Make Your Computer UPS Last for Hours Instead of Minutes

Intro: Make Your Computer UPS Last for Hours Instead of Minutes

For what would appear common sense to me, but perhaps not to all, I have all of my computers on UPS battery backups. After getting frustrated when the power flickered one day, I immediately went out and purchased a UPS. Well, shortly after, the power went out for longer than the battery could keep my computer afloat. I needed a better solution!

I wanted my UPS to be able to last for at least 60 minutes in a power outage. I needed more power! My solution: Car batteries.

Materials:
UPS that is rated at least double what you plan to draw (see step 8 to understand why).
Wire (12 awg or larger; two different colors)
Solder
Heat shrink tubing
Car battery with terminals on the top
Adapters to go from the car battery terminals to threaded rod.
Wing nuts the same size as this threaded rod
Wire crimp terminals that will fit over the threaded rod.
Plastic case for your car battery
Inline Fuse holder (radio shack)
30 amp fuse for holder (any auto store)

Tools:
Screwdrivers
Wire cutters
Wire strippers
Soldering iron
Scissors (optional)
heat gun or alternative
Drill
Drill bits

STEP 1: Evaluate Your Needs

I was trying to power two computers (desktop and file server), and two flat panel monitors. My total power consumption was roughly 500 watts peak. (yikes!) Currently I was running on two 300 watt UPS's (NOTE: VA is not equal to WATTS. Find the WATT rating) with one computer and one monitor on each. Even though the two monitors were hooked up to the same computer, I needed to distribute my power load more evenly to get longer battery life out of my petty UPS's.

CAUTION:
I discovered the hard way after nearly starting a fire and destroying a UPS that you need one that is rated at at least twice the wattage you are consuming. They can't handle being run for longer than a few minutes at this rating, but the batteries die before it's a problem normally.

So I now knew I needed 500 watts, and I wanted 60 minutes of power.. that means:
P / V = I
500 watts / 120 volts = 4.16 ampere hours (at 120 volts)

UPS batteries are usually 12 volts, but some are wired with two batteries in series. Check yours out first to make sure you won't need two car batteries.

So, assuming 12 volts, that means that, after adjusting for the voltage differences, I need a battery with at least 41.6 ampere hours. (yeah, I know there's inefficiencies in the UPS, but lets keep math easy)

STEP 2: Remove Battery From UPS

Unplug the UPS from the wall, and unplug all devices from it.
Remove any screws you fine, and open up the case.
If you are as lucky as I was, the battery will have terminals that you can slide off. If not, just cut the wires as close to the battery as you can.
Once you have removed the battery, you will find something like you see in the picture

NOTE: Pay attention to polarity on the battery, and which wire went to when polarity.

STEP 3: Extend Wires on UPS

The wires that are in a UPS are typically not long enough to reach much past where the battery sits. We will need to extend them to reach our car battery.

Cut off the the wire terminals (if any) on the wires from the UPS.
Strip at least 3/8 of an inch of the wire on the UPS
Strip at least 3/8 of an inch of the wire we are extending with.
I used a metal crimp to help me get a great connection, but this is optional.
Solder the wires together. This solder joint needs to be able to handle high current. We will be drawing lots of power through here and if we have a voltage drop, the UPS won't last as long.
After making sure the joint is well soldered, place some heat shrink over it, and seal it up good.

Note: Use colors that make sense to you, and will allow you to remember the polarity

STEP 4: Drill Hole for Wires

Next we need to make a place for the wires to leave the UPS and go to the car battery.
I drilled a hole. Use whatever size will fit both of your wires.
Add a strain relief so you can't pull on the joints you made, or on the PC board in the unit. I simply tied a knot in each of the wires.
Next pull the wires through the hole, and carefully put the unit back together.

Note: Remember the polarity!

STEP 5: Prepare Inline Fuse Holder

Since this is high current, coming from an extremely high current source (car battery), we need a fuse. and you want it as close to the battery as possible.
First, strip the wire on the fuse holder.
Place heat shrink on the wire.
Take your crimp wire terminal that is sized for the thread on your battery posts, or adapter and crimp it to the wire. Then solder. Nothing is complete until it's soldered. Why solder? It conducts electricity better. The joint won't get hot, and you will have a less drastic voltage drop.
Next shrink the tubing.

On the other side of the fuse holder, strip the wire, place the heat shrink on, strip the hot wire you've recently added to the UPS and solder together. Once completed shrink the tubing.

STEP 6: Prepare the Remaining Wire

Next, using the same strategy as connecting to the inline fuse holder, connect the Crimp terminal to the end of your ground wire, Solder, and heat shrink.

Remember: Put the heat shrink tubing on before you put the end on.

