Would This Work As A Solar Charger For 17670/18650?

[GreyShark]

I found this product,

http://www.batteryjunction.com/wagan-2448.html

That would seem to go well with the Pila charger to make a solar battery charger, just the ticket for TEOTWAWKI! :twothumbs Here's a thread with the Pila's specs.

http://www.candlepowerforums.com/vb/showthread.php?t=201323

I am not exactly the world's leading authority on electrical stuff but as I recall it's the voltage of a power supply that matters the most to power the device without frying it and the amperage basically determines how powerfully it can be driven. Based on that limited understanding it looks like I could just plug a Pila charger into this thing, stick it out in the sun for a long time and get my batteries charged up. Can anybody with a deeper understanding of these matters see a reason this wouldn't work or would be particularly dangerous?

Any idea how long it might take to charge a 17670 or 18650?

Is there anything apparent in this set up that would significantly reduce the working like of the cells?

 

[linterno]

I found this product,

http://www.batteryjunction.com/wagan-2448.html

That would seem to go well with the Pila charger to make a solar battery charger, just the ticket for TEOTWAWKI! :twothumbs Here's a thread with the Pila's specs.

http://www.candlepowerforums.com/vb/showthread.php?t=201323

I am not exactly the world's leading authority on electrical stuff but as I recall it's the voltage of a power supply that matters the most to power the device without frying it and the amperage basically determines how powerfully it can be driven. Based on that limited understanding it looks like I could just plug a Pila charger into this thing, stick it out in the sun for a long time and get my batteries charged up.

. Should work but you will not get 600ma for each battery. The solar panel output is only 800ma. If you consider some inefficiencies (assume 75 percent efficient) at the charger side (I am just guessing here) and not 800ma all the time from the panel (sun intensity varies along the day) then you get only ~500ma distributed in 2 batteries then you would get 250ma per charging bay.

Can anybody with a deeper understanding of these matters see a reason this wouldn't work or would be particularly dangerous?

Well, I am not an expert, but I have used solar cells to build chargers and I think there is no particular risk. I don't know what could happen to Pila IBC considering that the solar panel output depends on sun intensity. At full sun, 90º angle to the panel you will get those 800ma. Early in the morning and late in the afternoon the sun intensity is lower so less amps from the panel. What could happen to the charger with this variable current? I don't know.

Any idea how long it might take to charge a 17670 or 18650?

Considering not 100% efficient from the panel (remember sun intensity) and losses at the charger, I guess you could fully charge them (2 batteries at the same time) in a couple of days (or even 3 days), at 6 hours of full sun (all they day long sun) per day.

Is there anything apparent in this set up that would significantly reduce the working like of the cells?

Could be if the charge interruption is considered as a charging cycle. I don't really know. Silverfox could tell us.

 

[bluecrow76]

I was looking at that exact solar panel last night thinking the same thing, except using the Ultrafire WF-139 (I have two of these chargers already). The input is rated 12V@400mA, which in full sunlight that panel should have no problem with. The main concern with charging these batteries using solar is seeing if we can pack a single charge cycle in all at once. Charge time is supposed to be somewhere in the neighborhood of 4 hours for 2 x 18650 cells on the WF-139, which would be plenty of time to get a good charge in on a bright day.

 

[GreyShark]

This sounds like a pretty good deal to me so far! Based on my current rate of use it sounds like this setup would charge batteries twice as fast as I use them up. I could easily keep some spares on hand just in case I need a lot more light for some unforeseen reason.

I was hesitant to use the WF-139 charger because I want something reasonably safe to walk away from for a while and I have read that the WF-139 doesn't shut off completely when the batteries are fully charged. Given that the solar panel's output will fall off toward the end of the day anyway it sounds like that problem would be eliminated.

 

[bluecrow76]

I've never had a problem with my WF-139 chargers. I have never left them charging while I wasn't home and they've never over charged, in fact they always seem to cut off just below 4.2V.

 

[mdocod]

The question is, will the Pila IBC tolerate reduced power availability? Will it be willing to taper back it's charge rate to continue charging? or will it just shut off with the input voltage falling too low each time it tried to engage a charge at the full 600mA. Maybe it will only work with one channel, maybe not at all... Will the reduced power availability or fluctuating power input cause it to terminate properly? I have no clue, but these are the questions that need to be answered, and the only way they can be answered is through testing and observation.

