BLDC Outrunner Over-Voltage

[nemondemon]

Good afternoon, I'm currently in the process of building an electric scooter where I have chosen the APS 8072S 165KV as my motor. I had originally planned to use 3x 5S LiPo packs in series to match the maximum voltage of the motor (63V as stated on the website). I've since realised the packs I'd planned to use (GNB 8200mAh) are in fact LiHV chemistry meaning the voltage at full charge will be 65.25V. Do you think this voltage increase of 2.25V above maximum will be an issue? I'm also unsure whether a BMS exists which can manage balancing of LiHV cell voltages but that's another topic... TIA

 

[lnanek]

The motor wouldn't care. It's a big blob of electromagnets. Higher voltage just means it spins faster and might overheat a percent more. Hall sensors are voltage sensitive, but are normally fed 5V from a low voltage converter in your controller anyway.

Whatever controller you get might have voltage limits, though. The components in a controller, like the MOSFETs, all have a specified max voltage they break down at.

 

[nemondemon]

The motor wouldn't care. It's a big blob of electromagnets. Higher voltage just means it spins faster and might overheat a percent more. Hall sensors are voltage sensitive, but are normally fed 5V from a low voltage converter in your controller anyway.

Whatever controller you get might have voltage limits, though. The components in a controller, like the MOSFETs, all have a specified max voltage they break down at.

Thanks for your help. My controller will be rated at a voltage in excess of what's required so hopefully that shouldn't be an issue. Overheating of the motor is more my concern; I guess it's pretty hard to quantify without testing although I hoped someone might have experience trying something similar

 

[scianiac]

Yeah no issues if your controller is rated for the voltage but I would tend to stay away from LiHV packs since they are known to have poor lifespans. Although maybe that's not as true now, I remember when LiHV packs first gained popularity for drones, many made by GNB of course and they had good energy density, OK current density and meh lifespans. I don't know though since many electronics batteries (cell phones) now come with LiHV cells and those seem to have decent lifespans but they are a totally different beast considering they are max energy density and not power density. But if you consider RC lipos already have lower lifespans than commercial cylindrical cells, that being said I still use them and it's really a matter of how often you are cycling them and how much you care about replacing the battery someday. And they are of course technically more dangerous.

 

[nemondemon]

Yeah no issues if your controller is rated for the voltage but I would tend to stay away from LiHV packs since they are known to have poor lifespans. Although maybe that's not as true now, I remember when LiHV packs first gained popularity for drones, many made by GNB of course and they had good energy density, OK current density and meh lifespans. I don't know though since many electronics batteries (cell phones) now come with LiHV cells and those seem to have decent lifespans but they are a totally different beast considering they are max energy density and not power density. But if you consider RC lipos already have lower lifespans than commercial cylindrical cells, that being said I still use them and it's really a matter of how often you are cycling them and how much you care about replacing the battery someday. And they are of course technically more dangerous.

Thanks! All good points

 

[amberwolf]

Good afternoon, I'm currently in the process of building an electric scooter where I have chosen the APS 8072S 165KV as my motor. I had originally planned to use 3x 5S LiPo packs in series to match the maximum voltage of the motor (63V as stated on the website).

The only reason I can think of they might have a voltage limit that low, when they specify the kV that high, is if the motor is constructed so that it's physical RPM limit is close to or at that point, and they're not made to withstand spinning faster than that.

If they have a separate RPM limit that's higher than the voltage lmiit x kV (10,395RPM), then that's not the reason for the voltage limit.

The windings can probably take at least a couple hundred volts, depending on the enamel used.

Overheating of the motor is more my concern

This is pretty much down to cooling and usage scenario. These types of small high speed motors are intended to be used in low-load fast-spinup applications with high airflow (driving propellers in aircraft), so if you are using it in a ground vehicle application wehre it will have high loads at lower speeds, you'll probably have to create a forced-airflow cooling system driven by a separate motor to ensure no overheating.

They don't have the thermal mass to absorb a big heat spike, so the way they reliably create the power they are "rated" for is by spinning up to their operating RPM as close to instantly as possible, and using the massive airflow a prop / fan generates at that speed to keep themselves cool.