negative side of your battery, the fuse goes between the positive terminal of the battery and the contactor, and the other side of the contactor connects to the B+ terminal on the motor controller. The diagram above also shows a “Key Switch” in the 48V circuit to control the contactor. Since I’m using my 12V circuit to control the contactor, I did not place a switch here, but instead on the DC-DC converter.

You’ll notice that you’ll also want a pre-charge resistor across the 48V contactor terminals. You can read a good detailed explanation as to why here, but the basic idea is that the resistor allows a small amount of current through the circuit which “precharges” capacitors in the motor controller, preventing a potentially dangerous/destructive large inrush of current when the contactor is closed. 

Similarly, there is a diode across the control terminals of the contactor. This is to prevent a voltage spike from damaging the motor controller when the contactor is disengaged.

Now we need to connect the 12V circuit. You can use the wire gauge calculator from before, but unless you’re putting some crazy high-power accessories on, 14 or 12 gauge from Ace or an auto parts store should do just fine. The DC-DC converter will have 3 wires: A ground (the two circuits will share a common ground), a high-voltage system input (48V in my case), and a 12V output. You can simply connect the ground and input wires to the negative and positive terminals of the battery, but I would recommend putting a switch in line as well so that you can turn off the 12V circuit (no need for a vampiric load to slowly drain your batteries when you’re not using your bike!). Once you have a 12V output, you can connect this 12V signal to the control terminals of the contactor (remember, your 12V ground reference is your negative battery terminal still) to close the contactor and engage the 48V system. I wired my system such that one switch provided power to the motor controller (connected to pin 1 in the diagram above) and to the DC-DC converter, thus in effect controlling both the 12V and 48V systems with one switch.

Wiring the power cables from the motor to the controller is pretty straightforward. With a brushless motor, there are 3 cables to run from the controller to motor:

Controller terminal “A” --> Motor terminal “U”

Controller terminal “B” --> Motor terminal “V”

Controller terminal “C” --> Motor terminal “W”

Make sure to use your heavy gauge cables for this. You will also need to connect your motor’s “hall effect sensor” outputs to your controller, as outlined for the Kelly controller in the diagram above.

An electric motor is basically just a bunch of magnets. Some are fixed permanent magnets (think of a chunk of magnetized metal, just like a fridge or bar magnet) and others are electromagnets (basically just coils of wire that become magnets when you put electric current through the wires). By switching which electromagnets are active at a given time, you can use magnetic forces to create motion, causing the motor to spin.

You can arrange these magnets in different ways. The two main types of DC electric motors are brushed and brushless. As mentioned in my motor post, I am using a brushless motor.

To get a better feel for how the magnets in a motor create motion, and the difference between a brushed and brushless motor check out the pages below on each. They have great little animations to accompany their explanation.

Brushed Motors

Brushless Motors

As a brief summary, both types of DC motors each have a rotor -- the inner part that spins, and a stator -- the outer part that remains stationary. A brushed motor has permanent magnets on the stator and electromagnets on the rotor. A brushless motor is the opposite, with electromagnets composing the stator and permanent magnets for the rotor.

So, in order to run an electric motor, you need to be able to control the electromagnets correctly to cause the motor to spin in the right direction and at the speed you want it to spin. 

If you read the link above on brushed motors, you’ll see that that actual switching of which electromagnets to power is controlled by the physical movement of the motor itself. As the rotor moves, the brushes hit the next part of the commutator (attached to the rotor, which transfers the power from the brushes to the next electromagnet).

On a brushless motor, you do not have brushes or a commutator. This makes controlling the motor trickier, as you must know when to send power to which electromagnet. To do this, there are sensors inside the motor (called Hall Effect sensors) that detect where the magnets are aligned on the rotor, so that you know which electromagnets to power on the stator.

The key takeaway here is that brushed and brushless motors require different types of controllers to run the motor. 

Now, technically, you could make your own controller. Conceptually, you’re just controlling what electric pulses go where, and when//for how long. In practice, there is a lot of power going through this circuit (in my case, up to 4.47 kilowatts), and power electronics are definitely outside of my realm of expertise.

Some of the biggest names you’ll see in motor controllers are Alltrax, Sevcon, Curtis, and Kelly. Since I opted for a brushless motor, I set out in search of a brushless motor controller.

Through my preliminary research, the impressions that I got were:

Alltrax really just focuses on controllers for brushed motors

Sevcon makes pretty expensive stuff

Curtis makes a bunch of stuff for specific applications and didn’t quite seem to fit my need

Kelly makes a lot of brushless controllers

That said, getting a Kelly controller seemed to make the most sense for me.

When looking into buying a motor controller, outside of the type of motor controller you want (in my case brushless), there are other specifications you have to keep in mind. In particular, controllers have different voltage and current ratings that they safely support. 

My motor is a 4.47 kilowatt motor, but can support a peak output of 14.17 kilowatts for a short period of time. These are its power ratings. Power (P, in Watts) is calculated by current (I, in Amps) times voltage (V, in Volts). That gives us 

P = IV

Now, I can run my motor anywhere from 24-72 volts, but my plan is to run a 48 volt setup. At 48V and 14.17kW, that gives us a potential current of 

I = P/V = 14,170 Watts / 48 Volts = 295.2 Amps

So, I want a motor controller that supports at least 48V and 300A (rounding up).

When I first started researching electric motors, Kelly seemed to have 2 suitable lines of brushless controllers that could meet my specs: their KEB and their KBL lines. Truth be told, I’m not 100% sure what the difference between the 2 really is. Fortunately, the XM electric scooter that I got came with a KEB Kelly controller. It was only rated up to 220A, but that’s pretty close to my peak, and should definitely be plenty of power for testing.