The 24V, 300W, BLDC Kollmorgen motor integrated controller
A motor mixes mechanical and electrical beauty with questionable thermal design.
Paul Rako, Technical Editor -- EDN, September 22, 2011
Kollmorgen, a subsidiary of Danaher Corp, manufactures the 24V, 300W
BLDC (brushless-dc) motor in India. A true BLDC motor, it has
Hall-effect sensors that feed back the rotor position to the integrated
controller. This motor, whose part number begins with CTI, is not a
stepper motor, such as the CTM and CTP lines that Kollmorgen also sells;
it has significant performance advantages over stepper motors. For example, its rotor
incorporates closed-loop feedback and permanent magnets. Two pigtail leads come off
the motor, and you feed 24V power to the thicker wires. The motor’s thin harness allows
you to connect a potentiometer for speed control and a switch to disable the motor.
Kollmorgen most likely intended the motor for use in electric scooters and wheelchairs.
Although the integrated controller eases installation, the heat it produces affects the
electrolytic capacitors, reducing reliability.
1. This 0.031-in. FR
(flame-retardant)-4
board houses an
arc-shaped 0.042-in. FR-4 PCB
(printed-circuit
board) that holds
the three Hall-effect
sensors.2. The rotor is a steel shell with an outer black ring made of permanent-magnet material.
3. The rear bell of the motor holds the BLDC controller. The two large electrolytic capacitors provide a low-impedance dc bus, preventing large switching spikes due to wiring inductance. The toroidal inductor might reduce heat-producing harmonics to the windings. A potting compound helps the motor to resist vibration and conducts heat from the components.
4. One of the pliers
in the $6 Harbor
Freight 96512
snap-ring pliers
set eases
disassembly.
5. Kollmorgen engineers used insulated
tape to protect the windings from the
Hall-effect sensor’s PCB solder tails. They
also placed glass-reinforced tape over the
switching inductor in the controller.6. An O ring seals the motor’s end bell. The fit of the parts exhibits tightly held machining tolerances, even though the end bell does not hold a rotor bearing.
Talkback
-
Having designed a motor very much like this one, I would venture to say that it uses the OnSemi MC33033 or derivative, a low cost trapezoidal drive controller which has been around for a long time. Runs with Hall effect sensors, shown in the photo, mounted on the clear board. Looks like the rotor uses a ferrite magnet, not rare earth. The design of the rotor magnet is quite nice, single piece, no problems with magnets flying off. Would like to know whether motor exhibits low cogging.
Marc Tan - 2011-6-10 10:32:01 PDT -
@Brian Park
A magnet sticks to the rotor 8 times, a piece of steel sticks 16 times. I think that makes 16 magnetic poles. There are only three wires going to the 18 pole pieces, so it is a 3-phase machine with lots of poles to minimize cogging, something important on ebikes and scooters since they do a lot of starting up from zero speed.
Armature winding configuration? There are 3 wires going to 18 pole pieces. I can't see any paralleling wires, so I guess each of the three phases has the poles in series. I spent my own money to buy this and don't really want to ruin it unwinding the stator.
If it had sinusoidal commutation it would be a BLAC (brushless ac) servomotor, very doubtful for a cheap ebike motor.
The schematic of the controller? Kollmorgen is not too keen on spending hundreds of thousands of dollars on an integrated motor controller R&D project, and then handing the most precious bit of intellectual property over to me. To dig out the potting and reverse-engineer the schematic would take about two weeks. Sorry, I just don't have time, although it would be fascinating, I agree. You can get the motor on eBay for 80 bucks if you want to try it, and I will gladly publish the schematic for all to enjoy.
ebay[dot]com/itm/Electric-Bicycle-Scooter-Brushless-24V-24-Volt-DC-Motor-/350483743702
On/off or PWM, well I really doubt they did PWM flux-vector control on a low-cost product. You might be calling on/off like a stepper motor, and calling PWM the way simple BLDC motor controls work. To me PWM means the trapezoids are chopped and the controller can regulate the current profile of each trapezoid. To see how simple a BLDC with Hall switching can be, see the great animations a the following link, and single step them to see how simple logic (or a 3 by 6 PROM) can decode the Hall switch info to drive the half-bridge transistors.
townbiz[dot]com/animations/4-pole_bldc
@Cor van de Water
Sorry to not be clear, these one-page features don't allow elaboration, as Brian Park rightfully notes below. The end of the lead paragraph talks about how having electrolytic capacitors in the end bell subjects them to motor heat, and reduces their lifetime. Sorry, my buddies went to the Palo Alto EV gig, but I had to proof-read my upcoming cover story on Saturday.
Paul Rako - 2011-25-9 14:52:00 PDT -
Where are the details? How many poles does it have? What is the armature winding configuration? Is it sinusoidal commutation or trapezoidal commutation? What is the schematic of the controller? Do they use on-off or PWM control?
Brian Park - 2011-23-9 14:01:31 PDT -
Paul, this motor looks exactly like my e-Bike's first motor, including the positioning of the fins and mounting screw holes. I later replaced that motor with a Currie motor, because it failed soon.
For a description of my e-Bike see EValbum entry 720
(evalbum dot com slash 720)
When I disected the failing motor, it became clear: the motor mounting was such that the wires were pointing up, allowing rainwater to enter the motor and cause failure in the controller (as well as eventually seizing up the rotor) so I rotated the replacement motor to have the wires pointing down and it did not fail. Note that the first motor did not have the potting that this motor has on its PCB.
BTW, why is the thermal design suspect? I did not see a reference to that announcement in the text.
BTW2: are you visiting the EV show and rally in Palo Alto this Saturday? Palo Alto Highschool parking lot.
Cor van de Water - 2011-22-9 15:44:12 PDT
