The article presents a simple electric scooter circuit design which can be also modified to make an electric auto-rickshaw. The idea was requested by Mr. Steve.
The Circuit Request
I was lucky enough to find your blog, really amazing stuff that you've managed to design.
I'm looking for a DC to DC Step Up and Controller for Electric Scooter Motor
Input: SLA (sealed-lead-acid) Battery 12V, which is ~13.5V charged
minimum voltage - cut off at ~10.5V
Output: 60V DC motor 1000W.
Have you came across a circuit like that?
I can image it will be push-pull type, but have no idea of types of mosfets (give the wattage 80-100A), driving them, then the transformer, the core type and then diodes.
Plus the minimum voltage cut off to cap the PWM's duty cycle.
I have found some more information. The motor is 3 phase brushless with hall sensors.
There are two ways to approach it, a/ leave the existing controller in place and only do 12V to 60V step up or b/ replace the controller too.
There won't be any difference in power efficiency, the controller simply switches which phase get current based on the hall sensors. Therefore, sticking with plan a.
Thank you very much,
The Circuit Design
Today making an electric vehicle is much easier than it used to be earlier, and this has become possible due to two main elements in the design, namely the BLDC motors and the Li-ion or the Li-polymer batteries.
These two ultra efficient members have fundamentally allowed the concept of electric vehicles to become a reality and practically feasible.
Why BLDC Motor
The BLDC motor or the brushless motor is efficient because it's designed to run with no physical contacts except the ball bearings of the shaft.
In BLDC motors the rotor rotates solely through magnetic force making the system extremely efficient, contrary to the earlier brushed motors which had its rotors attached with the supply source through brushes, causing a lot of friction, sparking and wear and tear in the system.
Why Li-Ion Battery
On similar lines, with the advent of the much upgraded Li-ion batteries and the Lipo batteries today achieving electricity from batteries is no longer considered an inefficient concept.
Earlier we had only lead acid batteries at our disposal for all the DC back up systems which posed two major drawbacks: These counterparts needed much time to charge, possessed restricted rate of discharge, lower life, and were bulky and heavy, all these only adding to their inefficient nature of working.
Opposing to this, Li-ion, or Li-po batts are lighter, compact, quickly chargeable at high current rates and are dischargeable at any desired high current rate, these have higher run life, are SMF types, all these features making them the right candidate for applications such as electric scooters, electric rickshaws, quadcopter drones etc.
Although BLDC motors are extremely efficient, these require specialized ICs for driving their stator coils, today we have many manufacturers producing these exclusive next-generation IC modules which not only do the basic function of operating these motors, but are also specified with many advanced additional features, such as: PWM open loop control, sensor assisted closed loop control, multiple foolproof safeguards, motor reverse/forward control, braking control and a multitude of other state-of-the-art in-built features.
Using a BLDC Driver Circuit
I have already discussed one such excellent chip in my previous post, specifically designed for handling high wattage BLDC motors, it's the MC33035 IC from Motorola.
Let's learn how this module may be effectively implemented for making an electric scooter or an electric rickshaw, right in your home.
I won't be discussing the mechanical details of the vehicle, rather only the electrical circuit and the wiring details of the system.
All resistors including Rt but excluding Rs and R = 4k7, 1/4 watt
Ct = 10nF
Speed potentiometer = 10K Linear
Upper power BJTs = TIP147
Lower Mosfets = IRF540
Rs = 0.1/max stator current capacity
R = 1K
C = 0.1uF
The above figure shows a full-fledged high wattage brushless 3-phase DC motor driver IC MC33035 which becomes perfectly suitable for the proposed electric scooter or electric rickshaw application.
The device has all the basic features that may be expected to be in these vehicles, and if required the IC could be enhanced with additional advanced features through many alternative possible configurations.
The advanced features become specifically possible when the chip is configured in a closed loop mode, however the discussed application is an open loop configuration which is a more preferred configuration since it's much straightforward to configure, and yet is able to fulfill all of the required features that may be expected in a electric vehicle.
We have already discussed the pinout functions of this chip in the previous chapter, let's summarize the same and also understand how exactly the above IC may be required to be implemented for achieving the various operations involved in an electric vehicle.
How the IC Functions
The green shaded section is the MC 33035 IC itself which shows all the built-in sophisticated circuitry embedded inside the chip and what makes it so advanced with its performance.
The yellow shaded portion is the motor, which includes a 3-phase stator indicated by the three coils in the "Delta" configuration, the circular rotor indicated with the N/S poled magnets and three Hall effect sensors on the top.
