3 ms·

Why is the regenerative braking limited to .25g? Even if they can't charge the battery faster than that, couldn't they dissipate the extra power some other way

Why is the regenerative braking limited to .25g? Even if they can't charge the battery faster than that, couldn't they dissipate the extra power some other way?

kbuck 13y ago
They effectively do dissipate the extra energy already - as heat, from the physical brakes. If they can't charge the battery faster than .25g of breaking would provide, there's no reason to put increased stress on the engine (it's much more expensive than a physical braking system).
dmmalam 13y ago
Some electric trains actually do this, they dump the energy as heat in a bank of resistors. The motor on a tesla is on the rear axel, but most braking power is dissipated from the front axel due to the weight transfer. The question is if you also had a front axel motor (like the Model X), how much regen could you do. I remember reading somewhere that induction motors don't regen that well at low RPMs, hence you need to supplement with friction brakes. Anyone with a better understanding care to comment; would it be possible to build a car with no friction brakes, just 100% regen? I suppose you could always apply a counter torque to the motor.
- jstanley 13y ago
  "would it be possible to build a car with no friction brakes, just 100% regen?" No. The force provided by regenerative braking is proportional to your speed. Without friction, it would be impossible to reach 0 speed.
  - dmmalam 13y ago
    So the regen force would still exist (?), just it would be really small, and so taking a long time to fully stop. Would it be possible to apply a reverse torque to the electric motor to decelerate faster. For example, I'm thinking about a hypothetical race car that could have no traditional hydraulic braking system to save weight, a large amount unsprung.
deleted 13y ago
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sliverstorm 13y ago
Keep in mind the regenerative braking is only on the rear wheels, and it is the front wheels that usually do most of the braking.

Why is the regenerative braking limited to .25g? Even if they can't charge the battery faster than that, couldn't they dissipate the extra power some other way?

kbuck 13y ago

They effectively do dissipate the extra energy already - as heat, from the physical brakes. If they can't charge the battery faster than .25g of breaking would provide, there's no reason to put increased stress on the engine (it's much more expensive than a physical braking system).

dmmalam 13y ago

Some electric trains actually do this, they dump the energy as heat in a bank of resistors. The motor on a tesla is on the rear axel, but most braking power is dissipated from the front axel due to the weight transfer. The question is if you also had a front axel motor (like the Model X), how much regen could you do. I remember reading somewhere that induction motors don't regen that well at low RPMs, hence you need to supplement with friction brakes. Anyone with a better understanding care to comment; would it be possible to build a car with no friction brakes, just 100% regen? I suppose you could always apply a counter torque to the motor.

jstanley 13y ago
"would it be possible to build a car with no friction brakes, just 100% regen?" No. The force provided by regenerative braking is proportional to your speed. Without friction, it would be impossible to reach 0 speed.
- dmmalam 13y ago
  So the regen force would still exist (?), just it would be really small, and so taking a long time to fully stop. Would it be possible to apply a reverse torque to the electric motor to decelerate faster. For example, I'm thinking about a hypothetical race car that could have no traditional hydraulic braking system to save weight, a large amount unsprung.

deleted 13y ago

[deleted]

sliverstorm 13y ago

Keep in mind the regenerative braking is only on the rear wheels, and it is the front wheels that usually do most of the braking.