I would use a DSD for this, as the charge rate of the DSD is determined by the power supply, the electronics in the unit don't care much, you just supply ~5-6V ~100-1000mA and it seems to work fine (provided you don't get a dud)... Too bad the quality control on the DSDs is so hit and miss.

Eric

 

[GreyShark]

I was actually wondering about that myself. In the end I guess there's only one way to find out for sure.


Since I found that particular solar charger I've gotten bitten by the creep bug... just a little more money will buy a panel that outputs more amperage... just a little more money than that and then you can buy a panel that will charge a car battery for a 12v DC RV/marine type system. I live in a rural area in hurricane country so power outages, even for weeks on end, are not exactly unheard of. I may end up going with a more powerful panel that can handle a big 12v lead acid battery and the little flashlight batteries. My understanding is that as long as the voltage is ok the charger should only draw from the panel what it needs to charge the battery, right?

 

[mdocod]

My understanding is that as long as the voltage is ok the charger should only draw from the panel what it needs to charge the battery, right?

When it comes to something like a solar panel, the voltage will not remain constant regardless of how much amperage is drawn, like a battery or other source of electricity, as you increase the demand, the effective circuit voltage drops.

Linterno ran some numbers in his response above there, but I think they may be incorrect. I don't know how he came up with there not being enough power from that panel but after reviewing it, would have to disagree.....

A charger dumping ~600mA into 2 channels (1.2A total) at an average of say, 4.2V (high ball it for the sake of overhead in the assumptions here) would be charging at ~5W. Assuming the charger were only 50% efficient the thing would only pull about 10 watts from a power supply. But it's probably more efficient than that, so more than likely, this concept would work fine provided you have good sunlight. In my experience, solar panels rarely achieve their rated output, so over-sizing is important for any setup.

[edit in]
I would be tempted to put a small 12V SLA in parallel with the solar panel that is connected to the charger, this would act as a buffer that would help maintain ~12V operation even when the sun goes behind a cloud, and would also prevent the charger from seeing the open circuit voltage of the panel when the charge terminates, which may or may not be a problem.

[more edit in]
I was looking around the net, I won't say specifically, but there's this popular auction site that has various solar panels, and there are 15W rated panels available for under $100 there, not sure about the quality of them, but they are 3ft by 1ft in size, which seems large enough to live up to the 15W claim provided they are decent cells... no way to know though I guess.

Eric

 

[bluecrow76]

Just a little bit more... just a little bit more... why is it always just a little bit more!

That seems to be the road I always end up going down when I think of solar power. It seems like funds might be better spent building a proper PV system that the charger can be connected to. That way the solar panel will provide current when there is enough light and the battery can pick up the slack when there isn't enough from the solar cell.

Like you said... it's just a little bit more! :devil:

 

[mdocod]

Read additionally edited in comment above And consider, if you can get a panel for $40-50 less than the one you have in mind, and spend $20 on a little SLA, then you are still ahead of where you would have been, and probably have better performance, but hard to say

Eric

 

[roadie]

Soon after buying newer lights, i shall get a solar panel too, as its ouput are sometimes at 15.4v, its a ideal to charge a SLA, directly without a charge regulator as long as within 80watts, then get a 12v 7amp ?

then connect to my new FMA S4, and charge all lions!:naughty:

 

[bluecrow76]

Read additionally edited in comment above

Nice to see I'm not out in left field on this one!

 

[GreyShark]

I've been doing a little more research because I'm getting serious about this... from what I've been reading there are two main PV panel technologies. One is thin film and the other is crystalline. Thin film is less expensive but apparently its output can degrade rather quickly. It'll still work, just a steep drop off in output fairly early on in its working life.

As for the status of my creepism... I'm now looking at 60 watt/4 amp panels. :naughty:
From what I've been able to tell it seems like at this level it is more cost effective to buy multiple smaller panels than one real big one. If I wasn't trying to make this run other gadgets during a power outage I'd be reasonable and settle with a 15 watt panel, but once you get the ball rolling....

 

[GreyShark]

Oh yeah, just to throw a little more fuel on the fire the 15 watt charger could be used to top up your batteries during the day so a full charge wouldn't even be necessary which should make the system that much more practical in emergencies.

 

[bluecrow76]

I've been looking at getting this for my ham radio station and general emergency battery setup for a while... but I keep spending my money on new lights! It's basically a simple yet intelligent charge controller slash transfer switch. It is meant to be used connected directly to a regulated 13.8V power supply, so you would have to have some sort of regulator between this and the PV array.

I'm sure there's a better solution out there... I just noticed this box again.