Sorry Bendik for the delayed response. My mail client lost this thread.
My thinking is to use dc to ac inverters to supply the motor controller as I
was doing in my conversion.
A 3phs motor speed is not controlled the way a DC motor is controlled. With
PMDC motors RPM is controlled by input voltage, this is not the case with AC
motors even if they have PMs. The frequency determines the RPM.
For the battery bank, configurations to supply an inverter/DCtoDC converter if
that is your choice, is Dependant upon the converter/inverters supply voltage
requirement.
In my case the house 12v supply is charged and maintained by a 3 step
charge/converter. That in turn is supplied by 115vac inverter that in turn is
supplied by a 24vdc battery bank. The battery bank is supplied by a 3
step(stage) solar controller(s, future expansion). This configuration handles
Higher voltage panels (46.9voc) with a lower cost controller than I could use
otherwise. the panels are lower cost per watt than equivalent 12v system
panels would be.
Although the electronics may seem excessive I assure you it is not. I have
posted on using DC to AC inverters for conversion before on this list. The
panel wattage per cost factor more than covers conversion losses.
Much the way losses(efficiency) is considered paramount when we have limited
resource. If our boat is powered by fossil fuel we tend to accept lower
efficiency. If for the same cost our solar panels are 30% larger a 10% loss in
efficiency seems acceptable.
From personal experience I understand changing gears/thought process is hard,
but sometimes the rewards are greater if we do. An example of changing plans
could be explained by my panel purchase.
A few years ago I purchased my first panel, a 230w panels rated at 36voc. When
I desired to increase the capacity I could no longer find 230 watt 60cell
panels for a price. Fact is the supplier I use no longer had them in stock.
The smallest panel, excluding 12 volt system panels was 280w panels rated at
the 46.9 voc I described above. These panels are 72 cell panels. These panels
are not compatible with my old controller so I had a dilemma. That old 230w
panel is now reducing zinc oxide.
The controller rated for both 12 and 24 volt banks at 12 volts would only
handle 2 panels thus requiring two controllers. I wanted to make sure that the
controller was as advertised so only ordered one. On one panel and 12v battery
bank things seemed to work well, but adding the second panel caused the
controller to shut down due to over voltage. My supplier had to go to the
engineer to give me an answer. at the panel voc the bank needed to be set-up
as a 24volt system. No place in the documents was this requirement covered.
After almost returning the controller I did the math. Turns out that changing
my complete system to 24 volts I could save on controller cost and only needed
one controller for all 4 panels. A new 24dc to 115ac inverter was going to
cost less than the additional solar controller would have cost. My willingness
to change thought process turned out better even with the conversion losses to
run my house system at 12vdc, and my storage bank at a different 24vdc.
I believe that If I still had my sail boat I would have dis-masted it in favor
of a deck of unshaded panels. The 3phs 220vac motor would still use a vfd as
was originally designed powered by an inverter. As designed the losses drained
the battery bank to much. However that would not have been so had I considered
a complete deck covered with panels rather than generator backup. Of course in
that day panels were much more expensive than they are today, that is in
higher than 12v system configuration.
Kevin
On Wednesday, October 08, 2014 09:30:39 PM you wrote:
> Thanks for all comments and tips guys!
> Fitloose, thanks for the link. I will have a closer look when it is time to
> choose the right solar controllers!
>
>
>
> Kevin, I am trying to understand what you are suggesting. It is true that
>
> the voltage *over the motor *(3 phase induction motor) is far less than
> 120V when operating at lower speeds. From the torque-speed curves for my
> motor I have found that the "base speed" of the motor is 3400rpm (at this
> speed the voltage is 120V). So at lower speeds, say 800rpm, the voltage
> will be 120V* 800/3400=28V, since the voltage is proportional the speed.
> But, from the product info for the inverter (the motor controller) it says
> that the voltage should be between 110-350V. So I dont know how the
> inverter+motr will behave for lower system voltages than 110V (the motor
> itself would symply not be able to deliver the rated torque at base speed..)
> So what you mean is that I only need a small energy storage at 120V (a
> capasitor bank) for the short outburst of power demand at a higher
> propeller speed (typical hard maneuvers)? And the main energy storage could
> be at a lower voltage (i.e. 48V)? If I understood correct... how to connect
> these two different-votage energy storages to the motor and chargers etc??
> Or am I completely lost?
>
>
> Anyway, I think I will go for a "12V" solar system, where 11 panels + 11
> mppt controllers are connected to each of the eleven 12V batteries (which
> make up a 132V battery bank). This should work as long as the 11 panels
> recieve the same irradiation (same angle, no shadow)...
>
>
> Regards
> Bendik
>
>
> 2014-10-08 19:59 GMT+02:00 pembertonkevin@gmail.com [electricboats] <
>
> electricboats@yahoogroups.com>:
> > Hey Bendik,
> >
> > I understand your concern. I have house batteries at 12v charged from an
> > inverter on the solar system that runs on a 24v system. The system keeps
> > the
> > house system fully charged all the time.
