On Mon, 12 Oct 2020 23:53:38 +0100, Ian Jackson
wrote:

snip

I think we went to a small power station when I was at college doing
my HND in Electrical Engineering and I think they synched the
frequency of their output to that of the grid manually ... or hit the
big connection switch manually suggesting if they got it wrong by more
than a bit, it could rip the generators off their mounts?


I did a fair amount of 'heavy current' electrical engineering at
university, and one of the lab experiments was to run up a large (and
fairly ancient) three-phase generator (driven by a DC motor) and
synchronise it with the mains.

Not only did you have to get the speed right,

Ah, so I did remember it correctly then. ;-)

but (obviously) you had to
ensure that the three phases were correct. This was achieved by having a
lamp bulb across each of the contacts of the three-pole switch that
connected the three generator armature outputs to the mains. [I believe
the lamps were coloured red, blue and yellow.] As you approached
synchronous speed the fluctuations in their brightness would slow to a
stop - and when the brightness was at a minimum you then had to adjust
the generator field current to get the generator output voltage to
exactly match the mains voltage (when the lamps went out). Only then
could you throw the switch -

Clever.

and if there wasn't a big bang and a
grinding of metal you knew you had got the generator successfully locked
to the mains.

;-)

You then did various measurements about (for example) what happened when
you altered the drive power supplied by the DC motor and the amount of
generator field current. Again you had to be careful, because if you
varied things too far the system could unlock from the mains (with the
aforementioned spectacular results).

Ooops. I must admit that I assumed once 'locked in' the grid would
override anything feeding it.

All this was pretty scary stuff, and these days I expect that the
operation of power stations is far more automated and foolproof than it
used to be.

Yeah. ;-(

I had quite a long telephone chat with a neighbour / mate last night
about batteries. He is a fairly competent wrench but not very
confident, tending to push most non basic jobs elsewhere.

He has an expensive eBike and because he was tending his wife (home
dialysis etc) he didn't get to use it, it was left 'too long' and the
battery pack died. After she passed away (and hence the length of the
chat last night, he has good days and bad days and that was a bad day)
he has had a big clear / sort out and dug out this bike and wanted to
do something with it.

I told him what to do re the battery (open it up, check the contents,
we can get replacement cells, how to test it etc) and he bottled it
and said he was going to send it off. I must have sounded a bit
dismayed (the battery pack wasn't 'worth £900', it was fcuked so worth
nothing and so he had little to lose by trying with my help etc) so he
started looking around and at tab spot welders and cell suppliers etc.

I gave him a small list of simple tools (watt meters, car headlamps
etc) / connectors and he's been getting them together and last night
was about how he would use such and what sort of current would you
need / get when you connected stuff up various ways (for testing the
bike's electrics, testing the BMS, running a capacity test on another
eBike he has etc) and so we ended up at Ohms law and how to use that
to calculate / predict the resistance of loads (alone with power etc).

Even silly things that why 'current' is measured in 'amps' and has the
symbol of 'I'. ;-)

I think I left him enthused (and distracted) and I'm looking forward
to the next batch of Whatsapp pictures as he puts more kit together.
;-)

Cheers, T i m