Uncle Sayit
New Member
- Joined
- Apr 11, 2021
- Messages
- 5
I'm trying to size a battery for a rural solar PoE security camera setup.
The battery will be lithium titanate (LTO) because I will need to solar charge it at -20C (-4F). Due to the high cost of the battery I want to size it correctly.
I'm a bit confused how to calculate energy usage for PoE devices. The specs sheets for each product states wattage and voltages but I am not understanding something about POE voltages. All my devices seem to be 802.3af POE, the standard supports up to around 13 watts per port. My understanding is that power is injected onto the cable at a voltage between 44 and 57 volts DC, typically 48 volts is used, but many devices use only 24V. Maybe the reality is that POE switches can output either 48V or 24V?
I'll list my gear here.
3 x Dahua 5442 cameras, each one uses 7.2W maximum PoE so 21.6W total
1 x Ubiquiti Gigabeam Plus, 13W maximum, 24V DC PoE input
1 x POE switch, 5W maximum, 24V DC POE input
1 x Alpha Network 8-port POE injector, 12VDC - 48VDC input
1 MPPT solar charge controller that supports LTO batteries
1 or 2 solar panels, size TBD
1 LTO battery with BMS
I need to size the battery. I'd like to have one capable of running all my equipment for 2 or 3 days to address cloudy / snowy days that provide very little solar power.
Do I simply add up the wattage (39.6W) x 24 hours = 950.4Wh per day? Then divide by the battery voltage to determine the battery size needed per day in Ah?
Since Amps = Watts / Volts, a LTO battery at 23V would require 41.32h per day for my application, right? But maybe the average voltage would be closer to 18V due to the battery chemistry slowly draining from 23V to, hmm... maybe 12V, thus requiring more like 52.8Ah of battery power per day?
LTO cells commonly output 2.3V and I see a couple BMS for a 10S battery which is how I got to 23V. If I need 106Ah to 158Ah of LTO battery power that's not exactly cheap. Hopefully I am not calculating something correctly.
The battery will be lithium titanate (LTO) because I will need to solar charge it at -20C (-4F). Due to the high cost of the battery I want to size it correctly.
I'm a bit confused how to calculate energy usage for PoE devices. The specs sheets for each product states wattage and voltages but I am not understanding something about POE voltages. All my devices seem to be 802.3af POE, the standard supports up to around 13 watts per port. My understanding is that power is injected onto the cable at a voltage between 44 and 57 volts DC, typically 48 volts is used, but many devices use only 24V. Maybe the reality is that POE switches can output either 48V or 24V?
I'll list my gear here.
3 x Dahua 5442 cameras, each one uses 7.2W maximum PoE so 21.6W total
1 x Ubiquiti Gigabeam Plus, 13W maximum, 24V DC PoE input
1 x POE switch, 5W maximum, 24V DC POE input
1 x Alpha Network 8-port POE injector, 12VDC - 48VDC input
1 MPPT solar charge controller that supports LTO batteries
1 or 2 solar panels, size TBD
1 LTO battery with BMS
I need to size the battery. I'd like to have one capable of running all my equipment for 2 or 3 days to address cloudy / snowy days that provide very little solar power.
Do I simply add up the wattage (39.6W) x 24 hours = 950.4Wh per day? Then divide by the battery voltage to determine the battery size needed per day in Ah?
Since Amps = Watts / Volts, a LTO battery at 23V would require 41.32h per day for my application, right? But maybe the average voltage would be closer to 18V due to the battery chemistry slowly draining from 23V to, hmm... maybe 12V, thus requiring more like 52.8Ah of battery power per day?
LTO cells commonly output 2.3V and I see a couple BMS for a 10S battery which is how I got to 23V. If I need 106Ah to 158Ah of LTO battery power that's not exactly cheap. Hopefully I am not calculating something correctly.
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