# Will this system work?



## Nimrod (Jun 8, 2010)

I have a off grid piece of land and eventually I will build a house on it. In the mean time I am going to put my pop up tent trailer on it for the summer. The trailer has a 105 amp hour, deep cycle battery. I could hook up the battery charger to the generator to keep it charged but I don't like the noise and it seems like a PIA. 

I expect to run a 12 volt CFL (13 watts) a few hours a day and a 20 inch TV (120 volts and 105 watts) a few hours a day from a converter. The light will use 2.16 amp hours a day (13watts divided by 12 volts = 1.08 amps, 1.08 amps X 2 hours = 2.16 amp hours). The TV will use 17.5 amp hours a day. (105 watts divided by 120 volts X 10 X 2 hours = 17.5). Together they will use 19.66 amp hours a day plus about another 3 amp hours for innefficiencies so 22.66 total. 

The battery should go a bit over 2 days before it is run down 50% which is as much as you would ever want to run it down.

I want to use a solar system to charge the battery. At first the cheap (less than a hundred dollars) charge controllers looked like a good deal but you have to use 12 volt panels which cost $2 to $3 a watt so a 250 watt array costs $500 to $750. I am considering a Blue Sky 2512i-HV.
http://www.blueskyenergyinc.com/uploads/pdf/BSE_SB2512i(X)-HV_datasheet.pdf
This is an MPPT charge controller that will handle up to 50 volts from the panels. It is made for a 60 cell panel with up to 50 volt open circuit specs and a max of 270 watts. It will charge the battery at a max of 20 amps. Low price is $161.

There are many panels that are 250 to 260 watts, 60 cells, and under 50 Voc. Here is one I found and the company is located in my old neighborhood so I can just stop in and there shouldn't be any shipping. 
http://www.simpleray.com/Conergy-PH-Series-250-Watt-Solar-Panel-p/1122-250.htm

Here is where I get confused, The charge controller says it can only handle 270 watts of panels which I think means one panel. The charge controller puts out a maximum of 20 amps of current to charge the battery. The panels in the 250 watt range put out about 8 amps of current. What is the current delivered to the battery to charge it? (In writing this all down I may have answered this question. Does the charge controller change 8 amps at 30 volts to 20 amps at 12 volts?)

If the charge controller and panel combination will put out a maximum of 20 amps of charging current then it looks like the system can keep the battery charged as long as there are not too many cloudy days. Yes?

Last question. The panel is rated to put out up to 30 volts so I can use a smaller wire from the panel to the charge converter?

Looks like the system will cost $361 plus fuses and wire. I don't think the system is expandable but it seems like you would have to go to a Midnight Solar 150 lite at $500 (on sale) to have an expandable system. When I build a house and barn, I can use this system to power a 12 volt well pump in the barn to provide water for the critters.


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## TnAndy (Sep 15, 2005)

1. Yep.....that's what an MPPT controller will do....drop the voltage and up the amperage.

2. Yep. Assuming you get 4 good hours of sun/day, you should be OK. Problem may come when you get 3-4 days of crappy, rainy weather. You may want to consider adding another battery in parallel.

3. Well, you could I guess. Distance also becomes a factor. I'd probably wire the whole deal with #12 and not worry about the fact I might be slightly over on the panel to controller leg.


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## Allen15 (Apr 18, 2013)

Your battery will last much longer if you are only running it down to 80% DoD (depth of discharge), not 50%, but to do that, you'd need 2.5 times more battery; get 3 more to be safe, because that way, if later you wish to expand, you'll have the ability to switch to a 24 or 48 volt system, which will be more efficient, with less power loss in the wiring.

By then, you'd probably need that Midnight Classic too.


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## Jim-mi (May 15, 2002)

If you bite the bullet now and get the good controller ---Midnight Classic-Morningstar-Outback- then you can expand your system as you please......

You could go from 12 to 24 or 48 v as the system grows.
Also you can go with todays higher voltage PV panels . . .and not be concerned with the voltage limit as you posted above.

Going with the **big** controller now would be a win-win deal.........


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## idahodave (Jan 20, 2005)

You're on the right path, but I'd think about a new LCD LED TV...105 watts is a lot for TV.


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## Nimrod (Jun 8, 2010)

Thanks for the help. Good to know I am on the right track.

I'm trying to do this as cheap as possible. Going to the $500 charge controller or buying a new TV is not in the budget. Besides, when I am ready to do a bigger system in a few years, the technology and the prices will have changed a lot.


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## Allen15 (Apr 18, 2013)

The price for the TV will probably be less in a few years, but some things are pretty stable in price, like the good charge controllers aren't likely to change much sans inflation...

Good luck with your endeavors, but remember, like any tool, if you started out with a cheap one, and then it broke, you already needed a better one, so it's time to replace it with a good one, 'cause it's false economy to just go get another cheap one, if you needed to depend upon that tool.


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