Which battery to use?

[Mohamed Najiullah]

As some of u might have already seen my queries abt LiPo ICs in here

https://www.electro-tech-online.com/threads/lithium-ion-charging-ics.104595/

, i wont elaborate...

Which battery should I use if i wish to charge it under constant voltage of 4.2V and varying current of 20-200mA?

My preferences are good charge retention, small in size, less charging circuit complexity etc..

The current to the batteries will vary continuously from 20-200mA while the voltage can be fixed at 4.2 to 5V...

And the discharge should be fairly good too..

So which battery should I use? Lithium Polymer, NiMH or any other type of battery?

 

[Hero999]

I told you how to charge a Li-ion battery in the last thread.
https://www.electro-tech-online.com/threads/lithium-ion-charging-ics.104595/#post854068

Which part didn't you understand?

 

[Mohamed Najiullah]

I understood everything.. I jus wanna know if LiPo battery really are the ones that would be ideal for my project..

 

[Hero999]

No, I recommended using three NiMH cells in series in my first response you your thread.
https://www.electro-tech-online.com/threads/lithium-ion-charging-ics.104595/#post854014

 

[Mohamed Najiullah]

No, I recommended using three NiMH cells in series in my first response you your thread.
https://www.electro-tech-online.com/threads/lithium-ion-charging-ics.104595/#post854014

U recommended using button type NiMH cells of 1.2V...But their o/p current is very low, isn't it?

 

[Hero999]

Then use AAA or AA cells if button cells won't provide enough current.

 

[Mohamed Najiullah]

Then use AAA or AA cells if button cells won't provide enough current.

Ok.. I was going through a few websites.. I came across this..

How to charge Nickel Metal Hydride Batteries.

it says that NiMH batteries r among the hardest to charge..

 

[Ubergeek63]

Ok.. I was going through a few websites.. I came across this..

How to charge Nickel Metal Hydride Batteries.

it says that NiMH batteries r among the hardest to charge..

and LiPos are worse... LiFePos, on the other hand, are among the easiest.

 

[Hero999]

If the current is kept low enough, it's very easy.

The cheapest way to charge a nickel metal hydride battery is to charge at C/10 or below (10% of the rated capacity per hour). So a 100 mAH battery would be charged at 10 mA for 15 hours. This method does not require an end-of-charge sensor and ensures a full charge. Modern cells have an oxygen recycling catalyst which prevents damage to the battery on overcharge, but this recycling cannot keep up if the charge rate is over C/10.

You said your solar panels put out 200mA maximum, which is <0.1C for a 2500mAH NiMH cell.

Li-ion batteries can't do this and should never be charged continuously, even at very low currents.

 

[Mohamed Najiullah]

and LiPos are worse... LiFePos, on the other hand, are among the easiest.

But they have better charge density...

 

[audioguru]

Energizer says to reduce the trickle charge current to 1/40th of C for long life with their Ni-MH cells.

 

[Ubergeek63]

But they have better charge density...

moderately better charge density in exchange for instability and 5-10x worse cycle life

 

[Hero999]

Energizer says to reduce the trickle charge current to 1/40th of C for long life with their Ni-MH cells.

The datasheet assumes that the batteries are going to be left permanently connected to the mains 24/7, with no break.

In this case they are being charged from solar cells so they will have a break for at least 8 hours (in summer) so it doesn't matter, they'll be fine at 0.1C, if not even slightly higher.

Charge stability shouldn't be a problem if they're charged every day.

You can buy hybrid NiMH batteries which hold the charge more and come ready charged but their capacity is slightly lower than that of a normal cell of the same size.

 

[audioguru]

You can buy hybrid NiMH batteries which hold the charge more and come ready charged but their capacity is slightly lower than that of a normal cell of the same size.

All the Energizer Ni-MH cells are the new type. They are made in Japan maybe by Sanyo who also make the new ones.
Energizer's 9V Ni-MH battery is not the new type and is made in Germany.

 

[Mohamed Najiullah]

So NiMH batteries would be my best bet... Thanx guys.. Now the next step.. Any ICs for charging them under constant voltage and varying current?

 

[Mohamed Najiullah]

I've decided to use Energizer AA batteries..

https://www.electro-tech-online.com/custompdfs/2010/03/nh15-2450.pdf

Is it ok if i charge them under constantly varying current(100mA-500mA)?

What voltage should i give to a series of 4 batteries connected in series each of 1.2V?

Or would it be better if i charge them in parallel?

 

[Hero999]

Here's how I'd do it.

There's no need to limit the current, this circuit limits the voltage only.

It will only fully charge the cells if the voltage is above 5.1V.

I'm not 100% certain it's all right to charge NiMH cells in this manner, wait for Mr Al or someone who knows better to commend before building it.

EDIT:
This circuit charges three NiMH cells, if you need to charge four you'll need to increase the voltage.

 

[Mohamed Najiullah]

Here's how I'd do it.

There's no need to limit the current, this circuit limits the voltage only.

It will only fully charge the cells if the voltage is above 5.1V.

Do u mean the i/p voltage? I'l add an ic to regulate the voltage to 5V no matter whatever the i/p voltage is..

So no matter how long i charge the batteries they won't be fully charged?

And abt TL431, its a voltage regulator right?

 

[Hero999]

Yes, it's a voltage TL431.

As I said above, the input voltage needs to be above 5.1V in order to charge the batteries so if it's below 5.1V they will never fully charge.

 

[Mohamed Najiullah]

Yes, it's a voltage TL431.

As I said above, the input voltage needs to be above 5.1V in order to charge the batteries so if it's below 5.1V they will never fully charge.

U know i could set the ic to give a 5.1V o/p? What abt then?