computer power supply with built in battery backup

Hi Matt,

The APC supplies are set up like this because desk top computers and monitors can not run directly off a single DC voltage.  The ATX power supply creates + and - 12 volts, + 5 volts, and perhaps + 3.3 volts. The monitor probably runs on yet another voltage and if you have any other accessories they may also have different voltage requirements. By having the APC turn its battery backup power back into 120 VAC the individual power supplies can do their jobs of producing all the different required voltages.

John

Hi Matt,

The APC supplies are set up like this because desk top computers and monitors can not run directly off a single DC voltage.  The ATX power supply creates + and - 12 volts, + 5 volts, and perhaps + 3.3 volts. The monitor probably runs on yet another voltage and if you have any other accessories they may also have different voltage requirements. By having the APC turn its battery backup power back into 120 VAC the individual power supplies can do their jobs of producing all the different required voltages.

John

Informative!

Yes thank you I know that part.  They make 12 volt DC-DC power supplies for computers.  I want to avoid the power loss of conversion and only switch to DC once like a Laptop does.
In searching I think I may have found some products that would fulfill my needs. 
OpenUPS to regulate charging and pulling from Battery.  http://www.mini-box.com/OpenUPS?sc=8&category=981
and this 250W DC-DC power supply to take the DC from the openUPS and step up and down for the PC.  http://www.mini-box.com/M4-ATX?sc=8&category=981
Combine that with a LiPO battery pack and it's awesome.

There have been a couple of products on the market that do appear to achieve this sort of functionality. Something like this:

eNSP3-450P-S20-H1V - ATX Power Supply with UPS Function

The PSU unit replaces the existing ATX PSU and the battery(s), are designed to mount in a standard 5.25" drive bay.

I've been interested in this idea for a while myself as I've generally found the external UPS solutions to be notoriously unreliable whereas in comparison the laptop type mains/battery arrangement appears to be very reliable.

Hi Dave,

It looks like an interesting idea. At least it would conserve volatile memory until the unit could be shut down. Of course if you wanted to be able to see what you are doing you would still need power for your monitor.

John

Hi John,

For me it's more a case of covering two scenarios:

1. surviving the short blips that are long enough to cause a reboot
2. clean shut down of the system if the power is off for more than 30 seconds, as in most cases that means its going to be off for an hour or so. So saving files, suspending open virtual machines then a shut down.

So for me the monitor issue is not necessarily that big an issue, I'm not looking at continuing to work as normal through a significant outage.

These days though the chances are you could still remote in from a tablet if you really needed a terminal and grab any vital files you might need before powering down the desktop.

More often than not though I've found that the external UPS unit lets you down when you need it the most anyway. Out of the 40 or so UPS devices I've worked with, only the original APC RS1000 and RS1500 units still managed to perform to spec' after a year of use. In comparison I have a 7 year old laptop still working on its original battery.

Hi Dave,

It sounds like you have done a good job of analyzing what will work best for you. Personally I took an old APC and installed an external car battery. I have voltage and current monitors on the battery and I test it for proper operation monthly. I also have a separate APC on my Modem and Router which is tied to the local cable service. In the last couple power outages I was able to continue to work and monitor the weather on the computer without interruption. Here are a couple picture of my setup.

John

Hi John,

That's a nice set up you have there.

I like the idea of separating the electronics from the battery. I currently want to do something like this for a USB / coaxial power bank type scenario as well, as I've not been having much luck there with off-the-shelf products lately either. Was thinking of using some deep cycle leisure batteries as the power source as used in caravans and motorhomes for standby power.

The last significant power outage here took out the city's main substation (it is next to a river which burst its banks) last winter and left the city without power for 30+ hours over a weekend, then for another 10+ hours the following afternoon. The cell phone network was disrupted as were VDSL network services as the fibre convertors in the roadside cabinets require power. Landlines remained up as the telephone exchange had back-up supplies and I believe ADSL services stayed up for those that haven't yet moved to VDSL. It also took out many of the modern radio services. So it was dark, raining heavily, main roads were flooded, cold and for many people no access to telephones, information or entertainment. 

I thought I was better prepared with my solar charged standby 12v golf battery and mains inverter however I was to find out the hard way that it had partially dried out (downside to maintenance free batteries) and had little charge left in it but just enough for the battery indicator to remain green. Perhaps a similar reason behind a number of my UPS battery failures. The inverter automatically shuts down on low voltage to leave enough juice to still start the car it is intended to be connected too.

Rather than attempting to keep a desktop running throughout an outage like that, I was thinking more of just being able to keep something smaller like a tablet and a few accessories running which would at least allow for access to ebooks and videos, and be able to access data from USB drives, along with some network connectivity if it was available.

We used those type UPS in a former vocation.

If I recall they feed the mains directly through to the output via a transformer, that can compensate for +- xx%.

When the mains finally drops it then starts the inverter.

Much better than other UPS that are always driven from the inverter ...

Hi Mark,

Yes, this unit passes the mains through to the units when mains is available and charges the battery to 13.6 volts. When the mains drop down it switches on the inverter quickly enough so that the interruption is not relevant to the computers power supply. I was not aware that there was a different approach than this.

John

I was not aware that there was a different approach than this

Most UPS use the mains as a battery charger, and the inverter runs the load using the battery (which is being float charged normally)

Mark