Was about to get a toy- then I did some research...

[AndyUK]

Firstly, as the drives can take AC, is there any need to convert the output current from the torodial transformer to DC? As I've understood in case I go for AC to AC I could simply connect the first winding to the mains (with fuse for safety) and the second directly to the drives? Also, assuming no DC conversion, is it safe to use a 70VAC rated torodial transformer to power the drives rated at max 70VAC?

If the drives take AC, don't bother rectifying it into DC. Go straight from the transformer to the drives. Don't daisy chain them though. Size the transformer by taking the max motor current (e.g. 4A) times the number of motors (3 or 4), so lets say 12A, then reducing by 1/3rd, so 8A. Don't go too overboard on the VA of the transformer, get what you need. Bigger transformers can suffer from large amounts of inrush current which can trip the power and just be a pain without other compensation.

Now, if I've understood correctly the total amps my 4 steppers will draw is roughly 2/3 of the sum of the rated amps of the steppers, i.e. 4*5A*2/3=13,33A. So the PSU would have to supply (rounded up) at least 14A? As the torodial transformer is rated at only 6A, should I consider wiring several in parallel to get more amps or would it be better to simply look for a beefier one to supply all the current i need?

Well clearly I should have read ahead because you already know the method. Oh well, not editing it now. No just get a larger VA transformer. You probably need 1000VA based on your 13.3A current, but that seems a little high? Most of us have 500-600VA transformers when turning into DC, perhaps someone can shed more light on this.

And so the voltage. This has me the most confused, some recommend to not over do the voltage for fear of getting components burnt, while others prefer higher voltages in order to not lose out on max performance (however, in these cases drives usually have some sort of voltage regulators). Now, if I've done the math correctly the Vmax of my parallel wired steppers is 32*√(2.4mH) = 49.6V., so well within the 70VAC outputted by the torodial transformer so as to get the most out of the steppers, BUT (and see first question above) would I run the risk of overheating my drives/steppers with this setup? The drives I've been offered (Lichuan LCDA86H) do list "overvoltage protection", but this sounds to me more like a fuse type protection than active voltage regulation.

I think most people tend to ignore Vmax and just give them as much as the drivers can manage, then limit the current on the drives so they don't burn. Typically with 3.2mH motors with a Vmax around 58V people use 68V (convenient toroidals are available). Basically I think you want the motors to be warm but not burny hot (demagnetisation occurs when they hit a certain temp).

The overvoltage protection you talk about is interesting though - what do the drives spec for the voltage?

[NeoMorph]

What AndyUK said about larger transformers tending to pop breakers and blow fuses due to high inrush current is right. The less is said about the time I was working on a DIY boost converter for my electronics course, and blew out the power to an entire wing of the YMCA I was living in, the better. That was back in mid 86 so they might have forgiven me now lol.

That was down to high inrush current as well.

But the good news is inrush current can be reduced pretty easily. See here...

http://www.ti.com/lit/an/slva670a/slva670a.pdf

[Juranovich]

Well clearly I should have read ahead because you already know the method. Oh well, not editing it now. No just get a larger VA transformer. You probably need 1000VA based on your 13.3A current, but that seems a little high? Most of us have 500-600VA transformers when turning into DC, perhaps someone can shed more light on this.

Yes! Pretty please! The problem seems to be (assuming 1000VA is an issue- as I'm quite unqualified to judge) that 4-4.5nm steppers seem to be rated at 4-5A and with 4pcs that quickly adds up.

I think most people tend to ignore Vmax and just give them as much as the drivers can manage, then limit the current on the drives so they don't burn. Typically with 3.2mH motors with a Vmax around 58V people use 68V (convenient toroidals are available). Basically I think you want the motors to be warm but not burny hot (demagnetisation occurs when they hit a certain temp).

The overvoltage protection you talk about is interesting though - what do the drives spec for the voltage?

For the record it also lists overcurrent protection. If you're after the input rating it's 20-70VAC and 30-100VDC. Is that what you were looking for?

When your're saying to max the voltage, shouldn't there be some room for the transformer to fluctuate (upwards) from the rated voltage? In this case the transformer outputs 70V which is also the max of the drives. Also regarding overheating, is it the wattage/VA that is the decisive factor or can voltage alone cause over heating? I'm thinking if higher than rated voltage is passed through a circuit but at lower than rated current (i.e. less than rated watts are being fed), shouldn't there then be "unused" resistance in the circuit to avoid overheating? If so, is higher than rated voltage more a question of the structural integrity of the circuit? Or does it maybe manifest in the same way in the end, i.e. burning components...? In the current case the transformer outputs 70V at 6A = 420VA and the drivers can take 70V at 8Apeak = 560VA. Even if I had 4 transformers in parallel and 4 drives in parallel, respectively, the total wattage would still not exceed that of the drives' capabilities. So getting back to what you said about maxing voltage and limiting current, as the drives can take more current than the transformer outputs, I should be on the safe side?

sorry, for the ramblings, my thinking hat came on while writing this...also b/c curious!

[Clive S]

For the record it also lists overcurrent protection. If you're after the input rating it's 20-70VAC and 30-100VDC. Is that what you were looking for?

If you are just going to put AC in then I would not go more that 60V AC as the mains can and does fluctuate.

[NeoMorph]

If you are just going to put AC in then I would not go more that 60V AC as the mains can and does fluctuate.

This ^^^^^

Mains electricity is very “dirty” in some areas. Stick a scope on the mains and you would be shocked to see how bad it is at times. It’s the reason if it was me I would at least have a voltage regulator in the circuit at the very minimum. Cleans up that dirty power a treat.

[Clive S]

This ^^^^^

Mains electricity is very “dirty” in some areas. Stick a scope on the mains and you would be shocked to see how bad it is at times. It’s the reason if it was me I would at least have a voltage regulator in the circuit at the very minimum. Cleans up that dirty power a treat.

What are you on about You can supply a drive with a toroidal, rectifier and some caps ie DC or just use a toroidal and use the rectifier and caps in the drive.

That’s why I’m thinking a decent UPS would at least let you shut down safely. Or is my OCD going overboard again?

I think you are going overboard a bit here and frightening new users into things they just don't need

[NeoMorph]

What are you on about You can supply a drive with a toroidal, rectifier and some caps ie DC or just use a toroidal and use the rectifier and caps in the drive.



I think you are going overboard a bit here and frightening new users into things they just don't need

No no no, I’m asking the question of experienced users. I’ve only got experience of an openbuilds machine at present and haven’t had the pleasure of building a larger CNC so the op’s question and your reply about mains fluctuations made me think about running tests on the local power grid.

I can’t remember the figures from my last test but I do have the kit still.

I still remember the time back in Cannock where I was sitting in offices and suddenly the ceiling fans turned into scary propellers. Turned out the distribution centre had supplied twice the rated frequency for a while... blew a ton of mainframe terminals throughout the building and only the fact that it tripped the generators protected the two mainframes we had downstairs (IBM 370/158 and IBM 3033).

That truly is a worst case scenario but check your local power. Mine is ruddy awful at times, especially around 6pm. My oven is flashing the clock timer at me because we had a brownout yesterday.

But ultimately I don’t know much about mains system and I haven’t touched anything 3 phase or high voltage this millennium... so I’m very much the noob asking questions.