AA Batteries instead of a 12v Lead Acid

[syntaxrob]

I putting in a small 12v Solar system that will power a small PC fan and some 12v led strips as well as maybe a 5v USB socket. It will consist of a 12v PV panel, a charge controller, a small distro board and a battery bank. However, all the systems Ive seen use a 12v Lead Acid battery and I want to use a bank of 8 rechargable AA batteries.

Is this in any way possible?

Thanks in advance for the help!

[inetdog]

I assume that you are talking about either Nickel Cadmium or Nickel Metal Hydride AA cells. Both are usable for this purpose.
But NiCd, with a nominal voltage of 1.2V/cell would only give you 9.6V and NiMH can be difficult/dangerous to charge quickly unless you use a reliably designed well built charger.
You are not likely to find a commercial charge controller in the low price range that will take PV input and work well with 9.6V or with NiMH batteries.

[Logan5]

I use 18650 lith-ion's they are rechargeable and can be obtained with several times the power of ni-cad and ni-mh batteries at many times the life cycles. you can obtain 18650's in tabbed units that can be soldered together. or you can buy pop in battery modules to wire up. I use a desktop charger and charge individually then insert into different battery modules for the device I wish to power.

[syntaxrob]

Yeah Nickel Hydroxide.

So, if they have a nominal voltage of 1.2V, couldn't I just up the pack size to 10 cells? And if theres not likely to be a PV charge controlller that will work in that range with NiMH batteries, could a non PV panel be used instead?

This is the controller I was thinking of using:

http://www.ebay.co.uk/itm/10A-12V-24V-Intelligent-LCD-Solar-Charge-Controller-Auto-ID-PWM-Mode-5V-USB-Z1L2-/141971803588?tfrom=131121795602&tpos=top&ttype=price&talgo=undefined

[Sunking]

Yeah Nickel Hydroxide.

So, if they have a nominal voltage of 1.2V, couldn't I just up the pack size to 10 cells? And if theres not likely to be a PV charge controlller that will work in that range with NiMH batteries, could a non PV panel be used instead?

Look very few if anyone is going to make a solar charge controller for Nickel batteries. It is simple economics of biz. No company is going to make a line of products no one uses or buys. 1 customer is not a market. Nickel batteries use a very different algorithm and require a very special expensive type of Delta V chargers. That compounded with NiMh prices eliminates NiMh as a choice for solar power.

To compare battery prices you look at $/ watt hour cost.

Lead Acid sells for around $0.15 to $0.22
Lithium sells for $0.40 to $2
NiMh $1.10 to $4.00

The math is simple and NiMh got eliminated from solar. To expensive. You can buy 10 - 2.4 AH NiMh batteries for $25. They have a capacity of 26 watt hours. For the same $25 you can buy a 12 volt 20 AH battery roughly 9 times more capacity.

[syntaxrob]

Ok, all that makes sense... so this is the plan:

10W Photonic universe solar panel, hooked into a 10A 12V charge controller, with 3 x panasonic NCR18650B green Li-Ion 3.7V 3400mAh cell's.

That should all work, right?!

[SunEagle]

Ok, all that makes sense... so this is the plan:

10W Photonic universe solar panel, hooked into a 10A 12V charge controller, with 3 x panasonic NCR18650B green Li-Ion 3.7V 3400mAh cell's.

That should all work, right?!

Uh maybe and maybe not. Most solar charge controllers do not have the proper logic to charge a Li-Ion type battery. That usually requires a BMS charging system made for the battery chemistry.

[syntaxrob]

Uh maybe and maybe not. Most solar charge controllers do not have the proper logic to charge a Li-Ion type battery. That usually requires a BMS charging system made for the battery chemistry.

Which means, at a guess, a much higher cost... for a BMS system. If your'e saying its a maybe / maybe not situation, as in 50/50, Ill give it a go and see how it goes. Ill post results on this feed for anyone who wants to know!!

Thanks everyone for your input and help!

[Mike90250]

Charging Li batteries without a BMS is like lighting a 5 minute fuse on a keg of gunpowder. then snuff the fuse. light it the next day, snuff it out..... eventually, it goes boom

[PNPmacnab]

Have you heard of this thing called ebay? There are lots of BMS systems for Li. Can't vouch for how long they will last. In a pinch the LM2596 etc buck modules will work with standard solar panels and put out a fixed voltage that these BMS can probably use.

[PNjunction]

The catch 22 about diy li-ion projects is that if you have to ask, you are being unsafe and are a danger to yourself and others. Sorry, but that's the way it is unless you do a LOT of homework up front. You may want to visit the Candlepowerforums to get that background you desperately need.

OR, if you want to revisit your solar AA nimh project we can do easily:

The major problem to understand is that unless you want to trickle charge your AA's for a week or more, this involves a higher current charge circuitry that relies upon accurate charge termination methods. One of the common ones is dv/dt, which is simply that there is a "signal" (a very tiny short drop in terminal voltage from the battery) when it reaches a full charge.

The problem is that if your circuit misses that signal (bad detection, usually due to insufficient charge current in the first place), you cook the cells. This can happen with even "steady-state" charge sources - solar is even worse!

And this is where the typical AA solar charge toys go wrong - they are expecting a fully stable source of sun, and we know that is actually variable, which tends to cause missed end-of-charge terminations.

BUT, there is currently only ONE product on the market that KNOWS about the variable unsteady sun, and quick-charges AA nimh properly. The secret is that they quick-charge up to about 80% SOC, and THEN walk in the last 20% or so with a trickle, not relying on any dv/dt termination. This saves the cell from overcharge in a solar application:

http://www.powerfilmsolar.com/products/?aa_battery_foldable_solar_panel&show=product&productID=271505

You'll want two of these for an 8-cell holder to drive your fans. Charges in pairs, so be sure to give it an extra hour or so after the "finished" led goes solid to help ensure balance as it trickles that last little bit *safely*.

I wouldn't trust my costly Eneloops to anything else.