Servo power supply external or internal

Just few questions about power supply for a servo. The servo will be driving an electrode holder for spot welding, basically lowering and raising the electrodes.

  • Would it ideal to use a cap in parallel to the servo positive and GND would thereby avoiding an external power source
  • use another linear regulator for the servo or in parallel to the existing so as to get enough amps to all the components including the servo and the IC.
  • replace the transformer with a higher current rating and route an individual power to the servo using an npn transistor

I know the recommended way is to use an external source but am trying to avoid another PCB for power the servo.

The Spec to the Servo is
Dimensions(mm): 40.3x20.2x37.2
Weight(g):52.4
Speed(@4.8V sec/60): .18
Torque(@4.8V oz-in): 222.2
Speed(@6.0V sec/60): .15
Torque(@6.0V oz-in): 277.7
Gear: Titanium & Aluminum
Bearing: 2BB
Case: Aluminum
25 Tooth Spline
Frequency: 250-333
Pulse Width Frequency: 1520
Running current (at no load): 100 mA @ 4.8V
Running current (at no load): 120 mA @ 6.0V
Stall current (at locked): 4000 mA @ 4.8V
Stall current (at locked): 5000 mA @ 6.0V
Idle current (at stopped): 5 mA @ 4.8V
Idle current (at stopped): 5 mA @ 6.0V
Limit angle: 200°±10°
Connector wire gauge: #22 AWG
Connector wire length: 250 ±5 mm
Horn gear spline: 25T
Control system: Pulse width modification
Amplifier type: Digital Controller
Operating Travel: 100° (when1000→2000 μsec)
Neutral position: 1500 μsec
Dead band width: 3 μsec
Rotating direction: Counterclockwise (when1500→2000 μsec)
Pulse width range: 800→2200 μsec
Maximum travel: Approx 130°(when900→2100 μsec)

  1. No.
  2. best of the bunch.
  3. No. Silly idea.

Thanks Mike !

Generally, with a servo this size, I'd recommend against a linear regulator. If I read your schematic right, the input is rectified 50V, which would work out to an average of 35~volts. Dropping this to 6V for the servo at it's stall current (5A) would result in 5A*(35V-6V) = 145W of waste heat if I'm not mistaken!
Not only is this extremely high, the 50V input is too much atleast for the 7805 regulators I have anyway.

I would suggest a switching power supply, they are quite cheap and are much better when powering anything other than micro servos.

Jopj:
Generally, with a servo this size, I'd recommend against a linear regulator. If I read your schematic right, the input is rectified 50V, which would work out to an average of 35~volts. Dropping this to 6V for the servo at it's stall current (5A) would result in 5A*(35V-6V) = 145W of waste heat if I'm not mistaken!
Not only is this extremely high, the 50V input is too much atleast for the 7805 regulators I have anyway.

I would suggest a switching power supply, they are quite cheap and are much better when powering anything other than micro servos.

That is just the bridge is rated for not the actual voltage across it. The transformer spec is here. The voltage at the bridge is 11.4v. Moreover i was thinking of getting this servo. The servo in my previous post was something i had laying around.

anishkgt:
That is just the bridge is rated for not the actual voltage across it. The transformer spec is here. The voltage at the bridge is 11.4v. Moreover i was thinking of getting this servo. The servo in my previous post was something i had laying around.

Ah, makes sense. That other servo if a lot smaller, but would still likely need a heatsink on a TO-220 regulator. It's a shame that the switching power supplies sold at Hobbyking are not exactly pcb-friendly, those are great for powering the multiple servos on large RC models.

i was thinking of using the LM338T to power the board and this servo. Just a few questions about the IC before i order them.

Would it possible to get two different voltages like 5v and 7v from the LM338T. if so would this circuit be correct ?
7338T.png

Oh sorry drew it wrong the input will be about 11.2v But what about the dual voltage another LM338T perhaps ?

The way I read the LM338T data sheet, the input must be greater than the output, and you can't get 7v out of a 5v input.


Are you planning on using two parallel regulators? Even if the current can be supported, I don't think its a good idea to have the Arduino and the servo on the same regulator.

Just few questions about power supply for a servo. The servo will be driving an electrode holder for spot welding, basically lowering and raising the electrodes.

Spot welder? You will need to be aware of inductive interference from the high current paths, and keep
your stuff as far from those conductors as possible.

Initially, yes two parallel. Read it was a bad idea to have two regulators in parallel so was looking at this IC. yea of course not 7v from 5v regulated. What was i thinking ? all these to drive the servo. waiting for components to arrive. So nothing is confirmed with what i will go with. Quite some options to try before i can finalize.