> >
> > You could opt to run a capacitor bank for your 110v system and a inverter
> > to
> > keep it there. The problem with such a system is capacitors have a quick
> > high
> > amp discharge should anyone come in contact with it. You can protect the
> > circuitry however to keep such a mishap from happening. Your complete
> > battery
> > bank could then be at 12/24/36/48 volts depending on desire and equipment
> > you
> > scavenged. I would keep the capacitor bank charged vs. discharged to avoid
> > startup surge.
> >
> > Just a thought.
> >
> > Kevin Pemberton
> >
> > On Monday, October 06, 2014 04:15:33 PM you wrote:
> > > Thanks for your reply and comments Kevin!
> > > One comment on voltage: I undestand that charging voltage is different
> >
> > from
> >
> > > system voltage (battery voltage). The motor I am planning to use is a
> >
> > 120V
> >
> > > (might work fine on 96V). But I want to keep the voltage level on the
> > > *boat´s deck *as low as possible (higher voltage in the "machine room"
> > > is
> > >
> > >
> > > ok - there are no kids down there:)
> > > Regards Bendik
> > >
> > >
> > > 2014-10-06 15:35 GMT+02:00 pembertonkevin@gmail.com [electricboats] <
> > >
> > > electricboats@yahoogroups.com>:
> > > > Hello Bendik,
> > > >
> > > > Charging voltage is not system voltage. The cables that come out of
> > > > the
> > > > panel
> > > >
> > > > have connectors that are both water tight and safe around water and
> > > > people. A
> > > > 48 volt system will have anywhere from about 70 volts to over 100
> > > > volts
> > > > from
> > > > the panel but that is after they have been hooked up in series to
> >
> > produce
> >
> > > > it.
> > > > This will depend on the controller. MPPT controllers are the best bet.
> > > >
> > > > My system consists of 4 panels producing 1120 watts at peak bright
> > > > full
> > > > sun
> > > > day. On the water using reflection from the water this could be higher
> >
> > on
> >
> > > > some
> > > > days. The panels produce 49volts open circuit and the cheap MPPT
> > > > controller I
> > > > imported converts the voltage to a 24 volt system.
> > > >
> > > > Because the controller input voltage is the most important voltage of
> >
> > the
> >
> > > > system (No matter what voltage you choose) consider shopping for the
> > > > controller first, then find suitable panels for it.
> > > >
> > > > My crystaline panels cover an area of roughly 8 square meters, maybe a
> > > > little
> > > > more. Morph panels will require more space.
> > > >
> > > > My panels weigh in at over 50 lbs per panel. This makes using them as
> > > > a
> > > > shade
> > > > difficult on a boat but if the bank is low in the boat may work.
> > > >
> > > > Any shade on even one panel connected to a single controller will
> >
> > reduce
> >
> > > > output considerably. For this reason I do not suggest deck mount but
> > > > rather as
> > > > a shade over the cockpit, or davits. I have used small panels on my
> >
> > canoe
> >
> > > > for
> > > > shade and to extend the range. I would never be caught in a storm with
> >
> > the
> >
> > > > configuration but if prudent would work for others.
> > > >
> > > > Final point.
> > > >
> > > > Controllers are cheaper in the 24/12 volt variety than for higher
> >
> > voltages
> >
> > > > at
> > > > your wattage. Higher wattage and the 48 volt systems shine. The lower
> > > > voltage
> > > > panels are more per watt. A controller that works on 12/24 volts will
> >
> > not
> >
> > > > produce 12 volts with panels that are above about 28 volts ( this is a
> > > > gray
> > > > area). The controller for 24 volts will handle about twice the watts
> >
> > as it
> >
> > > > will if used on 12 volts.
> > > >
> > > > Considering the above information I would likely choose a 24 volt
> >
> > system
> >
> > > > for
> > > > the size of 1000 watts. Because of space limitations on boats I would
> >
> > only
> >
> > > > consider crystaline panels for a system of 1000 watts. I would keep an
> >
> > eye
> >
> > > > on
> > > >
> > > > the kids and keep them off the panels. If working with a sail boat I
> >
> > would
> >
> > > > make
> > > > sure no shackles ever found their way to the panel surface. I would
> > > > set
> > > > chores
> > > > for the kids to take care of those panels so they would take pride in
> > > >
> > > > them.
> > > > This could be the morning dew removal with a squeegee, and have them
> >
> > see
> >
> > > > the
> > > > increase from the panel from their effort, and give them a slap on the
> > > > back.
> > > >
> > > > All in all every watt you do not need to pull from the bank will save
> >
> > you
> >
> > > > the
> > > > resistance the bank charges in interest. May the sun and wind always
> >
> > be at
> >
> > > > your back.
> > > >
> > > > Kevin Pemberton
> > > >
> > > > On Tuesday, September 30, 2014 09:33:17 AM you wrote:
> > > > > Hi!
> > > > > What is safe voltage level for solar panels mounted in the "traffic
> > > >
> > > > zone" on
> > > >
> > > > > a boat deck? ...Kids playing around with wet hands...
> > > > >
> > > > >
> > > > > 12-20V?
> > > > > Or higher?
> > > > >
> > > > >
> > > > > I am planning a ~1kW array to power electric propulsion (120V motor)
> > > > >
> > > > >
> > > > > What are your opinions/experiences?
> > > > >
> > > > >
> > > > > Bendik
Posted by: Bendik Vignes <bendik.vignes@yahoo.com>
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