Question about batteries and solar charging

[LEDrock]

You have to use google to find it and it doesn't have much info on it there
https://sofirnlight.com/s11c-zoomable-flashlight-lh351d-90cri-p0133.html

Ah, I see it now. The fact that it's lower than even their "deals" page was offering in Facebook groups makes me suspicious of those groups now.
Using Google, I was able to find it on Amazon too, although they don't actually call it the Sofirn S11c on Amazon, it still shows up if you google, "Sofirn S11c amazon"

In those same google results, I found a post in a different forum that it was available for only $8.99 earlier this year: https://budgetlightforum.com/node/76778

 

[Lynx_Arc]

Ah, I see it now. The fact that it's lower than even their "deals" page was offering in Facebook groups makes me suspicious of those groups now.
Using Google, I was able to find it on Amazon too, although they don't actually call it the Sofirn S11c on Amazon, it still shows up if you google, "Sofirn S11c amazon"

In those same google results, I found a post in a different forum that it was available for only $8.99 earlier this year: https://budgetlightforum.com/node/76778

The difference may be in shipping perhaps free vs paying $3? I'm not really sure but I've found dealers that sell on various platforms the price sometimes differs. I've bought things on ebay cheaper than the dealers website which is a bit odd to me.

 

[Dave_H]

LED flashlights are out there with built-in Li-ion cell(s) with USB charging, which double as power-packs. I have a cheaper one, flashlight is not great but passable and has 4500mAh (two 18650's) capacity which makes it worth keeping.

https://www.naturepowerproducts.com/product-details.php?id=172

One has to be careful about capacity "specsmanship". 4500mAh at 3.7v cell voltage translates to only about 3000mAh at 5v output including inefficiency of the up-converter circuit. They should at least specify in watt-hours; in this case 16.6.

Dave

 

[Dave_H]

Sometimes you find a device which could do a reasonable job of charging cells. I happened on a small solar pump controller which runs from 4xAA. Its 5"x7" panel by my estimation could charge at up to 500mA peak. I has a charge state LED, so at least it terminates and indicates full charge. I could do a test though not today as it's overcast and rainy.

Regular price of this setup was about $40 and I would not have bought it if not seriously discounted; but you might find something similar.

Dave

Peak charge rate was measured at 300mA, so this setup should charge a set of low-capacity NiMH e.g. 1000mAh LADDA on a good day. For 2000mAh cells it would take two good days. Not bad considering its size.

Li-ion USB battery packs are relatively safe, loose cells are useful but have their risks and may not be for everyone.

Dave

 

[Lynx_Arc]

LED flashlights are out there with built-in Li-ion cell(s) with USB charging, which double as power-packs. I have a cheaper one, flashlight is not great but passable and has 4500mAh (two 18650's) capacity which makes it worth keeping.

https://www.naturepowerproducts.com/product-details.php?id=172

One has to be careful about capacity "specsmanship". 4500mAh at 3.7v cell voltage translates to only about 3000mAh at 5v output including inefficiency of the up-converter circuit. They should at least specify in watt-hours; in this case 16.6.

Dave

Yeah power banks all rate by the battery capacity and unless you test them no clue as to efficiency at all I just guess about 1/2 to 2/3 at most due to they are used a lot on phones and other USB rechargeable devices so you have a boost on the power bank from 3.6v or so to 5 and then it charges a lithium cell so loss twice in conversion. The loss may be lowered with devices that charge at lower rates some.

 

[Dave_H]

Peak charge rate was measured at 300mA, so this setup should charge a set of low-capacity NiMH e.g. 1000mAh LADDA on a good day. For 2000mAh cells it would take two good days. Not bad considering its size.

Li-ion USB battery packs are relatively safe, loose cells are useful but have their risks and may not be for everyone.

Dave

The 5"x7" panel managed to charge these four 1000mAh cells in about one good day. I "cheated" a bit by moving it around a few times due to shadowing in the back yard. So for those who use NiCd/NiMH, small-scale solar charging can be viable, perhaps just not using the smallest/cheapest lights.

Dave

 

[LEDrock]

The 5"x7" panel managed to charge these four 1000mAh cells in about one good day. I "cheated" a bit by moving it around a few times due to shadowing in the back yard. So for those who use NiCd/NiMH, small-scale solar charging can be viable, perhaps just not using the smallest/cheapest lights.

