considering 4ga wire upgrade?

[gornoman]

This is where I just sit back and read the mail. In a few hours I will learn something again. Gotta love this forum.

[TerryH]

Originally Posted by glassk

No more brushes in that Line, an extra set with separate power to add counter EMF voltage to the armature letting it build faster. Not sure if it could be done externally, anyway.

Hmmmm....couldn't imagine how to do that but sounds interesting.

[TerryH]

Originally Posted by gornoman

This is where I just sit back and read the mail. In a few hours I will learn something again. Gotta love this forum.

Is that good?

[gornoman]

Heck yeah it's good. Unlike some other forums in this hobby this one actually produces results people can use.

[TerryH]

Originally Posted by gornoman

Heck yeah it's good. Unlike some other forums in this hobby this one actually produces results people can use.

K. I was thinking that I was out on a limb.

[gornoman]

Nah, that's MY job!

[greg-g]

Sergio can you repost this 50% duty cycle, (PWM) is at full voltage. Agreed this looks like 24 volts to the motor as far as speed, the current should be the close throughout the system

Originally Posted by Sergio

Any time the PWM is less than 100% the current from controller to motor is higher than battery pack to controller.

At 50% Armature PWM (half-throttle), the motor side will be getting 24v (assuming a 48v system).

So 100 amps at 24v would be only 50 amps on the 48v side.

The current will never be higher than the maximum the controller can deliver, and being that it only happens at less than WOT (100% PWM), the current is likely always less than the maximum that could flow through all cables.



There is no benefit in making the motor cables of a heavier gauge.

Edit: Unless of course You have one of those "slightly" modified carts like TerryH, a Zilla controller with a specialized hairball that optimizes current ramp to neck braking rates and an over-sized battery pack used as an energy buffer .

[Sergio]

I will try to better explain my post, if we were talking about a simple switch turning a resistive load on/off, then I agree that the peak current would be the same in the entire circuit.

That simple linear model does not work for a dc motor controller for a few reasons:

Motor Inductance:

The motor is a big inductor, so when the PWM turns OFF, the motor will oppose the sudden change of current (like a relay coil), a circuit is provided to allow the motor current to continue to flow when the PWM is OFF.

Since the PWM frequency is ussualy very high, the motor inductance can easily smooth those transitions and the motor current will be almost constant due to this "flywheel" effect, which is also the name of the circuit that provides the current path for the OFF cycle.

On the Battery side:

When the PWM turns OFF, the battery current also stops immediately and a small voltage spike is created, the capacitors inside the controller absorb most of this spike (the battery also acts as a capacitor in this case).

When the PWM turns ON again, there is an immediate demand for current and the battery (plus wire inductance) cannot react that quickly, so the large filter capacitors in the controller provide that "peak" power.

Since the PWM frequency is again very high, that process "smooths" out the current flow.

If we use DC to represent PWM Dutty Cycle, and assuming a 100% efficient controller, we can build the simple equation:

Vbatt x Ibatt = Vmotor x Imotor

We also know that: Vmotor = Vbatt x DC

So if a motor is demanding 10amps from a 48v battery bank, the current in the motor circuit can be resolved by.

Imotor = (48v x 10amps) / (48v x 10%DC) = 100amps

I may have over simplified the explanation (the Back EMF when the motor is turning also affects the current equations), but there is a lot more in-depth information available in this subject from internet sources if You want to research.

[scooterman]

Good post Sergio.
Not to scramble eggs but before the controllers there was restive control to the motor, could you enlighten that process some because even as simple as they seem there is a lot to how it works.