Help in connecting Ground together for different Voltages

[Korawy]

Hi all...

I am making a robotic project, which I have to fix its speed whatever the slope of the surface.

The Problem is in The Power System..

First I have 3 different voltages one for the Microcontroller, the second for the Coil of the relays, The third for the Motors.

I was connecting the coil of the relays with the voltage of the micro, but i found problems in encoder readings, so i had to connect the coils of the relays to a different voltage.

But The Relays are controlled by the Micro, So i have to connect the ground of the micro voltage to the ground of the coil relays voltage.

Also I connected the ground of the motor voltage with the ground of the micro voltage( To control the speed using Mosfet).

Now i have three batteries each is 6V-4Ah , I connected them in series to get 18v (motor voltage), I want also to get 6v to the coils of the motor, so i took two wires from one battery (one of the three batteries connected in series) to get 6v and put them to the power of the relay, But when i do this I found that the wire get too hot (the ground wire), as i connect all grounds together...

Im sorry for long post..

Hope to find help

 

[phobos1]

check for any short

 

[HTA]

If you have three batteries in series you have a common ground(minus pole of the first battery) and the 6V, 12V and 18V. Correct? All ground connections need to be to route to the common ground(star connection) and have a low enough resistance to avoid too much voltage drop(or heat). The 5V(?) microcontroller needs also be able to drive the 12V relay and the 18V motor through special driver and protection against spikes when switching the coils. More interfacing hints: https://www.eevblog.com/forum/suggestions/interfacing-microcontrollers-with-industrial-devices/ .

Enjoy your design work!

 

[BradtheRad]

But when i do this I found that the wire get too hot (the ground wire), as i connect all grounds together

Assuming there is no short circuit...

Your ground wire may need to be thicker.

When all motors are on, the common (ground) wire probably carries several amps.

 

[Korawy]

Thanks All, i was mistaken in something and found that there's a short(as im connecting all grounds together), I was thinking to get 6v to pic and 6v to relays, but not from one battery...