When you done you should have something like:

STEP 7: Attach to Battery, and Test

Next, attach your battery terminals to the battery, and then your wires to the terminals.
Insert a fuse in the fuse holder.
And turn on your UPS.
It will take a long time to charge the battery, but it will also last for a long time in a power outage. Under this setup mine lasted for around 1.5 hours.

Be sure to put the battery in a plastic case with a lid, as, if something were to go wrong on the battery you would want to contain the acid as much as possible. Also, this will prevent you from dropping something and shorting out the battery.

STEP 8: A Word of Caution

I learned this the hard way.. it cost me a UPS, and nearly a fire.

The transformer in these UPS's are cheap. They are not designed to be run at 100% capacity for extended periods of time (such as what you will be capable of using this size battery) When I ran my UPS's at 300 watts for more than 30 minutes, the transformer melted through the case. When I pulled out my infrared thermometer it read nearly 400 degrees F!!

I had to redesign my system. I chose two UPS's that were rated at 600 watts each, but used 24 volts (2 twelve volt batteries in series). Under my new setup, I have over four hours of backup capacity as I have two car batteries.

Comments

[JEstebanMD]

If you plan on using your UPS for more than about 30 minutes, or if its potentially necessary, I would recommend using a quality 8 gauge pure copper stranded wire*. Early in my college career I worked part time installing custom car audio and video systems at a friend's shop. If I had a dollar for each time someone came in after a self install with a melted wire I wouldn't be working now. Think of a straw...the thinner the straw the harder you have to suck. With electricity, that "sucking energy" manifests as heat which is bad!
*The thinner the individual strand, the more flexible and more expensive the wire will be)

[James M.L]

Would a smart battery charger + auto or marine battery + dc/ac inverter function as a UPS?

[boobbert]

A UPS monitors the AC voltage input and switches the output between directly connected to mains (AC) and connected to the output of the inverter. A good UPS is also able to step up a low voltage (so given 100v mains, your computer still sees 120v without going on battery). The actual charge circuit is only intended to charge the battery when mains is powered. the charge circuit does not provide enough power to both charge the battery and run the inverter.

A small battery charger (12v 2a) can only provide 24w. Even if your inverter is 100% efficient (it's not), your load would be limited to 24w in that case. A larger battery charger (6a) is still limited to 72w.

[HaroldG29]

You would want some type of way to feed wall power to your stuff until the power goes out as many inverters output crap 60HZ that is absolutely horrible for your electronics. It would make no sense to convert 120vAC down to 12vDC, then back up to 120vAC, as this wastes a tremendous amount of energy. I would recommend 3 2-way relays (The kind that has a common and a normally open and closed.) and have them switch on the Inverter and connect it to the output and isolate the inverter from mains.

[darryl.kinslow]

Yes, that's essentially what a UPS is, except deep cycle batteries would be better.

[saadland]

Hi all, I know this post is very old but I will add some analysis and advises.
From my understanding you "fused" to UPS able to charge 7A Battery to be able to charge a bigger battery, this case a 40-50A Battery. I hope you explained that in your able from the start, and also provide a schematic since it is a electric project, and it is always easier to have a schematic.
1. Deep cycle battery or marine battery is used here, smart move, dont was your time with car battery, because even if you see a car battery rated 70A or more, it doesnt mean those kind of battery are made to produce 70A during a long period of time, not everybody understand this!! They are rated 70A or high, to be able to give a proper kick to start the engine, that all, after all that the car is running on gas, not on voltage either on Amps... I had to point this because some think because I got a high rated car battery so I may use it! You may be you should first know what kind of car battery it is!!
2. if you want do this type of project, with only 2 backup UPS 7A, do not go with to high rated battery!! 50A max!! Why, because the 2 UPS (2 in the case) are gona struggle constantly to be able to provide this big amount of current asked for such high rated battery (50A in our situation), to be able to fully charge it!! Even the autor say that it take a lot of time to charge it completly. Perso for me time is not an issue, I prefere slow and safe charging.
Plus
3- Dont attempt this project with Backup UPS that autoShunt down after some time, why?? because those Backup UPS are made just to give you anough time to save your work, and to shutdown your PC when there is a Power Outage!! Even if you increase battery capacity, you wont be able to keep the UPS running because the running time is set by the chip inside the UPS! Not necessarly batt the battery capacity...
4. it is a good idea to add a PC fan to cool the transformers, cause they gona get pretty hot!! not necessarly running them at 12v, even 5v or 9v is a good start, and giving an acceptable noise, or drill some addtionnal cooling hole into the UPS case, for additional passive cooling...

