Advice on buying servos.

**Agathon** · 10-07-2017

Originally Posted by Gary

Yes, but there are different types of absolute. you have single turn and multi-turn, the name is self-explanatory.
Also, Absolute encoders have a much higher resolution than incremental.

Thanks. I notice that you have both DC brushless and AC servos on your website - what are the advantages and disadvantages?

**Gary** · 10-07-2017

Originally Posted by Agathon

Thanks. I notice that you have both DC brushless and AC servos on your website - what are the advantages and disadvantages?

One take DC and the other takes AC, so the AC servo driver has a power supply built in that is rated to the nominal and peak rated current of the driver.
Also Just because it's a DC servo does not mean its brushed, a DC servo can be brushed or brushless.

**Agathon** · 10-07-2017

Originally Posted by Gary

One take DC and the other takes AC, so the AC servo driver has a power supply built in that is rated to the nominal and peak rated current of the driver.
Also Just because it's a DC servo does not mean its brushed, a DC servo can be brushed or brushless.

OK, that's a very concise reply, but why buy a DC over and AC and vice versa?

**Gary** · 10-07-2017

There are a few reasons, but this one normally gives you an indication.
Ok, lets say you have a machine with 8 axis and each axis needs a servo, that is not too large.
you can get 8 AC servo motors and driver and you will be paying more because each driver has its own power supply.
with the DC option, you will have 8 DC servo drivers and a large power supply.
Also DC servo motors are typically low voltage DC, so the current is higher, so typically the motors dont go too big (under a KW)
Personally, i would not even consider a DC servo system, unless you know why you need it. AN ac servo system is typically a better option.

Originally Posted by Agathon

OK, that's a very concise reply, but why buy a DC over and AC and vice versa?

**Agathon** · 10-07-2017

Originally Posted by Gary

There are a few reasons, but this one normally gives you an indication.
Ok, lets say you have a machine with 8 axis and each axis needs a servo, that is not too large.
you can get 8 AC servo motors and driver and you will be paying more because each driver has its own power supply.
with the DC option, you will have 8 DC servo drivers and a large power supply.
Also DC servo motors are typically low voltage DC, so the current is higher, so typically the motors dont go too big (under a KW)
Personally, i would not even consider a DC servo system, unless you know why you need it. AN ac servo system is typically a better option.

Right, so AC servo drivers aren't typically 240vac SP input then and need a step-down transformer?

**Gary** · 10-07-2017

No, AC is AC, regardless of the voltage.
Typically single phase goes up to about 1.5KW
For a hobby machine, its unlikely you will need anything that big.
Even a mill like Bridgeport MDI /Interact can use 750W easily.

Originally Posted by Agathon

Right, so AC servo drivers aren't typically 240vac SP input then and need a step-down transformer?

**Agathon** · 10-07-2017

Originally Posted by Gary

No, AC is AC, regardless of the voltage.
Typically single phase goes up to about 1.5KW
For a hobby machine, its unlikely you will need anything that big.
Even a mill like Bridgeport MDI /Interact can use 750W easily.

OK, so just to be clear. A 400W AC servo motor would typically be coupled to a driver powered by AC at a voltage less than 240v? So is the power supply simply a step-down transformer or is there more to it?