solar project

[yeeehaw]

Howdy Guys,
I have been absent from the forums for a little while (a year) for no other reasons besides sorting my priorities.

Project: solar powered enduro electric glider

I am going to enter our annual science fair and I wanted to do it all on solar power. I was thinking of using the Chandelle plans from rcstore.com 9ws79" l 41) and with a wing loading of .6 oz a sqare inch. or I was going to use the Super cirrus 2 with a wing span of 149 inches and a length of 61.5 inches.
I havent figured all of the lagistics yet other than if I go with the Chandelle I will use the Great planes t400gd motor system along with 15-500ma cells for a total of 7500ma.

if I go with the cirrus2 I will fabricate 2 nacelles with the same motor and esc system with twice as many cells.

my concerns is deffinately weight with the chandelle and I am confused on how many amps I will need the motor draws 22 amps but the batteries only have 1500 and up milli amps. it is confusing the heck outa me. and if something happens in the air I need enough capacitors to run the reciever, fabrication of this would use a relay that will pick the more powerful system. so how many capacitors will I need to run my reciever for approx 5 minutes.( or what system could I use to help this, I was also thinking of using a failsafe that would deploy a parachute as an alternitive.

the cells I am using are 4"1"

another Idea I had if this system works: a system that would be able to be charged and be able to fly during the day through a point in the night. (super enduro flying) i know it is a long shot but

I deffinately do not want battereis to be on board unless I cant find a way to run the reciever in a power loss, but there has to be some way that it will only be able to be turned on during a power loss.

I am building this as a science project/ experiment

any thoughts help comments are definately appreciated

thanks alot
matt

[yeeehaw]

Maybe I am confusing other members also lol

this is what I need help on:

the platform to use : chandelle or cirrus2

the chandelle would be powered by the greatplanes 400gd system
the chandelle has a 78 inch wing span and a length of 41 inches
it would be powered by 15 solar cells with a total of 7500 ma and 7.5 volts

the cirrus2 has a 148 inch wingspan and a length of 61.5 inches
it would be powered by 2x greatplanes 400gd system (along with two fabricated necelles) the juice would be coming from 30 cells (15 cells per motor) at 7500ma and 7.5 volts each.

speed is one area I would like to have on demand

my questions on the amperage is that the solar panels put out 500ma each but only.5 volts each so that is how I got my figure with a total of 7500ma and 7.5 volts to each motor. IS THIS ENOUGH TO RUN MY MOTOR AT OPTIMUM POWER or am I missing another varible.

I will run my reciever off of the bec with a relay in series with an alternative power system if something goes wrong. HOW WOULD BE THE BEST WAY TO DO THIS ( no batteries if possible)

as an alternitive I would use a failsafe with a seperate set of solar panels to deploy a parachute.

The rules I have set for myself is that this must be able to fly as long as it is sunny and it should be pretty fast and the most important it must bring me the GIRLS lol.

[Dave Robelen]

Hi Yeehaw,
It surely looks like you need quite a bit more power from the solar cells than you are planning on. 7500 ma= 7.5A 7.5A X 7.5V =56 watts. If this is the maximum power from the cells in bright sunlight, you will need to plan on a good bit less on the average. For example, in turning, the cells will bank away from the sun. Meanwhile, unless you live in Arizona, the cells output will be less than the specs in ma. Here in VA, on a sunny day, I was only able to get 1/2 of the rated power from a solar array.
You will definitely need to work with a really light and efficient airframe, models like the Super Cirrus would have way too much material to be pulled up by solar power.
The challenge of alternate power for the controls may best be worked out on the bench top. Take those capacitors and charge them (no more than 6V please) and see how long they will power the system. You really only need one servo for steering, and a very light receiver + ESC.
Have fun, Dave

[yeeehaw]

I live in the middle of nohwere in Oklahoma (near tulsa) so sun is not much of a problem. the most the motors will be used for is climbing and a speed pass (if the system is pretty quick) I was thinking that the cirrus2 was a big platform but I knew it would soar pretty good and it could hold quite a bit more weight. but transporting it may be a problem. But do you think I should go with 31 cells if I were to use the chandelle platform ( 8 on the bottom surface of the each wing also) ? and I was (if the system works for the reciever) going to use a bank of capacitors that will be charged off the solar cells witch will be running the motor(only if the system is proved to be worth the installation) so when the plane banks the motors will be running still then max power from the cells would be reinstated when I was not in a bank...right?
weight will be a deffinate issue but do you think that the chandelle could hold its own?

any suggestions is greatly appreciated
thanks all
matt

[yeeehaw]

another alternitive to gain more amperage,(if Im correct) is to run 30 cells with 15 in series that would have an additional 15 cells in parallel. please correct me if I am wrong.
thanks alot
I will post a pic of the schematic.

[Dave Robelen]

Hi,
A series parrallel hookup is quite normal to get both the current and voltage needed from a solar cell array. If you can locate a camera light meter that actually reads the light value, this can be very helpful in measuring your level of solar power at the surface.
You mentioned putting cells on the bottom of the model earlier. Why? One of the key ingredients to getting the rated output is to keep the cells facing squarely into the Sun. As the angle increases, the output drops in amps. The Paul McCready Solar plane, the Solar Challenger has a large flat centersection in the wing, with dihedral in the tips to give a nice large flat surface for the cells. The airfoil is kind of weird, because it is flat over much of the top, but it got the job done.
Another useful test would be to take just one or two of the cells, and connect a resistor across them that would draw the rated current. Take it out under the best conditions, and see if you still get the rated voltage. That was the problem I ran into. When I loaded my cells with anything resembling the motor current (well within their rated output) the voltage dropped way off, along with the current.
Regards, Dave

[yeeehaw]

well I got on another forum(electronics) and they told me that I needed 220-225 cells for the amperage draw the motor uses. if that is the case that is way too involve for the room that this monster would take up and too much for my budget. I guess this one will have to be put on the back burner.
thanks for all the help though it was greatly appreciated, better to find out now and not later
thanks
matt