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Easy Peezy Car Battery Solpow DIY Plan?

 
                      
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Location: Tejas
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Can anyone point me to the right direction--->

I need to find some information or perhaps a "how to"
on wiring single solar cells with a car battery to
power a small fan in my GH.

Maybe there is a thread that I have missed...

Thanks.

Weeza
 
            
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Car batteries are not the best choice for a solar panel to charge.  What you want to use is a 'deep cycle' battery, which looks just like a car battery, but whch can be drained much lower and be recharged without damaging, unlike car batteries. 
 
Jack Shawburn
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To what level can a Deep Cycle battery be used? 50%
 
                    
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Jen0454 wrote:
To what level can a Deep Cycle battery be used? 50%


Depends on how long you would like the batteries to last.

Battery life is directly related to how deep the battery is cycled each time. If a battery is discharged to 50% every day, it will last about twice as long as if it is cycled to 80% DOD. If cycled only 10% DOD, it will last about 5 times as long as one cycled to 50%.

Most golf cart batteries are rated for about 550 cycles to 50% discharge.
 
                    
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As far as wiring individual PV cells to charge a battery first you need to know the rated output voltage and current. If you will be charging a 12 volt battery you should have approx 18 volts output from the cells; those are series strings. Then you need to make enough series strings and connect those in parallel to achieve sufficient amperage output to be able to charge the battery properly. You may also need a charge controller to prevent damage to the battery from overcharging.
 
Robert Ray
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I currently cool both my greenhouses with solar power and automotive 12 volt radiator cooling fans.
I agree that deepcycle batteries are the correct choice. Marine/RV batteries are about  1/2 the cost of Trojan t105's (common golf cart battery) but have not lasted as long as the Trojan's. T105's are 6 volt so you need to buy 2, an RV battery is 12 volt and you could work with one, depending on the size and load used by whatever fan you use.
Scavenged automotive radiator cooling fans are what I started with, have since replaced them with new aftermarket radiator cooling fans.
I have a charge controller on both setups and a thermostat. You should use one to extend battery life.
Wiring a bunch of indicivual cells sounds like a tedious undertaking but as Don said if they are all rated similarly and you have them shouldn't be a problem.
Easy peezy.......................... all projects start out that way.
 
                    
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Sam's Club or Costco have had the best prices on golf cart batteries in my experience. They don't sell Trojan but the ones they sell have performed well for us. We got 5 years of good service out of the last set of four I used in the RV. Not all of their warehouses stock batteries though so sometimes you have to check around.
 
                      
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Ok.  I can see there is a lot to be considered.  I want to get a deep cycle battery-


I still have a few questions:


where can you get PV cells cheaply?
is there a laywoman's plan somewhere that I can follow
that will show how to hook this up?


I am not experienced with electricity at all so I'm a little
lost in the dark.
 
                      
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And thanks again for all the info everyone.
 
                    
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If you have not done so already I'd recommend starting this project by looking into how big a fan(s) you need. I have a couple 12 inch dia Hayden fan here. They are rated for 800 cu ft per minute free air flow, 12 VDC 8.8 amps. Twelve volts x 8.8 amps = 105.6 watts. We need to know the watts consumed.

If the fan was to be run for one hour it would consume 105 watt-hours; 2 hours run time = 105 x 2 = 210 watt hours.

Batteries are rated in amp-hours. A typical 6 volt golf cart battery has a rating of 210 - 224 amp-hours. If we use 50% as the maximum amount we can discharge the battery that gives us 105 amp-hours at 6 volts. We would need two batteries wired in series; negative to positive in a chain, to provide 12 volts. That would provide total capacity of 12 x 210 = 2520 watt hours. We should only use half; = 1260 watt hours.  1260 divided by 105 = 12 hours run time (approx, in theory).


I assume the fan would only be required to cool the greenhouse; is that right? If correct the PV cells/modules would be providing power while the sun was shining, so if the PV cells supplied enough power they could stay ahead of the batteries. If the charge current was less than the draw the battery drain would be slowed.

Lead acid batteries are not perfect, there is somewhere between 10 to 20% loss in power when the charge/discharge cycle is considered. That means the PV source should be sized about 20% larger than what may be drawn out. Very rough numbers.

Next the task would be to calculate how many cells would be required to supply the power needed to recharge the batteries before the next use cycle.

Different approach. I have a solar air collector. Actually two. I power those fans directly from a store bought solar module. No batteries, no charge controller. When the sun shines the panel is making power. When the air collector heats up a simple thermostat turns on the fan. It runs until the collector is cooler or the sun goes away. That works for that application quite well. Whether or not you can use a similar idea depends on if the fan only needs to run when the sun shines. The fan runs slower if a cloud suddenly obscures the sun, but overall it works and require no batteries and no battery maintenance.

Note that successful off grid power systems will normally be sized to provide three days of autonomous, no sun. power. Again, if this is for cooling, if their is not much sun the power requirements may be reduced as well, so that may not be a big deal.

Now the hard part, some of us will see this as an economically viable project. Other not so. I belong to the second camp. Yes a home made panel will cost less in dollar outlay, but requires a lot of labor. With the requirements of mounting the cells in a weatherproof assembly, something the sun will not degrade and that will keep out the water and humidity it's just too big a task to assemble enough cells to have meaningful power. Fans draw a lot of power. But that's just my take on it.

If you Goggle diy solar cells or something like that many results will come up. A lot of them want to sell books, instructions, etc. or kits. Caveat emptor.

Decades ago I assembled a small PV panel. It powered a radio; very small drain. It worked.
 
Robert Ray
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Check out E-how.com, Instructables.com there are many solar projects that you could look at.
It might make the project less intimidating.
 
                      
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Thanks again for the start up and information.

I'll let you know when I have something worth
talking about.

 
                                  
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Weeza,
  I too am putting up a green house that I want to run "off the grid".  I don't know much yet but if I come across any information that could be useful to both of us I will be sure to post and share with you all I can find.  Thanks for posting, it's nice to find another woman who's trying to do the same things as me.  Good luck and let me know if you find anything!!
 
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