help me for my school project. please :(

[FajarTriRamadhan]

hello guys, im here to ask you something. Well, im ordering a 6V 3.5 W 583 mAh solar panel. for the storage battery, im using 4 1.2V 1500mAh rechargeable batteries. so the total are 4.8 V 6000mAh storage. and as you can see, my solar panel voltage is 1.2 V greater than my batteries. the question is, anyone knows how to reduce my panel voltage ? i really need this problem solved

[N_las]

Something like this? http://en.wikipedia.org/wiki/Voltage_divider

[FajarTriRamadhan]

don't know for sure, cause im sucks about this

[Albert VDS]

Or you could solder a voltage 4.8V voltage regulator in between the solar panel en the batteries.

[steve_v]

Short answer: If they're NiCds, use a series resistor & basic ohms law.

Longer answer:

If they're NiCd or NiMH batteries, you don't really need to worry about the voltage, so long as it's greater than the charged voltage of the battteries.

What matters is charge *current*, and not over-charging the cells.

Ensure you stay below the maximum charge rate specification for the cells you are using, generally specified as a fraction of cell capacity in mAh.

To charge NiCd & NiMH cells properly, you really need a delta-peak (voltage) or temperature sensor charging controller to detect when they're 'done'. Otherwise 'bad things' can happen, in the worst case - explosions, I kid you not.

If they're NiCd cells (NOT NiMH) you can be really cheap, and just use a super low 'trickle' charge rate.

Here's a cheat sheet I found on the 'net: looks about right to me.

Lead-acid is easier, since cell voltage is fairly linear with charge state. All you really need is a constant voltage approx 1.5v higher than the nominal battery voltage, a reverse polarity diode and a charge rate within spec.

I'm not sure what you're using this for, or whether weight is an issue, but using a 6v SLA battery will probably make life somewhat easier.

Store bought solar car battery 'trickle' chargers really are as simple as a panel, a diode and a pair of alligator clips

I used to charge 7.2v NiCd battery packs from a 12v auto battery - ammeter and a length of toaster element in series to limit the current to maximum charge rate spec. Full charge detection by holding hand on battery pack

Not overly good for them, but it works.

Edited November 8, 2014 by steve_v

[FajarTriRamadhan]

well thanks a lot steve, i'm using NiMH batteries. and so that means i just need to find NiMH charge controller right ?

[steve_v]

'just' is relative.

There are many 'NiMH smart charge controller' ICs out there, (such as the MAX712) but implementation can be non-trivial depending on your level of electronics foo.

A charge controller IC may not work as well as you hope either, as most are designed to operate from a constant voltage supply. A solar panel is anything but constant & I have never tried this myself.

You could just limit the charge current to <1/10 C, where C is the capacity of your cells - in this case 1500mAh as you are connecting them in series to get 4.8v (not 6000mAh @ 1.2v as it would be in parallel - NB. NiCd/NiMH cells in parallel is a bad idea anyways), but you will reduce the lifetime of the cells.

Unfortunately a 580mA panel falls smack between 'really really slow, not good for the cells but you'll get away with it' and 'fast charge, where delta-peak detection works well'. This sucks, as there really is no easy answer, NiMH batteries are a pain in the ass.

You may find more knowledgeable answers on an electronics forum, I'm an industrial electrician so most of the stuff I work with is a little bigger than this

Why is this not easy?

Edited November 8, 2014 by steve_v

[FajarTriRamadhan]

alright the conclusion is... i need to connect the batteries in series and i get a total of 1500 mAh and 4.8 V, and also limit the solar charge current to only 150mA from the original 583mA right ?