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Home > Archive > Alternative Power sources > July 2005 > basic alternator questions
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basic alternator questions
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| peter E 2005-07-24, 11:21 pm |
| I am new to this field and have some very basic questions
Say I am looking at a 2kW generator with reasonably high efficiency and
moderate cost; what are my options?
Does the voltage of a DC system go up the higher the rpm? or does the
current increase the same and voltage remain unchanges?
I have seen these $199 petrol engine - generator units for sale.
Obviously they are not the best quality. Yes they are cheap but assume
the efficiency of the electric generator is not good, how durable would
they be.
How much does a good quality 24V Dc 3 phase alternator cost, around 2kW
What is the cost of converting junk car starter motors into
alternators, what is the perfromance (power/efficiecny) of these
modified motors.
Thanks for your patience
Peter Evans
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| Charles Foot 2005-07-25, 12:21 am |
| First some basic definitions might be in order.
A generator producess DC.
An alternator produces AC.
Therefore: a <quote>24V Dc 3 phase alternator<unquote> is a
contradiction in terms.
Although a car alternator does produce DC, it does this by means of
built-in diodes which rectify the AC being produced.
Yes, you can use a starter motor as a generator, but why bother? It
certainly won't be as efficient as a car alternator and you'll need some
external bits to regulate it and isolate it. If you're after 24v DC look
for a grunty truck or bus alternator from a wrecker. A friend of mine
recently bought a heap of Mercedes bus alternators which put out 24V at
around 90 Amps. I believe he paid about $300 each for them (New Zealand
dollars). Nice units.....
HTH
peter E wrote:
> I am new to this field and have some very basic questions
>
> Say I am looking at a 2kW generator with reasonably high efficiency and
> moderate cost; what are my options?
>
> Does the voltage of a DC system go up the higher the rpm? or does the
> current increase the same and voltage remain unchanges?
>
>
> I have seen these $199 petrol engine - generator units for sale.
> Obviously they are not the best quality. Yes they are cheap but assume
> the efficiency of the electric generator is not good, how durable would
> they be.
>
> How much does a good quality 24V Dc 3 phase alternator cost, around 2kW
>
> What is the cost of converting junk car starter motors into
> alternators, what is the perfromance (power/efficiecny) of these
> modified motors.
>
>
> Thanks for your patience
> Peter Evans
>
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| barry@sme-online.com 2005-07-25, 1:21 pm |
| May I suggest that you search your local library for basic reference on
regulation of automotive charging systems? Maybe ditto for intro
engineering references on such rotating machinery.
Background in mechanical arrangement and electrical function would be a
Good Thing (TM).
For prime-mover, certain aspects of engine design set the upper limit
on attainable efficiency. Like, diesel > ohv/ohc high-compression
"gas" > flat-head "gas". More than likely, the prime-mover will be of
much lower efficiency than the electrical power-head.
You do get what you pay for, sometimes. :')
HTH,
J
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