Help power 5x 15kg servos

Projects General Guidance
1

Hi everyone,

I’m building a small robot arm using 5 S1500M (15 kg) high-torque digital servos and a PCA9685 servo controller, controlled by an ESP32.

I’ve printed the arm to fit MG995/MG996R-sized servos, so I can’t change the form factor.

My problem: I need a reliable power supply to drive all 5 servos simultaneously. Some details:

Servo specs: 6 V nominal, ~2.6 A stall current per servo
Total current: ~ 16 A worst-case (all servos moving/stalled simultaneously)
Voltage: 6–7.4 V is fine
Controller: PCA9685 — it will handle PWM only; servo power comes from external supply
ESP32: powered separately (3.3–5 V), but shares ground with PCA/servos

I’m confused by all the different PSU types I see:

Some have screw terminals numbered 1–8 (I don’t know which are +V/-V)
Some have multiple wires (+, –, FG, etc.)
Some are AC/DC converters or DC/DC modules

What I’m looking for:

A specific, orderable power supply that can safely power all 5 S1500M servos (6 V, 16 A+)
Preferably a wall-powered or DC/DC supply (LiPo battery is okay too)
Something that’s easy to connect to the PCA9685 with screw terminals or wire leads
Bonus: any tips for smoothing current spikes or wiring safely

Thanks in advance for any recommendations I just want something I can plug in safely without guessing which terminals do what.

UPDATE:

Thanks to all the help i've come up with this final wiring and power plan if anyone sees something that might not work please let me know:

I am powering 5 high-torque servos using an ESP32 and a PCA9685. This is the setup I have decided to use:

Power source:
A 12-volt battery pack with around 20,000 to 30,000 mAh. The output connector is XT60.

Voltage regulation:
The battery connects into an SBEC (sometimes called an UBEC or SBEC). It is rated for around 15 to 20 amps peak. The SBEC steps the 12 volts down to 6 volts, which is the correct voltage for my servos.

Power distribution:
The 6-volt output of the SBEC goes into a power distribution board using an XT30 connector. All servo power wires (red and black) connect to the power distribution board. This way all servos get clean 6-volt power from the SBEC through the distribution board.

Servo signal control:
Only the signal wires from the servos go to the PCA9685. The PCA9685 sends only the PWM control signals, not power.

Controller power:
The PCA9685 is powered through its VCC pin from the ESP32’s 3.3-volt or 5-volt pin. I am not using the V+ power input on the PCA9685 since the servos are powered through the separate distribution board.

Grounding:
All grounds are connected together so that the PWM signals have a proper reference. The ESP32 ground, PCA9685 ground, power distribution board ground, SBEC ground, and battery ground are all tied together.

Wire gauges:
The battery to SBEC connection uses 12 AWG wire with the XT60 connector. The SBEC to power distribution board wiring uses around 14 to 16 AWG. Servo wires stay as they are, and signal wires can be thin since they carry almost no current.

This setup ensures the servos get enough current, the ESP32 stays safe, the PCA9685 only handles signals, and everything shares a common ground so the signals work correctly.

2

Please post a link to the servo datasheets to be sure. “Nominal stall” sounds strange.

3

You can buy a reliable 12 V 30–40 A SMPS (these are easier to find), then step down to 6 V with a 30 A adjustable buck converter (DC to DC).

1 Like
4

Servos rated for 7.4V can be powered directly from a 2S lithium battery pack, which is the simplest solution. Choose one with a C rating that allows for at least 16A peak current.

Note that most PCA9685 PCBs are not designed to handle such high currents, so don't try to power the servos from a single PCB. Best to wire the power in parallel.

2 Likes
5

I can give u the aliexpress link haha no datasheet to be found there i just lokked up the stats for this specific model

https://a.aliexpress.com/_EGPkXNK

6

They should be labeled...

7

Please do not go back and edit posts like this.

As you have made a major decision, it needs to be in a new post.

Can you please post a copy of your circuit, a picture of a hand drawn circuit in jpg, png?
Hand drawn and photographed is perfectly acceptable.
Please include ALL hardware, power supplies, component names and pin labels.

Thanks.. Tom.... :smiley: :+1: :coffee: :australia:

8

Nothing wrong with that approach, but instead of simple 6V/15A PSU you now need big battery, SBEC and balancing battery charger.
And you wrote wall-powered was preferred.

9

i know but since someone here said i should try looking into battery packs i just did and it seemed like the simplest solution

10

i dont know this is the first time i used this forum i just handled it like reddit, i havent even built the circuit yet i need to order all the parts.

11

Not to me.
Battery could be simple solution if you go with 7.4V pack (which your servo might/might not tollerate). Balancing charger needed anyway though...