Voltage and current protection for lighting project?

[gcmiller72]

Hi folks. This is my first post. I have a few solar/electrical questions about a lighting project I want to do and from reading this forum I think I

[NEOH]

re-post your message without any special characters or symbols.

[gcmiller72]

Hi folks. This is my first post. I have a few solar/electrical questions about a lighting project I want to do and from reading this forum I think I

[gcmiller72]

No special characters. I give up. I took a week to get permission to write a post and now I can't post more than one line.

[SunEagle]

No special characters. I give up. I took a week to get permission to write a post and now I can't post more than one line.

Are you just typing the information in or trying to cut and paste something that is already written? The cut and paste has issues.

[gcmiller72]

I'm copy/pasting. I wrote a fairly lengthy post with questions last week and I saved it to Word while I waited to be granted permission to post to the forum.

[AzRoute66]

The whole 'special character - copy/paste' issue here is frustrating for sure. Try saving the document as 'txt' format, then copy/paste from Notepad. I would be prepared to bring it across in small sections if need be by editing the post until it is all in there.

[sensij]

No special characters. I give up. I took a week to get permission to write a post and now I can't post more than one line.

"Special characters" include apostrophe's, quotation marks, and hyphens. If your pasted text includes those, and it isn't coming out of notepad as AzRoute66 suggested, you can delete and re-type just those characters where they occur in the text entry window and it ought to work.

Unfortunately, the "preview" function parses the text differently, and makes it look like what you've entered will be OK even if it will end up getting truncated.

[gcmiller72]

OK, I followed the advice above. Here's my next attempt.

I have a few solar/electrical questions about a lighting project I want to do and from reading this forum I think I have found the right people to help me out. I will apologize in advance for the length of the post, but I want to make sure I provide all the facts.

Here is my project, I have a pole barn that consists of nothing but six pilings and a metal roof. The structure is 22ft x 20ft and is in a pasture far from the house, meaning no available AC power. I have a fire pit, a couple of chairs, a picnic table and a charcoal grill out there and now I would like to add some LED lighting. I found a 165ft string of 12V LED fairy lights that consume 25W of power and a 5W solar trickle charger with built in overcharge discharge protection. The lights come with an AC to DC converter that outputs 12V and 2A. My thought is to wrap the lights around a 36in diameter wooden wagon wheel and hang it from the rafters as a chandelier. I will throw away the power converter and use a 100Ah, or larger, battery to power the lights. I will put the solar panel on the roof to keep the battery charged.

In theory, I should be able to power the lights for four hours. I figure realistically, I can run the lights for three hours or so as the battery ages. This is fine as I do not believe we will use this setup very often or for long periods of time. This is just a place my wife and I can go to hang out when the weather is nice. This is just aesthetic lighting for fun, not something important like heat or refrigeration, so I do not want to go overboard with this project money wise.

My questions are
1. What size fuse should I use? The lights are 25W and the battery is 12v, so that is 2.08A, which matches the 2A power converter that will come with the lights. It is a 25ft run from the battery to the light fixture. My wire calculator tells me I need 16awg wire, but I plan to use 12awg to be safe. I am thinking I will use a 3A fuse since that is plenty of current for the lights and plenty safe for the wire, but other than that I have no real scientific reason for using that size. Is there a better way to determine the fuse size?
2. Do I need voltage protection or a voltage regulator between the battery and the lights? Not between the battery and the charger since the solar panel has this built in. And if so, what kind? My thought here is if someone flips the lights on during the day when then solar charger is doing its thing is there a concern about the charger supplying greater than 12v to the lights? I cannot find the output of the solar panel other than it is 5W.
3. Does anyone see any issues or flaws or have any questions or comments about this setup or something I am missing?

Thanks in advance,
Gary

[sensij]

Very roughly, if you want to power the lights for four hours, that is 100 Wh. At 12 V, 8.33 Ah. You'd probably want to get a 50 Ah battery (or more).

