What’s wrong with this picture?

[ainley53]

What do you plan on powering? do you really need that much power?  Perhaps two flex panels on top of the cargo box?

A open roof on the trailer will make it like a sail.  There is a reason you do not see anything going down the road with that design.

Well, looks like I need to rethink my whole deal.

 

[akrvbob]

No, you have misunderstood the whole volts and amps things. Running them in series will not in any way reduce the amps you get into the battery as long as you have an MPPT controller. Using a MPPT controller will give you 33% more amps into the battery than a PWM controller no matter how the batteries are wired.

Running them in series you have everything to gain (you ca use smaller wires) and nothing to lose.

I've never heard of anything like that before about the panels in shadow in series. I don't believe it to be true.

I suspect it comes from the ideas of batteries. Any time you combine a weak battery with a strong battery, it brings down the strong battery to the level of the weak battery. It is also true of some types of the cells inside an individual solar panel, but not all.

I do not believe it to be true of solar panels wired in series or parallel.
Bob

 

[akrvbob]

About the trailer, i don't think putitng plywood over it will be a problem. Use proper construction techniques and a 70 mph wind shouldn't be a issue. If you are concerned build in a front wall to act as a spoiler to break the wind.
Bob

 

[ainley53]

About the trailer, i don't think putitng plywood over it will be a problem. Use proper construction techniques and a 70 mph wind shouldn't be a issue. If you are concerned build in a front wall to act as a spoiler to break the wind.
Bob

Okay. I think I solved the trailer issue. I'll loose the sheet of plywood and just weld together a grid of square tubing on which to mount the panels with a 6 inch gap between panels. That should significantly reduce the "sail" potential GotSmart warned me about and still allow me to tilt the panels 4 ways.

What I'm still not getting is the math. I'm setting up a 12 volt system. I have four 100 watt panels. Their max output is 18.9 volts and 5.29 amps per panel. Watts = Volts * Amps. If I wire the panels in series then the volts accumulate and the amps stay the same so it's 18.9 volts * 5.29 amps = 100 watts. If that's correct then according to the wire size tables for voltage, #10 AWG should be adequate for a maximum run of 32 feet. Of course that means I need to exchange my PWM for a MPPT. If this is wrong, please correct me while I eat my dunce cap!

 

[ainley53]

No. That's wrong. If they're wired in series it would be 18.9 volts per panel * 4 panels = 75.6 volts total * 5.29 amps = 400 watts which still needs #4 AWG for a run of 30 feet.

 

[GotSmart]

Look and learn, Grasshopper!

http://www.renogy-store.com/category-s/1853.htm

 

[MikeRuth]

No, you have misunderstood the whole volts and amps things. Running them in series will not in any way reduce the amps you get into the battery as long as you have an MPPT controller.  Using a MPPT controller will give you 33% more amps into the battery than a PWM controller no matter how the batteries are wired.

Running them in series you have everything to gain (you ca use smaller wires) and nothing to lose.

I've never heard of anything like that before about the panels in shadow in series. I don't believe it to be true.

I suspect it comes from the ideas of batteries. Any time you combine a weak battery with a strong battery, it brings down the strong battery to the level of the weak battery. It is also true of some types of the cells inside an individual solar panel, but not all.

I do not believe it to be true of solar panels wired in series or parallel.
Bob

I'd like for you to take note of your output and then place a quarter on any one of your panels and then check the output again :Give it a minute or two to adjust

 

[MikeRuth]

MikeRuth, pictures and specs can be found here:  http://www.baxleycompanies.com/SB001.html

I'm not sure that's possible.  These at 6 volt batteries wired together for a 12 volt system so they need to be next to each other.  At 66 pounds each that's 132 pounds more weight on one wheel/tire than the other.  Not sure that's a good idea.  Plus I'd have to put the charge controller, battery monitor and inverters out in the open since the trailer is not an enclosed type trailer.  Pretty sure that's not a good idea.  But I'm certainly open to suggestions.  That's why I'm on this website and not somewhere else.  If anyone in the world has the answers, it's the people on this website.  I've a least learned that much.

Nods to the good folks on this site. Now I see your project and and a good one at that. I don't have the answers on the panel mount that's for sure. Interesting project. Good luck with it. 

Mike R

 

[rvpopeye]

My first big class A had two 6 volt GC batts , one on each side in the rear "trunk" compartment ,approx 7 feet apart , they were connected together with a piece of 0 guage and worked perfectly.

 

[MikeRuth]

Bob and others, Ohms Law does not apply to the actual creation of a Battery source! Either a single battery or a BANK of batteries.

This is what applies.
1 The batteries used in a series or parallel configuration should all be rated the same. IE voltage and or capacity
2. When connecting batteries in Parallel the Voltage remains the same and the amp hours available double. (assuming Identical batteries)
3. When connecting batteries in Series the Voltage will be the total of the batteries rated voltages added together and the Amp Hours will remain the same. (assuming that the AH ratings are the same for each battery) 

Again this is not an Ohms Law issue, it's a battery building/configuration issue.

http://www.batterystuff.com/kb/articles/battery-articles/battery-bank-tutorial.html

 

[akrvbob]

Ainley, I was hoping you would just take my word for it or someone else would explain it.

