Solar Panel to Recharge eneloops 2000 mAh

[magnolia]

Hello,
I am interested to recharge four AA eneloops ( 2000 mAh , 1.2v each ) NiMh cells at a time within 4 / 5 hours by using solar power . I live in a tropical zone where bright sunlight stays from 7am to 5pm though in winter the time is aprox. 6 hrs . But winter is short only for 2 months here .
So I have decided to install solar panel to regularly recharge the eneloops for my flashlights . I have few eneloops 2000mAh and an eneloop charger to recharge them by electricity . I want to use them .

I know little about solar power etc . So please guide me .
- what things do I require for this ?
- the required watt and volt for the solar panel ?
- Do I need anything more ? Please inform me in details and also how to install these properly .
Hope you would help and guide me to my dream to come true !
Thank you !

[russ]

What is your zip code or approximate location?

[PNjunction]

The easiest way to charge the AA eneloops would be to use the PowerFilm Foldable Solar AA/AAA charger. I use one myself.

While I don't know your true solar-insolation hours (different from visible daylight - you can look up your hours online), I imagine they would be pretty good in India.

The PowerFilm has a decent charger designed for solar - it will rapidly charge up to about 85% SOC, and then slow charge the rest. This prevents fully charged batteries from repeatedly going into a delta-V trigger cycle if temporary shadows or loss of sunlight cross the panel. When it reaches 85%, the charge indicator will stay solid indicating that you *could* use them at that point, but it is best to let them continue to charge for at least another hour to reach full charge.

It charges 4 AA's in pairs, and if you only charge two at a time, the current doubles, and the charge time is reduced by half. So if super-speedy recharging is desired, I'd pick up two of them, and charge only 2 in each. It is best to keep the cells out of direct sunlight, so when charging, I face the cells away from the sun, and loosely fold the extra webbing back over the top of the charge element with a paperclip to keep it out of direct sunlight also.

If you wanted to use your existing charger, grab a 20-30 watt panel, a small charge controller, and attach to a 12ah agm battery. Connect your existing eneloop charger to that - if it will take dc of course. This way you could charge while sunny, or just charge at night from the energy stored in the agm battery. The problem here is that if shadows cross the panel or sunlight goes away, your eneloop charger will repeatedly go into a delta-v trigger detection when the cells are fully charged - which is not good for the batteries.

I'd go with the PowerFilm AA foldable chargers first.

[magnolia]

Hi
Thank you for your reply .
Previously I had thought of powerfilm also but few said that it is very slow and takes one day or more to recharge 800mAh 2 cells and besides it is not as durable as panels .
Thats why Im thinking of panels as it would run for years without a any or little maintaince .
Powerfilm is 1.5 wt . Is not it ?
Here few also suggesting for 5w panel but if I use panel , wish to go for the experts' view found here .
Please guide me .
Thanks !

[PNjunction]

Previously I had thought of powerfilm also but few said that it is very slow and takes one day or more to recharge 800mAh 2 cells and besides it is not as durable as panels .

That is why I mentioned that if you want to cut that time in half, you purchase two of them and charge only a single pair in each. This also assumes you are fully discharging them to nothing each day. If you aren't fully discharging them, of course your times would be much faster.

More detail on a bigger system: 60 watt panel. 12-18ah agm sealed lead acid. Morningstar SS-6 pwm controller. Don't skimp on bad quality chargers. Maha / Powerex MH-C9000. The Maha is an outstanding charger, able to run from AC or DC. It is also an analyzer if you want diagnostic/maintenance functions, yet is just plug and play if you don't need those features.

The Maha/Powerex MH-C9000 will properly charge eneloops at 0.5C default (1000mah) and will charge each cell individually in about 2 hours. Not mentioned in the manual is that if you want the absolute highest SOC, you will charge for an additional 2 hours after it signals a "done" condition, whereupon the Maha individually applies 60ma each hour (two hours max), and then drops to a 10ma trickle. Of course you can manually change these settings if you want.

Like all chargers that rely on the delta-v end-of-charge trigger, charging the AA's while doing solar recharging of the agm battery may end up in repetetive delta-v triggering in cases of passing shadows when the cells are full. Just like your existing eneloop charger will. While the eneloop charger is ok, if you really want to do it right, go for the Maha MH-C9000, and do a two-step charge routine - one for the large agm battery, and the again with the Maha charger for the AA's when convenient offline.

[Sunking]

Very simple problem to solve. Look in the specs and find out the maximum charge current for the batteries. Them buy a panel with a Imp 10% higher than the battery can take. Forget insolation hours or location. Charge at the max rate and none of that means anything.

[magnolia]

Very simple problem to solve. Look in the specs and find out the maximum charge current for the batteries. Them buy a panel with a Imp 10% higher than the battery can take. Forget insolation hours or location. Charge at the max rate and none of that means anything.

Hi
Let me say what Im tring to do .
Im going to buy a solar panel 5w , 6v , 0.575A output and directly use the cells in holders .
OR
I may use a 10 w , 12v , 1A panel and use a ic to drop the volt to 6v and use directly with the cell holders .

Please tell me which one is better .
Or simply tell me what things I need . Believe me I am really poor in Maths and Physics . So your suggestions will only be followed blindly .
Thanks .

