I want to add additional batteries to my UPS... How Many can I add?

Hey Guys,

I have an APC Back-Ups XS 1300 that the battery had died. The battery is a 12V with 9AH. I have been collecting old server ups devices over the last year. Some are good batties and some are bad. I have 16 out of 24 good batteries at 12V with 5.3AH. If I connect these batteries in parallel I would get a total of 12V with 84.8 AH. This should allow my system to run longer.

I understand that this is not the proper way and I should just go buy a big one. But since I have the parts, I figured to have some fun and it would be a bonus if it works.

My question is, Can adding this many batteries (84.8AH total) to a device that is suppose to only charge one battery (9AH) do any damage? I am not changing the voltage. In theory, I would think adding all batteries in parallel should combine them into one big battery.

Also... Would it matter if add another battery that is a different AH? For instance, If I add 9AH battery to a group described above? I would think NO but I am curious. I would like to get into solar power and want to know my Do's and Don't before playing.

Thanks,
Akaweb1

 

First, I applaud you for using a "good" UPS with AVR. I wish everyone was a conscientious about providing good power to their systems!

That said, I would not advise doing what you are considering. You are absolutely correct that 12V batteries in parallel essentially make a bigger 12V battery - thus the voltage would not be a problem. And you are correct again when you say the increased amp-hours would provide a longer - much longer "run time" but that assumes charged batteries, and I strongly believe the charging circuits would struggle (perhaps over heat, shutdown and fail) with the demand and take forever to fully charge all those cells - if it can.

How do you know your batteries are still good? You cannot simply stick a multi-meter on a battery to check its voltage. A battery (like all power supplies, including computer power supplies and car engines) must be tested while under a realistic load - to test it properly.

Note a battery is made up of "cells" and a cell can be a single cell (like a AAA battery) or several cells connected internally to make a single battery and/or larger cell - which can then be connected with other cells to make a bigger battery yet. These SLA (sealed lead-acid) batteries are made up of separate cells. As seen here your APC UPS uses two cells (batteries) to make one larger battery.

I personally recommend you do what I do. Replace your UPS batteries with new batteries when the old batteries wear out - which they do every 3 - 5 years - then take your old batteries to a battery recycling center. Note Radio Shack accepts these old batteries for recycling too.

If you decide to keep your old batteries for other projects - be sure to inspect each battery regularly for bulging, cracks, leaks, etc.

 

If you don't have a Radio Shack nearby, almost all auto parts stores (NAPA, AutoZone, etc.) accept them for recycling as well.

 

I'd recommend measuring some numbers with a cheap AC wattage meter and connect your ups with a drained battery, note the wattage. Add a second drained battery and let them both charge, note your wattage and check the temperature of the charging circuits/transformer. If your wattage doubles when you add a battery then you can't use that ups, the charge current isn't being limited and something bad will happen.

EDIT You may also notice the battery has a wire glued to it, this is to thermally throttle the charger when the battery gets hot, this can be used to determine charge rate or to prevent damage or fire, if you add more batteries these systems will no longer work as it will only know when one battery is hot and hence when only that one battery is fully charged.

None of this is a problem with wind or solar really, you will always be limited by the power cells or a turbine can provide.

Whatever Frankenstein UPS you end up creating just ask yourself is it safe enough to sleep next to? If so, is it safe enough for your children to sleep next to? If the answer is no then maybe it isn't a great idea 50lbs of hot acid,fire and main power is a dangerous mix.

Welcome to the forum

 

Just one personal experience:

I'm a computer tech, and several years ago one of my customers wanted me to remove an old APC 600W UPS from their business, because it was dead and leaking.

I took it home, cleaned it up and removed the two dead 6v batteries. They were in series to make 12v. I did a lot of puttering around and experimenting, till I came up with this replacement for the little gell cells.
http://i54.photobucket.com/albums/g90/DrWho1943/Computer%20Stuff/UPSBatteries-1.jpg

Two car batteries, in parallel, in a plastic dish pan. The charger in the UPS has no problem recharging these batteries and my run time is over 8 hours, powering my 27" TV, cable box, a small table lamp and a small personal fan.

This system kept my TV going for the five days I was without line power during Hurricane Frances. I did recharge the batteries off of my car, with jumper cables, twice during that time.

