RC charging station 100watt 12V

[ryanf55]

Hi. I am trying to make a portable home-built solar panel to power a video receiver and charger. I calculated the consumption to be 72 watts off a field battery. I am going to run the gear off a 12V 10Ah battery from a wheelchair. Normally, the 10Ah battery would go dead in 2 hours, but a 72 watt solar panel should keep the battery topped off.
Using the assumption of more is better, I want to build a 100watt solar panel, that folds and fits in a backpack. I will use a coroplast as a backing (cardboard but plastic). I can reinforce it with wood around the edges. Each panel will be about 10x12, and they will be taped together to fold into a backpack.
I have looked all over, and can't seem to find a reliable seller of just PV cells. I spoke to a local company, and they only sold panels. I hope to find cells for under $1/watt. Any suggestions?

If I can find reasonably priced cells, I will do a build on here with pictures

[russ]

Do a lot of studying before spending one cent - you have a real education to gain.

[ryanf55]

Yep. I have found some more reliable systems on ebay. I am mainly worried about cracking the cells during use. I saw one can buy mini solar panels and then solder them together, but I have not found any for sale.
For now I will continue my research, and start with a field battery. Maybe I can find a few free cells to experiment with before I drop $100 on the cells.

[Sunking]

Yep. I have found some more reliable systems on ebay. I am mainly worried about cracking the cells during use. I saw one can buy mini solar panels and then solder them together, but I have not found any for sale.
For now I will continue my research, and start with a field battery. Maybe I can find a few free cells to experiment with before I drop $100 on the cells.

That is not the kind of studying Russ is referring too. Non of what you say adds up or makes sense. If your device requires 72 watts to operate, a 12 volt 10 AH battery with a 100 watt panel is not going to work. Well unless you only want to run the device for 30 minutes a day and destroy your battery in a short time.

Secondly there is no way you can make a panel for less than you can buy one for. Better tap the brakes and do a few months of studying an dget a good grasp of the physics. Otherwise you are in for a very expensive lesson of failure.

[ryanf55]

Thanks for the reply Sunking.
below is what I wrote before your post.

The system I am building will never be unattended. From what I have gathered, charge controls normalize the voltage output, while monitoring the current. They shut off the solar panels if things get to hot, or the battery is full. I can and will be monitoring these things when I am flying. Then, won't the only thing I need to buy is a 12V voltage regulator to keep the voltage at 12V for the battery?

Max output: 100 watts /12V=8.33 amps. If battery is 10Ah, then the max charge rate is less than 1C. Is it true then that a smart charge controller is not needed as long as voltage stays at 12V?


I did some reading here. Very helpful. It looks like the battery will need 18V input or so. So a 120watt solar panel is still 6.67 amps which is a bit fast for even an AGM.

I normally draw about 6 amps out of the battery. If the solar panel produced that amount simultaneously (after losses and inefficiencies taken into account), then I do not need to worry much about the battery being charged/drained?

In response to your post:

I was told by a guy at batteries plus (who sells the AGM 10Ah for $40) that I can discharge it 50%. Maybe that is incorrect. Also, I will be starting on a smaller scale, with only a 1 amp draw from my devices. I am so used to using LiPo's for everything, where charge rates are 5C. I come from a background where the batteries are made to handle these things. Sorry if I make assumptions, I have realized solar is a whole different story.
Although my end goal is power the 6 amp draw, I will not be going for that right away.

As for the cost comment, I have yet to find a portable system around 100 watts that is not under $500. The portable ones are all made for rain and very durable, but I do not need that. The solar panel I am trying to make is only supplemental, as a method to allow more at-the-field charges. I will be happy if I even get 50 watts out of the panel.

My costs:
Solar system:
$80 for 120watt system, tabbing, flux pen
I already own a soldering iron and solder
$10 for the coroplast backplate
scrap wood for reinforcement, and tape
$30 12V charge controller
$10 wires and heatshrink.

Battery
$80: 20Ah should be large enough

Total cost: $200. Am I missing anything significant.

