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Old 20-07-2009, 16:38   #1
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Will This Work?

Ok first let me say that I just stumbled across this website through a Google search, and don't actually sail or have a boat. I know this forum is for sailing and boating, but figured I would ask on here because you sailing guys know more than anybody about battery current draw and solar recharging and such. So if you could help me out, it would be greatly appreciated.

Mods, if you feel this thread is inappropriate because it is not related to boating, I apologize - feel free to delete it.

But... if you guys would be willing to help me out, here is the question:



I have a street sign for my business in a place where I cannot get electric to it to light it up. So what I am wanting to do is put an auto or marine battery out there in a battery box, use some LED MR11 bulbs and outdoor fixtures, use a solar panel to recharge the battery, and put the lights on a timer.

I had just done a quick search for solar panels on eBay, but I cam across one like this:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280373082239&_trksid=p 2759.l1259

The lights would need to be on for probably 6 hours at a time.

Also, would I need any kind of regulator or could I just wire the lights and solar panel directly up to the battery?

Would something like this work, or am I on the right track at all?

Any help would be greatly appreciated.
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Old 20-07-2009, 17:09   #2
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Its an overall good idea. You are going to need a controller/battery charger for the solar panel(s) that takes the solar panels native voltage and converts it over to voltage that charges the batteries.

There are other factors such as having an adequately sized solar panel and an adequately sized battery that meets the power requirements of the sign. You will need a sign that runs on 12 volt DC otherwise you will need another power converter to convert the voltage from the battery over to what the sign requires.

For some reason, your link takes me straight to Ebay.com's home page, therefore I was not able to see what you were referring to.
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Old 20-07-2009, 17:24   #3
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Thanks for the reply

The link is doing the same thing for me for some reason, but if you copy and paste it goes directly auction. Let's try it again:

15W 15 Watt 12v Solar Panel Battery Charger - eBay (item 280373082239 end time Jul-23-09 18:50:11 PDT)

But, that solar panel is designed to charge a 12volt battery, so I guess it already has that controller on it.

I was planning on using MR11 bulbs, which I was under the impression they can run off AC or DC, but maybe I am wrong about that.

I was viewing a thread on this forum where a guy tested a bunch of different MR11 LED bulbs, and it appeard that he just had them hooked up to a 12 volt battery. Here's the thread:

http://www.cruisersforum.com/forums/...son-21839.html

The solar panel I was looking at on eBay is a 15 watt - would that be adequate? Also, what size battery would you recommend?
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Old 20-07-2009, 18:06   #4
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The link is still not working, copy and past this:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280373082239&_trksid=p 2759.l1259

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Old 20-07-2009, 18:44   #5
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Sorry the link still is not working.

OK, the standard MR11 bulb will run on 12 volts, but you can get an LED package that runs on 12 volts that will replace the standard MR11 bulb (uses the same socket). The LED uses FAR less power (Amps X Volts) = Watts. It also has more hours before they die (a whole lot more). They cost allot more too (you knew that was coming). It sort of comes down to how well does the sign need to be lit up and how much can you afford. You need to charge the battery fully during the day so you have full battery at dusk to light the sign until some time when the people who see the sign won't spend any money when they sober up. It really needs to happen every day so you start fresh or the magic won't last.

If you don't get the battery fully charged over time it will die. Batteries cost a lot of money (way more) so that means the solar panel needs to be big enough and they cost a lot money (even more than batteries).

How big is the sign and how much light do you need and how much do you think it might cost? How much would you hope it will cost? This is a pay me and / or pay me later issue. If you get this wrong a deep cycle 12 volt battery is in your future more often than you would expect. Done right you might get 5 years to 7 years. Weather and sun conditions will change the requirements. If you live in the Pacific NW there may not be enough sun.

Get a bid from an electrical contractor so you can set a stop limit on the loss. It matters.

It's OK you don't own a boat - but maybe you might some time soon. If you say you might we can let you stay. You don't have to promise. Liking boats might count too.
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Old 20-07-2009, 21:00   #6
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Quote:
Originally Posted by Pblais View Post
It's OK you don't own a boat - but maybe you might some time soon. If you say you might we can let you stay. You don't have to promise. Liking boats might count too.
lol, I really have always wanted to sail, maybe someday when my business blows up I will be able to buy one!

I've been searching all over the internet about this and what I have found.

