3cell NiMh charger circuit for backup

[oldmp]

Hi,

I'm looking for a simple NiMh charger, for backup use. It is for a GSM module, but the problem is, that the charger can't consume more, than 20mA from 12V car battery.. The NiMh battery pack contains 3*1200mAh NiMh cells...

The charging time is not critical, it is just for backup use, the NiMh battery will never discharged (i hope so )

the other variant for the charger is an automatic charger, which can consume 250-300mA, but it must shut down, after the charging...

It is for a car use, but i never wan't to discharge the car battery, whit this unit... so that is the main problem... Sometimes the car is standing more than 1 week at the same place..

Any ideas for this?

 

[nxtech]

Look at On Semis MC3334x series of battery charger control ICs. They also list a reference design for a charging circuit.

https://www.onsemi.com/PowerSolutions/product.do?id=MC33340

https://www.onsemi.com/PowerSolutions/product.do?id=MC33341

https://www.onsemi.com/PowerSolutions/product.do?id=MC33342

E

 

[inventor(y)]

Can you switch to Li-Ion batteries? They can do what you want with just 20mA or less. Ni-Mh batteries are not the best choice for this type of application.

For the Li-Ion charger: just make a constant voltage, constant current source. Set the current to whatever you want and carefully set the voltage to 4.2V for one cell. For better battery life you might adjust that voltage to something between 3.8V and 4.1V. But never go above 4.2V.

Regards, Inventor. Aka the battery geek.

 

[oldmp]

hi,

The space in the unit is made for 3cells, AA size... the Li-Ion variant sounds good, but i can' use them.. I try the mc3334x, it look's nice

 

[bikashh]

I've made a battery charger using MAX1811 for 1 Li-Ion cell.It is working perfectly. My question is can i use the same charger to charge 3 cell in parallel.Charging time is not a matter of concern.

thanks in advance