[PNjunction]

Max output: 100 watts /12V=8.33 amps. If battery is 10Ah, then the max charge rate is less than 1C. Is it true then that a smart charge controller is not needed as long as voltage stays at 12V?

What would help the most is to read the stickies and faqs at the top of the forums first. They contain the most information you can get in the least amount of time before opening the wallet.

For example, your calculations are a bit off. And YES, you will need a charge controller.

A nominal 12v panel has an open circuit voltage typically 18v. So 100w / 18v = 5.55a but under the BEST conditions. Expect a bit less due to losses in the entire system for the real world. Your 10ah battery is a sealed agm. On the front should be some specifications. If not, these ups-style agm's can only accept 0.25 to 0.3C max. Thus, your 10ah battery can only accept a sustained current of 3a, unless you want to smoke it or develop hot spots.

I normally draw about 6 amps out of the battery.

I'm assuming thats a total draw runtime. Ok, the quickest route is that you will need at least DOUBLE that in battery capacity, as one does not want to discharge a battery more than 50% DOD, or half-way if you want reasonable cycle life. Thus, your battery minimum will be 12ah. For even longer life, beef that up to perhaps 18ah in the same ups-style agm as a learner battery (powersonic, universal battery, B&B and so forth)

As for the cost comment, I have yet to find a portable system around 100 watts that is not under $500.

How about half that amount - put one together for a friend today... :

http://www.renogy-store.com/100W-Suitcase-p/kit-stcs100d.htm

If you use the ups-style agm's, then the *minimum* size to use would be 20 - 22ah or so assuming 0.25 to 0.3C max charge rate. That would also fulfill your 6ah load application requirement (if TOTAL runtime) without even going to the 50% DOD mark. Thus your battery will last longer.

Be sure to see / click on our own gracious hosts offerings as well.

I will be happy if I even get 50 watts out of the panel.

Ok, how's this for a 60w / 3.3a version again under best conditions.

http://www.renogy-store.com/60W-Suitcase-p/kit-stcs60d.htm

I'm not trying to push these specific panels on you, just pointing out that a bit more research needs to be done. Fortunately those answers are in the stickies and faqs right here. Right now you are winging it, and it is going to be expensive when you have purchase it all over again.

We also don't know what your solar insolation hours are. This is also something you need to look into as it differs from mere sunrise to sunset. At this small scale, it may not matter much if you overdo the requirements, but larger more critical systems certainly so.

[ryanf55]

Thanks for the speedy reply PNjunction.

When I go to the batteries store, I will for sure ask about the C rating of the AGM, and one that is 20Ah. From what I researched, AGM's are better in my application than a Gel.

The 6 amps is my estimated total draw. I use a 1200mAh lipo to power the video equipment, which I use for around an hour. It always has a bit of juice left. Now the remaining 5 amps come from the charger. The charger is to charge the plane's batteries. It goes through a 3s 5000mAh. I assume there is little loss(to heat) when using the charger because it doesn't get charging at 5 amps. This system is entirely optional, unless I want to fly more than 2 flights. That is why I do not need it to be top quality. 3 hours or more of flying is only for situations when extensive mapping or searching is needed. I will do more research as suggested before I put in money, as I probably won't be upgrading the system.

Thanks for the links to the portable solar panels. I will show them to my boss sometime. I do think I can make my own cheaper, and I the sort of person who likes to build it themselves. Although those are more professional looking, I will like to be able to change my setup for days when I only need 30 watts. If this doesn't work out, I will look into buying the panels you sent me.

I will now start from scratch, with a primary goal of powering the ground station that consumes 1 amp. I will do research, and slowly flesh out a system. From the watts the solar panel generates, what percent of that gets transferred to my ground station.
One big question I have:
Say the solar panel is hooked up, and I also am using the AGM. Does power necessarily have to transfer through the battery, or will it go straight to the systems from the charge controller since that is the path of least resistance?

[PNjunction]

When I go to the batteries store, I will for sure ask about the C rating of the AGM, and one that is 20Ah. From what I researched, AGM's are better in my application than a Gel.