Dave

That sounds good!
I did a little experiment with my little solar lights. I connected wires to the battery contacts to connect 2 of them together--1 wire from the negative battery terminal of one unit to the negative of the other, and another for the positives. Then I connected my battery tester to them--the positive to the positive of one unit, and the negative wire to the negative contact of the other unit. I went out in the sun and saw the needle on the tester go up a little higher than when doing the same thing with just one solar light. When I covered one of the solar lights from the sun, the needle went down a little. So this shows that both units were properly connected, and that they were combining together to put out more power.

I've seen Youtube videos that show how to connect the solar panels of these lights together, but it always involves dismantling the solar lights. Doing it my way, they stay intact.

 

[Lynx_Arc]

You can wire panels in parallel, series, and a combination of them to get more current and voltage. If you can get to the wires connected to the panels with and without the addition of diodes you got it made otherwise 2 panels in series may have 2 diodes in series dropping the voltage one more time than needed.

 

[LEDrock]

You can wire panels in parallel, series, and a combination of them to get more current and voltage. If you can get to the wires connected to the panels with and without the addition of diodes you got it made otherwise 2 panels in series may have 2 diodes in series dropping the voltage one more time than needed.

I guess that would explain why the needle on my tester didn't go up twice as far as when I do it with one solar light. It moved up a little ways farther, but not twice as far.

 

[Dave_H]

That sounds good!
I did a little experiment with my little solar lights. I connected wires to the battery contacts to connect 2 of them together--1 wire from the negative battery terminal of one unit to the negative of the other, and another for the positives. Then I connected my battery tester to them--the positive to the positive of one unit, and the negative wire to the negative contact of the other unit. I went out in the sun and saw the needle on the tester go up a little higher than when doing the same thing with just one solar light. When I covered one of the solar lights from the sun, the needle went down a little. So this shows that both units were properly connected, and that they were combining together to put out more power.

I've seen Youtube videos that show how to connect the solar panels of these lights together, but it always involves dismantling the solar lights. Doing it my way, they stay intact.

When connecting lights in parallel, recommend they are identical type, otherwise you may not be gaining much if the panels are not outputting close to the same voltage and same capacity; and they should be getting the same illumination.

I was checking out another smaller solar panel which is part of a 4-light wired set, which charges 3xAA. At first the panel was not charging the cells. I discovered that some cells have slightly shorter +ve end bumps and the cell holder design is such that some cell ends make contact, others do not. Not sure if this is deliberate, to limit cells to specific vendor(s). This could be solved with little wads of aluminum or copper foil but is annoying nonetheless.

It's also good to check cells first with a quick run in a charger, if they've been sitting around. Some cheaper cells which have gone flat seem to not want to take a charge. In the old days I recall "zapping" NiCd's with a large capacitor but that had limited success in revival. Cells which don't respond to slow charger go to recycle.


Dave

 

[LEDrock]

I came up with an idea. Instead of me trying to charge a single AA battery (which is all I hoped for to this point) with a solar panel, how about charging more than one together, and then use a larger panel such as this one: https://www.amazon.com/dp/B07TVHMMSK/?tag=cpf0b6-20

Or this one: https://www.harborfreight.com/15-watt-solar-battery-charger-62449.html

They're both 12 volt, 1.5 watt. What I was thinking of doing is attaching the positive/negative leads to the AA batteries, but I would be charging more than one AA at a time by connecting 2 or more together end-to-end, which I assume means in parallel. That way I wouldn't be connecting a 12volt panel to a 1.2volt battery, but rather multiple ones so that the batteries being charged would be 2.4v or 3.6v, etc. depending on how many I connected together.

If this were feasible, how many 1.2volt NiMH AAs would I have to connect together and charge at the same time to be safe and not overload the batteries?

BTW, that harbor freight one (and maybe the other one too) could serve double duty as not only a AA charger (in multiples), but also a maintainer for a car battery too.

