4 ms·

I'm doing an EV conversion, and have trouble wrapping my head around the idea that a motor controller that weighs about ten pounds or so and isn't much bigger t

by elihu 4y ago

I'm doing an EV conversion, and have trouble wrapping my head around the idea that a motor controller that weighs about ten pounds or so and isn't much bigger than a loaf of bread can handle about 100 kilowatts of power, converting DC at around 140-180 volts from the battery to 3-phase AC. And that's a relatively low-end inverter.

virginiadoolf 4y ago
the answer is liquid cooling. these Little Box and ATX power supplies have to rely on passive cooling (radiative, conductive, and convective) which is generally proportional to surface area == physical size ^ 3. if you halve the size, then, you lose 87.5% of the surface area! that's why these things can't shrink as much. but ultimately the silicon involved is miniscule.
- MauranKilom 4y ago
  Not to detract from your point, but surface area scales with size ^ 2.
- elihu 4y ago
  Technically my motor controller can be passively cooled too, it's just not recommended. (It automatically goes into a low-power "limp" mode rather than burn itself out.) I'm not sure how much power it can handle continuously in a pure passive-cooling mode.
- wolrah 4y ago
  It would also be worth noting that a typical EV doesn't have to run at anything close to 100% load for extended periods of time. What sort of power an electric drivetrain can handle for a burst of acceleration lasting a few seconds versus what that same drivetrain can handle as a continuous load are two very different things. The same even applies with combustion powered cars too, if you look at the pickup truck market you'll see massive power numbers on every manufacturer's diesel pickups. If you look at their chassis-cab commercial trucks those same diesel engines are often derated by 30-50% compared to the pickups even while being equipped with larger cooling systems. That's because the commercial variants are rated to perform to spec all day every day where the pickup version just needs to put a grin on the owner's face when they floor it off the line and then occasionally tow a boat or something.

by elihu 4y ago

virginiadoolf 4y ago

the answer is liquid cooling. these Little Box and ATX power supplies have to rely on passive cooling (radiative, conductive, and convective) which is generally proportional to surface area == physical size ^ 3. if you halve the size, then, you lose 87.5% of the surface area! that's why these things can't shrink as much. but ultimately the silicon involved is miniscule.

MauranKilom 4y ago
Not to detract from your point, but surface area scales with size ^ 2.
elihu 4y ago
Technically my motor controller can be passively cooled too, it's just not recommended. (It automatically goes into a low-power "limp" mode rather than burn itself out.) I'm not sure how much power it can handle continuously in a pure passive-cooling mode.
wolrah 4y ago
It would also be worth noting that a typical EV doesn't have to run at anything close to 100% load for extended periods of time. What sort of power an electric drivetrain can handle for a burst of acceleration lasting a few seconds versus what that same drivetrain can handle as a continuous load are two very different things. The same even applies with combustion powered cars too, if you look at the pickup truck market you'll see massive power numbers on every manufacturer's diesel pickups. If you look at their chassis-cab commercial trucks those same diesel engines are often derated by 30-50% compared to the pickups even while being equipped with larger cooling systems. That's because the commercial variants are rated to perform to spec all day every day where the pickup version just needs to put a grin on the owner's face when they floor it off the line and then occasionally tow a boat or something.