As far as the handset is concern what you said is exactly correct. The cordless base unit don't have any backup power. when power goes up in no way I can make a call. What exactly I want is a online UPS (with 5V 1A rating) capable of powering the cordless base unit.Welcome to AAC!
Doesn't your phone have its own internal overcharge/discharge protection built in? As far as I know most phones do, and just require a 5V external supply for charging.
That's a good solution.buy the smallest offline UPS you can find
I am a software guy. Have no idea about electronics. Just want to do this as hobby. What all I know is the spec. of the base. The base requires 5V and 1A. You suggest me anything in this regard including battery. may be 30 mins backup is enough for me.Welcome to AAC!
Post your schematic, the type of battery you plan to use, the voltage range for the base, the low voltage cut out point, and any other relevant details.
Yes I can buy a UPS. But that is bigger in size and I couldn't find a UPS which delivers 5V DC directly. So I thought of making it. But I am software guy with no electronics designing knowledge. Hence I posted here to get some help.If you really want to build something, what you are describing can be done safely and without a lot of complexity. However, it might actually cost less to buy the smallest offline UPS you can find and plug the base station wall wart into it. On the base station, what is the power rating on the model number label? It probably is the same or less than the ratings on the wall wart. With the base station voltage and current, you can calculate how big a battery you need depending on the hold-up time you want.
Thank you5 V x 1 A x 30 min = 2.5 watt hours (W-h) or 0.5 amp-hours (A-h) at 5 V.
AA lithium batteries are around 2000 mA-h, or 2 A-H at 1.5 V.
3 AA batteries are 2 A-h at 4.5 V
So a Ray-O Vac lithium battery charger and 4 batteries will do this with a battery holder and a cable. $20 at Kroger, less on ebay. Charge the batteries once month to keep them topped off.
Before you can design anything, you need to understand the requirements.I am a software guy. Have no idea about electronics. Just want to do this as hobby. What all I know is the spec. of the base. The base requires 5V and 1A. You suggest me anything in this regard including battery. may be 30 mins backup is enough for me.
Thanks for the reply. Why I was asking for a circuit is, I want to do it all my self including the step down stage, Charging circuit, Over Charge protection of battery etc.To be clear, whipping up a 5 V UPS is not a complex or difficult task, and you would get loads of help here. It could be a simple as a small sealed lead-acid battery (SLA), the smallest version of what is used in standard UPS's, plus a 9 V or 12 V wall wart and 1 resistor. From there you could add circuit features to get a faster recharge time, some blinky lights, etc. Some people ask about a circuit because they can't see any other way, and some ask because they want to solder stuff with blinky lights. Your call.
Before you can design anything, you need to understand the requirements.
I suspect when you're specifying 5V@1A (or is it 6V, you've mentioned both), you're reading something from the base unit and not measuring or examining the circuit/schematic. If you don't know if the requirements, you can't design a proper battery backup. No battery chemistry that I'm aware of will give you exactly 5V (or 6V). What is the tolerance of the circuit in question? You could use an LDO regulator, but doing that when you don't need one simply wastes power.
You could use the backup only when power is interrupted or you could use it to always power your base unit.
You want a low voltage cut out, but what voltage is appropriate?
I get that you want to expand your knowledge but, before you can start narrowing options, you need to establish requirements.
Thanks. But what I actually want is a circuit so that I can do it all by myself. Just curious.Two things come to mind. One is that if you just need the functionality, you can buy an external laptop battery from eBay, keep that plugged in, and plug the phone into the output of that. If mains power ever goes out, you should have hours of talk time.
The second thought is that the 1A requirement is probably just for charging the handset. When the handset is fully charged, maybe the phone doesn't take much power at all, even if people are talking on the phone. If that's the case, you may be able to get away with 2-3 supercapacitors in series, directly across the 5V or 6V power inside the phone.
by Jake Hertz
by Jake Hertz