Hi guys,

I was planning on using a battery bank in order to charge a separate battery with the help of the LM2577, but for some reason the battery bank stops after a few secconds and few flashes. I tried 2 battery banks and they both stop. Can someone tell me how does the battery bank detect when to stop and how can I bypass this?

 

Post your circuit schematic.

 

What battery bank (voltage and current specification)?
What battery are you trying to charge?
And schematic as requested by @crutschow

 

EDIT: The battery bank can supply 2A or 1A, it has 2 output ports(USB A), the output is set to 14V for a car battery.

 

What voltage is the battery bank?
What do you mean by '..can supply 2A or 1A' - which is it able to supply to the LM2577 circuit?
Are all the values in your circuit the same as the image in post #4 (except R1/R2)?

 

The battery bank has 2 ports, the first port can supply 1A, the second port can supply 2A, I can connect the USB to any port. Yes the values are the same and the LM2577 circuit works correctly, but the battery bank shuts down after a few sec.

 

If your battery bank is like the popular "Power Bank" products, the USB outputs need a minimum load to stay on. If the load is too small, they detect it and shut off after 10-20 seconds. The size of the minimum load varies but often is typically 100 mA. It depends on which controller is used in the Power Bank.

 

Assuming 100% efficiency (which won't happen) an output of 14V at 800mA is 11.2W. To get 11.2W at 5V from the powerbank would need a current of 2.24A so the powerbank would be overloaded.

 

The efficiency is 80 to 92%. What workarounds would you suggest for the undercurrent and overcurrent problems?

 

Limit the output current or use a heftier power supply.

 

Yes lower your output current and you should get better results.
The power bank can not put out the current you need right now (800ma at 14v after conversion) so you have to lower the output current which might mean lowering the voltage slightly.

You will also find that you lose some of your battery Ampere Hour rating because of the conversion.

 

The prolem really was in the overcurrent, but lowering the voltage and adding a series resistor did not help. I solved it by adding 2xLM2577 modules, the first one gives some very low voltage in order to limit the current and the second one increases the voltage to 14V.

Now I have a different problem, since the current drain is still high, the battery bank drops to "0%:" after a minute, but in truth its not "0%".