At 11:12 PM 26/12/2010, John wrote:
>Hi, James,
>Thanks for the reponse.
You are welcome, the point of these discussion lists is to assist
each other as far as we are all able, just contributing where I can.
>First of all, I don't have any intention of making my own batteries,
>I am far too lazy and old, and it was just an idea!
Good.
>Having said that, I do have a concern re having batteries mounted
>low in a boat, and it comes from watching some old U-Boat movies,
>where the sea water inundates the batteries, creating chlorine gas.
>I have experienced chlorine gas, so I take this seriously.
>I was thinking of totally enclosing the batteries, and venting up
>the hydrogen, probably by using modified plastic tote boxes or large
>tupperware, something with a sealable lid. Some of these are vented
>under the handles, so I would block those vents off and add a piped vent.
I've worked with chlorine in the past, and it probably wouldn't be
your biggest concern. Sea water is amazingly good as a conductor, and
copper immersed when connected to a battery electroplates off
incredibly fast. My father had a trawler sink under him years ago, he
called for help via the radio as soon as he realized the boat was
flooding, and just in time since the radio went dead as soon as the
batteries went under water. I don't know if it was simply pulling the
voltage down, or if the radio had a smaller feed wire to the
batteries that plated off in seconds, but loss of power soon after
the batteries went under was the result. In an emergency situation,
it may make all the difference to keep power available for as long as possible.
I worked on a project a few years ago for a boat that would have been
operated in a world-heritage area (the project was canned due to
increased competition in another area of the clients' operations).
The boat was to have been foam-filled (unsinkable) but to keep it the
right way up (so keep the tourists above water) the batteries had to
be low - below the flooding line. We knew that we wouldn't be able to
completely prevent water ingress to the battery compartments in a
flooded condition, so the batteries were going to be in semi-sealed
compartments, vented to well above the water line. The lids were to
be partially sealed - think a refrigerator laid on its' back. The
compartments were to have been a row of these, with each lid over a
low-voltage group, with isolators each side of the lid that had to be
out before the lid would open, but that was only due to the
high-voltage of the system. The compartment bases were to have been
continuous (one in each hull), with bilge pumps in wells each end, so
the battery tops should have stayed nicely dry in a worst-case
flooding. The boat would actually have been able to be driven with
the hulls fully flooded, as the motors were to have been IP68 rated
(wash-down, so short-term submersible) and the control gear in the
superstructure.
>As I don't yet sail, I have no idea what I need as far as speed
>goes. I presume that I will need a slow speed, so I don't hit
>things, and I will need high(er) speeds, to use as brakes and to go
>against wind and currents.
Don't forget that sailboats have a lot of wind-age with all the sails
furled, due to all the rigging, size of the mast, etc., but as long
as you are careful, and plan to stay out of trouble, then lack of
horsepower shouldn't be a problem - people sail with nothing other
than sails for propulsion and stay out of trouble.
>Seems to me that loads of sailboats seem to do a lot of moving
>around with no sails up, and I don't know if that is because they
>have insufficient room to tack, or are just driven lazily.
In my opinion mostly: 1) Lazily, 2) time-poor, fuel rich, 3)
inexperienced, would sail but being over-cautious.
>I do have an outboard, short shaft, unfortunately, but currently no
>(ugly) mounting for it, and am considering an outboard well, and I
>have an inboard that I regret starting spending on, and if I get any
>snags with the inboard as I try to get it running, then I will pull
>it out and start the electric fiddling sooner than otherwise planned.
The mention of short-shaft gives me a twinge of concern, I have in
the past experienced long-shaft in conditions where we were lifting
the prop out of the water and worried about dipping the power head
under the water, on a 21' sail boat in inshore waters when things got
nasty unexpectedly.
> From what you say, and show, it seems that I have more than the
> options I thought I had. Obviously, if I buy batteries in 6 volt
> 'lots', then I can go half speed easily by switching. Then you are
> showing 3 speeds, so that makes 6 in total. So I should get maybe 4
> that are all different. But can start with the 3 you mention.
With 6-volt batteries you have another option, a type of controller
called a 'rectactor' controller, using big diodes (rectifier diodes,
hence REC-) and contactors (-TACTOR) to get various steps. In your
case, this would be useable with your generators set up as shunt
motors, and later with a bit of rewiring to be usable as a series
motor controller, if your generators prove unsuitable. The rectactor
set-up discharges the batteries evenly, so you get maximum available
energy in any step.
You will need a 12V bank as the power source for the contactor coils,
unless you can find/make a suitable switch. You probably need 12V for
nav and the field power anyway.
This would give the following speeds, lowest to highest:
1) 12V fields, 3V armatures (two armatures in series, supplied from
6V), may be too slow to be useful.
2) 12V fields, 6V armatures (two armatures in series, supplied from 12V)
3) 12V fields, 12V armatures (two armatures in series, supplied from 24V)
4) 12V fields, 24V armatures (two armatures in parallel, supplied from 24V)
5) 6V fields (two fields in series), 24V armatures.
Reversing the polarity of the armatures to the fields will reverse
the motors, so give the same speeds in reverse.
With a single series motor (typical of forklift/etc motors) your speeds become:
6V
12V
24V
Then you can bypass some of the field current, called field
weakening, for a 4th (faster) speed.
