3 UPSes from a Single Battery

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FPLenin

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Hi all.

I recently bought a huge UPS Battery (kinda expensive), Keyko 12 v 28 Ah. I got pissed off about buying cheap stuff every year...so, I was thinking: may I take three small UPS and connect each one (+ to +) on my new big battery? Would there be any trouble about it? Is there any special connection that I should be warned about?

The UPS are Tripplite 750 VA Smart750 USB, Avtek 650 VA, Avtek 650 VA. I would simply take off their batteries and connect their cables to the new Keyko. The Tripplite battery (biggest one) said it was 36 Watts. Don't know how many Ah they had...if you have a power consumption calculator or something, it would be nice to see how much computers my battery might take...

The computers using that battery would be three 17" LCD Monitor, AMD Sempron 2600+, AMD Athlon XP 2500+ and AMD Athlon 64 3500+ CPUs, 80 GB, 80 GB and 250 GB HDDs, DVD Drives (rarely used), motherboard integrated GPUs (they usually use Office software, not a big deal...)

Thank you for your support (Y)
-Sorry about my English-
 
How often does the UPS actually trigger? Having that many devices powered by a UPS is unusual and often not needed, you need to ensure their data sources are secure not the PC's themselves more often than not. How often are the UPS(s) are actually used is very important to determining if this battery is satisfactory for your needs. If it never trips and this is just for emergencies... Almost any lead acid battery will do as long as it's kept peaked. If this battery will actually be USED for any length of time you need to determine your usage period's and charge times available to figure the long term.
 
Hi, thanks for your answer.

There's almost one blackout per day. The idea is to save the files and turn off the computers...


I was wondering if it is a good idea to connect 3 UPSes and that they use the same battery...some people told me it ain't a good idea because the big battery could overload the charging circuits of the small UPSes...
 
All three UPS's would try to charge the battery at the same time, this would be bad. You'd need to disable the charging ciruitry on two of the UPS's and use the large of the three to do the charging. A battery will not last long if it has to give a large amount of load like that on a regular basis. You says there's almost one blackout per day. Could you clarify that, how long is the power usually out for, and up for any given 24 hours period averaged over say... 6 months.
 
Hi. It doesn't sound kinda easy to shut off the charger of an UPS...I almost have no idea of electronics.

Power might be out for seconds, minuts or even hours. They usually save files and turn off the computers...The 650 and 750 VA old batteries had 7 Ah approximately...the new and big one haves 28 Ah (almost 4 times the older ones).

Main problem, I think, is the battery charging...
 
With the draw from 4 computers, or TVs, etc, all drawing from the 12v battery, YOU MAY get a voltage drop that will not sustain the UPS. Only test will tell

As for the charging, diodes on the other 2 UPS battery connection leads should keep them from charging the battery.

The proper thing to do would be to disable the charging circuits, as Sceadwian stated.
 
It's 3 computers, not 4.

If I connect 2 UPSes directly to the battery, there should not be any trouble about wiring?
And if they charge it, wouldn't they just give it 12 v or because they are simultaneusly connected will they give it 24 v or something like that?

(By now a single 750 VA tripplite UPS charged the battery from 12.0 v to 13.2 v and still charging-working - Haven't connected more than one UPS at the same time)
 
Something happend and the UPS got off...It seems this project is not going too far.

What do you think about using an inverter and a battery charger? So, the battery would continuosly run and charge, and the computer would run with power from the inverter...would this be unsustainable? is this kind of battery made to last with this kind of continuos charging-use? I would plug TWO OR THREE computers to it...
 
You could connect a NC relay to the battery leads from the "slave" UPS's.

The charge circuit would be connect to the relay coil.

That way, during the "charge" cycle, the battery would not be connected. A power outage would cause the relay to close, giving power to the PC.
 
RMMM said:
As for the charging, diodes on the other 2 UPS battery connection leads should keep them from charging the battery.
Click to expand...
Diodes would also keep the UPSes from getting power from the battery when the mains power quit. You need to use a relay, such as RMMM recommended, to isolate the UPSes when the mains power is on. You could use an AC relay powered from the AC line.

Edit: The above is incorrect. Diodes should work to isolate the UPSes. I was thinking backwards.
 
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Ok, lets see if I'd got your ideas:

**broken link removed**

Uploaded with ImageShack.us

Is this correct?
So, the NC relay would inmediatly switch from battery to normal power, and from normal power to battery (like some kind of true XOR - exclusive OR - )?

Is this switch fast enought to prevent power failure to the computers?
Wich are the caracteristics of the NC Relay that I need? is it Ohms? Watts? Volts?
 
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No. You need 2 relays. One for each UPS that will NOT BE charging the battery.

The relay will go in between the UPS and the battery on the battery connection cables.

This way, while you have AC-mains power, the relays will be OPEN and separating the 2 non-charging UPSs' from the battery.

As soon as the power goes out, both relays close and allow the UPS's to do their jobs.
 
wait... Do you have REAL UPS's? Or are you just using inverters as UPS's?

Do you have a separate battery charger?

This is how a 3 TYPICAL UPSs' could be done:
 

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I don't have a separate battery charger, but I would buy it if this is supposed to work...

I have lots of battery-less UPSes...lots. But it's really annoying to buy small and cheap batteries everytime...



Is this what you mean?
**broken link removed**

Uploaded with ImageShack.us
 
I would buy a Battery Charger because I'm thinking that the charging system of the first UPS that I used (750 VA) died because of trying to charge such a huge battery...
 
Would there be any problem if the UPSes try to charge the battery and the NC Relay make them to suppose that there's no battery? If a UPS is not in contact with it's battery it would not even turn on...
 
RMMM said:
No. You need 2 relays. One for each UPS that will NOT BE charging the battery.

The relay will go in between the UPS and the battery on the battery connection cables.
Click to expand...
You just need one DPDT relay.
 
crutschow said:
You just need one DPDT relay.
Click to expand...

True.. I dont know what I WASNT thinking.. Thanks for the catch.

@FPLenin, there May or may not be a problem with the UPS's not seeing the battery during charge, but there is an easy way to check.

Go to one of your UPS's while it is charging. Pull a battery cable. What happens? This will be the same effect as using a relay.
 
I'm thinking of just adding a battery charger specific for the battery and isolating each UPS with a schotkey diode. That way the battery charger does what it's expected to do and the UPS does what it's expected to do.

It's possible that the UPS could get upset and say the battery isn't charging or some such nonsense. You could try a few diodes first without investing in the battery charger.
 
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