First Build - Yet Another Alu Profile Router - 900 x 800

[CaptainBarnacles]

Just before I push the button on a transformer could I just have a quick sanity check please?

Here's my thinking:

I have 4 qty 3A max steppers and I've ordered 4 qty 2DM860H drivers. I reckon that it's highly unlikely to have all four motors chugging away pulling 3A each at any given time so I've assumed 10A as the max draw. The drivers will take AC so I won't have voltage drops and capacitance calcs to take into consideration. I am looking at a toroidal transformer with 2x35V AC secondary windings in series ie 70V AC (the drivers are rated up to 80V AC). Therefor 10A * 70V = 700VA (750VA is the closest standard size).

Am I missing anything?

[Neale]

Can't argue with your arithmetic, but the usual choice is 650VA. In fact, I ran mine with a 500VA toroidal for some time, until it failed. I don't believe that the failure was due to overloading - just one of those things - as it never became particularly warm. I went for one size up because it cost very little more and fitted the space available. There are a few factors here which mean that you tend to get more volts than you would expect. One of these factors is that the transformers will often deliver 5% or so over the nominal value on the basis that it will drop to nominal at full load. 2X35V in series will give you more than you expect, and input mains voltage is also often above nominal so the output volts go up a bit there. Keep this in mind when you are looking at the max voltage input of your drivers.

[Clive S]

Plus one.

[CaptainBarnacles]

Can't argue with your arithmetic, but the usual choice is 650VA. In fact, I ran mine with a 500VA toroidal for some time, until it failed. I don't believe that the failure was due to overloading - just one of those things - as it never became particularly warm. I went for one size up because it cost very little more and fitted the space available. There are a few factors here which mean that you tend to get more volts than you would expect. One of these factors is that the transformers will often deliver 5% or so over the nominal value on the basis that it will drop to nominal at full load. 2X35V in series will give you more than you expect, and input mains voltage is also often above nominal so the output volts go up a bit there. Keep this in mind when you are looking at the max voltage input of your drivers.

Thanks for that Neale. Good point about the output voltage. I have the option of 2x35V, 2x30V or 2x33V (from different suppliers), I think I'll plump for a slightly lower voltage just to be on the safe side.

Is there anything to be gained from using 4 qty 160VA transformers over a single 625VA? My thinking is that I could assign a transformer to each driver. I can get the 4 160's for about £15 more than a single 625VA so the price difference is neither here nor there. I suppose it would be cheaper to replace a 160VA in the even of a transformer failure but I wondered if there was any performance benefit to the system?

[Neale]

Can't think of any particular advantage of 4 individual transformers, except that it enforces good wiring practice - separate connections from PSU/transformer to drivers, with no daisy-chaining from one to another. Yes, could replace one if it fails, but you need more space to mount them. Swings and roundabouts!

[CaptainBarnacles]

Can't think of any particular advantage of 4 individual transformers, except that it enforces good wiring practice - separate connections from PSU/transformer to drivers, with no daisy-chaining from one to another. Yes, could replace one if it fails, but you need more space to mount them. Swings and roundabouts!

Yeah, I like the idea that there are four completely separate channels - I imagine it will help with fault finding too. Space isn't too much of an issue, I'll probably design an enclosure to suit the kit that I have rather than try and shoehorn everything into a given space.

I've been making some (albeit slow!) progress on my design over the weekend. I am getting frustrated with Fusion so I decided to go back to the beginning and watch some tutorial videos to try and understand the basic concepts, I am still thinking in Sketchup! I guess you can teach an old dog new tricks, it just takes a bit longer

Inspired by Joe Harris' YouTube series I thought it might be fun to try and document my build in the same way so I have started recording my build in the hope that something I have to say may help others. I am not sure I can add anything to Joe's impressive videos but I reckon the more information that's out there, the better. And if nothing else it should be entertaining to watch me bumble my way through the whole project!

[AndyUK]

And if nothing else it should be entertaining to watch me bumble my way through the whole project!

Can't wait! :D

[CaptainBarnacles]

I'm back!

It's been more than a year since my last confession. In that time I've moved house, changed jobs, started new projects and generally transitioned into a new life. The best part is that I now have a huge (but very cold) workshop in which to play and more time to play in it!

I have been slowly accumulating parts and ideas for my CNC router and I'm ready to pick up my project again from where I left off. I am currently pondering my motion controller choices (AXBB-E, Acorn, old PC with LinuxCNC or other - I think I've ruled out Mach3/4), sourcing some cheap aluminium plate (seemingly no such thing exists!) and refining my design (still struggling with Fusion).

When I get something that you won't laugh at I'll post my latest design for a bit of critique and guidance.

Cheers!

[Kitwn]

When I get something that you won't laugh at I'll post my latest design for a bit of critique and guidance.
Cheers!

That's exactly why there are no detailed photographs of my machine on the forum.

Re Fusion 360: I know it's very powerful, it's free and I would benefit significantly from mastering it, but every time I try to get competent in it's use I get frustrated instead and return to my old friend CamBam.

Kit

[Neale]

Personal view - F360 is well worth struggling with, although I'm not sure where you start. It is a steep learning curve at first and, to be honest, I suspect that personal tuition from a friend who knows it is the best way to go. Once you are off the ground, then the videos start to come into play. One problem is that based on reputation the best series of tutorials available online are those from Lars Christenson but they were made a couple of years ago and the F360 user interface has changed a bit since then. Not massively - an experienced user would very quickly see and adapt to the differences - but for a beginner, things like saying "Select the Model workspace" is a bit misleading when it is now called the Design workspace. I've done a bit of tuition for local model engineering club members so I'm aware of some of the problems beginners have and I'm not sure that they are addressed very well in the online tutorials. That's all true, anyway, for the CAD and modelling side of it. CAM and gcode production is a different issue where things are a whole lot more complicated but for design work, keep bashing at F360, get a bit of help if you can from someone you can actually ask questions, and you'll get there.

You will find a few photographs of my machine in a thread here somewhere. People did laugh. Nevertheless, the machine works, and it works better than i ever expected. I'm doing a fair bit of detailed machining in steel these days, which isn't bad for a machine designed and built for working with wood. Keep at it - you' ll get there!