To replace that energy in the battery, figure you need to generate 150 Wh to account for losses. Your generation potential will depend on where you are located, but something approaching a 50 W panel would probably be safe. A 5 W panel won't do much more than just compensate for the battery's own self-discharge... it could take weeks of charging to replace one night's energy use by the LED's.

[SunEagle]

OK, I followed the advice above. Here's my next attempt.

I have a few solar/electrical questions about a lighting project I want to do and from reading this forum I think I have found the right people to help me out. I will apologize in advance for the length of the post, but I want to make sure I provide all the facts.

Here is my project, I have a pole barn that consists of nothing but six pilings and a metal roof. The structure is 22ft x 20ft and is in a pasture far from the house, meaning no available AC power. I have a fire pit, a couple of chairs, a picnic table and a charcoal grill out there and now I would like to add some LED lighting. I found a 165ft string of 12V LED fairy lights that consume 25W of power and a 5W solar trickle charger with built in overcharge discharge protection. The lights come with an AC to DC converter that outputs 12V and 2A. My thought is to wrap the lights around a 36in diameter wooden wagon wheel and hang it from the rafters as a chandelier. I will throw away the power converter and use a 100Ah, or larger, battery to power the lights. I will put the solar panel on the roof to keep the battery charged.

In theory, I should be able to power the lights for four hours. I figure realistically, I can run the lights for three hours or so as the battery ages. This is fine as I do not believe we will use this setup very often or for long periods of time. This is just a place my wife and I can go to hang out when the weather is nice. This is just aesthetic lighting for fun, not something important like heat or refrigeration, so I do not want to go overboard with this project money wise.

My questions are
1. What size fuse should I use? The lights are 25W and the battery is 12v, so that is 2.08A, which matches the 2A power converter that will come with the lights. It is a 25ft run from the battery to the light fixture. My wire calculator tells me I need 16awg wire, but I plan to use 12awg to be safe. I am thinking I will use a 3A fuse since that is plenty of current for the lights and plenty safe for the wire, but other than that I have no real scientific reason for using that size. Is there a better way to determine the fuse size?
2. Do I need voltage protection or a voltage regulator between the battery and the lights? Not between the battery and the charger since the solar panel has this built in. And if so, what kind? My thought here is if someone flips the lights on during the day when then solar charger is doing its thing is there a concern about the charger supplying greater than 12v to the lights? I cannot find the output of the solar panel other than it is 5W.
3. Does anyone see any issues or flaws or have any questions or comments about this setup or something I am missing?

Thanks in advance,
Gary

1. #12 AWG wire with a 3 amp fuse should be fine
2. I do not see why you would need voltage protection unless the LED lights can't handle 15v -17v dc which is what the CC may pump into the battery.
3. Using a small battery, solar panel and charger sounds like a great little system to light those LEDs but to keep the battery happy you should provide about 1/10th the Ah rating as charging amps. Which is probably about 2 x 100 watt panels for a 100Ah battery. If you go with a 50Ah battery you can probably get away with one 100watt panel.

But that 5w panel is not going to do much to "recharge" a battery of any size. They were designed to "maintain" a battery that will slowly discharge if it just sits there to keep it at floating voltage.

[gcmiller72]

Thanks Sensij and Suneagle. That makes sense about the 5W panel being too small. It looks like I can buy 100W panels for roughly $100, instead of $40 for the 5W panel.

I'm in central NC, so we get some pretty good sun. Perhaps I will buy one 100W panel and see how well it works. I'm guessing I can add a second panel later.

[AzRoute66]

Because your lighting was 25W for 4 hours = 100Wh, and you proposed an 100 Ah (or larger) battery seemingly out of thin air, I think I detect a misconception that I can address. Your 100 Ah battery would 'contain' 12V x 100Ah = 1200 Wh of energy. As you would be using 100Wh at a time (per cycle as we say) you would be only using 1/12th or 8% of the energy in the battery.

