T-Pain Is On A Boat: Re: [Electric Boats] Solar panels on the boat deck: what are safe voltage level?

Wednesday, October 8, 2014

Re: [Electric Boats] Solar panels on the boat deck: what are safe voltage level?

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