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View Full Version : 400W servo - Leadshine ACS806 + ACM604V60 driver - PSU size?



dsc
22-04-2013, 03:36 PM
Gents,

thinking of getting this combo:

Leadshine ACS806 servo - ACM604V60 Brushless Servo Motor - Leadshine Technology Co., Ltd. (http://www.leadshine.com/Product_Show.aspx?ID=148)
Leadshine ACM604V60 driver - ACS806 Brushless Servo Drive - Leadshine Technology Co., Ltd. (http://www.leadshine.com/Product_Show.aspx?ID=72)

not sure on the PSU. Looking at the specs, servo can go up to 25A peak current, driver can do 18A peak current, so there's a rather big discrepancy there, but those two are suggested by Leadshine as a kit, so I'm assuming (yup, assumption, the mother of all f*ck ups) it's going to work. What I can't find is a suitable PSU for this lot, everything I keep finding is too low on current or I'm calculating something wrong. Servo is 60VDC nominal voltage, peak current 25A, that gives 1.5kW :O is that what I need for the PSU or am I going bonkers?

Regards,
dsc.

Treemonkey
22-04-2013, 05:03 PM
could be surge current or something of that nature when switching the kit on? Im sure if you email they will provide details for you :D

dsc
23-04-2013, 09:29 AM
Ah yes, but I did email them and got...well some information back, saying something along the line of a bigger PSU is not necessarily the best. The peak current of the motor is probably stall current, although I was under the impression that the motor will pull whatever current it needs and you need to provide protection in order to limit that and not fry stuff in the line (so for example stick a fuse in line). The driver can only supply 18A, so that's the first limitation, although I'm not sure what happens if you put a motor which wants 25A on it's end. The other limitation will be the PSU, again protected by it's internal elements and / or additional inline fuses. Teoretically I can use a smaller power supply which is capable of delivering the nominal current, but in case of peak demand it won't deliver more than nominal current, so the driver / servo won't perform very well or a fuse will go 'pop'.

I'm simply wondering what people use for servos, when the servo has very high peak current. Do you simply pick a bigger servo for the application to make sure that normal running conditions are met by the nominal current / torque and pick a supply capable of delivering only nominal current, ignoring peak demand?

Regards,
dsc.

Gary
23-04-2013, 11:57 AM
An AC servo system would be the better option because the power supply is built in.
The leadshine system is a good system, but you need a large power supply that can deliver the peaks that the application needs.

dsc
23-04-2013, 12:21 PM
Thanks for the reply Gary. I might be running well below the nominal torque, which means I'll never get above nominal current either. As I said before, the motor is overspec'd for the purpose, which is one way of getting out from having to buy / make a massive DC PSU. Surely the AC system with a built in supply will have limitations as well, won't it?

Am I correct to think that in heavy duty applications the PSU current capabilities are based on the peak current of the motor? that indeed means massive motors for the bigger servos, which can get up to 80A peak or more.

Regards,
dsc.

Gary
23-04-2013, 12:54 PM
An AC server driver will give you a continuous current and a peak current.
In the datasheet of the motor there will be a torque constant figure and this is typically Nm/A so from this you can work out the peak torque that you can get from the motor when used with that AC servo driver.
However, normally the smallest AC servo driver would be 750W and if we take this as an example the peak current would be 15A and the nominal would be 4A so is 3.75 times the nominal current.
A 750W AC servo driver would be rated to be able to handle the peak current of a 750W motor for the amount of time specified within the specifications.
This is assuming the motor is rated at the 300V DC bus.
A dc servo has a lower DC bus so the current is a lot higher, so that is why you need a larger power supply.
It makes no sense to spend the money on a servo system and then cripple it with a low powered power supply.
Also as a casing point AC servo systems out sell DC by 50:1.

dsc
23-04-2013, 03:07 PM
Again, thanks for the info.

Looked at the range of servos you've got, a 750W would work well I think. One other reason why I was looking at DC servos is that I already have a stepper motor, which will need it's driver and a power supply. That means loads of components, wires etc.

Regards,
dsc.

Gary
23-04-2013, 03:19 PM
Yes the CD422 is the smallest AC servo we do, but can be configured to use the SME60 range of motors that are either 200W or 400W.

dsc
23-04-2013, 06:06 PM
Gary,

good stuff, looking at the specs the CD422 can do upto 750W, so I'll go for a CD422 + 750W AC SMH80 servo.

Regards,
dsc.

Gary
23-04-2013, 06:18 PM
That's a big motor, with a 3:1 ratio that would be a continuous torque of 7.17Nm and a peak of 21.33Nm at 1000 RPM.
Thats a big jump up form 400W.

dsc
23-04-2013, 06:33 PM
I know Gary, but with the smaller 400W motor the peak torque is 3.82Nm and with a 2.5:1 ratio, this gives me less than 10Nm peak. From the tests I've done I need around 12Nm, so I'd rather go slightly bigger and later on downgrade. Plus the price difference between the 400W and 750W is almost nothing, size-wise it might matter, so I'll have a think about it.

Regards,
dsc.