EE questions

Before I start I am not an EE or anything close to that.
I have 4 peices of equipment.
All run on 120AC @ 1A ( MAX SPEC)
I need to build a battery back up for these systems that can last for
10-12 hours with out power. My boss does not want to spend the money on
a formal UPS solution because of the cost and since they will be at a
construction site will most likely get stolden.
So here are my questions:
1)If I have a battery bank of 12 volt batteries in pararel what would
the Ah rating I would need for each battery.
2)If I have a battey charger that is connected to a generator. What
would the power requirments be to chardge those batteries need to
chardge the battery?
3) What would be the requiments on the inverter?
Reply to
cisco sys kid
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4 times 120 watts = 500 watts
plus inverter efficiency. probably 550 to 600W out of he battery.
600 w/ 12.6 volts (asuming a 12 volt inverter) = 47.6 amps
then why bother? the batteries will be the biggest part of the cost.
lets assume you use 100 A-H deep cycle batteries
you would think 5 would give you 500 A-h for 50 amps times 10 hours but in reality you will need more.
you would, depending on the battery type, charge each battery with its own charger @ 10 amps for at least 10 hours (more likely 15 hours).
i'd pick a 1 kW or larger. make sure it will operate with lower voltages. some (like one i bought) are intended to run in vehicles under charge (i.e. the engine running) once the voltage drops to 11 it shuts itself off. i guess the idea here is to not kill the battery and leave you a chance to get the car/truck started.
you could also opt for 4 smaller systems, say four 200 W inverters (or UPS units with the battery cables brought out) each going to a couple of batteries. keep in mind that the charging circuits of small UPS will not be able to cope if these are to be used daily.
Reply to
I really don't think you can build cheaper than you can buy, but if I had to I'd use car batteries wired in parallel along with a regular inverter intended to be conencted to a car battery. I'm not sure exactly what I'd use for a charger, but presumably a 10A 12V charger would work. And all of this could be stolen just them same, but you know what they always say about the boss being right!
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