UNINTERRUPTIBLE POWER SUPPLY PROJECT

[grandestlama]

Hello,

Am currently designing an Uninterruptible power supply unit. I would like to implement the following features

1. An OVER-DISCHARGE protection scheme for the battery - such that the UPS automatically shuts down when the baterry reaches a specific lower voltage threshold in the absence of public power.

2. OVERCHARGE protection scheme for the battery - such that the the battery charging automatically stop when the battery is fully charged.

3. A form of output control/regulation such that when the battery voltage is reduced (before it reaches the lower threshold), the output voltage does not deviate much from the norminal value.

4. I would like to obtain a "reasonably" sinusoidal waveform as output.

5. Power cut warning (a beeping sound)

If anybody has a useful idea or any link or circuit diagram, PLEASE share it with me.

Thanks.

 

[tansis]

How a UPS works
**broken link removed**

The ever popular link to MAXIM ic application notes - battery chargers
**broken link removed**

You can get away with using just a pair of op amps for voltage sensing or use an LM3914 ic ,circuits abound on the web for voltage level indicators.

DC to AC step up conversion, again the circuits can be found on the web,
the output need not be a pure sine wave , the switch mode step down supply of your computer will run fine with a less than perfect waveform.

 

[grandestlama]

I would actually like to make a 1KVA UPS, not necessary for a PC but for any electrical equipment. I hear some equipments might not function with square waveform.

Thanks for your response.

 

[samcheetah]

yes thats one of the main considerations in UPS designs. u have to produce a perfect sine wave. producing a perfect sine wave is a bit harder than a square wave. but if u want to drive all kinds of loads with it u will have to make a UPS that give a sine wave

 

[tansis]

Here is the basic Inverter circuit, copied and repeated on many sites across the web, I know it says 300watts but larger transformers and higher rated transistors/mosfets will get you part of the way.
If I recall , the Maplin (uk) inverter project had the option to slave additional units together in order to achieve higher power outputs.
Basically you use the same time base / wave form source to drive many smaller transformers in synch.

https://www.aaroncake.net/circuits/inverter.htm

Inductive loads, such as motors should not be used with this type of circuit , apart from that it should be fine for most applications.
Somebody will have to help me out here , but i believe it is to do with the start up current requirements for AC motors , a PWM controller may make it posibble.

 

[Roff]

Here is the basic Inverter circuit, copied and repeated on many sites across the web, I know it says 300watts but larger transformers and higher rated transistors/mosfets will get you part of the way.
If I recall , the Maplin (uk) inverter project had the option to slave additional units together in order to achieve higher power outputs.
Basically you use the same time base / wave form source to drive many smaller transformers in synch.

https://www.aaroncake.net/circuits/inverter.htm

Inductive loads, such as motors should not be used with this type of circuit , apart from that it should be fine for most applications.
Somebody will have to help me out here , but i believe it is to do with the start up current requirements for AC motors , a PWM controller may make it posibble.

As I've said before on this forum, that circuit is a piece of crap. Unfortunately, it will live forever on the Web.

See
https://www.aaroncake.net/forum/top.../120V+inverter+again&Forum_Title=Power+Supply



https://www.electro-tech-online.com/threads/digital-pulse-analysis.8418/

 

[tansis]

Thankyou Ron for the benifit of your accumilated wisdom.

I was going to upload the Maplin schematic, but decided against doing so when I found this https://www.qsl.net/dg5sga/inverter.htm

 

[Nigel Goodwin]

Thankyou Ron for the benifit of your accumilated wisdom.

I was going to upload the Maplin schematic, but decided against doing so when I found this https://www.qsl.net/dg5sga/inverter.htm

That looks somewhat better! - it certainly has more chance of working than the other link :lol: