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Please suggest me UPS
dodheimsgard
Member
in Help
Hey guys, I have home router + two raspberry, all consumes 17W. I would like to run this setup for up to 24 hours in case of electricity outage. How many VA I need?
Comments
VA = Watts
You wanna run 17W for 24h you need 408 Wh or 408000 mWh or 0,408 kWh.
VA is a measure of power, not capacity
Do note that lead acid battery used in traditional UPS have less than what it advertises.
If Pike Trickfoot is correct in that you need 408Wh, you will probably want 800Wh UPS.
Or you can go with power stations (AKA solar generators).
Yes multiply it with power factor and you will definitely get wattage
Yes multiply it with power factor and you will definitely get wattage
Indeed, but the point is that what OP needs to look for is battery capacity, not the power (whether apparent or real).
This post from deank is useful and therefore should be flagged.
APC Smart-UPS SRT 1000 VA, 230 V should last you about 26 hours
(calculated with https://www.apc.com/shop/us/en/tools/ups_selector/home/load)
Thanks guys
Since watts = Amps x Volts... power supply with 40AH battery (12V) shoud produce 480 wats, considering 50% efficiency it should last for 12 hours if power draw would be 20W?
Please correct me if Im wrong
For UPS true capacity, you need to check what batteries it uses.
And then you actually need to substract 15% off it due to power loss from DC to AC. Lithium solution will probably be better.
Nope. There is no standard UPS that will survive more than 2 hours even with zero load.
Best choice - charge a large lead-acid battery with float charger. Use dc-dc step-down to make it 5V.
Provided that it will be DC to DC, roughly yeah. Lead acid batteries sometimes just fail when going under 50% of its charge though.
If it's DC to AC to DC, then do -15% on that. So, 480 Wh reduced to 400Wh - ish. Your actual stable power will be only 200Wh-ish.
What are you even talking about?
And yes, there are standard UPS' that would run 24h on 17W load. Standard being UPS' for offices and datacenters, not off the shelf Staples $100 special.
1000w - 100$
Not always true. This is only for OPEN lead batteries. Closed and gel (AGM) are near label capacity.
My solar system uses open lead acid and i get around 85AH per 100AH battery in summer, and 80AH in winter.
Also note that Li (any, LiPo, LiIon, LiFePo4) batteries are loosing 50% in extreme cold weather - WAY worse than lead acid.
Open lead acid is also not legal indoors - charging them produces highly explosive hydrogen gas. No UPS uses open lead acid.
Please what? I run a MPP Solar 5048G 5000W inverter with 16 100AH batteries (400AH @ 48V) - This runs my entire place including AC for a day, without AC 2-3days.
A cheap APC USV will easily run 17W for days.
Absolutely not true. You discharge them to exactly 12.5V and there will be zero problems. Low discharge is normal with lead acid and has to be calculated in.
They also do not 'fail', they just drop to low voltage and ARE ALWAYS RECOVERABLE.
I had batteriers stored outside in Croatia, a year, at 14.6V - Came back, 12.1V, trickle charge to 14.8V and it's still the same 85AH with some new distilled water.
Where are you located? 24 hours of power outage
Poland, more than few hours outage are rare but better safe than sorry