EDIT: I just noticed that the panel in the first link says "[FONT=&quot]The solar charger converts light energy from sun into 5.5 volt electricity", but then states that its output voltage is 12 volts. Not sure why the difference.[/FONT]

 

[Lynx_Arc]

Parallel means side by side and the voltage is the same as one battery but current is added together. Series means the voltage adds the current is the same as single battery. Even though you can charge batteries in series it is not recommended by default as if the cells are not all the same capacity they will both discharge and charge differently often the weakest cell will be overdischarged and overcharged as it can neither deliver the same capacity and can only accept a lower capacity finishing charging before the others and being overcharged till the others catch up.

It is best to charge cells in parallel and smart charging that detects end of charge can keep sells healthy longer (more cycles). but to smart charge each cell must be monitored separately. There are threads on solar charging I would suggest searching for them and start reading.
The solar setup may have a converter to drop the voltage but is natively 12v likely floating higher than that under light to no loads.

 

[LEDrock]

Parallel means side by side and the voltage is the same as one battery but current is added together. Series means the voltage adds the current is the same as single battery. Even though you can charge batteries in series it is not recommended by default as if the cells are not all the same capacity they will both discharge and charge differently often the weakest cell will be overdischarged and overcharged as it can neither deliver the same capacity and can only accept a lower capacity finishing charging before the others and being overcharged till the others catch up.

It is best to charge cells in parallel and smart charging that detects end of charge can keep sells healthy longer (more cycles). but to smart charge each cell must be monitored separately. There are threads on solar charging I would suggest searching for them and start reading.
The solar setup may have a converter to drop the voltage but is natively 12v likely floating higher than that under light to no loads.

Well, it's sounding more like I better abandon that idea then. I'll start looking for those other solar charging threads you mentioned. I noticed that there are a number of solar power forums to be found on the internet, but each one seems to be exclusively about powering big things, like entire homes and RVs. They don't address small stuff.
'

 

[Lynx_Arc]

Well, it's sounding more like I better abandon that idea then. I'll start looking for those other solar charging threads you mentioned. I noticed that there are a number of solar power forums to be found on the internet, but each one seems to be exclusively about powering big things, like entire homes and RVs. They don't address small stuff.
'

Try searching for portable solar charging

 

[Dave_H]

I came up with an idea. Instead of me trying to charge a single AA battery (which is all I hoped for to this point) with a solar panel, how about charging more than one together, and then use a larger panel such as this one: https://www.amazon.com/dp/B07TVHMMSK/?tag=cpf0b6-20

Or this one: https://www.harborfreight.com/15-watt-solar-battery-charger-62449.html

They're both 12 volt, 1.5 watt. What I was thinking of doing is attaching the positive/negative leads to the AA batteries, but I would be charging more than one AA at a time by connecting 2 or more together end-to-end, which I assume means in parallel. That way I wouldn't be connecting a 12volt panel to a 1.2volt battery, but rather multiple ones so that the batteries being charged would be 2.4v or 3.6v, etc. depending on how many I connected together.

If this were feasible, how many 1.2volt NiMH AAs would I have to connect together and charge at the same time to be safe and not overload the batteries?

BTW, that harbor freight one (and maybe the other one too) could serve double duty as not only a AA charger (in multiples), but also a maintainer for a car battery too.

EDIT: I just noticed that the panel in the first link says "The solar charger converts light energy from sun into 5.5 volt electricity", but then states that its output voltage is 12 volts. Not sure why the difference.

These "raw" solar panels and others like them which do not contain circuitry to limit charge current and terminate charge, won't do what you want.

12v panels charging 12v batteries are intended to go through a charge controller. In some cases people manage to get away without this with lead-acid batteries, but low-voltage NiMH and NiCd are a different story.

Cells can be charged in series or parallel but for the latter really should be isolated from each other; more complication but this is what good AA/AAA chargers do, which handle cells independently i.e not in pairs.

The 12v/1.5W panel specs are confusing, not sure exactly what it is. Caveat emptor as with many online products. For example, "short circuit voltage" of 13.5v makes no sense; short circuit would be zero volts. Open circuit voltage 13.5v is likely what it means; sloppy and/or someone doesn't know how to write specs.

Some options:

(1) Get a small solar device which is designed to (properly) charge AA such as solar 3AA spotlight or small pump controller I mentioned. Most of these will charge in series; can be done if the cells are identical and matched.

