160 vdc power rabbit hole...

On a sunny day (Sun, 30 Jan 2022 23:38:27 -0500) it happened DJ Delorie snipped-for-privacy@delorie.com wrote in snipped-for-privacy@delorie.com:

Meanwell switchmode power supplies with 15 V DC output at 2.4 A will work with AC or DC input and are dirt cheap

I have used the 12V version of that supply. They are nicely made and work fine. Meanwell have a USA and a UK website. The data sheets for most of their power supplies are reasonably good and it is often possible to find the technical reports used to support their regulatory submissions, but you may need to search different country websites to find them. John

Yup, and I've got one. I just thought a few dollars worth of on-board parts would save space and wiring. In the end, a separate "logic" power supply probably makes sense anyway. We'll see :-)

People make tiny pcb mount things that are AC-line to DC supplies, lower power.

Like this:

It's minor, but why bother with providing 240 to the machine in the first place? The losses from a full bridge rectfier will by minimal, and a half rectifier across 240 doesn't even balance the load, so you still need the neutral. There's just no benefit to this design. The fireworks factor goes up with 240, and while low rating double pole breakers exist, they are usually costly and hard to get.

Isolation won't kill you and smaller to even couple kVA machine tool transformers can be used for isolation, and don't cost too much, even off ebay. They usually come in 120/240 and sometmimes 480V primaries, all selectable and

The spindle needs 240 anyway.

Right, that's the benefit - you still use the neutral, and it's usable as the zero volt point. That means the circuit's "ground" won't be 120v away from earth ground.

And it's not quite a half rectifier; it's two half rectifiers on opposite polarities. The result across the caps is the same as a 120v full rectifier.

It shouldn't - 240 center tapped means no single wire is more than 120v away from earth ground, It's no more dangerous than a 120v circuit in that respect.

Note that in the USA the center tap is grounded, so we have two 120v live conductors of opposite polarity, or 240v across them.

Yeah, that becomes "power supply" which is what I did in the past, with bigger and bigger transformers...

Math-wise, the machine needs 4 servos at a nominal 2A, 8A peak, so 120v

• 8 * 4 = 1 KVA minimum, 4 KVA peak?

(and yes, there should be a betting pool on how long before the machine destroys itself ;)

fair enough.

You still have 240 across the two rectifiers, and the higher potential fault currents. I work with machines and the destruction, even with fuses on 208/240 circuit boards far exceeds anything you'll see with 120. It really is an entirely different game.

The rectification will decrease the power factor, so figure higher than that. Sustained full stall current on all axis sounds semi-unlikely unless you have some sort of incredible crash or like switching all directions at once under full load. Use lots of fuses.

I hope it's not the wooden one in the photos. It's nicely constructed.

Good to know. Maybe I'll design the driver boards "as if" they were live (isolated I/O) but use an isolated supply anyway, until I need more power.

The drivers can limit the current in a stall via software, but yeah. Peak power is if all three axes accelerate at the same time.

Worst case is a full deceleration of all three axis at once, because of the regenerative braking. My previous driver board didn't have a TVS on the driver board itself, and a loose power connection during hard braking resulted in a spike way outside what the board could handle.

I suspect the new software will need to watch for overvoltage, and either fault or at least stop using regen. I might use one of the old boards to *just* switch in braking resistors. And by "resistors" I mean "light bulbs" because who doesn't want a light show? ;-)

That's the old one, and yes, these servos were on it. It *did* self-destruct once. Drove the spindle right through the side upright. It's feeling much better now :-)

The nice thing about DIY is that it's also repair-it-yourself. Or at worst, you build another one ;-)

Chain driven machinery can do some scary stuff when timing is off or something does slip. The forces can be pretty wild. I like how belts will at least slip or break before thing get too nasty.