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Solar charging 2400 mAh batteries

Discussion in 'Power Electronics' started by mkuehlok2, Nov 23, 2020.

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  1. mkuehlok2

    mkuehlok2

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    Dec 16, 2014
    I'm wondering if someone has experience with this. I've bought some solar-powered lights for a project. They seem to work okay for a while, but the lights don't last very long. Then I saw a post suggesting swapping out the batteries that usually ship with these things with batteries with a higher mAh rating. Not being the sharpest knife in the drawer, that had never occurred to me, and sure enough, I found out that these lights had 600 mAh rechargeables in them, and when I put in my freshly charged 2400 mAh batteries, the lights were bright enough for an airstrip and they have lasted several nights indoors (I'm working the project indoors and I haven't set it up outside yet). Now, though, I'm wondering if 2400s are overkill. Will a single small solar cell recharge a 2400 battery with 8 to 10 hours of sunlight?
     
    EliasJonsson likes this.
  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    That depends on the size and quality of the solar cell and the charging circuit. Neither the cell nor the charger in your lights are likely to be designed to fully charge a 2400 mAh cell during the course of one day. But since you now have the cell, give it a try.
     
  3. mkuehlok2

    mkuehlok2

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    Dec 16, 2014
    Thanks! I will let you know how it works. I've been trying to figure out some way of testing for a measurable outcome (curiosity more than anything). Maybe I could try fully charging the 2400 in a charger, then keep track of how many days it takes for the light to start going out at midnight, which is the time I usually go to bed. Since winter is coming on, it gets dark now around 5:00 so 5:00 to midnight will be 7 hours. There will, of course, be a number of different variables because it is an outdoor light. The weather (cloudy vs sunny) will affect it and also temperature. Then I can try the same with the 600s it came with to see if I am gaining anything by using the 2400s.
     
  4. dave9

    dave9

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    Mar 5, 2017
    It doesn't necessarily matter if the solar panel can charge the battery fully in a day. It's still better to have more capacity and might even keep the battery from overcharging, depending on the size of the solar panel. "Probably" not, the solar panel is probably small and cost economized, but in a good design it would be large enough to charge the battery on shorter, cloudy winter days which is a significantly lower amount than on a long, sunny summer day.

    Anyway, there is a downside to the higher capacity cells, all else as equal as it can be. They would have fewer recharge cycles, probably are NiMH instead of NiCd, which may also mean lower performance in low temperatures too, but if they have fewer recharge cycles it is a better thing to not have them drain by as high a % every time.

    A cycle means a full cycle so if a smaller % is taken out and put back, it counts closer to that percentage of a cycle than to 1.0 cycles daily. Granted, 1 x AA cell is not expensive and the solar panel on the light will probably degrade from UV within a few years anyway if it is the typical cheap designs I've seen that use a 600mAh NiCd cell, where the solar panel is either epoxy encapsulated or behind a plastic window panel, either of which get hazy and progressively block more and more light.

    The other variable is that not all 2400mAh NiMH cells are created equal. That may or may not be an accurate rating (could be too high as is often the case with less than major brand cells) and they may or may not even exceed 2400mAh in such a low drain application.

    Personally, I would keep using the 600mAh cells until their runtime is insufficient, then switch to a quality ~2100mAh LSD cell like Eneloop.
     
  5. Audioguru

    Audioguru

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    Sep 24, 2016
    Details are missing. What type of rechargeable battery? What size?
    Dave mentioned 1.2V Ni-Cad and Ni-MH but I thought the replacement was 3.7V Lithium which would make the lights too bright..
    The battery type must match the charger circuit.
     
  6. dave9

    dave9

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    Mar 5, 2017
    ^ Yes I made some assumptions that could be in error.

    1) I assumed the new 2400mAh battery swapped in was the same size, a simple swap into an existing battery compartment with springs/tabs instead of soldered or a pigtail connector.

    2) The only thing as low as 600mAh that also comes in same size 2400mAh would be AA NiCd in the former vs NiMH in the latter capacity.

    Cheap solar lights are among the few things you can still buy that have NiCd cells that aren't soldered to the PCB. I wasn't aware of anything besides them until I recently opened up a timer AC outlet and found a tabbed/soldered NiCd in it for memory backup.
     
  7. Audioguru

    Audioguru

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    Sep 24, 2016
    Very cheap Chinese solar garden lights used a 1.2V 600mAh AA size Ni-Cad battery years ago. in the past 5 or 10 years they use a 1.2V 300mAh or 600mAh AAA Ni-MH cell but I have a new one that has a 3.7V AAA Li-PO battery cell.

    Energizer AA Ni-MH cells were 2500mAh for years until they began to make copies of Eneloop that hold a charge for one year and they are 2300mAh.
    Does anybody make or sell Ni-Cad toxic batteries anymore?
     
