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Increasing backup power to computer

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Posted by John on December 27, 2009, 5:56 am
 


I have a UPS for my computer that gives about 15 minutes max runtime
when there's a power cut.

I'd like to increase the time I can go during a power cut so am
thinking of adding a deep cycle battery between mains and ups for
computer.  What do I need besides the battery?

I am on 250 volts power supply. Computer usually draws between 80 to
130 watts max. It has a 430 watt psu but never goes past around 130
watts max.

If I wanted to extend the time by an hour in the event of a power cut,
what size of deep cycle battery would I need to go for? How many amp
hours?

Posted by clare on December 27, 2009, 6:30 am
 


wrote:


Get yourself a UPS with extended power option - they have a plug on
the back to connect extra batteries. If your UPS is a 24 volt unit
(most common on 430 watt units) you need 6 amp hours of useable power
to provide 130 watts  for 1 hour - so to stay within the proper
discharge limits you need a MINIMUM of a 12 ah battery pack. I'd be
aiming for 15 or more.

The problem , besides gaining access to the battery connections, is
the charging circuit on your wimpy UPS will not be able, in all
likelihood, to handle recharging the larger battery pack.

Most of the "extended" units use higher battery voltage, so draw less
current from the batteries.

Posted by Josepi on December 27, 2009, 3:06 pm
 

It would only be a trickle charger anyway so it would just take longer to
re-charge.

I suggest testing your UPS to see if you actually get the stated life out of
it.

How much time do you need to shut your computer down?

Look at the rating on the existing battery and multiply that by the time
increase factor to get a rating to buy. Don't put them in parallel.

Get yourself a UPS with extended power option - they have a plug on
the back to connect extra batteries. If your UPS is a 24 volt unit
(most common on 430 watt units) you need 6 amp hours of useable power
to provide 130 watts  for 1 hour - so to stay within the proper
discharge limits you need a MINIMUM of a 12 ah battery pack. I'd be
aiming for 15 or more.

The problem , besides gaining access to the battery connections, is
the charging circuit on your wimpy UPS will not be able, in all
likelihood, to handle recharging the larger battery pack.

Most of the "extended" units use higher battery voltage, so draw less
current from the batteries



wrote:
I have a UPS for my computer that gives about 15 minutes max runtime
when there's a power cut.

I'd like to increase the time I can go during a power cut so am
thinking of adding a deep cycle battery between mains and ups for
computer.  What do I need besides the battery?

I am on 250 volts power supply. Computer usually draws between 80 to
130 watts max. It has a 430 watt psu but never goes past around 130
watts max.

If I wanted to extend the time by an hour in the event of a power cut,
what size of deep cycle battery would I need to go for? How many amp
hours?



Posted by Jim Wilkins on December 27, 2009, 4:21 pm
 


Sealed lead-acid (SLA) batteries are rated at the 20 - hour discharge
rate. Figure half that capacity for a UPS that runs out in an hour or
two, in other words 100 W for an hour really requires 200 Watt-Hours
of battery, or 12 V 17 Amp-Hour. I got that 50% rule-of-thumb from a
former engineer at APS and it agrees with my measurements of a new
battery.

I've been playing around with power-out schemes and bought several
cheap second-hand UPSs to test. The one that works best and longest is
a Tripplite 1050, which puts out 700 W max of real power, this one
runs a 60 W bulb for nearly two hours. It cost $5 with apparently
worn-out batteries which recovered nicely after a few charge and
discharge cycles.

Overall, after considering the cost and maintenance of a generator or
a new and reliable UPS, I bought this used Latitude laptop instead. It
draws ~20 W from the AC line and runs 3 hours on battery.

Having batteries and loose jumper cables scattered around is dangerous
enough in a well-lit room, I don't want to be fussing with them by
flashlight when the fire department is busy elsewhere.

If you choose to, look into Anderson connectors:
http://www.andersonpower.com/

jsw

Posted by Josepi on December 27, 2009, 5:31 pm
 

Half?...maybe much less.

I doubt those cells have that good of a good Peukert factor rating.



Sealed lead-acid (SLA) batteries are rated at the 20 - hour discharge
rate. Figure half that capacity for a UPS that runs out in an hour or
two, in other words 100 W for an hour really requires 200 Watt-Hours
of battery, or 12 V 17 Amp-Hour. I got that 50% rule-of-thumb from a
former engineer at APS and it agrees with my measurements of a new
battery.

I've been playing around with power-out schemes and bought several
cheap second-hand UPSs to test. The one that works best and longest is
a Tripplite 1050, which puts out 700 W max of real power, this one
runs a 60 W bulb for nearly two hours. It cost $5 with apparently
worn-out batteries which recovered nicely after a few charge and
discharge cycles.

Overall, after considering the cost and maintenance of a generator or
a new and reliable UPS, I bought this used Latitude laptop instead. It
draws ~20 W from the AC line and runs 3 hours on battery.

Having batteries and loose jumper cables scattered around is dangerous
enough in a well-lit room, I don't want to be fussing with them by
flashlight when the fire department is busy elsewhere.

If you choose to, look into Anderson connectors:
http://www.andersonpower.com/

jsw



I have a UPS for my computer that gives about 15 minutes max runtime
when there's a power cut.

I'd like to increase the time I can go during a power cut so am
thinking of adding a deep cycle battery between mains and ups for
computer. What do I need besides the battery?

I am on 250 volts power supply. Computer usually draws between 80 to
130 watts max. It has a 430 watt psu but never goes past around 130
watts max.

If I wanted to extend the time by an hour in the event of a power cut,
what size of deep cycle battery would I need to go for? How many amp
hours?



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