Small system, easy or not?

[riff42]

I am starting to look into solar systems, and run across tons of "12v battery chargers" for 15$.  Simply plug it into your car, and it keeps it charged.

I want to start small, since our soon-to-be house most likely not be our perm. location, so I do not want to invest in a full house, grid-tied system.

So, I plan on just running our LED lights at night (we both will be gone most of the daylight hours) with one or three 12v batteries, since the systems I have now, run on 12v.

So, can I just get a few of these simple charging panels, maybe one per battery, and everyone is happy??  I only plan on running the lights right now, and for a few hours at night.  I'll worry about how many batteries I need later.

I do not know how much power I draw yet, I want to say 10amps if every lamp is on, but I will be installing more LED lights when we move into the house, and then I will be able to get a better power usage #.  

It is also next to a stream, so I'm hoping for more fun projects in the future

Thanks!

[wooferhound]

I think 10 amps for LED lighting sounds a bit high ?

Here is a story with many comments that talks about exactly what you are asking about.

http://www.fieldlines.com/story/2008/2/7/171927/1689

[commanda]

The solar panels of which you speak are really intended only to cover the normal self-discharge of the batteries, so they don't go flat from not being used.

Amanda

[asheets]

If you look on ebay hard enough, you can get them including SH+H for around $10 -- especially if you order in quantity.  Of course, I have found their claims to be 12VDC, 1 Watt somewhat suspicious.

[riff42]

well, when driving my 10 3w LED's at 700ma, and 2 more at 1a, yeah, I have a few amps being drawn.  Many more to come!!

That link sounds a bit insane.  80-100$ for PV cells just for one small LED?  I think my system is bit larger, and most cost effective, IF I am correct in thinking that I can possibly grab 2-3 batteries and charger panels.  shrugs

[riff42]

ah.  That can be a problem then.  

Second opinion on this?  (no offense, just wanna make sure )

[ghurd]

They make about 110ma into a battery.

About the best starter 'get your feet wet' system is the Harbor Freight 45W kit.  3 PVs at 1A each.  Often on sale for $200, $170 with a coupon.  Comes with 2, 5W CFLs and brackets too.

It needs a real controller like an SG-4. Don't use the one it comes with.

Not great panels... but certainly cheap.

G-

[riff42]

Well, if I'm running a 12v system, would I need a controller?  I already have drivers for each lamp.   So I think running it straight off the batteries would be fine?

or am I missing an important step in a PV system where the operating voltage is the same as the source?

[commanda]

The controller is to prevent over-charging the batteries, which tends to kill them in quick order.

In a solar setup, typically the controller goes between the solar panels and batteries, and acts as a switch to disconnect the panels once the batteries reach a certain voltage.

With a wind turbine, you don't want to open circuit the mill, because it will overspeed and self destruct with no load on it. In this case we use a dump load controller to use up the charging amps in some form of resistor which generates heat as a by-product.

Bigger systems with fancier controllers will include some sort of algorithm to bulk charge and then settle back to a float charge level.

Amanda

[elvin1949]

riff42

  Without a controller you take a chance of

COOKING your batteries.

later

Elvin

[greenene]

It's always a good idea to experiment with a few white Leds and a couple of batteries before you go solar. 1 Led requires 3.4 volts and 20ma.  So by taking 3 AA batteries , one 15 ohm resistor and one led, you've got the basic LED light circuit.

With this combination you start to get a feel for how much light one LED produces and the pros and cons of its "directional beam".  

from this point on, all you need to figure out is that as you add more LEDs , you simply need to add 20ma per LED. The voltage remains constant.

I build lights for Africans. With 4 LEds rated at 30,000mcd and 3 AA rechargeable batteries rated at 2500 ma and a 6 volt 250 ma panel, a light will work for many many hours during normal solar recharge periods.

It's the "small" modular way to understand small solar systems.

Please keep in mind that this is strictly a "simplistic" approach to getting started. As you learn more about LEDs, you'll learn about LED drivers and why they are called current driven devices instead of voltage. Besides, if you blow one LED, it'll cost pennies.

tony

[riff42]

Would the panels come with their own over-charge controller?  I would think so, so if you leave it plugged into your car, it wouldnt fry the battery.

[riff42]

Well yes, a full sized wind/hydro/solar system I would want to add the controller.  But using a 12v solar charger with 12v batteries and running a 12v system........

I'm looking for a cheap way to start because we don't plan on keeping this house for more than 8 years.  I rather not install a full solar AC system just yet!!!

I'm sure I can find a good battery charger controller for cheap, or I can make.  

Thanks for the ideas!

ps:  I saw a Round Tuit on eBay last week, do a search for it!

[ghurd]

The 110ma PVs don't make enough power to cook a car battery.

The 3A PV kit does.

G-

[riff42]

Did you read my posts?  I am running high-power LED arrays.  no 20ma bulbs here.  On a dark evening, I run 17 watts, and have more 9watt LED arrays.

I do not need to figure out my lighting system, the question was can I use the cheap-o-ebay 12vdc battery charging panels for a 12vdc power system, since I doubt I will need more than 2-3 batteries for my lighting system.  Instead of spending 1000$ on a "small" solar system, I want to see if 60$ (not including batteries) will work for what I plan on doing.

[riff42]

Yeah.  Does that Harbor kit charge the batteries, and then the inverter just changes it to 110v right?  I would hope they have a charge controller on it.

Their website lacks info

Maybe if that work, I'll just grab it, and use the inverter system to run my 12v power supplies which are a bit more regulated.  Or something else I can find laying around.

[ZooT]

Well 17 watts at 12 volts comes out to a bit more than 1 amp.

