AC-DC Power Supply

[TimDC]

I'm trying to find a power supply for a large 3-axis CNC mill. Please bare with me as this isn't my field (mechanical engineering student) and please tell me if there's any information that I've left out. That being said, I'll get right to the specifics:

Input: 220VAC (3 Phase)
Controller: G320 Servodrive Max VDC: 80V Max Current: 20A
Motors: MT-4525-BTYCN DC Servo Motor x 3

These are theoretical values at the moment, but, two motors will be run at 80V 15A, and the last will be run at 80V 20A.

The biggest power supply I've found so far is this DuraComm Corp. RM2548 (48VDC 20A).


Please leave you feedback if you've seen a power supply that would meet my needs, or think that my needs are a little unreasonable.

[Al_The_Man]

First, I would look at linear supplies, rather than switching type, also you do not really need regulated supply for servo's.
Are they going to be used on a 3 phase supplied machine or 1 phase?
Have you looked at building one, its fairly simple, lots of previous posts here covering it.
Al.

[TimDC]

Thanks for the feedback, I'm currently looking into exactly what we'll be using. (and what some of that means )

[TimDC]

Alright,

The unregulated linear looks like that way to go, thanks.
We'll have a 3 phase supply
And, I think that building one is looking like the only option, so I'll be looking around the forums for pointers on that (and seeking some in-person prof. help).

I still search for these every now and again but I keep coming up with variable ones that have their max's as their specs. For example, I found a 40V 50A DC supply, but it was actually a ~500W. I don't think the manufaturers realise that they're not making finding their products very easy

[pastera]

You are in a different realm when you are talking about supplying 1200+ watts to a motor.

Talk directly to several power supply manufacturers to get a solution.

Vicor has some units that can do what you need but they are in the $3400-$4000 range for a 80v 50A supply.

Aaron

[pastera]

Another question,

Are the currents you are quote the peaks currents for the motors?

If so, you will not actually be using anywhere near those figures. The peak currents are the max current before you get permanent damage to the motor so you never actually run the motor at or near those levels. Even if you do, the motor could only take the peak current for a few seconds max.

Aaron

[Al_The_Man]

Originally Posted by TimDC The unregulated linear looks like that way to go, thanks. We'll have a 3 phase supply And, I think that building one is looking like the only option, so I'll be looking around the forums for pointers on that (and seeking some in-person prof. help).

The reason I asked if you had three phase and the Mill already uses 3 phase, then I would be tempted to make one with 3 phase transformer for the DC supply as it is much more efficient that a 1 phase supply, especially if your motors do happen to be on the large side, you just need to use a three phase bridge instead of a 1ph, and they are not much more money.
Al.

[NC Cams]

Why do you need such large motors???

Even some "big iron" Bridgeport mills were powered with motors quite a bit smaller.

There is/may be a reasonable possibility that your "needs are a little unreasonable".

[Bubba]

Looking at the link given in post #1, 24 amp is the PEAK current.
If you do some research, Mariss is given some good formulas on converting forces>watts required and from that, you can derive voltage and current.
Remember also the 80V rating of the gecko's INCLUDES back EMF. Therefore, you don't really want to use an 80V supply. I have seen suggestions that 72V max is about it.
You need to do some calculations on what you expect your loads to be (use a safety factor) and then figure it out. Again, I have seen Mariss throw out a figure of about 500 lbf for the cutting force. In my case, with the mechanics that I have, it figures out to about 115 watts being required. Then if you have a three axis machine, you don't expect all axis to working at top figure all the time so you figure max VA required and multiply by 2/3's to come up with a reasonable power supply. I also second Al's recommendation for a linear supply vs a switching supply as there have been good reasons posted for NOT using a switcher for this type of application.

Bubba

[Al_The_Man]

Good points, The motors he quoted only take 6.6amps normal stall current.
Personally I design a power supply voltage for around 120% of motor max terminal voltage.
Also it has been my experience that normal cutting forces are not where max torque current occurs, but on accel/decel.
If you have a Y mill axis that has the combined weight of the X axis motor and table etc and also any part load that is carried by the table, you could be looking at a couple of hundred pounds at least, now if you rapid that load at 100 ipm, or even say milling a right-angle at 20ipm, this load is expected decel and accel from 20 to 0 to 20 in in an extremely short time, this combined with cutting force, places a high demand on any system.
This is where the motor/load inertia ratio calculation is important.
Al.

[TimDC]

Thanks all, this is giving me alot of things to bring to discuss with the guys I'm working with. We can hammer out some numbers out and see where we can go from there.

I think that we're going to have to just slow down the acel/decel and cutting speeds to whatever rate is managable with whatever reasonable power supply we're able to get.

Bubba: Who/what is Marris?

[Bubba]

"Mariss Freimanis" is the gentleman behind the gecko series of drives. He is very active on this and other on line activities and is/has been very helpful to the community providing a wealth of information in addition to producing great products. If you do a search, I think you will find more information than you really care to know on the subject.

Bubba