(2) Get a small 12v raw solar panel and connect to a proper AA charger which takes 12vdc input (many do).

(3) Continue to charge cells individually in garden lights, but find some which are bigger and won't take several days or a week or more to charge one 2000mAh cell. Problem here is the individual cells from different lights won't all be charged uniformly and put together in some device, will run into problems with cell mismatch.


Dave

 

[Timothybil]

I had the best luck using a portable panel array with USB output charging a power bank, then using the power bank to charge the cells. There are many good USB-fed chargers available, but for one or two cells at a time I think the single-cell magnet contacts work the best. And if you are in a hurry one can actually be plugged right into the solar panel as well.

 

[Dave_H]

USB AA/AAA chargers can work, I have a couple of older 2-cell ones. One downside is efficiency; by the look of these two, 50-60% at best, probably lower. With small solar setup, wasting power needs to be minimized.

Another downside is adding another level of inefficiency. Running from 12v panel, down-converting to 5v you should manage 75-90%. Then there's the charger, and the "charge efficiency" of cells themselves. In the end, overall efficiency could be rather low.

The charger should not allow cells to discharge into it when its input (solar) power goes away. One 12v charger I was using about 15 years ago did this, lighting up some status LEDs in the dark. Sometimes the only thing to do is test it out.

I also solar-charge USB Li-ion battery packs and use them to run small fans, lights, and charge phone battery.


Dave

 

[Lynx_Arc]

I think unless you want to charge batteries in a pack in series you have to convert the voltage difference usually via a buck circuit. Smart chargers pretty much have to drop voltage down to around 3v or less to charge a nimh cell you need a little headroom but need voltage in range of the battery voltage that is why 5V is good for lithium ion charging. A status LED at low power can be a fraction of a ma such that unless you leave it hooked up for days it is likely not a big issue. I don't recommend ever storing cells in a charger. The advantage of a USB charged power banks is that they have a set charging rate max and anything lower usually isn't an issue they will rise back up to that maximum when available.

 

[Dave_H]

I would not get too excited about these "dashboard" 12v solar charge panels typically 1.8W peak, intended to "trickle-charge" car batteries. Sure, they could offset parasitic drain on a 50Ah or larger battery if car is not driven much. You would be lucky to get 100mA out of one of these in bright sunlight, over a day possibly 0.5Ah. Even a 7Ah gel-cell could take up to two weeks to completely charge.

I would not pay more than $10 for one of these; have a few around, waited until they were on sale.

I tried a couple of these panels on 12v 7Ah gel-cells which were initially just above 50% charge (my usual minimum). Over several days, there was barely any increase. Illumination was not optimal, but something should have happened. Both panels appear to be working OK but the highest I measured was 40mA under bright sunlight.

On vehicle dash, panel would be subject to direction vehicle is pointed, shadowing from outside objects and car itself, and non-optimal, non-adjustable pointing angle.

Also keep in mind, amorphous is about twice as large as poly-crystaline for the same power, if compactness matters. It is deposited on glass plate so subject to cracking if dropped or heavy object falls on it.

Panels like these are good for charging small cells, with proper charge circuitry of course.

Dave

 

[Dave_H]

I think unless you want to charge batteries in a pack in series you have to convert the voltage difference usually via a buck circuit. Smart chargers pretty much have to drop voltage down to around 3v or less to charge a nimh cell you need a little headroom but need voltage in range of the battery voltage that is why 5V is good for lithium ion charging. A status LED at low power can be a fraction of a ma such that unless you leave it hooked up for days it is likely not a big issue. I don't recommend ever storing cells in a charger. The advantage of a USB charged power banks is that they have a set charging rate max and anything lower usually isn't an issue they will rise back up to that maximum when available.

These two "name brand" older chargers do not seem to have any sign of switching conversion inside. If two cells are charged in series from 5v it is not too bad, but they both charge one cell at a time which means drop from 5v to around 1.4v by linear means, which is dismal efficiency. Perhaps newer models are better but I hardly ever use these, so have not acquired any.

I suspect Li-ion packs in the charging direction typically use linear regulation which is not the most efficient, but not too bad from 5v down to between around 3.3v to 4.2v averaging around 75% .

Dave