By my calculations, two (2) Dr. LED G4 / MR-11 bulbs will draw .14 amps per hour. Therefore, if these 2 bulbs were to run for 7 hours (which would be about the max time I would need them running in the winter) they would drain 1Ah (amp hour) off the battery.

If I had a 55Ah deep cycle battery, they would drain the battery by only 2%.

A DC solar panel will charge at a rate of 1 amp per hour, per 15 watts the panel is rated at. ie, if I had a 50 watt solar panel it would charge at a rate of a little over 3 amps per hour of direct sunlight.

The one thing I have not been able to figure out yet is if battery Ah (amp hours) is directly related to the amp rate at which a battery is charged. ie, if a battery charger (or solar panel in my case) that charges at 3 amps per hour, would actually charge the battery back up by 3 amp hours.

Anybody know...

Again, these are my calculations and I suck at math and have no clue when it comes to physics - so these numbers could be way off, lol.
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Old 20-07-2009, 21:06   #7
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Originally Posted by Pblais View Post
If you don't get the battery fully charged over time it will die. Batteries cost a lot of money (way more) so that means the solar panel needs to be big enough and they cost a lot money (even more than batteries).
If my calculations are correct, then even a small 15 watt solar panel would be enough to fully charge the battery back up if it only had 1 hour of direct sunlight each day.

Quote:
Originally Posted by Pblais View Post
How big is the sign and how much light do you need and how much do you think it might cost? How much would you hope it will cost? This is a pay me and / or pay me later issue. If you get this wrong a deep cycle 12 volt battery is in your future more often than you would expect. Done right you might get 5 years to 7 years. Weather and sun conditions will change the requirements. If you live in the Pacific NW there may not be enough sun.
The sign is only about 36"x36", so 2 MR11 bulbs (1 for each side) should do it.

I was planning on spending at least $150 for a battery, $50-$100 for a solar panel, and then probably another $50-$100 for the bulbs and fixtures. So I was planning on spending in the neighborhood of $350 for just the lighting.

However, if my calculations above are correct I may not need a battery with such high amp hours or a high wattage solar panel.
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Old 20-07-2009, 21:17   #8
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Also, I just found this battery operating time calculator that seems like it confirms my calculations.

Battery is 55 Ah, lights are a combined 2 watts = the calculator says they would run a max of 137.5 hours off this battery before it was dead.

Although, this calculation indicates they would drain the battery by 5% per 7 hours of run time (my calculations came to 2%). Still close and easily chargeable via solar panel, I think anyways.

Xantrex Technology Inc. - Battery/Appliance Operating Times Calculator
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Old 21-07-2009, 01:06   #9
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There are always inefficiencies to consider

Quote:
…what I am wanting to do is put an auto or marine battery out there in a battery box…
The type of battery you need is a deep-cycle battery, designed to be discharged deeply over many cycles of discharge-recharge. An automotive battery could do the job at 5% discharge, but it is really designed to deliver maximum amp output over a short duration, like starting a car, and then re-charged immediately. It will likely fail early in the application you're contemplating.

A "marine" battery may be a hybrid— halfway between a starting battery and a true deep-cycle. Better, but the true deep-cycle is best.

You will also find industrial batteries that are used for the kind of application you intend, running remote street signs & such. That's a possibility, but as I recall, they are expensive.

A truism with deep-cycle batteries is that the deeper they are discharged, the fewer discharge/recharge cycles they will deliver over their lifetimes. As a compromise between performance and economy, a "only discharge to 50%" rule-of-thumb has been adopted by almost all cruisers. Fully discharging a battery will kill it in short order, and the lights will fail to work well before a full discharge anyway, as the voltage falls.

Using that discharge rule, from that 55 amp-hour, deep-cycle battery, you can draw some 25 amp-hours of energy before some recharging should occur: the 50% rule also demands that your 137 hours must be halved: 65+ hours of useable power, at the rate of draw in your example.

Divide that 65 hours by 7 hours a night, and you can run the lights in your example some 9 nights (with zero charging) and you'll be around 50% discharged. You can weather just about any storm w/ 8 nights of extra power while the solar panel puts out zero. But most of the time, you'll be looking at a 24-hr discharge/charge cycle that will not discharge that battery anywhere near the 50% mark.

