Linear Toroidal PSU for DYN2+400W DMM servos

I'm thinking of using the above servos and was looking at the option of putting together a linear PSU. (240 input)


Now, I have zero experience in CNC, or building a PSU. I'm busy learning what's needed, its a big subject which I'll have to break down into smaller projects, including the PSU.

I've done some rough calcs and I'm learning the theory but any helpful tips at this stage would be greatly appreciated.


What toroidal spec would I need to run 3x 400W servos, at their rated spec, and during peak torque? (i'll likely be using a Mitsubishi Inverter FR-D720S but that will run off mains. I'm thinking of using a small PC power unit 5/12v for any secondary control circuitry, and I know people add overwindings, which would be handy to run a timer on the inrush setup)


Also, what configuration do I use on the secondary windings. Serial/2 Hots + centre tap, Parallel etc
*some electrical engineers recommend not to use the PSU in balanced config, unless the upstream devices are built for that. i.e. 2 hots. Their argument being that if there is an internal fault/short, and even if one phase circuit breaks, the other side can remain hot.


Cheers


P.S I had thought of running the 640s with DYN4, as it negates the use of the linear supply, as a decent PSU build, might cost (in the UK) as much as the extra for the DYN4s?

I have modded a few Toroidal Transformers, the turns per volt works out to about 1.5 to 2 T/volt, if you don't need any regulation for the control circit, a simple bridge is all that is needed.
The Toroid needs to be sized for a suitable Va, for servo calc, they do not draw full power all at the same time.
I just add a single winding per supply with a full wave rectifier.
Al.

Thanks AI (I saw some of your previous posts with helpful info re linear PSU... actually I think it was why I started looking into it.)

I've got some idea of the circuit design, including the different rectifier options/smoothing etc but was wondering about specing the actual transformer, re the secondary winding(s), and how best to wire them for DYN2s use. E.g put them in serial, v- vmid v+, or in parallel.


So far I'm looking at a 1000VA Tx but not sure about picking the correct secondary winding combination. e.g 2x25v, to 2x33v, which would be used in series. Or go for higher voltage secondaries say 50-60V but run them in parallel to get the higher current.


I had been working on the assumption of calculating backwards. i.e DYN2 need 60v + 10-20% headroom, then reduce by a peak factor, to get a working RMS value... so roughly 50-55v with 15-20A
These Tx seem to output more volts than their datasheet, and I didn't want to risk an overvolt, although I've now seen others mention using a 68v Tx.

Not sure what you mean by picking the secondary winding's, what supply voltages are you wanting to end up with, When winding on it pays to go full circle with the winding if it is a low turn one, space the conductors in order to get the whole winding on a 360deg pattern, if that is what you mean.
Al.

I'm referring to the secondary outputs that already come with the Tx when purchased, rather than custom overwinding. The overwinding was only a possible option, the main area was picking the correct secondary winding for the DYN2 setup.


So e.g, the Tx will come with 2x25v, i.e 4 cable ends that can be joined in series to get 50v, with a centre tap as gnd. This creates two hots, or some call it balanced V- (-25), V+ (+25) plus Vmid

Or, the 4 wires can be joined in parallel producing 0-25v. (you'd pick a higher voltage, this was just to illustrate what I mean). My confusion is whether the DYN2 needs a circuit design that has two hots (series) or needs to see 0 to 25v (or whatever you eventually pick for the max voltage).


Sorry if I'm not making myself clear.

Sounds like you're over-complicating things. The DYN2 needs 60V DC. Simple.
Max RPM will be dictated by the voltage, if you choose to use less than 60V.

If using the two 25v winding's, I would not GND the CT, if rectifying 50vAC followed with a smoothing capacitor you end up with close to 70VDC.
You could reduce accordingly by removing a few turns of one winding if needed.
Al.

Thanks guys.

ger21. True but I've read many conflicting 'best practice' designs, and a few electrical engineers get hot under the collar when people suggest using two hots (series), rather than 0-to whatever voltage value, if the upstream device hasn't been design to to handle that arrangement.
Also, as AI mentions, the final voltage output can be higher, so was wondering what Tx others have used for their linear PSU.

My rough PSU framework: inrush circuit, Tx, rectifier, capacitors + bleed resistors, (optionally some additional filters and or something to prevent spikes but this maybe overkill)

with most transformers sold in the UK designed for Europes 230V and not the UK's 240V supply
what is your mains supply voltage ?

In my part of Lancashire the mains voltage is 243 to 248V depending on the time of day (now at 14:37 its 247V)

if your mains supply is 240 V and your aim is to get 60V DC output you may need a transformer like this from RS components

RS Stock No. 123-4005

input 230V +/- 10%
output 40V ( 41.76 V off load )

https://uk.rs-online.com/web/p/produ...B&gclsrc=aw.ds

PDF data sheet

https://docs-emea.rs-online.com/webd...6b81524cbe.pdf

John

Quote:

---

Originally Posted by rvectors

Thanks guys.

ger21. True but I've read many conflicting 'best practice' designs, and a few electrical engineers get hot under the collar when people suggest using two hots (series), rather than 0-to whatever voltage value, if the upstream device hasn't been design to to handle that arrangement.
Also, as AI mentions, the final voltage output can be higher, so was wondering what Tx others have used for their linear PSU.

My rough PSU framework: inrush circuit, Tx, rectifier, capacitors + bleed resistors, (optionally some additional filters and or something to prevent spikes but this maybe overkill)

---

You do need to use an output filter as per Dmm spec's, Dc voltage up to 68v Dc to 70v Dc filtered is fine for the DYN2 drives

Thanks John, Mactec appreciate the help.

I must confess I do not (yet) have the required tools to give me that granular measurement... I had been working on the assumption of around that variation, based on other discussions, even into the low 250s.


I might see how much this guy charges, canterburywindings, his temp rise specs are all 40c and below, and since the machine would eventfully sit in a space that gets hot in the summer, heat is a consideration. I imagine his prices will reflect his quality.