Solar Battery Chargers - any thoughts.

[cmlotito]

I was wondering if a solar powered battery charger actually works. It's like getting something for nothing the way I look at it. Would it be a good idea to have one just as a backup charger if for some reason I wouldn't have access to a power outlet for a few days for whatever reason (ie: extended blackouts, natural disaster, etc.)

I've seen one model which isn't expenseive which is good because the way I look at it is it's something I hope I would never have to use but would really like to have if I needed it.

 

[SilverFox]

Hello Cmlotito,

The only problem is that their output is low. You need full sunlight for several days to charge up today's high capacity cells. They do work, it just takes a long time to charge.

For example, to charge AA cells you need somewhere near 500 mAh of current capacity for 4+ hours. Check the output capacity of the solar powered charger for a comparison.

Tom

 

[RobD]

While you can get a solar panel to charge batteries you will also need a charge controller to keep the batts from over charging, batteries and an inverter to convert 12 volts DC to 120 AC.
If you just want to charge ni-cads I think they make small solar charges for this.
RobD

 

[PsycoBob[Q2]]

If you get a decently large (10-20 watt) panel and 12 of Rayovac's IC3 2AH AA's you can get away with no controller. As long as you keep the cells at the same charge level, you can let those special cells shut themselves off when fully charged. Put a 12v lighter-socket on it, and you can run a lot of 12v accessories (like AA/AAA battery chargers).

Solar is neat, but it costs a lot up-front, and the panels needed to recharge batteries reasonably quick are rather large. With a pair of 10w monocrystaline panels, I was realistically getting around 6watts out of them, in full sun with the panels sligned for peak output. Any shading on the panels, or the slightest cloud caused output to drop like a rock. At the moment, the live in the back window of my car- they're huge compared to most 'battery maintainers.'

 

[MikeF]

Have you looked at the Brunton Solar stuff?
Link

 

[Doug Owen]

You can get the same unit from C Crane for two thirds the same bucks ($15).

I've got one, although don't use it as the mains powered versions have clear advantages when available. A perhaps better solution is one of the small, very rugged, panels from Silicon Solar , their 'EpoxLite' line. I've used the two $15 versions for four cells (6 volter) and 2 (four volter) with more success. They include a diode, but you need to add a meter (or run on faith).

More compact, better output, far tougher.

Doug Owen

 

[SilverFox]

Hello MikeF,

The Brunton Solarport 4.4 is a good example of what is available right now.

The maximum output is 585 mAh at 7.52 volts. It comes with a 4 cell charging cradle. Let's see, 4 cells at 2000 mAh each = 8000 mAh required if there are no losses. The charger puts out 585 mAh maximum. This means that it would take almost 14 hours of direct sunlight to charge 4 cells (assuming no losses). I would expect that it would take about 3 days to complete a charge.

Will it work? YES. It just takes some time.

The application that I have heard of is on kayaks. People charge a spare set of cells for their GPS. After 3-4 days they are ready to change batteries and the spent ones go back on the charger. I believe some of them are using larger than standard solar panels as well.

Tom

 

[raggie33]

at big lots i saw a garden light that uses sor cells and if i recall it had rechagbale aa batts inside .at a cost if i recall 5.99 but that was back in summmer but i thought of makeing something from it

 

[Sub_Umbra]

raggie,

I love Big Lots.

cmlotito,

I bought the one from CCRANE a few years ago that someone else linked to. I really didn't take it too seriously and have never used it. I got it for the reason you stated -- backup when/if things get really bad.

A couple of points from other threads:

IN GENERAL solar chargers are going to perform better with AAAs and AAs because they will take less time to charge. (I have NiMH Ds that take over 24 hrs to charge when my everyday charger is plugged into the wall. Throw in your own particular latitude, season and weather and it's easy to see how large sized cells can be problematical.)

Even though I own one of these self-contained units myself, I have to admit that I'm very concerned about the combined effect that charging and sitting in a box in the sun may have on my cells. Location, location, location.

I also have no idea whether these self-contained solar units are up to the task of charging NiMH cells. I just don't know. Would Nicads be more feasible for that situation? (I just noticed that in the CCrane blurb only Nicads are pictured with the charger.)

If I owned my own home I would opt for a solar panel that I could use with my AC2020. Even this solution becomes more complex during a 'long term emergency' because of the danger of theft of the panel if it is in a location where it can be seen from any location that you do not have control of.

You may find some interesting information by searching for some of the 'My friend is moving to Africa...' type threads.

I find this a very interesting subject.

 

[Saaby]

I wanted to charge cells from the sun, but didn't want to wait -- so I got a C. Crane 4 watt panel and use it with a Maha charer.

Works like a charm. Charges batteries almost as fast as they would charge from wall plug. Only problem is you have to watch the setup carefully as partial sun can confuse the charger computer.

