Battery bank / choosing batteries

terminator

Could someone tell me how many Trojan T105 6 Volt, 225 AH Deep Cycle Batteries
http://www.solar-electric.com/trt16vo225ah1.html

I would need to have the capacity to run 500 watt load for 24hrs?

vtmaps

Re: Battery bank / choosing batteries

terminator wrote: »

Could someone tell me how many Trojan T105 6 Volt, 225 AH Deep Cycle Batteries
http://www.solar-electric.com/trt16vo225ah1.html

I would need to have the capacity to run 500 watt load for 24hrs?

Is this just a one time load, deplete the batteries and then recharge them? Or is this a constant load, day after day? How will you charge the batteries? Will you be charging them while the load is still connected?

Also, is that a 500 watt DC load? or is that 500 watts being produced from an inverter (which will require more than 500 watts from the battery)?

Your load is (at least) 12 kwh per day. Those batteries store about 1.3 kwh of energy (assuming you deplete them). You would probably need 40 of those batteries, in five parallel strings at 48 volts. That's unworkable and impractical. You need fewer, but much larger batteries to design a reasonable system.

--vtMaps

terminator

Re: Battery bank / choosing batteries

vtmaps wrote: »

Is this just a one time load, deplete the batteries and then recharge them? Or is this a constant load, day after day? How will you charge the batteries? Will you be charging them while the load is still connected?

Also, is that a 500 watt DC load? or is that 500 watts being produced from an inverter (which will require more than 500 watts from the battery)?

Your load is (at least) 12 kwh per day. Those batteries store about 1.3 kwh of energy (assuming you deplete them). You would probably need 40 of those batteries, in five parallel strings at 48 volts. That's unworkable and impractical. You need fewer, but much larger batteries to design a reasonable system.

--vtMaps

Hi,
I am asking for 500 watt continuous DC load off an inverter. thanks

"Is this just a one time load, deplete the batteries and then recharge them?" It's just a theory that it would be the most I would need over 24hrs without sunlight or wind.

BB.

Re: Battery bank / choosing batteries

Roughly, assuming you discharge the battery by 80% (to 20% state of charge), batteries perform to specifications (i.e., 75F or warmer, good cells, etc.):

500 Watts DC * 24 hours * 1/0.80 max discharge * 1/5.25 volt near dead battery = 2,857 AH of 6 volt batteries

2,857 AH / 220 AH per battery = 12.98 batteries

Or, 2 batteries in series (12 volt) * 7 parallel strings; 4 batteries (24 volt) * 4 parallel strings; 8 batteries (48 volts) * 2 parallel strings...

There is not a lot of excess capacity in the smaller capacity strings. Also, not quite sure about your loads:

With an inverter (500 Watt input constant power):
500 Watts/12.7 volts = 39.4 amps
500 Watts/10.5 volts = 47.6 amps

With a fixed resistance load:
V=I*R, R=V/I= 12.7 volts / 39 amps = 0.3256 ohms
10.5 amps / 10.5 Ohms = 32 Amps

So, depending on your loads, the current may rise or fall as the battery bank discharges (or in some cases, can remain the same).

The above ~13 batteries is a nominal worst case room temperature guess at a working battery bank configuration with limited life (deep cycling to 20% SOC is not "great" for battery life).

-Bill

Cariboocoot

Re: Battery bank / choosing batteries

Basic math: 500 Watts * 24 hours = 12 kW hours.
On a 48 Volt system that's (12,000 / 48 ) = 250 Amp hours used.
Discounting losses that would be a minimum 500 Amp hour battery bank, or twenty-four 225 Amp hour 6 Volt batteries configures as three parallel strings of eight in series for 675 Amp hours @ 48 Volts.

As vtMaps suggests, look at larger capacity batteries if you need that much power.