For a project I need to control a DC Motor I ll state the specifications of the motor and also the issues we are facing :-

Motor Specifications :-
7800 rpm
12V
15 amps
torque 50 kgf/cm (That is what the seller told us)
185 watts

Load Specs :-
A solid Wheel around 1.5-2 kg with diameter 32cm is mounted on it

Motor Driver :-
16 amps continuous
30 Amps peak

The problem :-
When connecting a 12V lipo battery directly the motor runs continuously but the connecting wires get way too hot.
When connecting through the motor driver the motor starts and stops almost immediately and the wires are also heated up as before.
As I need speed control removing the motor driver is not an option. Please let me know asap if i am doing something wrong

 

When you say the wires heat up- are they sized for the high current this motor draws?

What happens when you run the motor with no load? (no wheel)

That big wheel is going to store a lot of energy going 7800 RPM, when the motor starts up - the current will be limited only by the armature resistance, which is very low. Once the thing spins up, the current will be lower.

You are going to need a soft-start system to keep the current within bounds while the wheel spins up.
It's probably tripping your driver's current limit, shutting it down.

 

Start-up current for that motor could be over 100A! Use heavier gauge wire.

 

What is the format of the drive for the motor? PWM etc?
Max.

 

When you say the wires heat up- are they sized for the high current this motor draws?

What happens when you run the motor with no load? (no wheel)

That big wheel is going to store a lot of energy going 7800 RPM, when the motor starts up - the current will be limited only by the armature resistance, which is very low. Once the thing spins up, the current will be lower.

You are going to need a soft-start system to keep the current within bounds while the wheel spins up.
It's probably tripping your driver's current limit, shutting it down.

The same wires had been used before for a bldc which used to draw 30 amps current. With no wheel it runs without a problem. Could you elaborate what a soft start system is?

 

Start-up current for that motor could be over 100A! Use heavier gauge wire.

How do you determine max current it draws ??(100Amps) Also what should be the ideal gauge of the wire for 100amps

 

What is the format of the drive for the motor? PWM etc?
Max.

PWM through an Atmega2560

 

You need to have the PWM start at a very low duty cycle until the motor spins up.
Ideally, the PWM could be controlled to set a current limit.

The full-on starting current is limited by the internal resistance of the motor and battery, these values can be very low- leading to damaging levels of current flow.

 

How do you determine max current it draws ?

Find out its DC resistance Rdc (manufacturer data, or measure it). Imax = Supply volts / (Rdc + Rbattery). Since the 100A (or whatever) is for a relatively short time and the rated current (for full load running) is 15A, wire rated for ~ 30A continuous should barely get warm.

 

You just need something to give that wheel a little shove right as you apply power.
Can you find room to put something small like a spring?
Adding that additional energy from the rim of the mass at startup will let the motor begin acceleration immediately instead of just drawing massive current until it can nudge the mass to make any movement at all.

Forgive the suggestion being mechanical. I tend to look for better ways to perform a job from that approach first.

 

50 kgf-cm is only 3.62 ft-lb of torque, max.
It may be that the motor is sized too small for the load and speed requirement.

 

Like others said, hot wire means there is a lot of current going though the wire. Be glad that it only gets hot. If you had even more current, you would have melted the insulation, if you had even more current, you would have started fire because insulation would have started to burn.

You need bigger wire. I sort of assume that the battery is using 18 or 16 AWG wire. 18 AWG is rated for 7 A of current. 16 AWG is rated for 10 A of current. You said it yourself that the motor will draw during normal operation as much as 15 A, that is 14 AWG wire, to be safe use 12 AWG which is rated for 20 A.

 

You need to find a method to gradually ramp up the angular acceleration. A single step increase is more than the motor can comply with.

 

How do you determine max current it draws ??(100Amps) Also what should be the ideal gauge of the wire for 100amps

The method for detecting the maximum current draw, (when stationary) is to apply a very small DC voltage to the motor with a locked rotor, then measure the current draw, this will give you the armature resistance.
Use a couple of positions on the armature, take the lowest reading.
Do NOT use an Ohm meter as the results are not so reliable.
You can also calculate the load current by rpm measurement when running at a certain DC voltage, and compare to the expected rpm at the no-load rpm.
Max.