Trickle Charge Batteries

[spike47]

Hi

I am wanting to know how I can rig up a simple trickle charge for 4 x AAA Ni-MH Rechargeable Batteries .I need them to run a 5 volt laser for a security set up I am making .

cheers

spike

 

[ericgibbs]

hi Spike,
This link is a good info source for batteries.
**broken link removed**

 

[spike47]

Hi ericgibbs

Thanks for your reply good info , but what I am wanting to do is make my own trickle charge with some electronic parts ie build my own to fit into a ip6 case .

cheers

spike

 

[audioguru]

Why do you need to trickle charge? Modern (for at least 3 years) Ni-MH batteries hold a charge for one year. Energizer and a Japanese battery manufacturer say that a trickle charge current should be less than 1/40th its mAh rating.

 

[spike47]

Why do you need to trickle charge? Modern (for at least 3 years) Ni-MH batteries hold a charge for one year. Energizer and a Japanese battery manufacturer say that a trickle charge current should be less than 1/40th its mAh rating.

Hi audioguru

Thanks for your reply , they probably will hold the charge for a year , but not if they are being used ! , I need them to stay fully charged I will have 2 Laser beams on 24/7 ! , and they need a full charge all the time to give a good bright beam to operate 2 CDS photo cells .

cheers

spike

 

[alec_t]

How much current is being drawn 24/7 by the lasers etc? You'll need to maintain a charge current equal to that plus a tiny bit more. Is it the total, or just that tiny bit, which you are referring to as the trickle charge?

 

[MrAl]

Hi,

The right way to do this is to use a power supply (the power supply) to power both the trickle charging AND the lasers.
In other words, the lasers main power is the power supply, and only use the batteries if the power goes out from the power supply.
Whenever the power supply is on, the batteries are getting a trickle charge. The lasers do not use any battery power at this time, only when the main power goes down, all other times they use the main power itself.
This preserves the life of the batteries.

If you have to run the laser for long periods without the power supply power you may have to use a different method to charge the batteries as they might take too long to charge back up on a low trickle charge like C/40.

 

[audioguru]

You need a battery charger IC designed to charge Ni-MH battery cells. It is smart enough to detect that the battery needs charging and it shuts off (or you can add a low current trickle charge) when the battery is fully charged. A few battery charging ICs have an output to power the load (your lasers) when there is power then it switches to the battery powering the load when there is no power.