I am using a power supply with a DC 12v 10amp output and I want to use two of the outputs to control multiple Arduino server motors. Each servo motor needs about 6v and I want to be able to control 15 of them. I was thinking of taking one of the outputs and make a positive and negative rail with a terminal block to power all my servos. I was going to use resistors to step down the voltage first, but I don't know if 12v 10amps is too much to put through a resistor.
1 Like
If the motors draw 10 amps under 6V you would burn (12-6) x 10 = 60w in your resistance…. That a lot…
Use a few step down modules
Is there any way to step down the voltage using resistors?
The motors don't draw 10 amps, the power supply I'm using supplies 10 amps
There is no good way. For the circuit you describe, it would mean gross power waste, clunky big components, and really bad voltage regulation.
Not really.
I was using that power supply to power stepper motors and I had 2 left over. I was hoping I could use them to power the servos too.
two output pins left over*
Electrons don't care what you hope.
should I get another power supply that supplies 6v?
See reply #2
The servo motors don't need 10 amps
You already told us that.
He said
i.e. read the whole response...
What if I get resistors that have a higher current rating?
If you want to understand WHY THIS WON'T WORK you need to understand a few things.
-
Ohm's Law defines the relationship between voltage, resistance, and current. For example, 12V across 1.2 Ohms means 10 Amps through the resistor.
-
The power supply doesn't put-out 10A unless you have a 1.2 Ohm load.
-
Power (related to heat) is calculated as Voltage X Current so in the above example the resistor would have to handle 120W. The average resistors we use everyday are usually 1/4W or less. But there are big high-power resistors. Resistors have a power (wattage) rating, not a current rating. (Of course the maximum current can be calculated from the resistance & power rating.)
-
The resistance of a motor isn't constant... It's resistance changes depending on conditions and it "craws" more current with a heavy load or when accelerating.
-
You CAN make a voltage divider (where the voltage is divided proportionally to the resistance). If the resistors are equal you'll get 6V across each resistor. You can make a voltage divider where the "bottom" resistor is the motor instead of a resistor but the problem is that the motor's resistance isn't constant.
As long as you understand the same current flows through series components you can use Ohm's Law and then you should be able to understand how a voltage divider works.
Voltage dividers are used all the time with low-current signals but they are not used for power. The same concept is how a current-limiting resistor works with an LED. LEDs are non-linear (their resistance varies with voltage) but they are predictable and it's low-power so it works. (High power LEDs use different methods of controlling/limiting current.)
Then you will have a clunky, power wasting circuit but with improved voltage stability.
Use a 6V regulator, e.g a 7806 and supply it from your 12V supply. You also need a few filtering capacitors on the input and output of the 7806. It's capable of up to 1A maximum. If you need more use two or three of them and split your servos supply between them.
This is a good page explaining these regulators. (It's using the 7805 5V but the 7806 6V is used in exactly the same way.) https://www.electronicshub.org/understanding-7805-ic-voltage-regulator/
No offence, but that one is an elegant, power wasting circuit with great voltage stability.
and how do you suggest the OP gets 6V from his 12V supply?