That is correct. Gel's have no place in solar because they have very low charging current limitations, and are easy to abuse. Also, in this case, "C" is the capacity rating. Ie, your 10ah agm can accept no more than 0.25C surge current (10 * 0.25 = 2.5A). That is also the maximum continuous discharge current limitation. You may see 0.3C. But that battery is too small, your minimum needed is 12ah.

But, instead of guesstimating, measure your current draw with a multimeter for your RC plane usage to get a better handle on how much capacity you really need.

Solar is fun, and homebrew can be ok for educational purposes, but at this point, why not just overdo it, and take a fully charged, easy to obtain 18-22ah agm battery similar to the one you have now to the field, and just put it on a battery-tender when you get home?

[ryanf55]

I am familiar with C ratings from Lipos, just not C rating under 1

My school chem teacher can sell me a cheap multimeter for $10. I saw not to buy cheapo ones, but it is better than nothing. I could set it up with a fully charged lipo. Run for exactly 30 minutes, and then recharge the lipo. My charger will tell me how many milliamps I put in, so I may try that first.

The issue with a large AGM battery is that after two hours it needs to be charged. I am hoping a simple solar panel can be used in conjunction with the battery to let me stay out there longer. Also the summer is starting which means more time, money, and sun.

I am pretty certain I am going to start with a 60 watt system, and a 20Ah AGM, except if I expanded it to 120watt, I would need to buy a new charge controller, which is wasteful. My research will continue until I can better assess the need for a solar panel, and how reliable it is.

In aiding my research, I was wondering if anyone has built a panel not made to withstand weather. Just a really lightweight panel. I can't find a way to protect the solar cells without adding glass or plexi on the front. Is it true they denature (Denaturing to my knowledge is when proteins break apart)?

edit: Any idea how this semi flexible solar panel was made? http://www.ebay.com/itm/USA-stock-10...item51b163a366

[Mike90250]

...... I can't find a way to protect the solar cells without adding glass or plexi on the front. Is it true they denature (Denaturing to my knowledge is when proteins break apart)? ....

It's mostly water vapor that gets trapped inside imperfect panels, and then condenses. That water corrodes the cells' metallic coatings in hours. Then you have junk.

[ryanf55]

What if I don't encase them? I am thinking of just gluing them on the backing. Something similar to this in which he used just resin. https://www.youtube.com/watch?v=-Oxg7o9OEgs

I don't have to worry about wind because I will only be flying if the skies are mostly clear.

I have watched a bunch of videos, and it looks like I can do 1ft by 1ft acrylic sheets with resin. The solar panels are glued onto the acrylic. I can then continue to use a coroplast backing.

---I am going to the battery store friday or saturday. Any ideas where to get slightly used/ returned agm batteries?

[russ]

What if I don't encase them? I am thinking of just gluing them on the backing. Something similar to this in which he used just resin. https://www.youtube.com/watch?v=-Oxg7o9OEgs

You can find most anything you want on youtube if you look hard enough - probably 99% is wrong - just some clown that wants to look important.

[PNjunction]

---I am going to the battery store friday or saturday. Any ideas where to get slightly used/ returned agm batteries?

That's like using somebody else's toothbrush. You don't know where it's been, nor how it's been treated. Basically you'll be starting out on the wrong foot since you can't trust one of the major components of your project.

I think I see the problem. Homebrew panel (first timer too), penny pinching on the battery, no charge controller, and guessing at your power draw.

No disrespect, but you've made yourself a target for scammers, or props from those that don't really know solar including battery salesman, that will be more than happy to sell you poor or mismatched parts, hopefully more than once as you are winging it. Educational fun taking shortcuts around engineering is one thing. A succesful project is another.

What you are discovering is that doing solar *right* isn't going to be cheap. There are plenty out there to convince you otherwise. We're not just a bunch of old grumps trying to complicate things.

[ryanf55]

Today I decided to scale down my project.


I went to the batteries store, and after I told him what I needed, he introduced me to true deep cycle batteries. They are a subcategory of AGM's ment to be discharded 100%. I asked if I discharged it 100% and brought it back up right after, how many cycles until the battery goes bad. He said 200. Basing the cost of a 10Ah true deep cycle being $40, I may stick with that. Anyone skeptical of this battery spec, because I sure as hell am.

I have decided I will not be doing any large battery charging due to solar panel cost, battery weight, and effort. I now just want to power my 12 watt combined monitor and transmitter. Anything larger is just too ambitious for my skillset and knowledge.

This weekend I am going to buy my first multimeter and I'll try to find a mid-range one for $25 or so. I can then test the current draw of my fpv, and also the loss of the lipo charger if I want to charge my small 700mAh packs.

In response to PNjunction:
AGM batteries aren't as expensive as I thought, so I will be buying a new one. I would only pick up someones toothbrush (used battery) if it was free.

I hope to solve the power draw guess with a multimeter, but I have a pretty good idea already. In fact I will be using a charge controller. They are also relatively cheap. would this charge controller work if I made a 30 watt panel? http://www.amazon.com/Instapark-SS12.../dp/B004XCZN5S

I have no rush for this project, but in my mind a deadline of july to get a working system.

I feel a scaling down from 6A draw, to 1A will lower the cost of this project, and make it more portable. I am going to sacrifice quantity of watts for a quality setup. Upgrade to aluminum backing (need to check thermal expansion coefficient to match it with silicon panels) for heat dispersion and rigidity. I will make a semi-flexible panel, use bypass diodes and charge controller, hooked up to 12V battery. Sound better?


edit for thermal expansion: found a table, and silicon's expansion is very low compared to almost all other materials. Shouldn't I match the resin to the silicon, and have the silicon cells submerged in resin. Then tape/hot glue the resin/cell piece onto a sturdy backplate? As long as the cells are encapsulated in resin, I assume they can stand alone. Only reason for adding glass and frame is to make it sturdy?

[PNjunction]

Now we're talking.

I don't know anything about that charge controller. However I can say that for a just a little bit more, you can enjoy a quality / PROVEN build from a manufacturer you may want to deal with in the future. It would make a nice fit for those little agms, and can handle up to about 60 watts, so you would have room to grow a little:

Morningstar 4.5ah SunGuard SG-4. It is potted/sealed to the environment, temp compensated, nothing to adjust or worry about aside from not going over 80 watts - although I'd stick to 60 max just to be conservative. It will work with your small panel too. The charge controller is the brains of your outfit, and one shouldn't skimp here if they don't have to.

No, you don't want to go down to 100% DOD even if you can. Bad practice aside from costly replacements. In solar, we generally shoot for using no more than half the battery capacity or 50% Depth-Of-Discharge.

How to tell? With your new multimeter coming, measure across the battery terminals after it has sat around for about 4 hours doing nothing. That is, NO charge, and No load. For these ups style agm's, here is the breakout:

12.8v and higher = fully charged 100%
12.5v = 75% charge
12.2v = 50% charge (this is the target not to go below)
12.0v = 25% charge (try not to go here, cycle life is reduced.
< 12 = bad news!

While I don't agree with your choice of building your own panel at this stage, I can't stop you. Strangely enough, building your own panel AFTER you have a commercial one in your posession as a reference to compare to is a better idea. IMO of course.

Tip: when you get the multimeter, see if you can get spare fuses right away. If you forget to move the leads when measuring voltage or current, and the rotary switch is in the wrong position - POP! Ask me how I know.

But what about a backup charge source? We're talking rain, or maybe your panel fails, or you just want to make absolutely sure you have a full charge when you bring it home. Here, something small like a 12v Battery-Tender 021-0123 or Battery-Minder model 1500 will do the job. Yep, another thing to put on the shopping list, but worth it if your panel does not come up to snuff or it rains for a week straight.

SAFETY - grab a pair of goggles like painters goggles to shield your eyes. Slow down. Even a 5ah agm can be dangerous in the wrong hands. Earlier this week, my coworker put his hands inside a dinky computer ups containing a small agm, and shorted the chassis with his metal wristwatch. It heated up so fast that the links froze and he couldn't even throw it off his wrist. He now has a painful burn / tribal-tatoo to deal with.