You're absolutely right, the number of volts going across the line is multiplied by 4 and the number of amps is cut by a quarter.

When that power gets to the MPPT controller, it will bring the voltage down to 14 volt (or whatever volt your battery can take at that moment) and multiply the amps by that same number. If it divides the volts by 4.1, it will multiply the amps by that number.

That's Ohms law, volts and amps always have to go up and down in equally in opposition: one goes up, the other has to go down equally or vice versa.

It's also the magic of MPPT versus PWM; a PWM controller can't make that conversion.

If you wire one of those 19 volt panels to your PWM controller, the controller will receive the 19 volts from the panel and step it down to whatever the battery will take, during bulk charge that may be 14.4 volts, or it might be 13 volts. If it's 13 volts what happens to the other 6 volts the panel is producing? It flushes them down the toilet, they go totally unused!!!!!!!!!

The PWM controller is not smart enough to reduce the volts and raise the amps, it can only reduce the voltage. Only a MPPT controller can do that.

Here it is very simple: Wiring them in series with a MPPT controller will let you use a smaller wire and it will put more amps into the battery than in parallel and a PWM controller.
Bob

 

[ainley53]

Thanks guys for all the input.

Bob, no offense intended to you or anyone else, I'm just one of those skeptics who has to confirm everything before believing anything. Sent the PWM back and ordered the MPPT Tristar TS-30.

GotSmart, do you think loosing the sheet of plywood and bolting the panels to the square tubing framework with 4-6 inch gaps between the panels will be enough to negate the "sail" effect? Or should I put some kind of "mini" side panels on. I don't want to fully enclose the motorcycle trailer as I still need access to the crank to lift the tongue and the tie down strap releases.

 

[GotSmart]

You still have not said how much power you will be using.

I have 1 100w panel, and 448 AH 12v storage.  (4 6v 224 wired series and paralel) I also have the batteries wired to the alternator so when I need it I can input that way.  I have not needed to do that as my power use is never more than I can put back by noon.  

What will you be powering?

Is there possibly room on your van?

 

[akrvbob]

Ainley, no offense taken at all!! I'm just really lazy!!!!

Another way to think of the serial versus parallel is to think of your local power company. When they transmit power long distances they step up the voltage to huge numbers, 1000s of volts. When it gets to your house, they step it back down to 110.

That's exactly what you are doing! Your power plant is on the trailer so you are stepping it up to transmit it a relatively long distance and stepping it down at the house.

The Tristar is a great controller!
Bob

 

[akrvbob]

Gotsmart, he already answered your question in post number 6:

"As for "that's a lot of power" you may be right but everyone keeps saying to buy as much solar power as you can and this is as much as I can fit on a 4" x 8" sheet of plywood which is what will fit over my motorcycle trailer without hanging over anywhere. I originally planned on putting two 100W panels on the roof of my SUV but decided I could use that space for a cargo box to store winter clothes and other items not frequently needed. Plus "the roof on the trailer" let's me double the amount of power I can have."

He's a very smart man, he's following my advice!!!

Plus, something he didn't add, he can park the trailer in the sun and the SUV in the shade. That's worth it all by itself!!

I think it's a great plan!
Bob

 

[highdesertranger]

x2 on what bob just said. I couldn't agree more. highdesertranger

 

[GotSmart]

I guess I have too much education.  It just seems to me that would create wing lift.  The open area under the plywood or panels just seem wrong.  Dangerous even.

IMHO, why buy a 5,000 W generator when you only need a 2,000 W one?  More is not always better.

I have seen plywood, mattresses, and carpet lift off of slat sided trailers because the wind from the tow vehicle created a wing lift effect and ripped the item strapped down off.  

Towing a big bike on a custom trailer at 60 mph with a big flat wing mounted 6 feet above it.  Then you top a hill and suddenly are in the path of a large wind gust.    That is bad enough when you have a square U-Haul, but if the side wind can catch the panel???  My trip across Kansas was enough to make me remove the plywood sheet and mount my panel lower between the roof rack.  That was on top of my loaded van and not where the wind would get a better grip on it!

This is not the place to ask that one.  Take it to a university that specializes in higher mathematics, or even better, at a flight school.  Draw yourself a picture and think about the Superbird.

 

[ainley53]

Thanks Guys. I don't know a lot about living off the grid but however much I learned was from y'all. I'm sure I'm not the only one that owes all of you on this Forum a HUGE THANK YOU for all you have shared. It is greatly appreciated.

GotSmart, you're probably right. You usually are. Since I plan to mount the panels to the frame work with hinges and the hinges will have pull pins (clevis pins so I can tilt the panels four ways) I could just take them off and store them in my tow vehicle when driving. If I use hinges to fasten two panels together I'll have 2 "books" of panels that weigh 33 pounds each. Quite manageable. It will be a bit of a hassle having to mount/dismount the panels but probably butter than imitating Dorothy in The Wizard of Oz. At least until I come up with a better solution.