Battery Charger --- Technical Issues

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Dear Power Integrations, I am designing +13.8V/1A battery charger for emergency light application by using TNY278PN, secondary zener diode feedback, and LowDrop-CC (0.3V) circuit for this battery charger with good efficiency. The control current setpoint is approximately limited at 1.2A. These informations below are our battery specifications: - Seal lead-acid battery 12V/12AH. - Standard Use: 13.5~13.8V that initial current has no limit. - Cycle Use: 14.4~15.0V that initial current is less than 3.6A. I firstly tested with electronic load in CR-mode, the CC circuit is normally operated and cut-off at 1.2A with approximation. My problem is if I directly connected this 13.8V charger with this battery which has the current voltage at 11.5 volts (after discharging), the charger looks auto-restart (Hiccup) mode and can not charge more current into battery. Then I try to disconnect CC circuit from this charger, it also looks auto-restart mode. I guessed that the battery seems draw the output current from charger more than 1.5A during initial charging in first time. Therefore, I try to charge it with higher power battery as such as 13.8V/30W, it can be normally charged. I'm not sure this battery charger specification is suitably selected for this battery or not. Attached pdf file is shown you my battery charger circuit. Please kindly advise me how to solve this problem. Thank you and Best Regards, Terayouth W.
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Battery Charger 13.8W.pdf45.77 KB

No. something does not make sense here. Even if you charged the battery with smaller charging current the battery should start charging... the only difference is that it will take a little longer time to charge. It should not go into auto restart as you describe. I can think of two possible reasons this may be happening
1) The size of the device you are using TNY277 is too small for this 17 W design. Plus you are using standard current limit mode. I would use the TNY279 instead. (This will require transformer redesign) Please attach your PI Expert design file so I can take a look and comment further...

2) Another reason it may be doing this is that you do not have a UV lockout circuit. Can you connect two 2Meg resistors in series from the DC bus to the EN/UV pin and retry? This is will make sure the switch does not try to start-up unless it has sufficient voltage to continue to deliver the power.

Dear Spock, Thank you for your recommendations. I need to solve and close this problem but it still not initially charging the battery if the backup voltage of battery is less than 11.5 volts. If the backup voltage of battery is higher than 12 volts, it can be normally charged. The main root cause is the initial charging current is higher than 1.5A so the switched charger will be cut-off. I try to connect a resistor or NTC thermistor with low resistance series between charger and battery to limit the initial current, switched charger can be normally charged but I thought it is not suitable solution because a resistor will be too hot during initial charging. How to solve this problem correctly? Please kindly advise me. Attached files are shown you PI Expert 7 worksheet and transformer designs. Thank you so much. Terayouth W.

Can you attach your CV/CC characteristics? The value of R10 in your schematic sets the CC set-point. By my calculations this set-point is at 1.8A which is higher than what the supply was designed for. Can you try to increase R10 to say 0.33 ohms and see what happens.