UC2906 battery charger entering and staying at float stage (Pls Help me :( )

[Labmat]

Hi All,

I have a problem with my battery charger circuit.
Basically, I have designed the system to charge 4 batteries at once from a single power supply using 4 individual UC2906 battery charger ICs. Given below are the details.

Vsupply = 18V
Isupply = 3.6A

Battery requirement:

Battery technology: Lead Acid
Vbattery = 12V
Capacity = 2.6Ah
Charge regime = C/5

now I used the application note and the datasheet from TI to design my circuit and it kinda works. Here is my problem.
My application requires me to disconnect charged batteries and connect discharged batteries. This is done via relays which are controlled by Labview USB DAQ 6009. The whole point of using Labview is that it can calculate if the given battery is good or bad. SO it employs a Charge - Discharge - Charge test.

what I have found is that when I connect a battery that is in need of a bulk charge, the charger is stuck in float mode and will not go into the bulk charge mode. I am truly lost here as I first thought it could be noise putting the system in float mode. but even with the caps in place, the result is the same.

Can any one please help me out?

thanks
Labmat

 

[Labmat]

Here is my circuit diagram.. if this helps you guys out

thanks

Labmat

 

[Labmat]

From the application sheets, I know it says that the battery voltage needs to go below 90% of the float voltage for it to be kicked into the Bulk charging mode.

but even if I connect a battery which is below the 90% threshold, the unit goes into the float mode instead of the bulk charge mode.

Thanks