Battry charge cut & on

[Rakesh Sharma]

I need a circuit for my Battry Charger Cut off after 7.2v DC.
It is a emergency light and i want automatic cut off my (6 Volts)
battry charge with 9-0-9 ac transfarmer and on low position automatic
charge on.
Battry- 6 Volts
Transfarmer- 9-0-9 Volts
Charge cut of Volt - 7.2 V
Charge on Volts Below - 6.0 V [/quote]

 

[Nigel Goodwin]

I need a circuit for my Battry Charger Cut off after 7.2v DC.
It is a emergency light and i want automatic cut off my (6 Volts)
battry charge with 9-0-9 ac transfarmer and on low position automatic
charge on.
Battry- 6 Volts
Transfarmer- 9-0-9 Volts
Charge cut of Volt - 7.2 V
Charge on Volts Below - 6.0 V

You don't mention what type of batteries?, and this is crucial to a charging scheme.

Assuming they are either NiCd or NiMh a simple voltage monitoring method isn't much use - I suggest you google for designs, 'delta V' charging is one popular method, or temperature monitoring of the batteries.

However, for an emergency light it's probably not required anyway, just leave the batteries on permanent trickle charge - this is a charging level which will in no way damage the batteries, and should be given in their specs.

 

[Edmond]

Battery charger.

Like Nigel said, the charging method depends of the battery type (chemicals). Charging the Li-ion batteries, at the end (4,2V/cell) the charging current must be cut off. In other case the battery may explode. At the end of charging the Ni-Cd or Ni-Mh batteries, you can use the trickle charging methods. The trickle charge current must be C/25…C/50 (C=capacity in Ah). I think that you are using an SLA battery. The SLA battery’s cell voltage is 2V, then you have 3 cells serial connected 2*3=6V. The SLA battery must be charged with constant voltage and charge current limit. The maximum current is C/10, so you can’t use a rapid charger. The maximum voltage limit is 7,2V (2,4V/cell). You can use a 7,2V power supply with C/10 current limit as a charger. The current will drop down at the end of charge. You can live the battery on the charger.

I am familiar with a lot of batteries types and chargers. I will send a simple charger schematics for your battery, if you send me the battery type. What does it mean: "Transfarmer- 9-0-9 Volts" ?

 

[kinjalgp]

Re: Battery charger.

What does it mean: "Transfarmer- 9-0-9 Volts" ?

9-0-9 volts means he is using centre-tapped transformer giving two 9V outputs with respect to the centre tap.

 

[samcheetah]

try the MAX846A which is a multi-chemistry (Li-ion, NiMH, NiCd) charger. or try the MAX713 which is a NiMH/NiCd charger. there are pretty good application notes for battery chargers on the maxim website. i would suggest that you first find out which type of battery you are charging and then see if the above recommended ICs fullfil your need

i hope that helps