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  #31  
Old 4th October 2019
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Re: Best AA Batteries

Everything is relative I suppose

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  #32  
Old 4th October 2019
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Re: Best AA Batteries

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Originally Posted by MJ224 View Post
4 AA's, thus a nominal voltage of 6v. Putting a solar panel might blow re-chargeables without some sort of controller/voltage limiter. But I have limited knowledge about these things.

I do have solar panels on the boat, and they go through a controller....


Edit...I see on Ebay you can buy a 6v solar panel.....:-)
I like Henry's suggestion of a 6 Volt lithium ion battery with a solar cell to charge it. I presume it comes with some kind of charge regulator? If necessary it would be easy to provide a simple series regulator to reduce the voltage supplied to the device. I presume your Weather Station talks to your computer via Bluetooth or similar, in which case I wonder whether it could be configured to signal battery condition as well?

Reverting to my original suggestion of using Sanyo/Panasonic Eneloop cells I should mention that most of the reputable manufacturers are using similar technology now. Eneloop only make AA and AAA cells, but other manufactures such as GP Cell make other types of battery. It has since occurred to me that the D-Cell variants can provide up to 9,000 mA/Hr capacity (compared with 2,800 mA/Hr for Eneloop AA cells) which should keep you going for a while. Just make sure you don't buy an AA cell in a D-Cell housing which are sold by many high street outlets. (Their light weight is usually a giveaway.)

One of the joys of the Eneloop cells is that they have excellent long term energy retention properties, and unlike disposable alkaline cells they do not leak. For some unknown I have had far to many alkaline cells leak into equipment of late to take that chance again, and none of them were flat.

NiMh and NiCd cells can be tricky to charge because their terminal voltage actually falls slightly when they are fully charged, rather that rising as it does with lead acid or lithium ion cells. The only other clue is an increase in temperature when charge completes. Overcharging at high current will shorten the cell life by boiling off the electrolyte, but the output current from a small solar cell (say 10 or 20 mA) should do little harm. The bigger D-Cells would be even more robust.

Your device will only be using a few A at most so a 5 mA charge would soon return the cells to a fully charged condition and would be unlikely to damage them even without a charge regulator. If necessary you could fit a series resistor to reduce charge current. A set of 2,000 mA/Hr cells would provide plenty of power even if we had a month or more without sun!

Note: One Amp = 1,000 mA or 1,000,000 A.
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  #33  
Old 5th October 2019
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Re: Best AA Batteries

Thanks for that comprehensive reply Nigel. Yes the weather station talks to a dedicated terminal via bluetooth, and does tell when the batteries are low. Typically, on a cold night, the battery warning is flashing away, but when the day warms up the station, that goes away. I am in the process of buying the 6v solar panel, and will test it on the ground first with my eneloop batteries, before trying it out up the pole...

Do you need a diode in the circuit? As said I have no significant knowledge of electronics.

By the way, I have read somewhere (here perhaps) that IKEA's rechargeable's are the spec as eneloopes...at quite a reduced price......
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Old 5th October 2019
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Re: Best AA Batteries

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Your device will only be using a few A at most
I would think that it's probably in the mA range, rather than A.

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Old 5th October 2019
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Re: Best AA Batteries

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Originally Posted by MJ224 View Post
By the way, I have read somewhere (here perhaps) that IKEA's rechargeable's are the spec as eneloopes...at quite a reduced price......
I believe there are quite a few copies around, or rather, Sanyo/Panasonic manufacture them for the likes of Ikea. I think most manufacturers are now using similar technology now because nearly all NiMh cells have much better charge retention properties than they did.

And yes, I would use a simple blocking diode between the solar cell and the battery pack. A 1N4004 or 1N4007 would do fine and is as cheap as chips. (The final number denotes the maximum reverse voltage, which will not concern you.)

Quote:
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I would think that it's probably in the mA range, rather than A.

Jim
I would have expected average current to be in the A range Jim but you may be right, which will change calculations slightly.

If we assume a current drain of (say) 5 mA a 2,000 mA/Hr battery pack should have a useful life of at least 200 hours between charges, or in other words at least a week. Charging current will need to be higher, but not too high. I would suggest about 25 mA which won't harm the batteries.
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  #36  
Old 8th October 2019
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Re: Best AA Batteries

You need is 6vdc. Any powerbank gives an output of 5vdc. I think your weather unit can run on 5vdc as batteries do deplete downwards from the 6v. also the rechargeable (1.25X4) do not give you a full 6v.

I think you can get one of those Solar rechargeable powerbank and hook it up to the unit. You can just cut one of the old mouse or any old USB wire use the + and - leads. That should be stable enough and will work for a pretty long time.
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