I know, it looks like a Kluge, but it does work.

I tried a larger battery on a "Cyber Power" UPS, but the UPS seemed to reject it.
With the APC brand, NO Problem.

I currently have another APC 850, with a 12v tractor battery powering it.
Works great! That too was given to me by a customer, when the OEM battery died.

For safety, always use an in-line fuse, between the battery and the UPS, so if the UPS should short out internally, it will blow the fuse and not start a fire.

The two batteries in my picture (above) will produce over 500 Amps of current, if short circuited.

Cheers Mates!
The Shadow

 

That's an interesting setup - thanks for sharing that. My big concern would be charging circuit overload if one of those batteries has a cell short out. That said, smart move using a fusible link in there. :dood

 

I no longer have schematics for APC's. (I used to repair them, years ago) but I suspect that the charging circuit is current limited, just for the reason you mention.
I know if I were building it, there would be both voltage and current limiting.

One battery is always best, but if two or more are to be used, they should be of good quality and similar size and age.

I check my batteries often, and inspect the fluid levels, etc.
I will only use "Full Maintenance" batteries. They will charge quicker and with less voltage applied, than Maintenance Free batteries.

The inline fuse should be of the "Fast Blow" variety, so if there's a short, the line will open quickly. Slo-Blow fuses take 200% to 300% of rated current to make them blow out.

Oft times, success is all in the details.

Cheers Mates!
:cool

 

If I made one I'd probably have two fuses, one from the charger to the battery I'd guess around 10amp to protect the charger from over current and one on the 12V that powers your gear around 50 amps which would be at the limit of your 500W to protect your inverter from over current.

I'd also use an plug-in, inline RCD for any AC shorts.

I guess safety is ones own personal preference, I don't think there are any regulations regarding DIY franken-ups:-D

 

Rikki
Have you ever seen a UPS?

The UPS IS the charger, and there are only two wires involved. + and -

The UPS charges the batteries (continuously) untill the line power drops and then a Relay pulls in to switch from charger mode to UPS mode.

The charger and the UPS are NOT separate entities.
One 'safety' fuse is all that's required. or even possible. Eh?

 

No I've not seen inside 'your' UPS since I've only looked at two wires connected to two car batteries :confused When I describe the charger and ups as separate I mean from an electrical engineering standpoint. Electronics is my hobby and I understand the theory of their operation Do you understand the theory of their operation? I'm joking I don't want a peeing contest it's aka's help thread.

You quoted 600W as the limit of your UPS when the 'relay' switches and all your gear is being powered by the inverter at 12V you could have 50amps going through those two skinny wires on the left of your picture, they look like 2.5mm2, 2.5mm2 has a max limit 20-30amps depending on quality but at those kind of currents it will burn, for safety you really need to double the max current of you could theoretically pull from the batteries.

So I would use the same cable you have joining your batteries together to power your inverter, 6mm2-10mm2 at a guess?:confused

This is the reason I assumed you've disconnected it from the inverter, those two wires are too skinny to power your gear 600W,12V,50amps. Also I've only seen two wires connected to two car batteries I don't know what the rest of the circuit looks like or any numbers, what is that fuse rated to? You'll have to give me some leway, I can only go off your picture and description, it's not in front of me.

 

Just because the rating on the UPS is 600, that doesn't mean that it puts out anyways near that, continuously, during normal operation.

The actual wires inside the UPS are only about maybe 14ga. My wires from my batteries to the UPS are like 10ga. (Much thicker)
My fuse is a 30 A. fast blow fuse.

Don't nit pick it! It works and I've had many more UPS's running off of similar Lead/Acid batteries over the years.

My most recent is an APC 650va that had just one, small 12v gel cell battery.
I just extended the little wires out (about 2' ) to a 230 CCA tractor battery, using 10ga copper wire.

During my last test run, the UPS ran for over an hour and did not drain the battery, but finally did shut down, probably due to internal temperature.

These home-type UPS's were never designed to run full time. But just for a short time, to give the user time to shut down their devices and prepare for an extended power failure. Replacing that little OEM battery with a larger one can greatly extend the run time of the UPS, but it's still not designed to run forever.

There are different types of UPS's that ARE designed for that purpose. Some can even run a whole household, for days, without any line input. It all depends on just how many batteries are connected to the system.

Cheers Mates!