NIMH Charging

[horizontech08]

Hi !

I am looking to put 4 AA NIMH batteries in the PCB design. I am looking
to find simple example and schematics to make slow charger with 12Vdc
input ?

I can use pic to monitor the charging !

Thanks for your help

Alain Tanguay

[SherpaDoug]

Look at the Maxim DS2715 or other battery charging chips from Maxim. Some of the more advanced chips have serial data readable by a PIC.
_________________
The search for better is endless. Instead simply find very good and get the job done.

[libor]

Depends on the application how much intelligence I would put into the charger.
Is the battery a backup only in normally from mains operated device ?
Or is it a charge it quickly - then take it with you - device ?

[Steve H]

For a really simple slow charger simply use a voltage source that is 50% to 100% higher than the fully charged battery voltage (calculated at about 1.5 volts per cell) and use a dropping resistor (with the value calculated to 1.25 volts per cell) to get a charging current of about C/10. Where C is the 1 hour amp rating of the cell (or pack).

This is the way it was done in the 'old days' to get a 10-14 hour overnight charge. You can't get cheaper or simpler than a single resistor.

:-)

HTH - Steve H.

[PCM programmer]

NiMH batteries require special procedures to charge them.
They require protection to prevent overcharging and they require
temperature monitoring. Read the User's Guide for the Microchip
MCP1630 NiMH charging chip:
http://ww1.microchip.com/downloads/en/DeviceDoc/51505b.pdf

[Steve H]

That's a nice chip - but it is a C/2 fast charger really. I thought the original question was for a slow charger - slow charging or 'Trickle' charging can be safely done unmonitored by keeping the charge current to around the C/10 rate. There are many commercial chargers / products that operate like this and work reliably.

HTH - Steve H.