Which battery to use?

[Hero999]

Why would you want to do that?

 

[Mohamed Najiullah]

to fully charge the batteries?

 

[audioguru]

You cannot charge Ni-MH cells with a constant voltage. You must limit the current because an extremely high current will flow when a dead cell is beginning to be charged.
Most semiconductor manufacturers have battery charging ICs.

 

[Hero999]

You cannot charge Ni-MH cells with a constant voltage. You must limit the current because an extremely high current will flow when a dead cell is beginning to be charged.

I thought it was running off a solar cell which already limits the current?

 

[Mohamed Najiullah]

You cannot charge Ni-MH cells with a constant voltage. You must limit the current because an extremely high current will flow when a dead cell is beginning to be charged.
Most semiconductor manufacturers have battery charging ICs.

I've seen the maximum o/p of the solar cell is abt 140mA to be exact...

If i give the batteries a constant voltage and a varying current, will they charge or not?

 

[audioguru]

A solar panel does not have a constant voltage. If the voltage is high enough then the battery will charge.

 

[Mohamed Najiullah]

A solar panel does not have a constant voltage. If the voltage is high enough then the battery will charge.

I'l use a dc-dc step up IC to maintain constant voltage.. Only the current will vary..

 

[Hero999]

No, the voltage will vary, you wouldnt' expect the voltage to be as high at twilight as you would at midday would you?

 

[Mohamed Najiullah]

No, the voltage will vary, you wouldnt' expect the voltage to be as high at twilight as you would at midday would you?

No...What i mean is the IC will give a constant o/p for an i/p voltage ranging between 3-8V, right?

I wont switch on the solar circuit unless the sun is out...

 

[audioguru]

You cannot use a constant voltage to charge a battery. When the battery is discharged then the charging current will be much too high.
But the solar panel limits the current so that the voltage will not be constant.

 

[Mohamed Najiullah]

You cannot use a constant voltage to charge a battery. When the battery is discharged then the charging current will be much too high.
But the solar panel limits the current so that the voltage will not be constant.

Then how do i charge a battery? I have a Duracell NiMH charger which runs off the wall port and it says that the charging voltage and current per sortie(i.e two cells of 1.2V each) is 3V and 360mA respectively...

 

[audioguru]

Your Duracell charger limits the charging current to 360mA and it limits the voltage to 3.0V. It is not "constant voltage".

When two dead cells are charged in series and have a total voltage of only 1V or less, the 360mA current charges them until the voltage rises.
The voltage is not 3.0V until both cells are nearly fully charged.

 

[Mohamed Najiullah]

Your Duracell charger limits the charging current to 360mA and it limits the voltage to 3.0V. It is not "constant voltage".

When two dead cells are charged in series and have a total voltage of only 1V or less, the 360mA current charges them until the voltage rises.
The voltage is not 3.0V until both cells are nearly fully charged.

so how do i charge a NiMH cell with a solar cell or hand crank? I'm sure its not impossible...

 

[Ubergeek63]

so how do i charge a NiMH cell with a solar cell or hand crank? I'm sure its not impossible...

a sepic converter with a charge built in charge algorithm... https://focus.ti.com.cn/cn/general/docs/lit/getliterature.tsp?literatureNumber=slyt309&fileType=pdf

or just hang a charger off the sepic... the sepic will let the charger run with less than the battery voltage supplied. I did a power LED driver with one before driver chips were available. the LED ran from 2.5V to 5V... more actually but that is all i needed to say, a single lithium cell.

dan