Aluminium Profile Type Router - Initial questions

[Doddy]

Re. your 70VAC. The rated 65VAC would be at the rated power of the transformer, and off-load (or lighter loaded) you would expect the terminal voltage to rise. There's normally an attribute "regulation" applied to the transformer that describes the difference from full load to off load - typically 5-10%, which looks to be the sort of zone that you're looking at here. Reading AirLinks's technical data sheet I can't find the regulation value (though I clearly struggle with their site), although they identify the attribute, and strangely relate it to efficiency which is a new one on me (they're kind of right, but the actual attribute of regulation is in the context of change-of-voltage).

Others here will (rightly, in my eyes) present a cautious (but reliable) approach to all this and recommend a 10% headroom on supply voltage to rated voltage. For a drive with 70VAC max input this is likely to result in a recommendation of 60VAC. Even that's a bit simplistic but it's a useful rule-of-thumb. So lets have a think about where you are now (no-man's land).

Firstly, what you know is what your meter is telling you. That's probably +/-1% or so, and realistically on a cheap meter (just making a blind assumption here) which isn't calibrated and on an AC supply that's probably going to give you +/-2V uncertainty on the display.

Next you're going to have an issue with line regulation. The UK grid used to be 240VAC (domestic), it's currently around 230VAC (-6%/+10%) trying to get to a EU standard of 220VAC (-10%/+6%). Your transformer is likely rated with primaries at 220VAC. If the mains is at 230VAC then you have a 5% uplift on the primary voltage - which will translate to a 5% uplift on the secondary voltage. That's also about where you find your measured secondary. Worryingly the mains supply can rise a fair bit above this - if you're sited close to a big transformer (e.g. on an industrial estate) you might find the supply around the 250VAC mark, with an appropriate rise in terminal voltage on the secondaries.

So, in a nutshell, you're likely to be at or slightly above the rated voltage of the drivers. And you have to figure on this before you consider any load from the drivers on the transformer. And, in an e-stop situation the load from the drivers is likely negligible, so you should design with this open-circuit terminal voltage in mind. I am a bit surprised that your build has got to this stage without attracting some concern from this thread.

Now, I don't know where to start with the driver. Quickly looking back I thought you was looking at LCDA86's - but one of your diagrams shows a LCDA86H - I think that 'H' is significant here as it raises the operating voltage and introduces a AC-supply option to what was previously a DC supply-only, and at a higher voltage. Clearly the non-H variant would require you to rectify the supply and you'd be so far beyond the rating I'd expect you to blow the drivers. If you do have the 'H' variants, then I think you're on the ragged edge.

You might, on paper, be in spec, but only just. You might also be conscious of supply line regulation and want to consider a little head room between the transformer output voltage and the max input voltage of the driver. You might (I would) also squint at the max rating of the driver and wonder if the designer built in some spare float in the electrical design - but the accountants usually engineer that out. Clearly I'm uncomfortable at the voltages (and power!) that you're playing with. It will probably work, but you might expect that the driver to be running to the limit of what it can, and you might find that the life of the driver is compromised, or, that it lets the magic smoke out when you first apply power, or that it runs fine until the end of time. The problem is you're essentially on/outside of the specification of the device and all bets are off.

Personally I'd probably risk it if I could afford to replace the drivers if needed. But, that's a personal (and some would say foolish) choice.

Ideally I'd have chosen a transformer closer to 55VAC secondary and give myself plenty of headroom.

Other than swapping components (drivers or transformer) for others, is there anything you can cheaply do?... not easily - you are looking to drop the terminal voltage without dissipating huge power (heat).

You could add a couple of bridge rectifiers on the secondaries, in series - rely on the non-linear behaviour of the diodes to introduce a typical drop of a couple of volts per device, and throw them onto the cabinet to passively cool them. At full chat these would dissipate about 20W each - not insignificant, but they would provide better regulation than a chunky resistor. The first thing that the driver would do internally is rectify and smooth the supply - all you're doing is adding a pre-rectifier rectifier... it'd work but it's not elegant.

In theory, you could remove a number of windings from the transformer. I wouldn't touch this solution myself - if only for the buggeration involved with this.

Beyond that you're talking serious solutions that would add cost, weight and power. Nothing springs to mind that provides an elegant solution.

Are you beyond the point of returning and swapping the transformer? If not, I'd give that a shot. Next I'd look to sell/swap on the transformer as near-new here, you might be lucky. Or, you can risk it. You might be lucky.

EDIT:

Going back to where I came into this thread... you could always short out the mounting bolt on the toroidal... I hear that puts a bit of a load on the transformer

I'll get my coat.


There's another option with transformer design. You could wind maybe 10 - 20 turns of 13A-rated (min) insulated flex in the opposite direction onto the transformer per secondary, and feed this in series with each secondary. If in phase it'll add a few volts, or if you swap the phase it'll reduce by a few volts (you'll not be able to tell the phasing - just try either way to wire them and measure to work it out). I'm not advocating this, nor will I do the experiment to prove it. It'd introduce additional losses (power) into the transformer but if you was in a corner it might offer a solution.

[JAZZCNC]

Now, I don't know where to start with the driver. Quickly looking back I thought you was looking at LCDA86's - but one of your diagrams shows a LCDA86H - I think that 'H' is significant here as it raises the operating voltage and introduces a AC-supply option to what was previously a DC supply-only, and at a higher voltage. Clearly the non-H variant would require you to rectify the supply and you'd be so far beyond the rating I'd expect you to blow the drivers. If you do have the 'H' variants, then I think you're on the ragged edge.

As far as I know there as never been an "S" version of this drive. I think you may be confusing these with the AM882S which did have an AC "H" version. These drives take both AC or DC.

Now your right on the edge with the voltage so your incoming supply must be on the high side. These drives will run at that voltage and won't give you any trouble provided your incoming supply doesn't fluctuate. The drives do have over-voltage protection, so they should protect them selfs from slight peaks and you will probably get a drop when under load. Only you know your incoming supply so only you can evaluate the risk.

The other option if you don't want to risk it is to throw a bridge rectifier and some Caps on it and go with DC.

If it helps you decide all I can say is I've run these drives at the ragged edge on volts before (I live next to the transformer and my supply can hit 256Vac so my supply is like a box of chocolates.!) without any troubles but I've also blown one of the smaller 50v versions by accidentally pushing too far so they only protect upto a point.!

Or buy a lower-rated supply that suits your incoming supply better. ( If it helps I'll take that one from you )