The signals from the three Hall effect sensors are fed to the pin nos 4, 5, 6 of the IC for internal processing and generating the corresponding output switching sequence across the connected output power devices.
Pinout Functions adn Controls
Pinouts 2, 1 and 24 control the externally configured upper power devices while the pins 19, 20, 21 are assigned to control the complementing lower series power devices. which together control the connected BLDC automotive motor as per the various fed commands.
Since the IC is configured in an open loop mode, it's supposed to be activated and controlled using external PWM signals, whose duty cycle is supposed to determine the speed of the motor.
However this smart IC does not require an external circuit for generating the PWMs, rather it's handled by an in-built oscillator and a couple of error amp circuitry.
The Rt, and Ct components are appropriately selected for generating the frequency (20 to 30 kHz) for the PWMs, which is fed to pin#10 of the IC for further processing.
The above is done through a 5V supply voltage generated by the IC itself at pin#8, this supply is simultaneous used for feeding the Hall effect devices, it seems everything is precisely done here....nothing is wasted.
The portion shaded in red forms the speed control section of the configuration, as can be seen it's simply made using a single ordinary potentiometer....pushing it upwards increases the speed and vice versa. This is in turn made possible through the correspondingly varying PWM duty cycles across the pin#10, 11, 12, 13.
The potentiometer could be converted into an LDR/LED assembly circuit, for achieving a friction-less pedal speed control in the vehicle.
Pin#3 is for determining the forward, reverse direction of the motor rotation, or rather the scooter or the rickshaw direction. It implies that now your electric scooter or your electric rickshaw will have the facility of reversing back....just imagine a two-wheeler with a reverse facility, .....interesting?
Pin#3 can be seen with a switch, closing this switch renders the pin#3 to ground enabling a "forward" motion to the motor, while opening it causes the motor to spin in the opposite direction (pin3 has an internal pull up resistor, so opening the switch does not cause anything detrimental to the IC).
Identically, pin#22 switch selects the phase-shift signal response of the connected motor, this switch needs to be appropriately switched ON or OFF with reference to the motor specs, if a 60 degree phased motor is used then the switch needs to stay closed, and open for a 120 degree phased motor.
Pin#16 is the ground pin of the IC and needs to be connected with the battery negative line and/or the common ground line associated with the system.
Pin#17 is the Vcc, or the positive input pin, this pin needs to be connected to a supply voltage between 10V and 30V, 10V being the minimum value and 30V the maximum breakdown limit for the IC.
Pin#17 may be integrated with the "Vm" or the motor supply line if the motor supply specs matches the IC Vcc specs, otherwise pin17 could be supplied from a separate step down regulator stage.
Pin#7 is the "enable" pinout of the IC, this pin can be seen terminated to ground via a switch, for so long as it is switched ON and the pin#7 remains grounded, the motor is allowed to stay activated, when switched OFF, the motor is disabled resulting the motor to coast until finally it comes to a halt. The coasting mode may quickly come to a halt if the motor or the vehicle is under some load.
Pin#23 is assigned with the "braking" ability, and causes the motor to stop and halt almost instantly when the associated switch is opened. The motor is allowed to run normally as long as this switch is kept closed and the pin#7 is held grounded.
I would recommended to Gang-up the switch at pin#7 (enable) and pin#23 (brake) together so that these are switched with a dual action and together, this would probably help to "kill" the motor rotation effectively and collectively and also enable the motor to run with a combined signal from the two pnouts.
"Rs" forms the sense resistor responsible for checking the overload or over current conditions for the motor, under such situations. the "fault" condition is instantly triggered switching off the motor immediately and the IC going into a lock-out mode internally. The condition stays in this mode until the fault is corrected and normalcy is restored.
This concludes the detailed explanation regarding the various pinouts of the proposed electric scooter/rickshaw control module pinouts. It just needs to be correctly implemented as per the shown connection info in the diagram for successfully and safely implementing the vehicle operations.
Additionally, the IC MC33035 also includes a couple of in-built protection features such as under-volatge lockout which ensures that the vehicle is switched off if in case the IC is inhibited from the required minimum supply voltage, and also a thermal overload protection ensuring that the IC never works with over temperatures.
How to Connect the Battery (Power Supply)
As per the request, the electric vehicle is specified to work with a 60V input and the user requests for a boost converter for acquiring this higher level of voltage from a smaller 12V or a 24V battery.
However, adding a boost converter could unnecessarily make the circuit more complex and might add to a possible inefficiency. The better idea is to use 5nos of 12V batteries in series. For sufficient back up time and current for the 1000 watt motor, each battery could be rated at 25AH or more.
The wiring of the batteries may be implemented by referring to the following connection details: