Using a solar panel to charge 18650's

I apologize for using this forum for tech support but I have come to realize that there are some very experienced folks here when it comes to battery charging so here goes.

I’m going to build a 30 watt solar charger for lightweight backpacking and this is what I have come up with and I would like to run it by you guys to see if I’m missing something:

This 30W flexible panel: http://www.ebay.com/itm/Semi-Flexible-30-Watt-Solar-Panel-12V-High-Efficiency-Sunpower-Marine-Rated-/131268389129
Connected to this MPPT charge controller: BatterySpace.com/AA Portable Power Corp. Tel: 510-525-2328 - Powerizer Battery Official Site
then connect the charge controller to 3 18650’s in a holder like this: http://www.dx.com/p/11-1v-3-x-18650-battery-holder-case-box-with-leads-100996

Does this sound correct and is using unprotected 18650’s a bad idea?

Lightweight backpacking and solar panels don't go together. Let's put it this way. A 14500 will get me through a week of camping in the winter, with those long nights and lots of hours of reading. When I do long distance hikes, it's with shorter nights and hardly any reading because I'm incredibly tired from hiking ~20 miles every day, so the light is maybe for half an hour at the end of the day if I'm late finding a campsite and need to read my maps and notes for the next day, then another half hour in the morning to break camp and hike while waiting for the sun to rise. I hiked for about a month a couple years ago and only needed a single lithium AA the entire time. I didn't change the batteries in my gps either because I only turned it on long enough to write down my coordinates, which I then used with downsized paper maps. I used my phone a lot because the nature of the hike called for a lot of involvement on social sites, but I charged that in town.

You'll save weight carrying extra 18650's, or charging in town if you're on a hike that's weeks/months long where you only walk into a town once every 4-7 days. Just look at the weight of that panel. It's almost two pounds. You could carry enough 18650's to last me a full year of backpacking. Then the charge controller, cradle and wiring adds another half pound or more.

I use a Levin 14W panel with a Miller charger / power pack and I think it’s a good setup.

Just for giggles, I also carry a couple of those USB LED chips for backup.

Does you controller have a connection for balance leads?

I'd not be wanting to charge 3 cells in series without balancing, especially if you are planning to use the cells individually in different lights.

Unless you really need 12V or lead-acid charging capability, you'd be better off with a folding panel with USB outputs. Plenty of USB chargers available including cheap and cheerful ML-102.

Racer's post above is a good illustration.

Have a look at the GoalZero range of products for ideas, or Cottonpickers at CPFmarketplace. Plenty of similar stuff on ebay or the usual sellers such as Fasttech and the like.

I think this approach would be more suitable.

Just love seeing that backpack image :slight_smile:

Basically the setup looks ok-ish. But is 30 watts really needed? That is a medium soldering iron.

How much other gear are you wanting to charge/power?

And is the goal total independence from the grid like some of those prepper guys that have massive bug out bags for armageddon scenarios? (Why would you need a bug out bag for that? Armageddon is supposed to end the world. Not just turn off the internet and television. The end. Period.)

Anyhow I concur with leftye. The added weight of that setup would suck big time compared to a set of 5 18650 batteries that would last even me a whole week when hiking. And I like to light everything up all the time.

Tech support…it’s what we do :wink:

You are in good company here…we won’t yell at you, and we don’t bite…hard :smiley:

My purpose for having 30w panel is to use it for extended tent camping but have it light and small enough to attach to a backpack.

gadabout: I had not thought of balancing on 3 cells. I’m not sure how much of a problem that will be but I keep my 18650’s in groups of 4 that are from the same torn apart laptop batteries so I’m hoping they were balanced from being all together in 1 pack but I do not know if it works that way.

Ledsmoke: 30 watts is what I want for extended camping so I can have sufficient off grid power. I was thinking that I could charge all my 18650’s in 1 day in case there are a few days of bad weather. I would have 16 or more 18650 cells with me plus an Intel tablet, smartphone, and small 4G hotspot. The 30 watt panel and charge controller I’m getting is the most power in the smallest form factor and lowest weight I could come up with.

We do a lot of Canoe backcountry camping, but in our case we have a bit more space to carry gear. I have built a folding 30 watt off-grid power unit with a Powerpack, and it runs my Nitecore i4 charger all day for charging our Lithium cells and it also has a USB set up for charging our phones, GPS unit, etc. on our 1 to 2 week long trips.

There are balance and protection PCBs that you could buy to use with that charge controller. The added weight would be tiny compared to what you are already planning to lug.

What is the capacity of your batteries? Assuming 2,600 mAh laptop pulls, 16 are going to hold about 154 Wh of power. That is about two full charges for a healthy-sized laptop battery. How big are the batteries in your tablet, cell-phone and hotspot? How many hours/day are you planning on using them, are you going to be leaving them powered on when you aren’t using them? It seems to me that at least part of your reserve power would be in the devices themselves, and if they don’t have enough runtime for that to be a serious possibility, I’d be reconsidering the devices themselves.

Another thing to think about is whether you’ve really optimized your power setup. That controller may optimize power from the panel, but does it make optimal use of it for charging? When charging a single bank of batteries, whether in series or parallel, the total required power rises gradually over the CC phase and then declines relatively quickly over the CV phase. That panel and charge controller can deliver 2-3x more power in full sun than you can stuff into three cells at a time. Perhaps some combo of a smaller panel, and overlapped charging cycles would allow you to store more power with less weight.

There is a thread chock full of info here: http://www.candlepowerforums.com/vb/showthread.php?342073-Portable-solar-charging-setup-I-just-built

This thread is primarily based around using twelve volt sealed lead acid batteries but there is a wealth of information on other components that you may find useful.

I'm not sure about the charge controller that you've linked to but many of them require the full-time presence of a battery in place in order to function correctly.

Perhaps you could consider carrying one made-up LiPo pack from somewhere like Hobby King. http://www.hobbyking.com/hobbyking/store/__9163__Turnigy_1000mAh_3S_20C_Lipo_Pack.html

Also, this gadget could also be useful as it can be plugged directly into the LiPo pack to give it 2 USB outputs suitable for running small USB chargers. In my experience each port won't deliver much more than 1.2A. http://www.hobbyking.com/hobbyking/store/__46361__Turnigy_USB_Charging_Adapter_2_6_Cell_LiPoly_2Amp_Output_XT60_.html

Does your Intel tablet charge from USB or does it have a dedicated input socket of some other voltage?

Since your 18650s are laptop pulls they will be unprotected cells. You should not be charging them in series without a balancing circuit - period. You would probably be better off fitting them into a USB battery box where they are all put together in parallel and these boxes mostly allow charging via USB input. Some of the larger battery boxes also offer output voltages of up to 12V. There are plenty of threads and reviews here at BLF describing these.

Anyway, just some more reading and thinking for you.

I’m guessing you have some sort of controller into the powerpack? I’m interested in having the ~18v output stepped down to ~12v and also gaining some amps in the process like MPPT controllers do but as cheaply as possible.

I am interested in balancing 3-4 cells so links to a PCB would help.

I have 4 NCR 2900mAh cells I bought new plus 8 18650’s from high end Lenovo laptops(don’t know the capacity of these cells) and 8 cells of unknown capacity from another laptop battery. Toshiba Encore is a Quad core Intel tablet with a 19.5Wh 2 cell battery. Smartphone has a 1700mAh battery and the 4G hotspot has a 3600mAh battery. I have not thought about how much I will use each device per day but will be powered off when not in use.

My only thought so far is having enough solor power in 1 day to charge everything to last through a few days of bad weather.

MicroUSB input with a special cable that from my research has shorted data lines that tells the tablet that it can handle 2.1A current.

A small SLA Battery will regulate the Solar charge power to 12 - 14 volts on its own, but its better to use a controller/regulator.
i use two different Powerpacks for different purposes, and different Solar panel setups for each one.
One is a “Modified” Portable 12v Self-contained Power supply with a built-in 120 volt AC inverter, 12 volt outputs, & 5 volt USB charging outputs, and the other is a small 12v SLA battery and a small Solar Controller/Regulator.
( i can take photos of the unit if you wish.

Interested in your small 12v SLA battery and the small Solar Controller/Regulator. No pics necessary, just manufacturer part numbers if you have them.

Your idea of using a small SLA battery fixes my problem of regulating for 12v into a 18650 charger…I think I will use this: http://genasun.com/all-products/solar-charge-controllers/for-lead/gv-4-pb-4a-solar-charge-controller/
connected to a small SLA battery and then connect it to my NITECORE i2.

The sun cranks out around 100 watts per square foot. 30 watts is around 1/3 sq foot. A REALLY good solar cell system might yield 10% real efficiency… and you are not going to get that from flexible panels. So figure you are going to need more than 3 square feet of panels… probably twice that.

A small SLA Battery will regulate the Solar charge power to 12 - 14 volts on its own, but its better to use a controller/regulator.
i use two different Powerpacks for different purposes, and different Solar panel setups for each one.
One is a “Modified” Portable 12v Self-contained Power supply with a built-in 120 volt AC inverter, 12 volt outputs, & 5 volt USB charging outputs, and the other is a small 12v SLA battery and a small Solar Controller/Regulator.
( i can take photos of the unit if you wish.

Interested in your small 12v SLA battery and the small Solar Controller/Regulator. No pics necessary, just manufacturer part numbers if you have them.
[/quote]

I use this controller for the “small” unit:
>> Solar Panel Charger Controller Regulator PWM 12V 3A for Street Park Solar Light | eBay

and a 5AH 12v cell like this: >> http://www.ebay.ca/itm/Mighty-Max-Battery-12V-5AH-Electric-Scooter-Battery-for-4-5ah-Razor-W13111612003-/131287245761?pt=US_Rechargeable_Batteries&hash=item1e915463c1

i made a small pouch for the battery, cables, sockets, & controller and use either 2.5W solar panel or a larger 30W panel to charge/power it.
My larger unit has a built-in controller/regulator.

true, the Polycrystalline or Monocrystalline rigid panels are more efficient than the flexible thin-film cells or the glass Cadmium telluride cells. (the all black lower-cost glass panel type)

Yeah poly is more efficient if you live in the desert like us. It has better efficiency when the heat gets ridiculous least over mono. I kind of like the cadmium panels but my buddy is all against it, says it’s too new to know what it’ll be like in 20 years and if a burglar is running around on the roof and faceplants into it, he’ll get burned on his parts. Like our poly panels are ~16% efficient on the panels and the inverter is ~96% eff. You lose about 400 watts under the rating every 10 panels to just shadowing, wire, etc…

You had to, didnt you :stuck_out_tongue: And +1 for great advice, This definitely a place where you can post whatever it is that any one else can relate to.

Protection and balancing PCB Protection Circuit Module (PCM) with Equilibrium Function & Fuel Gauge for 11.1V Li-Ion Battery Pack at 10A limit