If you use a permanent-magnet motor, you loose the 4th speed.
>But the main thing is, I already have the initial parts to start
>getting things together, as pension flow allows!
>So, I can now do some 'hand-held' tests on the generators, and if
>they seem to give a good kick, and running speed, I can get going on
>making a mounting plate. This can then be either used as an inboard,
>or as the top part of an outboard.
That's right. Will probably be under-powered, but if you can use that
to get started, you can get going sooner than you could otherwise
afford. Also by building the controls yourself you get a much better
understanding of the system and can fix it if something goes wrong.
>I am not trying to set up electric as a sole means of power. I
>believe that low HP ICE has some uses that cannot be currently
>competed with, that include long distance motor use and energy
>storage, and supplying hot water. By retaining at least partial ICE,
>I also eliminate the need for total prop efficiency. Also the need
>to be totally paranoid about saving amps. Politically, I believe it
>is generally a mistake to try to have electric compete with ICE on
>every level, and this is possibly cultural to the automotive
>applications that are currently driving the technology.
I firmly believe that today we no longer need the traditional marine
gearbox for many smaller vessels. All that we need is a propshaft
disconnect, a dog clutch or single-disconnect gearbox, with the
necessary reduction. Use electric for reverse, manoevering and
starting the diesel (put it into gear and drive forward with the
electric once forward cruising is needed, diesel starts and the
electric is shut down).
>I seem to remember that generator fields need to be 'sparked' to
>create residual magnetivity and set the polarity.
As a generator, they needed to start generating before the regulator
would 'cut in' so needed to be "flashed". Not an issue when using
them as a motor.
>Your observation regarding the speed INCREASING with less field
>power is an eye-opener. This maybe opens up a possibility of speed
>control of PM motors using sliding magnets that can be physically
>moved away from the armature to increase the speed.
Probably not, since if you weaken the magnetic path of a permag motor
too much, the magnets will weaken. It would be possible to build a
new type motor from "scratch" that has an alternative magnetic field
path away from the armature, and shunt out a percentage of the
magnetic fiels, but would be a lot of work.
High-torque servo motors are magnetised once fully assembled, since
taking them apart ONCE is enough to weaken them beyond use. More
typical permag motors if you leave the armature out overnight may be
enough to weaken them too much - I have seen this done with a MIG
welder wire-feed motor, one of my techs took it apart, left it apart
overnight, put new brushes in it the next day and once put back
together it was drawing too many amps and not driving even a quarter
of the power that it should.
>Seems that I can keep away from flywheels, clutches etc. That's
>good. This raises the issue of maybe the shaft stopping/slowing as I
>change the switching,
Certainly it won't stop, unless you are stopped in the water. Shaft
speed will drop to a little below prop pitch speed (the movement
through the water will turn the shaft by the prop). You'll get a bit
extra surge of current when changing up, but shouldn't be a big worry
as long as you design your switching to handle it.
The bigger worry is the arc flash from voltage on disconnect
(electrical equivalent of water hammer), you need diodes or snubbers
to protect the contacts against that.
>so my switching might have to be designed a bit slicker, to take
>place faster - I will probably use Ford style remote starter
>solenoids (as opposed to the ones that are mounted upon the starter)
>to start with, as they seem reasonably weatherproof. I don't know if
>they are continuous duty.
Starter motor ones are NOT rated continuously, but you can get the
same type of thing in continuous duty with no problem, you just might
have to go to an automotive wholesaler to get them at a good price.
>This might not be an issue, as it might turn out that the electric
>drive is only ever used on a single speed, or maybe just 2, in which
>case blade switches can be used,
You can get solenoid-contactors with 4 power terminals, two are a
normally closed contact, two are normally open, it would be possible
to use them so you have a big mechanical switch to power the motor,
and turn contactors on for 6V and 24V but coils off are the 12V setting.
>or possibly the rotary big switch that seems to be the main switch
>currently on the boat, and that I haven't really ever looked at as
>far as configuration goes.
Battery isolator switches are not designed to switch under load, and
will have a short life if you try to.
>And I still want to look at just simply switching the motors on, and
>allowing a large load that will be for a few moments only,
>particularly if the gearing of the pulley drive is low.
If you are mechanically inclined, and have access to a machine shop,
it is possible to make a drum controller (a set of combined switching
contacts using fixed (motor type) brushes and moving contact groups,
used in the 1900's to 1930's for cars) that would take the place of
the contactors and switches. I could provide you with some ideas if
you feel you want to explore this further.
>Or variable gearing, and set low when starting. For what I am trying
>to do, staying with everything electrically controlled might not be
>as good as something with a mechanical (reliable in salt water)
>element as well, such as cone pulleys, or tapered wall variable
>width pulleys such as are used on snowmobile drives, and I believe
>used to be used on little Dutch made cars called DAF's, that were
>taken over by Volvo years ago. My thinking here is to have nothing
>sucking up electricity once the drive is actually set to whatever
>speed is needed, other than the actual motor.
Unfortunately all those mechanical arrangements are likely to be far
less reliable in salt air, unless you are right on top of the
maintenance, and more importantly will suck a lot of energy out of
the drive system when you compare it to the amount of energy a
contactor coil requires.
Hope this helps
Regards
[Technik] James
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