[DRIFT_BUGGY]

Just came accross this

The load from the motor determines how much current is drawn from the batteries. Batteries don’t push current, hence you cannot have too large or too high a discharge battery. The ESC, between the motor and the batteries has two jobs. First, it run the motor by analyzing the motors back EMF then sending commutation pulses to the motor based on its analysis of the motor. This involves much more than knowing the position of the rotor, there are several complex algorithms that, by analyzing the back EMF, set the computation pulse advance to get the most power and efficiency of out any motor is it running.

Its second task is to control the speed of the motor to the users command. It does this with Pulse Width Modulation or PWM. PWM works by turning full throttle current on and off very fast. The portion of the pulse that is 'on' in relation to the part that is 'off' determines how much power the motor sees. I.E 50% on, 50% off the motor sees 50% power. The PWM switching rate is 13,000 times per second (13 khz). DC power sources, in this case batteries, do not like high current being switched on and off, they want to put out steady current. The ESC wants to see square waves, instant full on, instant full off. However, the battery takes time to go to full on and won't switch off immediately. This creates a sloped instead of a square wave. The caps on the ESC are there to get the PWM pulse back closer to a square wave. The reluctance of a battery to put out pulsed current also creates a side affect called 'ripple current.' The caps also control ripple current. The less capable a battery is of keeping up with the current demands of the motor the higher the ripple current. If the capacitor overheats or get completely drained from inadequate batteries the caps will burn or blow up and the ripple current cascades thought the power board burning up the ESC. The other primary cause of ripple current is resistance on the battery side of the circuit. A plug with too much resistance, long or too small battery wires, bad connections etc. will increase ripple current, possibly to catastrophic levels. I cannot prove it but my guess is that more of our ESCS are burned up from inadequate batteries than over current.

The minimum discharge rating for cells used with a Monster Max is 75 amps continuous, burst to 150 amps. This is a minimum to keep ripple current low enough to make sure the batteries don’t damage the ESC, more is better. Also, the more capable the batteries the more torque the motor will produce.

To answer the question of why don’t NiMh batteries damage the ESC is the fact that these cells voltage drop quickly under load then climb back. The drop in voltage protects the system from the motor pulling too much amperage and creating too much ripple current.

With high power electrical systems, the battery is the most important part of the system. Saving money on batteries not only gives lower performance, it puts the ESC at risk. Choose your batteries wisely.

Bernie Wolfard
Supervisor, Product Support
Castle Creations
235 S Kansas Ave.
Olathe, KS 66061