 

[Lux Luthor]

This brings up another question. How efficient are the typical NiMH/NiCad chargers that you use with either a walwart or cigarette lighter plug?

If for my home I get a small 12V solar panel, charge controller and 12V SLA, then run that to my standard chargers, will this last step cost me a lot by way of efficiency?

 

[Doug Owen]

[ QUOTE ]
SilverFox said:
The maximum output is 585 mAh at 7.52 volts. It comes with a 4 cell charging cradle. Let's see, 4 cells at 2000 mAh each = 8000 mAh required if there are no losses. The charger puts out 585 mAh maximum. This means that it would take almost 14 hours of direct sunlight to charge 4 cells (assuming no losses). I would expect that it would take about 3 days to complete a charge.



[/ QUOTE ]

Actually, you'd either chage the cells in series or do a converter per cell, it'd only take a bit over four hours total. On average, you get five hours sun per day at reasonable lattitudes so 'one recharge per day' seems at least a reasonable goal. There is a penalty for the boaties (and the rest of us) that need to mount them flat, you don't get full output.

Doug Owen

 

[Josey]

Hook a small solar panel up to a 100 Amp hour, deep cycle battery. Then hook your charger to the battery. The panel will keep the deep cycle battery charged, and that battery will have enough amp hours to charge whatever flashlight batteries you want anytime you want without having to watch the sun.

 

[Sub_Umbra]

That's cool. How much of a panel would that take?

 

[SilverFox]

Hello Doug,

Help me out here... I thought I was describing a series set up...

4 cells at 1.5 volts = 6 volts
4 cells at 2000 mAh = 8000 mAh

The information I have received from kayakers is that it takes about 4 days to re-charge cells. I must agree that a set up on a kayak deck is less than optimal.

Tom

 

[Doug Owen]

Tom,

Yer on the right track. Each cell is a nominal 1.2 Volts making the total 4.8. However, when charging the voltage needs to be a bit higher, but the total should still be fine with the available 7.5 Volts from the panel.

In a series circuit the current goes through each element in turn. Therefore each mA flows through all four cells, charging each.

Another way to look at it is each cell is about 2.4 Watt hours (1.2 Volts times 2 Amp hours, 2000 mAh), the panel can put out (7.5 Volts times .6 Amps), 4.5 Watts. In a perfect world, it takes less than an hour (closer to half an hour) of full sun to charge each cell. Four can be done in a single day (more or less).

Doug Owen

 

[eluminator]

[ QUOTE ]
SilverFox said:

Help me out here... I thought I was describing a series set up...

4 cells at 1.5 volts = 6 volts
4 cells at 2000 mAh = 8000 mAh

Tom

[/ QUOTE ]

Four 1.5v 2000 mah cells in series gives you 2000 mah at a nominal 6 volts, not 8000 mah.

If you connect them in parallel you would have 1.5 volts, 8000 mah.

This should apply whether you are charging or discharging. Of course there are always energy losses you have to consider.

The trick here is to watch out for mah or ampere-hours, for that matter. This is a unit of measurement of ... well nothing, I guess.

Just a goofball way the battery crowd rates their batteries, and I guess it works. If they would use a unit of energy like watt-hours instead of a unit of ??? like amp-hours, you would have been right.

 

[eluminator]

Concerning the solar powered yard lights, they will work with NiMH cells, but I don't know how well they charge.

I inherited 10 of those lights that no longer worked.
I got 20 cheap NiMH 1500 mah generic AA cells and put them in those lights 3 years ago. They all still come on every night. They have had over 1000 charge cycles in air temperatures ranging from -10F to 90F. The lights don't last all night though.

 

[SilverFox]

Hello Doug and Eluminator,

Oops, I was mixing series for voltage and parallel for capacity. Need more coffee...

I am going to have to check out why it was taking the kayakers 3-4 days to re-charge their cells...

I have solar yard lights as well. They came with NiCd's and a year or so ago I had to replace two sets. I decided to go with NiCd's because there is no limit on the charge cycle. I felt that NiCd's could withstand summer time charging (and overcharging) better than NiMh. When fully charged (good sunny day) my lights stay lit all night. I believe the cells are rated at 1200 mAh and each light has two cells.

Tom

 

[SilverFox]

I found my notes on the kayak use of solar panels and they were using 8 cell packs (to get 12 volts). The charging times reflected the less than optimum placement of the panel (flexible panels were glued to the top deck of the kayak) and less than perfectly sunny days.

With an 8 cell pack it was taking them 4 days to fully re-charge the 8 cell pack. The full charge measurement was determined by taking the cells off the charger, letting them rest for 30 minutes, measuring voltage, installing them in a Mini Mag flashlight and measuring the voltage as the light was turned on. If the voltage dropped quickly, the cell was determined to not be fully charged.

Tom