If it's not some sort of constant velocity engine how on earth do they get
it to generate 50Hz.
The obvious answer is that it's a 12 or 24 volt alternator that is connected
to some sort of regenerator which is buried somewhere within the guts of the
Generating AC power at a constant frequency by mechanical means in not a
trivial matter, even for generating companies.
As a general rule an alternator produces a form of AC, albeit usually of a
rather distorted nature. This is then passed through a 'diode bridge' to
AC can then be generated by an AC inverter.
It's a hell of a lot more rugged than a DC dynamo because the DC dynamo uses
a comutator, and comutators fall to bits with depressing regularity.
That's not hard to do.
What's really really hard is keeping the phase and frequency constant and
managing the 'power factor' in such a way that it doesn't all run a touch
hotter than the design temperature.
"When I we'r an apprentice" I was taught at Hull Tech by an old guy who
remembered balancing power stations coming on-line with two phase meters and
a clutch lever...
The trick I saw was three light bulbs across the switches.
As you came to speed they flicker more and more slowly
and finally as they creep through the 'out' part of the
cycle and you drop it onto the grid and it is locked
Then you can wind up the power and the speed doesn't
change, you just watch the power meters start to run up
until it's 'about right' and then you can come off the
grid. I think it was a similar trick to come back on.
<sigh> This was in the days when UPS meant a big set
of Napier Deltics ready to roll and I was a raw, new
graduate who thought he knew about transmitters because
he understood big transistors.
Posted via a free Usenet account from http://www.teranews.com
When I we'r an EE student, we had a motor/alternator set that we ran
into the grid, synced up etc, then drove harder and harder until we
broke sync - then the motor starts to accelerate out of control....
Bloody machines lab is all computer trickery now - not proper
engineering at all.
This is certainly not common - I've never heard of it being done at all.
Many yachts fit additional 12v alternators and use fancy charge control
but the idea of 240v on a yacht at sea is a bit scary in my opinion.
Quite a few plug into 240v shore power and do indeed have a 240v circuit
but unless you are talking ships rather than boats it's new to me.
I have a circuit diagram (well more of a "which wire to swap") to convert a
normal 12/24V Alternator into a 240V genny - just depends on engine speed as
to what Volts you get. Big problem is that you also get the rated amps of
the alternator, if any part of the circuit fails you get an onsite
I'll not contradict any of the experts here, I'm only stating the fact that
they are readily available and commonly used on yachts (not ships).
Quote from Living On Board:-
240 volt AC Alternator
These devices attach to the boats main engine. They are similar to a car
alternator except they produce 240 volts AC current instead of 12 volt DC
current as a car does.
Again, these come in different outputs to suit your needs but remember power
is only generated when the boats main engine is running. If your mooring
dries out at low tide this could be a problem.
I've since found that the engine must be set to run at a certain revs to
give 50Hz. If the alternator needs 3000rpm then a smaller pulley on the
engine end will mean the engine only has to run at low speed to provide the
correct Hz. (Still can't find who sells them though). Apparently there was a
US version that controlled itself at any speed, but it wasn't reliable!
But after all this it seems that this may not be ideal for water wheel
design after all!
Actually it may be.
Water wheels are reasonably constant in speed because the mill pond will
have a weir with a 'gate' that allows the level to be regulated, and you're
going to need some sort of gear box or heavy duty clutch between the
generator and the wheel or any problems will tend to do some serious
And reasonable constant is all the OP needs. He isn't trying to sync to
the mains. He simply wants to run a small pump and a relatively low
powered immersion heater, neither of which are over sensitive to
Reply to address is valid at the time of posting
Oily, you're right, I meant a smaller pulley on the alternator end, or as
you say a bigger pulley on the engine end.
Although your comment on marine engine revs, doesn't apply anymore to the
modern high revving Volvo's etc.
I dont know if any of your saw the programmes "Its not easy being green" on
BBC a year or so ago - With Dick Smallbridge.
He looked into all this, and sourced a fancy alternator/dynamo/power source
which he connected to a water wheel. He accepted that the power went into
12/24v batteries and then was inverted to basically light the house. He also
had a wind turbine which via a battery powered a water pump to fill the cold
I am no engineer, but I suspect that the OP should give up on the idea of
heating water with this power, and just set up a thermostat to control a
switch to power a 12V pump for the swimming pool water.
Just as an aside, today was the first sunny morning (here) for a while,
and our solar water heating kicked in at around 0930. Currently (midday)
the panel temp is around 46C and the tank coil exit temp (roughly equals
tank temp) is 40C. We've got about 8sqm of panels on the roof, but at
this time of year there are long shadows across it cast by the chimney
stack, so probably only about 4-6sqm actually productive for most of the
morning. I don't know how much energy the pump has used - I ought to
measure it really (see another thread, etc.).
That's about 30 gallons worth, not counting the upper part of the tank
which _may_ also have been solar heated to a similar temp (depends
exactly when the rest of the family showered this morning!).
It's not 'free' energy, of course, but IMHO it's paying back the
SIMON MUIR, BRISTOL UK www.ukip.org
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