# How to calculate required voltage + amperage for a linear servo array?

I would like to control a set of 10 Linear actuators for a robotics project.

The actuators require:

• 3.7VDC operating voltage
• 150mA unloaded travelling current draw
• 450mA stalled current draw

The Arduino UNO requires 5VDC to operate. Say I power the linear actuators externally, what kind of calculations do I make to figure out how much power I need to get them to work for at least two hours?

So worst case scenario is that the 10 actuators are constantly drawing 450mA, so I need a power source that can provide 10 X 450mA = 4500mA.

So this means I need to purchase something like this battery which provides 12v at 4500mA assuming I also connect a voltage regulator to drop to 3.7V?

## Update #1

It was suggested (thank you Douglas B. Staple) that I use a Lithium IOn battery because they are a standard at 3.7V this way I would not need to use a regulator.

However, how can I account for the duration of servo usage based on mAh? I previously calculated that since I have 10 servos I would need 4500mAh battery. But how long will that last?

## Update #2

Just so that I understand this correctly: Say I want to extend the number of actuators to 32. This means 32 x 150 mA = 4,800 mAh. This means I would need 5 x "18650 cells" to run all 32 actuators continuously for 2 hours?

Using a voltage regulator to drop to 3.7 V is a bad idea, that would generate (12V - 3.7V) * 4.5 A = 37 W of heat. However, note that 3.7 V is the voltage of a Li-ion cell, which is great for you, because Li-ion batteries are the standard for energy-density per unit weight in batteries.

The capacity in mAh will be determined by how long do you need your battery life to be. Unless your actuators are stalled all the time (bad), you will only need 150 mA / actuator while they're running. 150 mA * 10 = 1500 mA, which means that if you run all 10 actuators continuously for 1 h, you will use 1500 mAh.

I would probably try a single modern 18650 cell, they can provide up 3.7 V at up to 20 A: with a capacity of 3000 mAh, a single one of these batteries would be (nominally) able to run all ten actuators continuously for 2h.

Be careful, though:

1. Li-ion cells should have protection circuitry to prevent under-voltage or over-charging.
2. I have not built anything with 18650 cells before. I'm suggesting them because they have the right rating for your task, and they're really popular (probably the most popular type of Li-ion cell).
3. Not all 18650 cells are created equal.
• I see, so I should use something like this: ebay.com/itm/like/… Commented Oct 28, 2016 at 16:50
• Just updated my answer to address the rest of your questions. Commented Oct 28, 2016 at 17:15