Charging a AA battery

[vermiman]

Am I looking at this right?

a 2100 mAh 1.2v battery is 2.52 wh

So wouldn't a three cell 3 amp solar panel(4.5w) charge that battery in less than an hour?

How about four AA batteries arranged in parallel. Could they be charged by the same solar panel in less than four hours?

[Sunking]

Dpends on what battery chemistry you are talking about and how high of a charge rate they can take..

At 1.2 volts I assume NiMh?

[vermiman]

At 1.2 volts I assume NiMh?

Yes

As for charge rate I don't know. I have both Rayovac(2100 mAh) and Energiser(2500 mAh) NiMh batteries.

I thought that I'd experiment with charging AA batteries with a small array of cells before building a larger panel and charging a deep cycle battery.

How would I change the charge rate? Find smaller size cells(lower amps) or build a bigger parallel NiMh AA battery bank(more mAh)?

Sorry for the newbeeish questions. I've just started getting interested in solar power. Learning a little about electricity on the way. Learned about amps being additive in parallel and volts being additive in series. Learning to wire series circuits within parallel circuits.

[Sunking]

Ok you have some serious challenges with MiMh batteries. Let's start with the easy one.

You cannot charge NiMh batteries in parallel, well you can, but it is very difficult.

Now for the tough issue. There are no solar charge controllers that I know of made for NiMh batteries. If you are wanting a fast charger you will have to design and build it yourself. MiMh have a very unusual charging algorithm where they are current charge until a minus delta V bump is reached. This take processing logic controls to detect the V bump.

However you can build a slow charger for them fairly easily, but you using a solar panel to do it is pointless because there are not enough sun hours in a day at a C/20 rate. C/20 means the rated amp hour capacity divided by 20. So a 2000 mah battery would be charge at a constant current of 100 milli-amps for 20 hours.

Ok enough of the bad news. What you can do is find you an inexpensive NiMH charger that that uses a wall transformer. You would have to shop around and find with the voltage output of the transformer in the 12 volt range. Cut the transformer off and connect the to the solar panel. Now with that said the charger would have to be a fast charger due to the limitations of day light.

[vermiman]

What if I wired a USB connection to the panel using a five volt voltage regulator and then plugged my Rayovac USB charger into that?

MiMh have a very unusual charging algorithm where they are current charge until a minus delta V bump is reached.

What is a minus delta V bump? And is it bad taking an NiMH to fast full charge? Does a 15 minute charger take it to the delta V bump and then trickle charge?

[Sunking]

What if I wired a USB connection to the panel using a five volt voltage regulator and then plugged my Rayovac USB charger into that?

Well that is one possible work around but I see some efficiency issue for you. I assume your are talking about using something like a LM-317 shunt voltage regulator?

Problem with shunt type regulators is input current = output current
So just picking numbers out of the air let's say you use a 16 watt solar panel made for a 12 volt system. Using the panel to charge 4 NiMh cells in series at 1 amp. Well at the input of the regulator you have 16 volts @ 1 amp. At the output you have 5 volts at 1 amp. Now this may not mean much to you now until you realize at the input of the regulator is 16 watts, and 5 watts at the output. 11 watts are being wasted as heat or 69% power conversion loss. It works, just a lot of loss. To me it doesn't make sense because there is nothing to gain economically. You spend a $100 to make a $5 charger. However if you are in RC competition out in the field I could see it, or a science fair project, but not for real applications like home use.

What is a minus delta V bump? And is it bad taking an NiMH to fast full charge? Does a 15 minute charger take it to the delta V bump and then trickle charge?

Minus delta V bump is the algorithm of charging NiMh and NiCd batteries. You apply a constant current of C/5 to C/1. As the battery charges the voltage and temperature begin to rise. When the battery is saturated or fully charged the voltage quickly bumps up, then drops. After it drops if the charge is not terminated immediately the temperature sky rockets. If the vents are working properly on the battery they open and vent the electrolyte and pressure off which destroys the battery. If the vents fail then the battery explodes.

You cannot charge a NiMh or NiCd in 15 minutes or a 4C rate. If you tried it would get way to hot too fast and explode before the vents could operate.The maximum charge rate is 1C using a constant current and you have to monitor temperature and voltage to detect the Minus Delta V Bump. That takes signal precessing and logic controls. This is what I meant when I said charging NiMh is tricky and difficult.

[Mike90250]

Ther are some fast NiMh chargers that have forced fan cooling, and give you 80% charge in 15 minutes. They are also very hard on the batteries.

[vermiman]

Ok Sunking,

Is possible to wire a battery pack, solar panel and USB port in such a way that it uses solar power while there's sunlight, but when there's no sunlight it pulls power from the batteries? And not charging the batteries.

[Sunking]

Ok Sunking,

Is possible to wire a battery pack, solar panel and USB port in such a way that it uses solar power while there's sunlight, but when there's no sunlight it pulls power from the batteries? And not charging the batteries.

Not quite sure I understand what you are asking. Are you concerned with the batteries discharging back into the solar panel at night?

If so that is a concern but easily dealt with. If you have some type of voltage regulator of charge controller of some type between the solar panel and batteries, the very nature of the regulator prevents that from happening. In some small installation that just use a solar panel connected directly to a battery all you need is diode to prevent back feeding of the battery to the panel.

[vermiman]

No, I want to use solar power to listen to some music outside. When I hook the player straight up to the solar panel, I loose everything when I theres cloud coverage. So I thought that I would incorporate some AA batteries and keep them charged in the process. But after what I've learned about NiMH batteries the charging part seems to be a no go. I was wondering if a circuit could be wired where the cd player would get its power from the solar panel when there's direct sunlight, otherwise the batteries would power it. No charging batteries. It will only be used in daylight and disconnected after use.

[Sunking]

vermiman Ok now I got the picture of what you are trying to do. No sense re-inventing the wheel partner, there are already systems made to do exactly what you want. Google the term SOLAR PV USB CHARGER and you will get something like this

[vermiman]

Would this work for a charger? Would NiCD work better than NiMH?

[Mike90250]

NiCad is a little more forgiving on the overcharge than NiMh, but really, when chargeing sealed batteries, you SHOULD use a charge circuit.

[Sunking]

Would this work for a charger? Would NiCD work better than NiMH?

Technically there is no difference between NiMh and NiCd. Only real difference is one is toxic, and the other is not.

If should work but you stand a chance of ever charging the batteries. If you are going to do this the best method is select a panel where its Imp is no more than 10% of the battery AH capacity.

Take note here one day you may notice when you open the battery compartment up a going stinking mess from the batteries venting expelling electrolyte. If that happens toss the whole thing in the garbage because the electrolyte is very corrosive and will destroy your gizmo. If it is NiCd the the mess will be very toxic.

[vermiman]

If I am pulling a load through the USB wouldn't the batteries be just trickle charging?