The most respected authorities on the subject I have read caution that you should count on getting about 5 hours or so of good output per day from the solar panel in a fixed orientation, loosely from 10AM-3PM, when the sun is high & relatively perpendicular to the panel. Outside that peak window, you will see (much) less than the rated output. Use 5 hours in your math, and tilt the panel 15° or so to the south, if you're in the Northern Hemisphere, to maximize that window.

The battery you're looking at seems to have plenty of capacity. Looking at your numbers, the panel seems to be able to keep the battery "topped-off" under normal conditions (healthy for the battery) and to replace amp-hours after a few cloudy days reasonably quickly.

I'll leave discussion of controllers & such to those more knowledgeable than I.
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Old 21-07-2009, 01:09   #10
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I've been swaping out some of my boat cabin lights for LED's party for heat and partly for power use. The new LED bulb replacements work pretty well. I would more concerned with the fixtures being weather proof than anyting else.

Your calculations probably are close. The key is you don't discharge the battery to more than 50% of the amp hour rating for maximum battery lifespan. That makes it pretty good. The key is also the rate of acceptance for the battery decreases as it gets closer to being full. It means you can't just dump lots of power back in without problems. This is where the regualtor comes in. The state of the battery dermines it's rate of charge. "Smart Chargers" can read the state based on the battery type and compute a charging profile. This means when the battery is very low it can handle a higher input than as it gets closer to full. If you can find a decent regualator then you should be fine. When the battery is close to full you can only put in a few amps at a time.
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Old 21-07-2009, 01:16   #11
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All true, Paul, but with a panel, you're just trickling anyway…
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Old 21-07-2009, 03:23   #12
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Have you considered the security aspects of this - a solar panel is a desirable item that some low-life may take a fancy to.
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Old 21-07-2009, 08:23   #13
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Thanks again for the replies everybody!

Quote:
Originally Posted by Pblais View Post
If you can find a decent regualator then you should be fine. When the battery is close to full you can only put in a few amps at a time.
Can anyone recommend a regulator? What price range are they in? Is there a certain name for these regulators so I can search for them?

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Have you considered the security aspects of this - a solar panel is a desirable item that some low-life may take a fancy to.
Yes, I had though about that. I am planning on laying the panel flat on top of my sign to minimize the visual of it. I am also planning on burying the battery in a battery box, this way it will be completely out of site, plus if I go about 12" deep or so this will keep the battery warmer in the winter. Battery amp hours can drop off by 60% when the temp falls under 40 degrees, and I live in the mountains of North Carolina where it is often snowy and under 30 degrees in the winter.

Also, my sign is actually in my very good friend/neighbor's yard, who is an older gentleman that has signs in his yard and all over his windows that say "We have guns and we will use them", "We don't dial 911", "nevermind the dog, beware of owner", "insured by Colt", and so on, lol, gotta love the south! It's a small town and he has a pretty good reputation of having a house loaded with guns and that you'll die if you plan on stealing from his property, lol!

Like I said, it's a small town in the south and I live on a main road and will leave my doors unlocked and garage open pretty much 24/7 and not have to worry about it. Not nearly as many low-lifes down here in the south, but not completely out of the question.
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Old 21-07-2009, 10:47   #14
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If you can find a decent regualator then you should be fine. When the battery is close to full you can only put in a few amps at a time.
From what I have been reading, you only need a regulator with a high amperage charging unit. A "trickle charger" is ok to leave hooked up to a battery 24/7 because it charges at a maximum of 1.5 amps per hour. If I had a 15w solar panel that would be charging at 1amp per hour, which would be equivalent to a trickle charge.

Although, I am thinking about going with a 50w solar panel, just to be sure it charges the battery fully. In that case I think I would need a regulator. Are these the right kind of product I would want?

12v Solar Regulator Panel Charge Controller 6A: Virtual Village - US

Brunton Solar Controller 12 Volt Battery Charge Regulator :: Instrument Accessories :: Instruments & electronics :: Moontrail

24A 12V/24V Solar Power Charger Regulator: Virtual Village - US

Steca PR 1010 Solar Charge Controller, 10 Amp, 12/24 volt


That last one is spendy, but it looks very nice because over the other controllers, it not only will cut off my lights if the battery drops below 11 volts saving the battery, but it also has a built in timer that will turn my lights on at dusk or whatever time I choose, and set them to stay on for 0-8 hours after sunset. It also has an LCD readout with the state of charge, amp hours remaining in the battery and more. Seems like a very nice piece of equipment.
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