G'day John, All
At 06:02 AM 22/12/2010, John wrote:
><snipabit>
>I have the two automotive 'generators' (with brushes, not
>alternators) already, and all I am interested in doing right now is
>having a motor or two that is DC, can run (performance not important
>- that comes later!) on 12 volts, and will not end up overheating at
>a rate so fast that destruction occurs before I can unhook it.
Since you're mostly in the "thinking and playing" mode, use your
generators to set something up, and get a feel for what is needed,
and what you are comfortable with doing yourself. Keep a backup
(outboard) available whilst you play and don't count on it until you
know you can (as much as anything can be).
>There are some information sources online regarding the use of
>automotive (or marine!) starter motors, <snip>
No, no, no, no... Starter motors are great for short high-power runs
(I've built a couple of air compressors for low duty cycle
applications using starter motors and aircon compressors) but their
run time is in count the seconds until overheat.
>A simple pulley on a generator is a far better beginning point.
>So, by using a generator, I can fiddle, and any work and money spent
>will have a possibility of getting used on the final setup.
Correct.
>For a marine environment I see the weak point as being the
>controller. I would like to experiment on ways around this, mainly
>for cost reasons also, but also I have a suspicion that the use of
>controllers is a result of basing boat systems upon vehicle systems,
>where there is no natural slippage. This would also be driven by the
>manufacturers and sales sources for the controllers.
Has the potential to be a weak point. Also could be "bulletproof". If
your boat is always damp, or often wet, then you need to be very
careful with your controller.
I will say this once and clearly: There are no truly waterproof motor
controllers.
There are manufacturers' who claim to have waterproof controllers,
but they are really only splash/spray resistant. Most of the time
this will be fine, until the day salty water gets on the speed
control wires and bridges them out and you get surging or cutting out
(had that happen). Or a wire is installed in such a way as to allow
moisture to wick up inside the wire to get into the controller. Or it
is nice and warm, in a humid environment that suddenly cools down
(starts pidding down with cold rain) causing the controller to cool
down and as the air cools inside it contracts, causing the controller
to suck in moist air, that then as things cool further condenses out.
It is possible to install any controller in a manner that makes it to
all intents and purposes waterproof (virtually submergible). It is
also possible to take any controller and install it in such a way as
to make it very susceptible to moisture.
>I can remember years ago in a machine shop seeing an electric motor
>that required a lever to be slowly moved up a series of contacts,
>arranged in an arc, as the motor speed increased. Presumably each
>contact had a heavy-duty resistor in the circuit. Simple and safe,
>no electronics to burn out just when needed.
If an AC motor, that would use inductors (behaves the same as
resistors to AC, but without the heat). Doing that with resistors is
quite inefficient. In ye olden days used with electric cars and
forklifts, etc., for starting, but switched out as soon as possible.
Trams and similar continued to switch speeds, but mostly switching
motor connections, not resistors once started-up. Their motors
are/were specially wound with a big range of field strengths (speeds)
available by taps on the fields. You will not want to do anything
with fields, other than possibly bringing out the join between the
two field windings, giving another speed option.
>Another idea I wish to fiddle with/look into is electric clutches
>from automotive air-conditioning compressors, and/or chainsaw style
>centrifugal clutches. I have the idea that maybe if combined with a
>flywheel, or maybe not, this might be another way to get things
>turning with less shock loads than a simple blade switch gives. I
>know that there will be an increase in power loss that cannot really
>be afforded, but feel that this is an initial capital cost tradeoff.
I did that with the compressors that I built, but unless you have a
particularly long/heavy prop shaft I think the cost (time and money)
could be better spent on other things.
Since you have two generators, assuming they are close to the same
you can connect them as follows:
Speed 1 - slowest) 12V on both fields, two armatures connected in series.
Speed 2) 12V on both fields, 12V on both armatures
Speed 3) both fields connected in series, 12V on both armatures.
If you can find more generators of the same type, this can be
extended as far as you can be bothered to take it - but with
increasing complexity comes increasing number of points to fail.
You need to be sure that you do not connect the armatures without the
fields connected, or they will draw a high surge of current and want
to rev to the sky.
The fields will draw less than 10 amps each, but the armatures will
draw a fair bit more, you will need to use a very large switches, or
better use solenoid-switches (contactors or heavy relays). Reversing
the polarity between the armature and field connections gives you reverse, too.
>Then there are batteries. I once visited a house that was off-grid,
>and the guy had made his own batteries, <snip>
Off grid, weight is not important. On land, spillage is a manageable
risk. Please don't go that way on a boat.
Hope this helps
Regards
[Technik] James
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