[chbot] Notes for Robotics Group meeting, Monday 20 Aug 2018, 6:30pm, 5 Idris Road

[Trevor Wignall]

I had a chat to Henry about his 415 Volt requirement, and it looks as if it
may be all a non-issue. A 230 Volt RMS phase to neutral system has about
400 Volts RMS phase to phase (3 phases), which is nearly the 415 Volts
mentioned. The ratio is 2 * cos(30), which is 1.732 (i.e. SQRT(3)). So why
the small difference? 415 divided by 1.732 gives 240 Volts, not 230 Volts -
the nominal Australian voltage. Aha!
So it all depends on whether you connect the AC voltmeter from phase to
neutral or from phase to phase. The conclusion is that the VFD should be
able to drive the 3 phase motor at its full voltage rating probably without
needing the transformer at all, because that is the type of motor that the
VFD is designed to drive - 400-415 Volts RMS phase to phase.
However I am not an electrical engineer so I am not sure this is totally
correct. Anyone able to confirm this thinking?
Cheers
Trevor


On Tue, Aug 21, 2018 at 10:19 PM Mark Atherton <markaren1 at xtra.co.nz> wrote:

> Hello everyone,
>
> Sorry for the late summary.
>
> Enthusiastic turnout with 26 attendees, and lots of huddles-of
> tech-talk. $101 + change (in gold, and flat-money) collected and
> transferred into the robotics loose-change jar (for later banking).
>
> Quick reminder: equipment donations are welcome for the trading table,
> but no CRT based product, printers, fax machines, toner or items that
> are likely to be a disposal burden. All sales from the trading table
> should go into the brown box on the wall, and are directly for the
> benefit of our host club, NZART Branch 05.
>
> With thanks on behalf of the group,
>
> Mark Atherton
>
> ============
>
> Thank you Chris for bringing a huge pile of interesting stuff, including
> several servers as well as four and eight channel examples of ex-DSIR
> bi-lateral unimix diverters. Mike donated some lighting product, and
> Russel brought in an unopened (!) Zilog Z8 emulator. Peter H brought in
> a used 250W solar panel, which was immediately snapped up. Quite an
> amazing evening for donated stuff. Also, the group is now the proud (?)
> owner of an 8 inch reel of 6250 BPI mag tape. Thank you everyone.
>
> Charles brought in an enclosure he had fabricated from his 3D printer,
> along with a cross-axis power test he carried out using his laser
> cutter. Most interesting.
>
> Andrew E talked about some projects he has on the go, including the
> Oxford Men’s Shed Maslow CNC, as well as his ‘junk CNC’ project.
>
> Andrew talked about the ‘Crate Escape’ project, and how his contribution
> is progressing.
>
> Andy brought in, and discussed some LiIon battery management modules he
> had purchased from Ali-Express.
>
> William gave us an update on his 8 bit machine including steps towards
> adding a video output.
>
> Rudy talked about some Ali Express security issues. It appears that new
> accounts requires significant amounts of personal information be entered
> which may not be acceptable, or appropriate.
>
> Andrew Sands talked about linux.conf.au which is coming to Christchurch
> in 2019. He strongly recommended that our members attend. He also kindly
> handed out some LCA bags, and more interestingly, some tiny conference
> badges, based on the EFM32HG309 controller. This part is a 32-bit ARM
> Cortex M0+ processor with USB device, and a ton of other peripherals.
> Stay tuned, Andrew will be posting updates on this list as they become
> available.
>
> Henry talked about his three-phase woes, including the possibility of
> running the output of a VSD through a transformer to drive 415V three
> phase motors.
>
> Robin is interested in sourcing some 4mm+ thick steel sheet for a
> 'Rocket Heater' project, and asked for low cost potential sources since
> it appears that almost all of the local scrap yards are closing their
> doors to the public.
>
>
>
>
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