Battery Voltage Dilemma!

[cjdelphi]

I've decided i'm going to make a UPS for my pc, however ditching the need for a PSU in a blackout.. (eg power it directly by battery and the desktop psu becomes the power supply and charger)

My idea was to buy a car mini atx however it requires 12v max (a car's alternator / 13.8v) looks like it could damage it (150w dc to dc switch mode supply)

So i have an old lead acid battery, and 12v ah.. problem 1, to charge the battery it needs 13.8v to 15v...

But the dc dc device Input requires 11.4v to 12.6v max! (Unless the voltage sags on load?)

So sure i can use the existing 240vac pc psu to deliver 12v at 15amp to this device and it will be fine, but how am i going to sort out the batyery voltage issue, another battery topology? Or another buck converter lol

 

[Harald Kapp]

1. If you use a "car mini atx psu", then this unit should be able to handle the voltage from a car battery over the full range up to 14+ V. What use were a unit sold for use in a car if it doesn't handle the voltage from the car's battery?
2. You can't simply use an "existing 240vac pc psu to deliver 12v at 15amp". Any rechargeable battery will need a suitable charger with current and voltaeg limiting.

First you should be aware of the UPS (Uninterruptible Power Supply) topology you are going to use. The main principles are online UPS or offline UPS.
Next you need to decide a few parameters:

• power drawn by the load (PC).
• the time you want the UPS to keep the load powered in case of a mains outage.
• the means to handle the dropout of the UPS when the battery has been drained and mains is still unavailable. Usually you'd want to shut down the PC in an orderly manner before the UPS stalls.

The first two parameters give you an idea of the battery capacity required. Add a generous amount of spare capacity to account for loss of capacity due to e.g. ageing, varying temperature etc.
The last information will give you an idea how to supervise the battery voltage to generate a shutdown signal for the PC.
The search term "build your own ups" will give you heaps of ideas and information on this topic.

 

[Colin Mitchell]

Simply connect them in parallel and see what happens. Nothing.

 

[cjdelphi]

240vac to 12v 15amp via pc psu

From there into the atx mini car thingy, that powers the pc... if Harald is correct i can simply charge the battery with a regular lead charger (15amp one) and supply the mini atx car supply and pc from that..

But the specs, really does say 12.8v max input, but i'll give it go lol

Thanks!