Inverter to battery sizing using 315w panel

[Teocalli]

Greetings:

My system consists of a LG 315w panel to a Blue Sky 3024 charger feeding a pair of Trojan T-105's 6v in series totaling 225Ah's.
My inverter needs are laptop, cell phone, small TV and maybe an occasional hairdryer, fan, curling iron ?

This results in a possible load of maybe 400-500w depending on run time which should be minimal except for chargers which would probably be continuous.

Based on a 12v battery bank I cannot run a 1000w inverter anyway right ?
Should I spec in a 600w inverter ?
Any particular brand ?

cheers,

Dave

[SunEagle]

I own a Xantrex Prowatt SW 600W pure sine wave inverter which seems to do the trick for me. There are others out there just as good and may be lower in price. Just make sure you get a pure or true sine wave model which has the GFI outlet on the front.

You also need the wire between the battery and inverter to be sized to handle at least 60 amps along with a 50 amp fuse to protect it. Normally an inverter rated for continuous wattage also can be push to about 2x that for short periods. If that is your desire then the wire needs to be increased to handle that current surge along with the fuse to protect it.

[Teocalli]

Thanks for the info with my main concern being that a 600w inverter will function reasonably well @225Ah, I will be using 4AWG wire about 4 feet long and plan on using a 80 amp fuse to allow for potential surges.

[inetdog]

Another thing to watch out for is that 315 watts of panel is a trifle large for a 225AH battery bank. You may need to limit the charging current to no more than about 28 amps (C/8). But it is unlikely that a 315W panel will in fact be able to deliver that much power, even with an MPPT CC.

[Teocalli]

Thanks for the tip, I am going to use a 30amp breaker and counting on the Blue Sky 3024 to regulate the current properly to the bank.
The panel is a bit large for the bank and initially I thought of using 240 or 260Ah Trojans. My next task is to figure out what 6/2 UV rated THHN style wire I can connect to the panel. Don't want to use a combiner box so thinking of soldering and shrink wrap the 6/2 - 12/2.

[Sunking]

T-105's can easily handle C/5 Charge Current, and C/4 continuous discharge currents. Technically they are not a Deep Cycle battery, they are a hybrid battery marketed as Golf Cart batteries. At 315 watts with a MPPT controller you are generating up to 25 amps of charge current, and that is OK as many Golf Cart Chargers are 25 amps. At 25 amps is C/9 on a 225 AH battery. So no problem.

Technically You can discharge them at 1C or 130 amps, but voltage sag is significant. It will not damage the battery as golf carts demand up to 500 amps. The issue is Voltage Sag when used on an Inverter. Any decent Inverter has a Low Voltage Disconnect circuit designed to disconnect from the battery if the voltage dips to a set value usually 10.5 volts is default. When you take into account the voltage sag of a battery, and wire voltage losses in the wring will cause an Inverter to trip off-line prematurely. It is very possible for the Inverter to trip Off-Line immediately despite having a fully charged battery. The reason is the battery is too small and not matched to the Inverter.

For FLA batteries rule of thumb is maximum discharge current should be limited to C/8, and cable losses limited to 1%. So if you have a 12 volt 225 AH battery, maximum Inverter size is 350 watts. With a pair Trojan t-105's configured as 12 volts you can go up to 600 watts. Can you use a 1000 watt Inverter? Yes you can assuming the wiring is capable of 100+ amps, and you understand if you are running more than 600 watts you will likely trip the Inverter Off-Line prematurely if you do for any length of time.

[Teocalli]

Thanks for the detailed information, I was under the impression the FLA T-105's are in fact deep-cycle ? The spec sheets and performance charts along with casing markings do not indicate any different, no CCA's anywhere but wondering how you know this ? I will be using wire that limits loss to less than 1% fused with 80amp just in case of momentary surges in demand. Mostly my demands should be limited to below 300w for continuous duty, chargers, phones, TV etc. I bought a Xantrex 600w even though I have read where they might be a p.o.s but if it fails I haven't spent a ton of money buying a Magnum just yet Hopefully the low voltage disconnect does it's job if I ever ramp up too much demand.

cheers,

Dave