Thx for everybody that contributed to this ible, there are a lot to leaning about UPS and battery from the comments

[boobbert]

It's a 40Ah battery, not a 40A battery. Huge difference between Ah (amp-hours) and A (amps). You don't need a 40A fuse for a 40Ah battery. You need a fuse that matches the max amps you're going to pull at 12v (or rather, 24v in his case). The 40Ah is the capacity he needed for 60minute runtime. I think he sized the fuse for 300w (half of 600w) for each of the UPSs at 24v. That should be 12.5A by my math, so 7 does seem low, but not an order of magnitude.

And yes, the charger circuit in the UPS is going to charge this really slowly, who cares? If your power goes out frequently for more than an hour in the same day, this probably isn't a good solution; look into a natural gas generator maybe.

I really like your cooling fan idea. And you might be able to add it to the relay that powers the inverter so that the fan isn't running if the UPS is running from mains.

[jcorbin787]

Did your UPS automatically adjust to the extra amp hours with the extra batteries? Basically what I’m asking for example I have a load going and the power goes out. The UPS says it has 18 minutes of power supply left until shutdown. If I were to add 4 extra 12v sealed batteries (the ones that are in the UPS) so it will have a total of 6 batteries. When the power goes out will it display the correct time left with the extra batteries? Example: With the same load as the previous example. Will it now read 55 minutes of power supply left until shutdown? Basically will UPS display the correct amount of time remaining even with the extra batteries? Thank you in advance for answering my questions. -J

[JUICER]

Do not use Car Battery used for starting the car, it has a low recharge cycle opt for a Deep Cycle battery. They are meant for a constant load where a car battery is used to supply a High amperage for starting the engine.

[StephenM34]

Speaking from experience here, what you have done may very well destroy the charging circuit of the UPS. The extra load of an exhausted car battery (obviously after hours of use) could cause the Charger to fail. I too thought I would be clever and try this. Lets just say, I now have a brand new, larger backup supply designed to take their additional battery packs.

I'm not suggesting that no-one gives this a go, just that those doing so should be prepared for this failure.

[Murmur1986]

I have a 430W UPS with a dead battery. I want to power a 55" LED TV during load shedding. I think that 430W is roughly 4 times as much wattage as I need, probably closer to 5 times. I also believe I need minimum a 6ah battery to cover 4 hours, in the best case scenario (no losses). I plan on making a box with an intake and exhaust fan for cooling, and will position the components optimally for cooling purposes.

My questions are:

Is an 18ah battery big enough to power a 55" LED TV for 2.5 hours, without damaging the batteries?

Will my UPS be able to charge a 12v 18ah battery? Even if it takes 20 hours?

Who killed Roger Rabbit?

[Jason South Africa]

@Murmur1986

Your 430watt UPS is theoretically capable of powering your TV since the TV is probably less than 100Watt. Fairly similar to an office PC & monitor. Mid upper range gaming PCs pull just over 200Watt under load - based on my Core i7, 32GB RAM, 7x 3TB HDDs, GTX2060 Super - it pulls around 212Watt playing 2021/2022 games at 4K. Excluding the monitor...

An 18Ah battery is probably not going to give you much of a lifespan unfortunately. Your UPS is probably equipped with a 9Ah (or maybe 7Ah) battery as standard, so an 18Ah is only double the capacity/ runtime.

UPS internal inverters are sadly rather inefficient and waste a lot of energy compared to dedicated inverters, the reason being that a UPS is designed to run for 15 to 20 minutes for a computer user to save their work and shut down, or for the generator to kick in and power the building.

The UPS would be able to charge an 18Ah battery, time would be the limiting factor mostly since chargers don't have a high output (you've probably seen that they have fairly thin wires).

For a load shedding TV power solution you'd be best off getting a dedicated inverter, e.g. a 650watt camping/caravaning inverter and a car battery/ or a deep cycle battery of say 65Ah or a pair of batteries if your inverter of choice is 24V instead of 12V. Though I suggest a camping unit because many of them are 12V. And get a nice automotive charger like an Optimate.

Asking at the camping shops will get you a lot of information for free based on their experiences so far battery life and so on are concerned.

Also, going with a big'ish battery is better, the less you draw from it, the longer the theoretical life span of the battery will be.

The moment you start using UPS as a solution for loadshedding you'll start to see how quickly those little 9Ah batteries go vrot. Running them flat twice a day for a week or two will already start having a negative impact on how long they can deliver.

So yeah, rather buy a car battery for a grand and a half than spend R450 on an 18Ah that's going to go bad in a month or two and need to be replaced. They aren't covered by warranties for anything other than manufacturing defects.

Alternatively you can go with a real inverter +/- 5kVA and a Lithium Iron-Phosphate battery or two. That sort of setup is in the region of R50K, plus another +/- R18K for 4x 650watt solar panels. That would get a smartly configured home almost totally off grid. You'd literally just power your geyser now and then from mains.