A more useful way of thinking about battery size would comprise two calculations. First, a rule of thumb in battery longevity is to not discharge the battery below 50% capacity, with shallower discharge leading to longer battery life. In this case, you will be discharging 100Wh, so anything over 200 Wh will satisfy the 50% rule of thumb. 200Wh / 12V = a 17 Ah battery minimum. Second, undercharging a battery is also undesirable as it leads to stratification, also reducing battery lifetime. Charging at a rate 1/10th of a batteries capacity is a 'sweet spot' for a battery for which you do not have a manufacturers specification. 1/10th of a 17Ah battery would be 1.7 amps. Your trickle charger is capable of no more than 5W / 12 v = 0.4 amps, less if you count the very likely PWM loss.

This trickle charger 'might' overcome self-discharge given enough time, but might not. If you don't think you would ever want to use it like that twice in the same week/month you could give it a shot knowing that you are undercharging most anything.

So, replacing the 5W trickle charger is probably the best thing you can do. many PWM 3A, 4A, and 10A chargers are under $10, not hard to find.

So, I would be looking for a great deal on a deep cycle battery that was over 17 Ah, knowing that an appropriate charge controller/panel combo will be a pretty easy fit. Probably found sold together as a cheap starter kit.

Let's say you found that 50Ah battery sensij suggested. You would be looking for a 5 amp charge controller to charge it. But you can't find one so you go with a 4A charge controller I just saw on Amazon for $6. To get that 4A out of it you will want 12V x 4A x 1.5 (PWM fudge factor) = 72 W or larger panel. Should you have found the 5A controller you would want a 12V x 5A x 1.5 = 90 W or larger panel. How much larger? Doesn't matter, your controller will limit it.

If you had found a free 10 A charge controller, you would be looking for around a 100 Ah battery for optimal charging purposes, but you would be looking at 10A x 12 V x 1.5 = 180W of panel to charge it. Bah, overkill, but you knew that when you considered a 100 Ah battery for a 17 Ah job. Buy the 'great deal' 50 Ah battery, use the 10A free controller, but use the panel to limit the current to around 5A by not buying a panel much over 12V x 5A x 1.5 = 90W. 100W is common, if you had it you would have 100W / 12V / 1.5 = 5.5 A. Close enough.

That whole thought experiment was to show you the flexibility towards cost you can have, if it just confused I apologize.

Your ideas that the fuse is to protect the wire, not the charger or load was spot on. Also, no 12 V battery or charger will put out enough voltage to harm the 12V load/lights.

[gcmiller72]

Wow, I can't believe I was confusing Watts and amps. That was a complete brain fart on my part. I might not be an expert, but I do know better than that.

AzRoute66, thank you. That's some fabulous information you provided. Thanks for taking the time to write it. I'm happy I found this community.

[sensij]

Let's say you found that 50Ah battery sensij suggested. You would be looking for a 5 amp charge controller to charge it. But you can't find one so you go with a 4A charge controller I just saw on Amazon for $6. To get that 4A out of it you will want 12V x 4A x 1.5 (PWM fudge factor) = 72 W or larger panel. Should you have found the 5A controller you would want a 12V x 5A x 1.5 = 90 W or larger panel. How much larger? Doesn't matter, your controller will limit it.

<Snip>

Also, no 12 V battery or charger will put out enough voltage to harm the 12V load/lights.

Quick point of clarification... Not every charge controller will handle over-current gracefully. PWM in particular, it is important to make sure the Isc is less than the controller rating. For example, a 100 W panel might have an Isc of 5.75 A... That is too much for a 5 A PWM controller.



For the LED's, the full battery voltage of 14.4 V *might* not be good for them, since they were packaged with a regulated 12 V supply. Some LED's are touchy about this, although I've seen those light strings powered off batteries before so they will probably be ok. Worth looking for specs, anyway.