Hello!

I've seen a few YouTube videos that explain how to turn a regular cheap computer UPS into a UPS with a huge runtime by swapping the 12V 7ah battery for a large deep cycle marine battery.

This seems pretty straightforward as long as you have basic electric knowledge, and i'm seriously looking into this. Things to keep in mind :

-The built-in charger in the UPS (mine is an APC ES 550) has very low amps (1A or so) so it might take WEEKS to top off the deep cycle battery once it's partially depleted.

So yeah, i'm thinking about drilling holes on the UPS battery panel, pull the battery out and use 14AWG cables to extend the leads so I can connect them to the deep cycle battery.

I was wondering...

1) Will the APC Powerchute software report correct runtime once it runs off the deep cycle battery? (i.e. 623 minutes of runtime rather than 8 minutes).

2) Would it be safe to permanently attach a trickle charger to the battery, to top it off, even through there already is a "tiny" charger on the UPS?

Your thoughts are welcome! Try everything you try at your own risk, always.

Thanks!

Not sure I would do that. I have limited faith in the safety of mods such as that. Where I used to work we made satellites and of course they have rechargeable batteries. Our battery testing lab caught fire one weekend when there was no one but security on site, the alarm worked and the FD came but the lab and all the computers monitoring the testing were toast, along with a lot of building damage. YMMV

Curious, why rewire a UPS to do this? If its a matter of the UPS being available 24x7 in order to power down you PC, you should have that already - switching out the UPS battery for a marine battery voids the warranty and makes the UPS begin to operate in an unwarranted and possibly dangerous configuration. I would rather take the deep cycle marine battery and apply your wiring skills to create a hot back up power supply: so you should plan to power down your PC like any other UPS user, and then maybe power it back up with your separate but more rational marine battery power backup. I'm sure there are videos out there to get you started. I do appreciate the impulse to tinker. I am electrically deficient myself, but I suspect I could match up the right inverter and connections to power a few necessaries - like my ham radio if I had a hankerin to do that.

Trying things at your own risk is just that, at your risk - god bless you and your local responding fire dept if you get this retrofit wrong.

PowerChute works on the reported battery model and measured voltage, so I doubt you could get it to report the correct runtime.

It's easy to wire things wrong and get hurt. I would recommend against this course of action.

I have thought of this too.

Here are some toys to consider:

http://www.mini-box.com/DC-DC

Cut out the PC Power supply and go right from battery to motherboard.

This certainly wouldn't be as efficient, but it would be much safer (I'm assuming you're not an electrical engineer to do the UPS mod correctly):

Buy a deep cycle marine battery, a car battery charger, and a power inverter. This would work fine if you're willing to let your computer go down with a power failure, then boot it up later on your backup setup. But if you want your computer to stay UP during the whole ordeal, yeah, you need a UPS. Buy one, don't try to make one. Heck, I *am* an electical engineer and would be considered technically competant to do what you're proposing. But I'd definitely buy rather than make myself, even though I *could* make if I really wanted to.

With a good quality charger and/or inverter that can be more efficient. What you described is an online ups, lots of ham radio guys do it. And you don't need to be an electrical or electronic engineer to do it, you can buy basic off the shelf components.

Most of your inexpensive made for home use ups's are the offline type and when you try using a larger battery you have the issue of longer charge time and you could even run into an issue where the inverter is not designed to run longer then the original run time so it cold overheat.

Thanks for your advice, everyone. Guess i'm going to keep reading before I actually begin experimenting, maybe it's not worth the hassle in the end.

Thanks again!

I did this many years ago. An APC BackUPS 500 connected to two Yuasa 38Ah batteries in parallel. Big cables to the batteries and quality connections on everything. Works like a dream. It powers all of my computer setup for hours and I use the 12V directly for my ham station.

The 500 cannot run Powerchute unfortunately so I can't help there.

Why not just get a bigger UPS and avoid the liability of making your own? The risk is real.