  8. dave9

    dave9

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    Mar 5, 2017
    ^ Of course, https://www.amazon.com/s?k=NiCd+battery

    I don't consider the toxicity much of an issue if you recycle them. There are tons of places that recycle for free in the US, from hardware stores to office supply chains, even the local public library here does. *Some* of these don't take lead acid, some don't take Li-Ion or alkaline, but most if not all take NiCd.

    I assumed the light doesn't take AAA because there are no (honestly rated) 2400mAh AAA cells of any chemistry, nor would a 600mAh to 2400mAh spread exist for Li-Ion of same size.
     
    Last edited: Nov 24, 2020
  9. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    In Germany (Europe?) it's the law: whoever sells batteries also has to take them back and send them to recycling.
     
  10. Audioguru

    Audioguru

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    Sep 24, 2016
    Then people buy them online and throw away worn out ones in the garbage as landfill.
    .In Canada, libraries collect old batteries and send them to recycling.
     
  11. Harald Kapp

    Harald Kapp Moderator Moderator

    10,833
    2,442
    Nov 17, 2011
    Not necessarily. Buy online: yes. Throw in the garbage: no (at least not the responsible ones :(). The return boxes are usually located at the entrance to the store and you can put any household batteries in there, regardless of the place of purchase. The boxes are usually well filled :).
    I doubt that in Germany people would undertake to go to a separate place (library) that collects batteries. But dropping them while shopping is convenient.
    Car batteries even come with a deposit (currently 7.50 €). Not a lot but a good incentive to return your old battery to the store for recycling.
     
  12. Audioguru

    Audioguru

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    Sep 24, 2016
    Many people (animals?) deposit beer cans on the street.
    Some people (animals?) have the muffler and pollution controls removed from their cars.
    Some people (animals?) do not pickup their dog's droppings.
     
  13. dave9

    dave9

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    Mar 5, 2017
    There will always be a sociopolitical issue of how much to limit the whole due to the few who cause problems, or how much our freedom should be restricted for our own good and safety.

    There are no easy answers. We can't imprison everyone for minor offenses, but fines typically aren't on a sliding scale based on income, so serve more to punish the poor than the rich.

    A deposit on NiCd might help reduce slippage, but IMO the problem is going away by itself due to tech advances and EU leadership.
     
    Last edited: Nov 24, 2020
  14. Audioguru

    Audioguru

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    Sep 24, 2016
    Punish the poor but not the rich?
    My local university has MANY students from (name of foreign country) who drive very expensive new sport cars that have had their mufflers and pollution controls removed. Some of them are fined but the thousands of dollars is nothing to them.
    The poor kids also pay thousands of dollars for a mechanic to mod their noisy stinking old cars. They rarely get fined.
     
  15. mkuehlok2

    mkuehlok2

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    1
    Dec 16, 2014
    This cracks me up! My simple little project and curiosity has netted me a WEALTH of new insight and information. Thanks all! The total value of your time in answering and commenting on my question is probably worth two or three times what my project is worth! At any rate, I am indeed swapping out batteries of the same size (AA) but at a different mAh rating, but I may have swapped out battery types as well. When I took out the old one I just figured it was cheap and useless and I disposed of it because it was only 600 mAh. I thought it was NiMh but after reading the above posts, I'm not sure now. At any rate, I replaced it with a 2400 NiMh (!) and it lit the light at night indoors for two straight nights without charging. I now have it mounted on a post outside, so we will see how that fares. The second and third parts of my project involve solar-powered Christmas lights. I swapped out a 1200 NiMh with another 2400 NiMh, and they seem to work indoors nicely, but I haven't put them outside yet. Thanks again for all of the insights!
     
  16. Audioguru

    Audioguru

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    Sep 24, 2016
    Look what I found on my desk! It is a very lightweight AA Ni-Cad cell Made in China with a 250mAh rating. It is dated 2018.
    I betcha it is mostly filled with rice instead of with battery chemicals. I have never used it but it still holds a charge from the factory.
    I found another Ni-Cad AA cell dated 2006. It is rated 600mAh, I charged it and it works fine.
     
    mkuehlok2 likes this.
  17. VincentBowman

    VincentBowman

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    Dec 19, 2020
    Hi, mkuehlok2. I bought BONAI AA rechargeable batteries to replace the cheap ones in outdoor solar lights. Some of you have asked if these batteries were the same size as the standard battery. Yes they are except some of them on the positive end are a tiny bit smaller. If you run into this all you have to do is pull out the positive plate just a bit on whatever you're putting the batteries into.
     
  18. Audioguru

    Audioguru

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    Sep 24, 2016
    I wonder how much Amazon will pay me if I give a good review of their cheap Chinese batteries that are not even made to a standard AA size?
     
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