[inetdog]

Hi
Or simply tell me what things I need . Believe me I am really poor in Maths and Physics . So your suggestions will only be followed blindly .
Thanks .

Just a word of caution, magnolia: For liability reasons, my attorney has advised me not to give advice to anyone who will follow it blindly.
If I teach a man to fish, I am not responsible if the fish spoils.

[Sunking]

Hi
Let me say what Im tring to do .
Im going to buy a solar panel 5w , 6v , 0.575A output and directly use the cells in holders .
OR
I may use a 10 w , 12v , 1A panel and use a ic to drop the volt to 6v and use directly with the cell holders .

Please tell me which one is better .
Or simply tell me what things I need . Believe me I am really poor in Maths and Physics . So your suggestions will only be followed blindly .
Thanks .

No you have not told me what you are trying to do. I get the impression you are looking to charge at the fastest rate possible. If speed is the concern you charge at the highest current the battery manufacture specifies, but it comes with risk and you had better know the math and physics or else you are literally playing with fire.

[inetdog]

No you have not told me what you are trying to do. I get the impression you are looking to charge at the fastest rate possible. If speed is the concern you charge at the highest current the battery manufacture specifies, but it comes with risk and you had better know the math and physics or else you are literally playing with fire.

From the OP's language ("directly use the cells in holders") I get the impression that he does not see the need for a charge controller. That makes high rate charging impossible. Instead he would have to size the panels for the maximum allowed constant current charging (and even switch that depending on the number of cells being charged.
Not using a controller is just not consistent with fast charging.

[Sunking]

From the OP's language ("directly use the cells in holders") I get the impression that he does not see the need for a charge controller. That makes high rate charging impossible.

OK, but I strongly disagree. Here is why. A solar panel is a current source correct? For purposes to make things simple let's say you have a 6 volt 1 AH battery and the manufacture specifies the maximum charge rate is 1C or in this example 1 amp. If I go out on the market and find a 18 watt standard 12 volt battery panel its spec is 18 volts Vmp and 1 amp Imp. With me so far? I can very easily connect that panel directly to the battery assuming good sun light, and that panel will deliver 1 amp of charge current because I have forced the panel to operate below the Vmp, and it effectively goes into current limit of 1 amp. That is the basic premisses of a PWM controller operating at 100 % duty cycle.

Now to your point is a terrible design and application simply because it would reley on th eoperator to terminate the charge and in all likely hood would over charge the battery and destroy it. It is even possible to start a fire or spew the contents of the battery. However a simple series or shunt voltage regulator would do the trick of terminating the charge.

Now there is a flaw with that concept if speed is the goal. In order for the above to work would require excellent sun and only work in a 1 to 2 hour window around solar noon. If money is no object and only speed is a concern I would use a much larger panels of say 50 watts 12 volt battery panel and a 1 amp MPPT charge controller with a Bulk constant current charge algorithm. Even in lower light condititons down to a reasonable point will produce 1 amp which would mean a much wider window of opportunity during the day from a couple of hours to several hours. Downside is it is a waste of resourves as you would only utilize 6 to 9 watts of a 50 watt panel.

[magnolia]

No you have not told me what you are trying to do. I get the impression you are looking to charge at the fastest rate possible. If speed is the concern you charge at the highest current the battery manufacture specifies, but it comes with risk and you had better know the math and physics or else you are literally playing with fire.

Oh Sunking , sorry not to inform you .
Im tring to recharge four eneloops ( 1.2 v , 2000 mAh each ) at a time within four hours using solar panel .
Please inform me what I need to do so ( say clearly what watt , volt , Amp etc of the required things ) .
Hope you would help me ( Be sure Ill not contact my lawer if any problem arises !!! ) .

[PNjunction]

Magnolia - the ONLY way you are going to charge directly from a panel without the need for a charger, is to use a VERY small panel that limits the current to the C/20 rate, in this case, a panel limiting the voltage to about 9 - 12v, and only 100mah. This is a very slow charge - if you go faster, you need to have a dedicated charger.

BUT, this will take you about 6 days or so via solar, which doesn't fit your timeframe.

Project over. You only have two choices. Charge fast with the right equipment, or charge very slow and take days to do so. There is no getting around it no matter how many times it is asked.

[magnolia]

Magnolia - the ONLY way you are going to charge directly from a panel without the need for a charger, is to use a VERY small panel that limits the current to the C/20 rate, in this case, a panel limiting the voltage to about 9 - 12v, and only 100mah. This is a very slow charge - if you go faster, you need to have a dedicated charger.

BUT, this will take you about 6 days or so via solar, which doesn't fit your timeframe.

Project over. You only have two choices. Charge fast with the right equipment, or charge very slow and take days to do so. There is no getting around it no matter how many times it is asked.

Ok. I under stood ! If want to charge within 4 hours using charge controller etc , what right equipment - ( watt , volt etc panel and charge controller and more ) should I need ?

[PNjunction]

That would be about what is described in msg #5. The good thing is that with the Maha Powerex c9000 charger, the default is set up to charge 2000ma eneloops in 2 hours, and will charge them correctly without you having to do anything more than insert them.