I use a high-end Dell laptop which has as internal battery so all I needed was something to continue powering the battery to extend on-time. For that purpose I have a Xantrex 400 Plus. It's available in bigger sizes such as the Xantrex XPower Powerpack 600HD. The Xantrex 802-1500 XPower 1,500 Watt Portable Powerpack is probably a little bigger than necessary. All of these units can output 120VAC or 12VDC.

Duracell markets similar units such as the Duracell DPP-300EP Powerpack 300.

I think it's a worthwhile experiment. The wiring is dirt simple, and the batteries run in the same voltage range. A deep-cycle battery is not necessarily required. It would certainly be useful in a longer-term power outage for lights and laptops; but don't expect to run a refrigerator.

There's no reason why a small solar panel (up to 5 watts) can't be used as a trickle charger while connected to the UPS. But pre-charge the battery before connecting, and shut down the UPS before using a line-powered battery charger.

Be aware that some UPS units, APC in particular, will not fire up on the inverter side after the battery has discharged. They have to see line (grid) voltage.

Risk: this depends on where you plan to use it.

I would never put a setup like this in a house. If something goes wrong, you are liable. (And insurance will probably laugh at you if try to make a claim.)

However, for a small off-grid outbuilding, it would be less of a risk. The battery and inverter should both be outside, in separate, weather resistant, ventilated enclosures.

The primary danger is a short across the battery terminals or the wiring. There is a lot of energy in a larger battery -- enough to start a fire or damage the battery in a dangerous way.

If you decide to build it:
- use very heavy wire from the battery to the UPS, and as short a run as possible
- install a 12V fuse or circuit breaker right at the battery to protect against a short circuit
- double-check polarity
- use good mechanical connections, with lots of wire overlap; spring-loaded clips are a recipe for trouble
- heavily insulate all connections
- monitor closely for overheating and odd smells

Personally, I would only use a hotwired setup under direct supervision, and only for light loads.

I have done this many times, and it should be safe provided that proper care is taken.
The external battery must be the same voltage as the original internal battery, normally 12 volts for the smaller units, 24 volts for larger ones, and more than 24 for very large ones.

Remember that the original battery was enclosed within the UPS and not readily touched, therefore the battery terminals MAY NOT be isolated from the line supply. That is a potentialy fatal line voltage shock could be received from the 12 volt battery leads.
Even if testing shows that the battery leads are isolated from the line supply, do not count on this !
UL or equivalent listing sets very strict standards for isolating line voltage from low voltage connections that can be touched, for example on consumer electronics.
These standards DO NOT apply to UPS units with internal batteries, since when used as intended the battery terminals cant be touched.
I would put the external battery in a large plastic crate with the lid secured to protect the terminals form touch.

The cable to the external battery needs for very thick and not too long. Suggest at least one size larger than the internal battery leads.

Fit an external fuse as close as possible to one battery terminal, size this at about 150% of the running current.

Remember that the inverter may only be designed for short term use, limited by the run time of the small internal battery, and may be killed by overheating if run continually at full power.
If extending the run time with an external battery, I would limit the load to less than 50% of the rating.

The external battery will take longer to charge.

I would accept this and not try and connect any other charger.

The powerchute shutdown software should still work to an extent, but dont count on it being accurate, I dont use it.

The UPS in my office is an APC smart UPS, 700 VA and is intended to use an internal battery of 24 volts 7 A/H.
I have fitted an external battery of 200 A/H and it works just fine, and has seen regular use for years.
The load varies but is typicly about 250 watts
desktop PC, flourescent light, desk fan, router, cellphone charger, Moterola radio charger, inkjet printer.

It certainly ran for a 9 hour working day without problems.

At my Mothers home I installed a 3,000VA UPS with a large external battery bank.
That runs basic lighting, fridge, freezer, TV, cordless phone base unit, cellphone charger, and so on on for several days.
The actual load is probably only about 100 watts average, 500 watts maximum.
I selected a 3,000 VA UPS to ensure that it will start the fridege and freezer.
Computer type UPS units are not ideal for starting motors, and as a crude guide the UPS needs to be rated at TEN times the rating of the connected motor load.
200 watt fridge=min 2,000VA UPS.