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Desktop PC DC - DC UPS ? Answered

This might sound stupid, but I was watching some guys build batteries to Electrical Cars using Laptop batteries like Tesla does (18650 battery Cells)  and I got thinking about creating an UPS for my PC.

If Im not mistaken, most UPS convert AC to DC current and in a mains power loss they convert back DC to AC which is not very efficient I assume. So why not instead of going thru that process, why not power the PC components directly from the UPS in the event of a power loss or power supply failure??

My idea was to build a UPS that works completely on DC power, from its input to its output. So the PC power supply would charge it and the UPS would power the PC components in case of a power failure. I would be using this on a server so I dont need monitors or other stuff. All that would be require would be power regulators for 12V, 5V and 3.3V right?

Wouldn't that be more efficient? (the battery would last longer due to less power loss on conversions I think) 
And wouldn't it be cheaper? 

Thanks,
Ralms

Discussions

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verence

2 years ago

There is no such thing as a xV battery, that keeps itself
charged when connected to an xV supply and delviers stable xV when
discharged until empty.

You
will still have DC/DC converters and regulators. To get e.g. 5V for the
PC, you need either a battery with a higher voltage than 5V that can be
(lossy) regulated down to 5V or you need a DC/DC converter that
converts the changing battery voltage to stable 5V (potentially less
lossy, but still).

On the charging side, you need a voltage that
is higher than the battery voltage and circuits to control the voltage
(or current - depending on battery technology) to make sure the battery
does not overcharge (and does charge at all).

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RicardoM146verence

Answer 2 years ago

But isnt there less power loss by doing DC/DC converters instead of AC/DC and DC/AC?

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Downunder35mRicardoM146

Answer 2 years ago

Don't you think that if any of your thought would be viable that the big manufacturers would have done it already? ;)

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-max-

2 years ago

Here, watch this video. I think it will answer all your questions.

The type of UPS you describe is "online" or "double conversion" whereby power is basically converted to DC and then converted back to AC again 100% of the time. The types Dave talks about are just the basic fundamental designs. There may be other compercially availible options that are some sort of hybrid between the 3 main ones Dave mentions.

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Josehf Murchison

2 years ago

OK your understanding of a UPS is not quite right for all UPS's.

With some UPS's the line power goes straight through to your computer running the computer and a small amount keeps the batteries charged.

When the power goes out the battery power kicks in and converts the battery power to service power.

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RicardoM146Josehf Murchison

Answer 2 years ago

I know that, that is why I said that in the event of a mains power loss it will convert DC to AC back. Now while it has mains power there are many types where the most expensive ones dont do straight through and do the double conversion all the time for stability and safety. I was just wondering if every time you convert power from AC to DC and back to AC, if you dont have a bigger power loss than just doing DC to DC conversions.

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Josehf MurchisonRicardoM146

Answer 2 years ago

DC to DC converters are just as inefficient if not more in some cases as DC to AC converters, square wave and modified sine wave as much as 90% efficient, pure sine wave as little as 50% efficient.

A DC to DC converter converts the DC to AC passes it through a step up or a step down circuit and then converts it back to DC.

It does the same thing as a UPS only DC to AC to DC instead of AC to DC to AC.