Hello, I have developed a portable GSM alarm system that naturally requires the use of batteries.
So, I have space for 1 x 18650 in which I also utilized the use of "5V/2.1A Out UPS mobile power" from china only to realize that it powers the unit from the battery even if mains is available. Which doesn't make any sense.

So all that is required is to power the board from a 5v/3A adapter and once fails from the battery.

The voltage required to power the system is 5V with a maximum current required of 2A.

Any suggestions are welcome.

Thanks.

 

You have a "3.7V" battery and want to power a 5V GSM system. There is a problem.
You have 5V available but no battery charger.
Is less than 2 hours of battery time OK?
options:
You probably could find a "buck/boost" supply that will input 3 to 6 volts and output 5V.

5V 3A ----diode>|------- buck boost -------GSM (use Schottky diode)
5V 3A ---battery charger ---- 3.7V battery---diode>| ------buck boost ----GSM
When power is available the 5V does through a diode, drops a little but is boosted back up to power the GSM.
At the same time 5V drives the battery charger to charge the battery.

When power is lost the battery powers the buck boost.

The two diodes, act to power the buck boost supply from two sources, which ever is higher.

usb battery charger.
buck boost This will not work because it needs a input of 3.7V or more to work. Other wise it is close.

 

Thank you for your reply. I'll try it.
Quick questions please:
1. Can you recommend a suitable Schottky diode (e.g. BAT85, MBR560, etc..)
2. from the battery to buck-boost is it also Schottky ?

 

only to realize that it powers the unit from the battery even if mains is available. Which doesn't make any sense.

It actually makes sense. Cell phones do it all the time. You get higher peak currents from the battery.

Check some of the ideal diode parts at Analog Devices.

 

only to realize that it powers the unit from the battery even if mains is available. Which doesn't make any sense.

In many UPS designs, it does make sense.

For a data center UPS (AC), switching between mains and the UPS system is a little complicated. The AC frequency must synch up, or attached equipment might fail.

Even in a DC UPS, if you have to switch between mains and UPS, there will be a brief power interruption. Any attached equipment may fail.

So, since some sort of battery backup is necessary, it may as well be the UPS batteries.