Solar Panel Charging NiMH Batteries

[westkid85]

I would like to use Solar Panel to charge 3 AA 1.2V battery which total 3.6V output. the battery capacity for a single battery is 2.2Ah

I do need recommandation for what specification of solar panel i need for a fast charging (perhaps 2~3 days)

In addition, do i still need a charging IC from Maxim-ic or texas ins?

 

[audioguru]

Energizer has a website with the spec's for their batteries. They have an Applications Manual for their Ni-MH cells and say that when they are fully charged then a circuit should reduce the charging current to nothing or to a very low trickle charge current.
Solar cells without the circuit would keep overcharging a Ni-MH battery which would shorten their life.

Solar panels are frequently advertized to have an output when they are in the Sahara Desert at noon with the panel pointing directly at the sun. The current is less at other times and at other locations on earth. Guess what clouds do to the output?

 

[adaminc]

You can use a microcontroller to charge a nimh battery if you want.

Check this one out, it uses a PIC.
NiCd/NiMH Battery Charger

 

[westkid85]

hmmm...i juz checked a type of solar panel which is rated as (Volt nom:6V and 1.2W output. output current max 0.15A) (i guess the real output current would be much lesser since it is measure in Sahara Dessert )
is this solar panel optimum for charging my battery? If let say i change to a sonal panel to 9 V or even higher output voltage, my question is would the higher voltage cause any negative effect to my batteries?

i been doing survey around, there are two type of Charging ICs, which are the Ni-Cad/Ni-MH battery charger from Maxim-IC or Texas Ins, and the second is the Programmable Smart Charging ICs such as PIC mention above, (i realise audioguru are perfer in the 1st type of ICs )
Actually what are their pros and cons of this two type of ICs? which type of ICs are more suitable for the solar charging application?

 

[audioguru]

Solar garden lights have the solar panel blasting its max current (which isn't much) into the Ni-Cad or Ni-MH battery for 1 hour at noon when the sun is almost overhead and it is not cloudy, then less current at other times. They don't use a charging IC. They overcharge a little in the middle of summer and don't fully charge at other times. They last for years.

Your little solar panel might have a max current of 100mA or 80mA in your location for the hour near noon and less current during other hours of the day. The solar panel probably does not follow the sun across the sky so its charging current will be even less.
It might take a week or more to fully charge 3 dead AA cells. If the cells are not discharged daily then they will be overcharged and will have a short life.

 

[westkid85]

basically i m using the battery for a robot alarm clock, it use an Light Dectating Resistor to seek for light spot in a room for recharging everyday
my robot actually consume not large power. It can sustain without recharge for around 1week with 3 AA battery.
for my case, which the battery will not fully discharged daily and will be recharged daily, so i think it is better to include an Charging ICs? The Ni-Cad/Ni-MH battery charger from Maxim-IC or Texas Ins or Programmer Charging ICs such as PIC?

 

[audioguru]

A solar panel is designed to have bright sunlight, not a little room light.
You must calculate or measure how much current the circuit uses then how much current the solar panel supplies. I don't think a charger IC will do anything useful with such a low charging current.

 

[westkid85]

Sorry for asking a stupid question
i wan to ask if it is possible to change the solar panel to a higher load voltage (example 7.5 Volt or higher) in order to obtain higher output current / output power to recharge my battery? ( my battery is 3.6V total)

 

[audioguru]

I have never seen the spec's for your solar panel and I haven't measured its output voltage and current in room lights.