Those $10 panels are sold as producing 100 milliamps(1.5 watts) so that means "in theory" you'd need at least twelve panels.(12x1.5 watts=18watts)

And the reason why I say "in theory" is because you're going to have losses.

So figure 15 panels(1.5 amps) to be safe for 17 watts, and you're talking $170.

Add another $30 which makes $200 and you can get the 45 watt kit that's rated at 3 amps which should run your LED's and one more set like it.

The folks here are going to scream and holler at me for simplifying things WAY too much.

but then again.....probably a lot of folks here would consider me to be simple minded 8^P

Look at it in (watts in/watts out) in that if you have a 1 watt panel in the sun for one hour "in unrealistic theory" it should produce enough to run a 1 watt LED for 1 hour....

From what I'm learning here you could apply the same oversimplistic projections and use (amps in/amp out).

So you have 17 "watts out" an hour for the time the lights are on, so you'd have to put 17 "watts in" for an hour for every hour you want to run the lights.

If you're only putting one "watt in"......it'll take 17 hours of sun to run the lights for 1 hour.....

[Electron Skipper]

Power is power.

Power is Volts times Amps

Power in does not equal power out because of losses.

Too many people get hung up on "controllers," and with a modest system, such as is described in the initial post, one really is not needed at levels below 4 amps, and really of limited value at 5 Amps- as long as water levels are maintained.  45 Watts at 12 volts is not even 4 amps.  It takes at least 13.8 volts applied to overcome internal resistance within the battery.  

10 Amps at 12 volts is 120 Watts- You can do a lot of lighting with LEDs these days, especially with the newer "Power LED" options, and used without a focusing lens, will radiate close to 180 degree dispersion from the mounting plane.

If you take a shortcut and use the homecenter undercounter puck lights, measure your current draw, each puck light should be in the neighborhood of 60 milliamps.  At 12 volts, it is less than 1 Watt.  Lite On has a 1 WattPower LED comparable in light output to that of about a 20 Watt incandescent light bulb.  At about 6 bucks a pop- easy.

The power LEDs are supposed to have a heatsink behind them for their own heat- but mounting them with a little heatsink compound on a metal surface is actually adequate for the 1 watt power LEDs as they do get warm, but not at all a fire hazard.

So- Step 1- Determine how much lighting you need.  try www.digikey.com, and order a catalog- they ship worldwide.  You can look at pages online too, and you can enter the manufacturers into the search box, Lamina, Lite On, Lumex, Avago, and there are a couple more too, plus you can edit the pageurl to move through the pages too.

Step 2- Determine your total load, and length of time of that load. to come up with your ampere hours.  With LEDs and good lighting habits, a single Deep cycle may be adequate.  Size your batteries accordingly.  Well maintained batteries will last well beyond their designed life expectancy.  So oversize your needs 50% to 100% for "busy days" or emergencies  If not even slightly more.  At most, you only want to draw down to 80% of battery charge capacity regularly.  

Step 3- From the above numbers generated for your expected load, What are you going to need for recharge capacity on December 23- right around the shortest amount of daylight per year?  Select 50% above this amount to compensate for circuit losses.

Oversimplified in many ways, yes.  But it gets to the heart of what people so far have been trying to put into words.

[ZooT]

Quote:

Too many people get hung up on "controllers," and with a modest system,

Well I got hung up on a controller because I wanted to put up a small system at a place that I only visit once a year, and have some lights there when I get there every year

[VisualMonster]

Here's a link to that 45watt kit that ghurd's talking about:

http://www.harborfreightusa.com/usa/itemdisplay/displayItemList.do

It's an awesome deal, they're on sale for $179.99 (I think until end of this month).

You wont see anywhere near the advertised 45w's though.  I've accepted that and am still happy with them considering everything they came with and the price paid.

[ghurd]

They should be operating as advertised. 1A per PV, 3A per kit, under good sun.

Most do, at least for a few years.  And they should do better for the first few months, then settle down to the rated output. (1A at 15V)

If they made 1A at 12.6V, they'd never get the battery full.

G-

[riff42]

Hmm, I like that explanation, even if people might say it is over-simplifying things.

I'll keep that in mind for the system!

Thanks!

 

[riff42]

Yes, but the question is, will these cheap solar chargers work for a battery system that is being used every day, OR are they only to keep the battery trickle charged when not in use.   Yeah, I can get the 140$ system from Harbor Freight, OR 30$ of cheap panels for a small system.

[Electron Skipper]

This may be a bit late, or it might be timely,  who knows?

Essentially, the reason you want to control voltage is to keep from overcharging the batteries.  All that means is you charge at a higher rate than needed, and that extra energy is released in the battery as heat.  In the case of most deep cycle and golf cart batteries, this extra power is really a non factor because your peak panel output potentials are not for excessively long periods, and in most areas of the US, not every single day.  Plus a battery under charge will be able to accept that higher potential, and because this need for energy is a load on the panel, you may not be able to measure significant potentials much above 15 volts.

When looking at around 3 amps current, if you are checking water levels on a regular basis, no controller is needed.- in this case all a controller is for "cut in"/"cut out" operation, with voltage regulation (a voltage chopper circuit is used in the small controllers) this really only would be needed if you were not checking water levels on a regular basis.

Above 3 amps, you want to consider voltage regulation, and there are numerous ways to achieve that.

If the draw is 120 Watts on the battery for several hours each night, you want to invest in the larger system.   Figure your draw for the longest period of use, and double that value for watt/hours= size your charging panels accordingly for the shortest daylight length for your lattitude.

Harbor Freight, Tractor Supply, and Northern Tool have similar systems, and they can be mounted to a structure, or assembled with their own frame to stand on the ground where it might go for a walk if you have no way to secure the area.  You could see if you could fit the panels into the upper portion of a window that faces South. Not the most efficient, but it will still work.