# Thread: Help w/ power supply for a 3-axis servo system

1. ## Help w/ power supply for a 3-axis servo system

I am attempting to assemble a power supply for my servo system and want to make sure that I am making the proper calculations necessary for a suitable match. I could really use any help or advice that anyone can offer me on this since I am a complete newbie when it comes to electronics.

Here's the data that I'm basing my power supply requirements on:

motor specs:

model: KL23-120-36 (keling nema23)

terminal voltage: 36VDC
cont. current: 4A
peak current: 19A
torque constant: 420z/in.
torque peak: 230 0z/in.

amplifier specs:

model: Gecko G320

under voltage rating: 18V
over voltage rating: 80V
current limit: 0-20A

servo gear ratio: 3:1 (precision planetary gearhead)
ballscrew pitch: 5mm (5tpi)

With this setup I calculate approximately 220 ipm @ 690 oz/in at it's full potential power limit. Since I will be fitting this system to a small x3 benchtop mill I will likely never have a need to reach half that speed or torque but I'm hoping that this system will make a nice match for the x3 nonetheless. (If I can get this pwr supply sorted out!)

So, here are my system's power requirements:

system voltage requirement: 36V
amplifier under voltage limit: 18V
amplifier over voltage limit: 80V

Based on the above data I calculated the following values:

Acceptable power supply range: 42-60V
power supply output current: 13.7A per axis [Based on this formula > IPS=Vm x Im / Vps x (.98)]

From what I've read and understand, the ouptut current requirement will increase for each axis so these need to be added together. However, this is where things get real unclear for me because it becomes a matter of theoretical requirements which are based on averages, etc..., and so this is where I could use some help from a member with some real-world hand's on experience.

If I add the max current for each axis together then I end up with a pwr supply current requirement of 41.1A and this seems like overkill to me. All three axis would have to be at peak power to pull this kind of current and unless I'm missing something here it seems like that would never happen in this application.

So, my question is this then; if I can get by with a lower current value then what value would be ideal? Is there a formula or a value that I can factor in that will help me calculate this or is it all theoretical speculation requiring a trial and error method? I imagine that the intended load requirement is one of the biggest factors in determining the output current requirement but this makes it difficult to determine. It's also difficult to commit to a specific load range because, ideally, it would be great to have a system that could take advantage of the full-range of the mill's mechanical capabilities and work envelope - rather than being biased in one direction or the other. In other words, a well-balanced system that is a good overall match for the mill it's driving. This may all be wishfull thinking right?!

So, based on the information I've provided would this torroidal transformer be a good fit to base my power supply system on?

power output: 1294W
voltage output: 40V
current output: 32A

2. I think I might have found a solution hopefully. I ended up getting 3 separate regulated supplies so I can dedicate one for each axis. They're pretty high-quality Lambda's rated at 48V / 10amp but are set to output 42V and I got them off the block for \$25/ea.

I have read mixed things about regulated supplies so I'm going to have to find out how these work w/ my setup once I get them in hand. Anxious to see how it can handle the spikes that might occur. Will post my results when I have them.

3. You should be able to base your servo current requirements on the cont. current, the peak is the absolute maximum before demagnetization, which you should never approach, your drives should be set to max out at a little over the cont. current rating.
Al.