h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

* while the kettbe biols *

Wouldnt that depend on what Univers we were in at the time?

* decides to re type the previous post in English *

* while the kettle boils *

Wouldnt that depend on what Unvierse we were in at the time?

erm... i suppose so...

why? are we thinking of leaving this present one anytime soon??

alec.

You never can tell in this ship!

This one seems quite OK right now though!

* hands Alec a *

mmm...thanks luz...,

this vat of looks just about ready for falling in

*attaches bungee cord to right ankle and launches himself into kiddy pool from hastily constructed diving platform*

alec.

So you think that after over a century of wiring the world up for AC power grids that DC is going to make a come back? Wasn't the debate over AC vs DC a major thing around the turn of the century with what is now General Electric winning the day with AC? Could it be that now they will all be proved wrong? I suppose the advances in brushless DC motors are the real break through. The start torque and simplicity of a three phase motor has been complicated by the convience of variable frequency drives and DC motors have always had a lot of advantages that were ofset by the pain of changing brushes at regular intervals. I work almost exculsively in AC power. I understand that you work in marine applications Shagbark which are mostly DC. What's your take on it? Will DC be making inroads on land applications?

Were you on Celebdaq the otherday Lighthouse girl, or was it someone with a similar name!!!

Twas not me - must have been an imposter ........

*surfaces from bottom of chocolate-filled kiddy pool*

harry

the seminar was mainly on DC systems for marine applications, localised power generation and storage.

AC still has the edge on DC for power TRANSMISSION cos only AC works in a transformer.

But with boat systems it is different. Several factors come into play.

1. A Diesel generator should always be run at a minimum of 75% of its full load, otherwise the maintenance interval is drastically reduced.
The cylinders coke up quickly,and all those moving bits wear out.
(75% full load is usually achieved by wasting power, special heaters built into the bowels of the boat will just warm up sea-water for no other purpose than to waste power).

The problem being that just to run the fridge overnight and to be able to turn the bathroom light on at 4am, you have to leave the gen running all night.

2. Stuff like your Air-Con compressors, motors, pumps etc. have a disproportionately high starting current in comparison with the run current. That is why the Generators are oversized : not for the running load but for the starting surge load.

But now, with the advances made in electronics, inverters are becoming more efficient and effective. They are able to handle high starting currents for short periods of time, and settle into providing the run loads quite happily.

So the ideal system is now turning out to be small DC diesel generators whose job is simply to charge a big bank of batteries. The gen. will start/stop automatically according to the level of charge. This can be supplemented with Solar power panels, even hydrogen cells.

The batteries supply an inverter for each AC load.
You don't need to change your compressors or anything, just add an inverter and run the whole thing off the batteries.

i hope this makes sense to the thousands of researchers who drop into the Generator room to catch up on the latest trends in high technology.

Now here's a coincidence : Detroit and other manufacturers are moving toward changing a vehicles battery voltage as 12V power needs too much current.(hence more copper in the fat cables, switches and contactors ) The voltage they have decided to standardise upon :


42 VOLTS ...no...seriously, 42 Volts.

alec. *techie speech over *

There are no accidents in this world. 42 is in fact the answer, now we have a new question that it answers. What is the idea voltage at which to operate a DC power supply? And Voila, DNA is once again exposed as the true visionary genius that we all know him to be.
In this I am reminded of how Kurt Vonnegut foretold the existence of interstellar black holes in one of his early books, Sirens of Titan I believe, he gave them a very accurate if non technical discription and called them Space Boojums but the did recieve credit from the Nobel Prize winning physicists officialy credited with "discovering" them.
Life imitates art.
BTW I had a lovley time this morning with our experiment at work when we had to start the 75 hp motor aross the line (460/3/60) after deliberatly installing a drive set that would overload it. I invited the visiting engineer to witness the power draw on start up. It was amusing as the meter started at 450 amps and over 10 seconds or so worked it's way down to 300 before the motor took off amid much buzzing and humming from the fan unit. She was decidedly a bit nervous. Just a small amusement. It acutally ran quite cool for a motor drawing 100 out of 86 FLA.

Although most generators are measured in KVA (Kilovolt amps), it gives you sensible power readings with saying "watt?" everytime you mention number, making the other person say "I did'nt say owt (or if you live in Newcastle nowt)"!!!

Future discussions in the Generator room will include:
-Line reactors vs symetrical grounded cables. Which is best for modern variable frequency drives?
-400hz AC power and why it suits the aviation industry so well.
-Motor branch circuit protection via magnetic trip breakers. When and where should we use them?

...Gosh Harry, can hardly wait for that to come up...

I do warn you though, i have very strong opinions on each of those subjects, so it could get knock-down and nasty

some have even called me a reactive load of ...er ...oh no, that was in another thr*ad of course.



alec.

An AC power supply is pointless, it's average is about zero watts unless you have a hell of a high current, what you want is a DC adapter that way you can power the generater the right standard without energy going all over the shop!!!

So we are not talking AC?DC as in the band then

More anyone?

ooooh ! yes please luz...

my current is a bit cold

alec

We cant have that now can we Alec


* passes Alec a new *

Mind you with all this elctricity surely we can manage to keep it warm this time!

There seems to be an invasion of suddenly aboard ship. Has anyone invented a better mousetrap reciently?
I do hope the problem doesn't reach the point where the stocks of makings are in jeopardy.

*falls in through a hatch in the ceiling*

Oh... hello there...

*eyes the chocolate-pool, scanning for distressed swimmers*