With the price of electricity in South africa, spending 40 grand on just panels and an inverter will break even after maybe 4 years - I paid around R16 000p/a for electricity before the most recent price increase.

TBH I don't actually know what I'm paying right now for electricity because I haven't received an invoice for more than 18 months and my Tshwane metro online account is "inaccessible".

I just go to Pick 'n Pay and drop 3 grand every month. Should be okay since I switched to a gas stove/oven end of last year and every light is now LED... so far so good, they haven't cut off my power yet...

[Jason South Africa]

Flash forward a few years...

I live in South Africa, we have power problems because there is only 1 parastatal that has the electrical supply monopoly in South Africa.

Due to gross mismanagement and squandering of taxpayers funds, maintenance on power generation, power distribution etc. has been neglected nationwide.

The unfortunate upshot of this is that we regularly have scheduled power outages to divert power to other areas when repairs need to be affected. Google "South Africa Load Shedding" if you need more info or a chuckle.

I've been meaning to buy an expandable UPS for ages now but haven't ever gotten around to it, we've kind of just gotten used to living with the scheduled power outages.

The UPS I was looking at was the APC Smart RT2000 -- it's a 2kva "48volt" sinewave unit with a jack on the back to daisy chain in more "48volt" battery banks.
The unit features an RS232 like interface for programming, but not quite RS232.

https://www.apc.com/shop/id/en/products/APC-Smart-UPS-RT-2000VA-230V/P-SURT2000XLI

The APC banks are 48v x2 packs per bank (the UPS is 48v x1 battery pack) and according to APC the charge circuit can handle 10 banks inside of 12 hours - the UPS being 9Ah and the banks being 18Ah or the capacity to charge 189 amps worth of batteries (and 22U of rackspace) in 12 hours as the recommended maximum, but as they also state, there is no theoretical limit on battery banks as long as sufficient time is given to charge them...

Not a shabby little UPS if you are looking for a stretchable unit that doesn't need to run a server farm, just a few hundred watt.

It is however now discontinued, and has been replaced with an RT2200 or some such. Not a problem for me since a client hospital recently threw out a perfectly good RT2000 that was running the PC on a Philips screening table, and paid us to replace it with a 3kVA unit, and I was requested to please dispose of the "faulty" unit because they didn't want it any more.

As I'd suspected one of the individual batteries had failed, it's neighbour was also quite sick and the other 2 were still pretty decent

I've since cleaned and serviced the unit and replaced all 4 batteries with 4x new 9Ah Yuasa batteries and it's working like a charm, gives me 4 hours as is running my home networking gear.

Now to fix the front grille that's been kicked to hell, and shop around for another 48v single deep cycle battery or some big 12's - something with a similar charge profile.

TL;DR Don't be afraid to adopt a dead UPS, it's quite possibly just the batteries that need replacement, and the expandable units offer a lot more flexibility provided you access their software and tell them what their battery monitor is looking at.

[Murmur1986]

If you have time, please check my comment above out.

Basically, do you know if a small ups will charge an 18ah battery?

[lightmaster]

Planning to do this with 2 100Ah Marine Deep Cycle batteries I have. To overcome the very slow charging of the UPS, it should be fine to connect a 12V battery charger and maintainer, right? External charger will do the bulk of the charging while power is on and will be off when mains power is off.

[tommixoft]

All the wires used in this project are WAYYY too thin!

[xenoscientific]

The main problem with this project is that lead acid batteries for cars will go bad after about a year if they are not used. This is common knowledge -- and I know this from personal experience from having thrown together a such a UPS from an inverter and an extra car battery I had laying around. If using a car battery (and maybe even a deep charge lead acid, don't know about those so much) it needs to be discharged and recharged every so often. A really nice project would be to design an Arduino based UPS that both functions as a UPS and maintains the car battery. The only problem is if the power happens to go out just as the system has (partially) discharged the battery. But it is only a partial discharge. Another solution is to have two lead acid batteries.

[abdo421997]

I made it!!!
I also put in two cooling fans (one sucks in and the other blows out air)
I ran it for hours (although only a 120 watt laptop)
It was as cold as in idle
Before it heated up alot even when used for 10 minutes
I am using a seperate charger (20AH) to charge my 100AH flooded battery (I know this is not ideal but I change one each year already so it doesn't matter, the cheaper the better )
And it is working like a charm

[IsaacP3]

i HOPE THAT BATTERY IS DESIGNED TO SIT ON THE SIDE LIKE THAT!? Lead acid's don't like this type of thing usully.

[RamK4]

how long can you run your pc now? how many hours?