View Full Version : Supercharge your UPS(backup power supply)

01-03-2012, 12:04 AM
Many of us own a UPS(uninterruptable power supply) to keep our computers from going down and loosing data. Or maybe for some of us just from going down and having god knows what issues when we reboot a system that is normally up for months at a time.

The batteries in these things eventually give out. They're sealed lead-acid type. Similar to what is found in those self-powered jump start packs that have become popular in recent years. These batteries are expensive and if you have a big system may not last for more than a couple of minutes.

The UPS is basically an inverter and battery charger combined. When you loose power it kicks on the inverter, converting the DC power in the battery to AC for your computer. When power is restored, a trickle charge re-charges the battery.

Here's what I did with a free one I got many years ago:

Remove the 2 old batteries that were no longer working. This was a bigger UPS and it had 2 12V batteries wired in series for 24v. Most UPSs I've found actually only use one 12v battery. If the one you get your hands on uses batteries of some other voltage quit now, this won't work.

You need a car battery(in my case 2 since my unit used 2 batteries), something to put the battery in in case it leaks. Battery boxes are perfect, although the first time I did this I used a turkey pan, some wire(12gauge or so), and a fuse holder&fuse(15-20a should do).

Note that marine batteries are preferable for this application because they were designed to discharge slowly over a long time instead of rapidly over a short time. You can use a regular old car battery, just be aware it's not the ideal.

When you make your wire connections either solder & shrink wrap or wrap them up in electrical tape for safety.
Connect your fuse holder to the + side wire on the UPS, to the other end go to your battery + side. Wire up the - battery to - side on the unit. As soon as you have both + and - the UPS will have power so careful not to zap yourself.(it's designed to keep stuff running when the power goes out, remember). If you leave the fuse out until you're ready to turn it on, you'll have a little more control.

In my case with 2 batteries wired together it was + UPS to battery#1 + side, then battery#1 - side to battery #2 + Then battery #2 - goes to the UPS -.
Like I said, most units just have one battery and it will be more straightforward.

At this point you should be good to go. Plug in and use.

I've done this a couple times now and it works great. Backup power time is best measured in HOURS instead of minutes. Never had one problem until the batteries got old after a couple years and needed to be replaced(that happens with the un-hacked ones too). That said, I'm not responsible for your work so don't call me to complain if you burn your house down.

Here's my current setup in use..



01-08-2012, 04:18 PM
One other thing to consider with this setup - if you use car batteries (or marine batteries) they need to be in a well ventilated area. When these type of batteries are discharged rapidly, they tend to off-gas, which can be very dangerous if you are sitting next to it when this happens.

Check out the following:


Another good source regarding batteries is: http://www.k0bg.com/alternator.html - scroll down to the section on Auxiliary Batteries; it's a good read.

I also wouldn't use 12g ; considering the amperage theses batteries can generate, 12g is probably a fire risk. I would use no less than 4g, probably 0g would be better, but correct wiring sizing really depends on the length of wire and the load it's designed to carry. Keep in mind, even though a car battery is only 12v, it still has enough available amperage to kill, so be really, really careful.

01-08-2012, 05:15 PM
I've heard some of this before, and you're right in theory... but...

Unless you're in a small room with poor ventilation there really isn't enough hydrogen gas put out to cause an explosion. If you look at how much hydrogen is actually put off by a battery, it's a few small bubbles coming out of the electrolyte solution. Think about what a glass of coke would look like after sitting for half an hour... a few bubbles, but not a lot.

While it's absolutely true there's enough power in a car battery to burn up a 12g wire in a couple seconds, you're not going to be drawing that kind of current unless something has gone horribly wrong with your UPS- and that's why we always use fuses!

Think about this way: putting a bigger battery on won't change the current draw of the device(assuming the voltage is the same). Consumer/prosumer sized UPS units do not have 4 or 0 gauge wires in them. Usually 12g, maybe 10.

Or another way of looking at the same thing- if you put a bigger gas tank on your car, your car doesn't use the gas at a faster rate, it just has more available and can run longer.

01-08-2012, 07:22 PM
In my old place, back when I had a fractional T1 hosted before I got the co-lo, I had an old TES/APC 20U node backup system (the thing that's made to take the draw from the data center as the big flywheel systems ramp up and to smooth as the generators come up). I got the thing for free because it was an older one with a load of lead acids in it (turned em all in for core charges, woo). I read the specs on the $215 a pop replacement cells, they were essentially car batteries the manufacturer had put a tiny vent on so that they wouldn't puff and go boom. Other than the large loop going from the main breaker to the distribution panel and the ground wire, there wasn't anything in that cabinet bigger than 8 ga stranded copper. I know, I replaced most of it so I could put different terminal mounts on them and run car batteries.

Now I wouldn't seal that in a tiny room, but I never blew myself up and the thing ran a lot when they were re-doing the power grids in downtown Springfield.

01-08-2012, 08:46 PM
Just saying these are things to be aware of when selecting to do a project like this.

Once again, you have to know what the load is (current draw) to properly size the wiring as well as the distance. For a distance of less than 2 feet, you should be OK running 40 amps at 12v on 12g wire for a short period of time. Trying to run 400 amps at 12v over the same 12g wire for 25 feet would be a bad idea for more than a few seconds. I seriously doubt a simple UPS that would run a system or 2 would draw that much, but it's just something to consider. Last thing you want to find out is the wire is under sized and started a fire after losing main power.

01-08-2012, 08:52 PM
This is gonna degrade into engineers vs mechanics :lol:

I may seem caviler, but I've got a shepherd's crook scar from a 5 phase arc when I was 18 :look: I've also seen the destruction first hand from when an electrician hooked the wrong sized main from a Cat XQ2K into building service :run:

01-08-2012, 09:10 PM
Pulling 400A@12V would mean that your UPS is, like, 5KVA... and if that were the case it would be 24 or 48V and therefore using multiple batteries. I can't think of anything short of maybe a mechanical siren or the starter on a diesel engine that draws that much juice...

01-08-2012, 10:08 PM
My shop at the height of everything did.... but that's also why that thing had a bank of capacitors the size of 40's :look:

01-08-2012, 11:56 PM
Pulling 400A@12V would mean that your UPS is, like, 5KVA... and if that were the case it would be 24 or 48V and therefore using multiple batteries. I can't think of anything short of maybe a mechanical siren or the starter on a diesel engine that draws that much juice...

Those were random numbers to illustrate a point.

01-09-2012, 02:32 AM
I work at a PC Recycling center. We destroy UPS's on a regular basis. I should save one and try this simple little trick.