# max current for a servo high torque

Hello,

I uses that servo

So I will powered it with 2 lipo battery of 3.7v & 2200mah in parallels so I have 7.4v & 2200mah.
because lipo battery voltage variate between 6.0 and 8.4v, a step down module power will assure me that I always have 7.4v.

But I can’t find anywhere the max current and the stall current for the servo.

some specs of the servo
Operating Voltage: DC 6.0V-7.4V
Operating Speed: (6.0V) 0.15 sec/60°
Operating Speed: (7.4V) 0.13 sec/60°
Stall Torque: (6.0V) 48kg.cm
Stall Torque: (7.4V) 62kg.cm
Dimensions: 65.8X30X57.4mm.

thanks for all.
Paul

The rule of thumb for a standard servo of about 3-4kg.cm is 1A, and yours is about 15x as torquey (62 vs 3-4) at about the same speed. Since power = torque x speed, if the torque’s 15x higher then you’re up in the realms of 15A.

Let’s check that: 62 kg.cm is 6.1Nm and 0.13 s/60 is 8.3 rad/s so the power is 6.1x8.3 = 50W mechanical. Allow for double that for the electrical supply for losses, and yep that’s 100-odd watts which is 14A.

I didn't knew the "rule of thumb for a standard servo of about 3-4kg.cm is 1A"

Again thanks.

Pavlacki:
I didn't knew the "rule of thumb for a standard servo of about 3-4kg.cm is 1A"

Nor did I but it seems to be the number thrown around the forum

Pavlacki:
So I will powered it with 2 lipo battery of 3.7v & 2200mah in parallels so I have 7.4v & 2200mah.

And just to be clear, if you want 7.4V you need to connect in SERIES not in parallel.

Steve

I wonder if that battery can produce the best part of 20A though.

Even if it can, with 2Ah @ 20A that's 2/20 hours, not much more than 5 minutes.

Pavlacki:
Hello,

That probably takes over 10A peak current, BTW, its mechanical output power is of the order of 50W
calculated from the torque and speed

So I will powered it with 2 lipo battery of 3.7v & 2200mah in parallels so I have 7.4v & 2200mah.

In series, not paralllel, and the symbol for amp is A, never a.

because lipo battery voltage variate between 6.0 and 8.4v, a step down module power will assure me that I always have 7.4v.

A step down module cannot turn 6.0V to 7.4V. You’ll struggle to find one at 15A, you don’t need it
anyway.

But I can’t find anywhere the max current and the stall current for the servo.

Same thing. The torque is 6Nm, the speed about 8rad/s, so 48W mechanical (roughly)

some specs of the servo
Operating Voltage: DC 6.0V-7.4V
Operating Speed: (6.0V) 0.15 sec/60°
Operating Speed: (7.4V) 0.13 sec/60° <<- ie 8 rad/s in SI units
Stall Torque: (6.0V) 48kg.cm
Stall Torque: (7.4V) 62kg.cm <<- ie 6.2Nm in SI units
Dimensions: 65.8X30X57.4mm.

thanks for all.
Paul

Again Again Again great thanks.

I make a mistake : of course my battery are in series (shame on me ).

I think that I will put 6 x ( 2 x 2200mah) so I will have 13.2A in 7.4 v.
That will put lot of weight on my robot.

@MarkT

2 lipo in series provides
charged at 0% : 6.0V
charged at 20% : 7.4V
charged at 100% : 8.4V

so i need to step-down the voltage
and never used the battery under 20% of charge

am i correct?

Pavlacki:
I think that I will put 6 x ( 2 x 2200mah) so I will have 13.2A in 7.4 v.
That will put lot of weight on my robot.

No, no no....

Capacity is not current. Capacity is charge. 13.2Ah is nothing to do with 13.2A.

Its like confusing distance for speed!

2 x 2.2Ah cells in series will be fine if they are 10C or above... You actual longevity from a full
charge depends on the average current draw, not the peak, so that depends a lot on what you
do with the servo.

thanks,

I forget that point.
I check, they are 20C.

So it enough.

Again thanks for all the people who kindly help me.

62 kg.cm is 6.1Nm and 0.13 s/60

62 kg.cm is the stall torque.
And I'd guess 0.13s/60 is the unloaded speed.

The greater the load, the slower the speed.

14A is really not realistic.
Look at the wires. You think that little connector can handle 14A?
I have no idea how much current that servo draws, but it's not 14A!

Probably closer to 4A then 14A.

Good point on the puny wiring.

With a DC motor one could simply measure the winding resistance but of course with a servo the control electronics masks that: I suppose one could take one to pieces.

Buy one and measure the current?

Side note: why do so few servo specs state the current? (I've only seen a few that give it.)

Daenerys:

62 kg.cm is 6.1Nm and 0.13 s/60

62 kg.cm is the stall torque.
And I'd guess 0.13s/60 is the unloaded speed.

The greater the load, the slower the speed.

14A is really not realistic.
Look at the wires. You think that little connector can handle 14A?
I have no idea how much current that servo draws, but it's not 14A!

Probably closer to 4A then 14A.

Why not - this is an RC device, its normal to run things very hard (silicone insulated wire and
gold-plated connectors are commonplace because the wires get very hot). If the ratings are
accurate that servo is 50W mechanical at 7.4V, so the current will be high, 10+A is likely.