Hi everyone!
Together with a couple of friends I am converting a small 18ft canal boat (about 750 kgs unloaded) to electric.
We hope you can provide us with some help in the motor selection.
The required motor power is roughly 1.5 kW constant, with peaks up to 3 kW. The propeller shaft rotational speed is max 800 rpm.
We are planning to use a belt transmission (ratio obviously dependent on the motor, but probably around 1:3 - 1:4).
For us, it most important that the motor runs at a high efficiency at low powers (400-1000 W), and that the motor has a long lifetime (a couple thousand hours).
We plan on DIY'ing a LiFePo4 battery pack. We can cheaply get 3.2 V, 90 Ah cells, but these are 2 kg/piece which limits the maximum voltage of the pack since the battery has to be portable. Therefore, the max system voltage is 48 V, though lower would be better.
Currently, we are considering this (BLDC synchronous) motor:
- Golden motor HPM3000B 48V 3kW (https://www.goldenmotor.com/)
There is a performance curve of the motor on the website, but that is at max power. What would happen to the efficiency curve of the motor when lower powers are required? I ask this because we would have to select the gear ratio, and are wondering how to size that so that the efficiency is as high as possible when cruising at low speeds (while retaining peak power at max speed). Is the efficiency curve for BLDC motors roughly constant relative to torque, or more relative to rpm when the controller limits the power? My best guess was that it would be pretty much constant to torque, but will shift a bit to the left (so higher efficiencies at low torques) but I am not sure.
Also, would it be a good idea to undervolt the motor? Say we put in a 36V battery pack and run the motor on 36V instead of 48V. How much lower would the power and efficiency of the motor be? We would still be able to use the same controller, right?
If undervolting is not too bad for efficiency but only significantly lowers power, could we also run one of the following motors on, say, 36V? If their output power drops by half, that wouldn't be a issue for us.
- QSmotor QS138 72V 3kW (http://www.cnqsmotor.com/en/article_read/QS%20138%203kW%2072V80KPH%20Mid%20drive%20motor%20with%20new%20appearance%20belt%20design/869.html)
- LMX motor 60mm 72V 3.1kW (https://lmxbikes.com/en/drivetrain/138-moteur-lmx-60mm-2018.html)
Ideally, we would find a high efficiency motor which we can run at 24V, get peak powers from of 3 kW for under €750 including vat and shipping to the Netherlands.
Together with a couple of friends I am converting a small 18ft canal boat (about 750 kgs unloaded) to electric.
We hope you can provide us with some help in the motor selection.
The required motor power is roughly 1.5 kW constant, with peaks up to 3 kW. The propeller shaft rotational speed is max 800 rpm.
We are planning to use a belt transmission (ratio obviously dependent on the motor, but probably around 1:3 - 1:4).
For us, it most important that the motor runs at a high efficiency at low powers (400-1000 W), and that the motor has a long lifetime (a couple thousand hours).
We plan on DIY'ing a LiFePo4 battery pack. We can cheaply get 3.2 V, 90 Ah cells, but these are 2 kg/piece which limits the maximum voltage of the pack since the battery has to be portable. Therefore, the max system voltage is 48 V, though lower would be better.
Currently, we are considering this (BLDC synchronous) motor:
- Golden motor HPM3000B 48V 3kW (https://www.goldenmotor.com/)
There is a performance curve of the motor on the website, but that is at max power. What would happen to the efficiency curve of the motor when lower powers are required? I ask this because we would have to select the gear ratio, and are wondering how to size that so that the efficiency is as high as possible when cruising at low speeds (while retaining peak power at max speed). Is the efficiency curve for BLDC motors roughly constant relative to torque, or more relative to rpm when the controller limits the power? My best guess was that it would be pretty much constant to torque, but will shift a bit to the left (so higher efficiencies at low torques) but I am not sure.
Also, would it be a good idea to undervolt the motor? Say we put in a 36V battery pack and run the motor on 36V instead of 48V. How much lower would the power and efficiency of the motor be? We would still be able to use the same controller, right?
If undervolting is not too bad for efficiency but only significantly lowers power, could we also run one of the following motors on, say, 36V? If their output power drops by half, that wouldn't be a issue for us.
- QSmotor QS138 72V 3kW (http://www.cnqsmotor.com/en/article_read/QS%20138%203kW%2072V80KPH%20Mid%20drive%20motor%20with%20new%20appearance%20belt%20design/869.html)
- LMX motor 60mm 72V 3.1kW (https://lmxbikes.com/en/drivetrain/138-moteur-lmx-60mm-2018.html)
Ideally, we would find a high efficiency motor which we can run at 24V, get peak powers from of 3 kW for under €750 including vat and shipping to the Netherlands.