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I'm running an RC car which has two zytd520 12V 150rpm dc motors run through an L298N motor controller. I'm going to use reverse current braking to save on weight and complexity of mechanical parts. I'm just not sure how to calculate the size of the dynamic braking resistor I'll need to attach to each motor circuit.

Any help?

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  • \$\begingroup\$ P = t * w, where 'P' is power (in Watts), 't' is torque (in Nm) and 'w' is rotational speed (in rad/sec). So start by figuring out how much power the brake resistor will be dissipating. Then you can use P = V^2/R. For 'V' use the back emf of the motor at the fastest speed you need to brake at. You can calculate the back emf using the KV of the motor. V = rpm/KV. Then solve for 'R.' \$\endgroup\$ – mkeith Sep 21 '17 at 4:28
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L298 is not the best full bridge unless it for higher voltage since it is only rated for 2A with 4.9V total drop and thus the VI loss itself is like a 2.5 Ohm power resistor. A MOSFET bridge is far more efficient. so if you motors are rated for they are a poor match for 12V motors.

That being said the brake R is determined by the max colling heatsink for 2Adc with total resistance in both coils 7.1V drop on the motor 2A. then using current sensing and PWM, regulate the current to 2A until stopped.

Lets say the motor DCR of both coils is 1.5 ohms then the surge current is 7.1V/1.5A% to maintain 2A.

If you can afford and want full power consider. http://www.robotshop.com/en/sabertooth-dual-5a-motor-driver.html

A cheaper solution is two of these https://www.amazon.com/dp/B01H1W79S0/?tag=stackoverfl08-20

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