Need help designing off-grid system

[Bigbus]

Got it. So where does that leave me? What do you suggest I change? The datasheet says the 240ah battery is 132 minutes at 75 amps. It doesn't list anything for 50 amps. 25 amps is 488.

Just to make sure I'm following you...... Trojan posts that limit just because consumers are stupid and they want to protect themselves from people boiling the battery and suing them. You're suggesting that I charge the batteries with a much higher current in order to capitalize on the potential charge from my panels. Would I keep the same charging voltage? Trojan recommends 59.28v bulk charge for a 48v bank.

[Sunking]

The datasheet says the 240ah battery is 132 minutes at 75 amps. It doesn't list anything for 50 amps. 25 amps is 488.

I believe you.

Just to make sure I'm following you...... Trojan posts that limit just because consumers are stupid and they want to protect themselves from people boiling the battery and suing them.

And significantly lowering warranty claims.

You're suggesting that I charge the batteries with a much higher current in order to capitalize on the potential charge from my panels.

What are you calling a much larger current? I am telling you with proper care you can charge those Trojan Batteries up to roughly C/4.

You are mixing up design priorities. Panels are sized to fully charge a battery under worse case conditions using winter sun hours. Current is going to be whatever it is based on battery voltage. Charge Controller is sized to handle all the power the panels can provide, so if you have 1000 watts and 24 volt battery requires at least a 40 amp charger. Battery is sized to provide 5 days of power. Once you get that worked out then look at charge rates. Unless you live in Seattle or Portland with less than 3 Sun Hours in winter, charge rate will fall right in the window of C/12 and C/8. If it exceeds C/8 select a battery that can handle more than C/8 which any Hybrid Battery can do like a Trojan. Trojan can handle C/4 just fine, just watch water usage and specific gravity.

Would I keep the same charging voltage? Trojan recommends 59.28v bulk charge for a 48v bank.

Just like Charge Rate it is a recommendation and may or may not be right. Your Hydrometer would tell you what voltage to use. If at the end of the day, and specific gravity is too low, turn up the voltage. If specific gravity is too high, lower the voltage. Changes with the time and year and temps. But it will be 57 to 61 volt range.

[Bigbus]

What are you calling a much larger current? I am telling you with proper care you can charge those Trojan Batteries up to roughly C/4.

Current meaning amps. Are you saying I should get a charge controller that can charge at C/4 which is 60amps (240/4)?

Charge Controller is sized to handle all the power the panels can provide, so if you have 1000 watts and 24 volt battery requires at least a 40 amp charger.

1470w/48v battery = 30 amp charger. Which is what I've been saying. Again, I'm not sure what you're saying I should do. Doesn't that number mean that if I am using my 1470w to charge a 48v I will only get 30amps? I suppose in literally perfect conditions it could be 40 amps. (37.37 voc x 8.61 isc x 6 panels / 48v) but that will never happen.

Once you get that worked out then look at charge rates. Unless you live in Seattle or Portland with less than 3 Sun Hours in winter, charge rate will fall right in the window of C/12 and C/8. If it exceeds C/8 select a battery that can handle more than C/8 which any Hybrid Battery can do like a Trojan. Trojan can handle C/4 just fine, just watch water usage and specific gravity.

I will get an yearly average of 5.7 kwh/m^2/day with 2.8 being my worst in December. What does that mean for my charge rate? That number refers to the hours of sun I will get in a day, I don't understand how that relates to the voltage or amperage.

[Sunking]

Current meaning amps. Are you saying I should get a charge controller that can charge at C/4 which is 60amps (240/4)?

Quit making this complicated. All I am saying is you can charge that battery up to C/4 if required. That does not imply or mean you should. It just means you can go that high if needed. With the Trojan 240 AH you have a big window to fit inside of at C/12 (20 amps) up to C/4 or (60 amps). Anywhere between 20 to 60 amps fits. A 30 amp controller would work just fine with 1470 watts, but no future growth potential.

[Bigbus]

Oh! Well hell! That's all you meant? That makes perfect sense.

Next question - I am not able to find an inverter that is 48v to match my battery bank but only 300w which is my peak usage. Not surprising. Do I just get the smallest 48v inverter I can find? I would also think that it is important to have a inverter/charger so I can easily charge my batteries with a generator. I would love if anyone had a specific model suggestion!

[ButchDeal]

Next question - I am not able to find an inverter that is 48v to match my battery bank but only 300w which is my daily usage. Not surprising. Do I just get the smallest 48v inverter I can find?

Daily usage???? usage is in Wh not watts.

a 300w inverter could spit out 7.2kWh in 24 hours

You want to size the inverter for your peak demand so that you can run your loads.

[Bigbus]

I misspoke. 300w is peak load. I just edited my last post to correct that

[jflorey2]

Next question - I am not able to find an inverter that is 48v to match my battery bank but only 300w which is my peak usage. Not surprising. Do I just get the smallest 48v inverter I can find?

Well, I'd get the best inverter for your application. GENERALLY smaller inverters have lower tare losses, so that's usually a good plan. But if you go really small/cheap, you could find a lousy inverter that works more poorly than a larger one would.

Cotek is about as low as I would go on quality. They have a 350 and 700 watt 48 volt inverter (SE350-148 and SP700-148.) It will be hard to find an inverter/charger under about 2000 watts. A lot of EV people are using Meanwell LED ballasts for battery chargers; they have a 54 volt version which allows you to adjust both current and voltage. It is a two stage charger (no float) so it's not ideal.

[Xplode]

Definitely look around to find something with low losses. I did not mean to say you had to find a 300w inverter exactly.... Just that you should be aware of the losses. If your peak load is 300W then finding one sized a little bigger is not bad. Less heat and wear on the electronics if they're not running right at their Max.

Just check the idle losses on whatever you look at. Find one that's not too high .

[Sunking]

I misspoke. 300w is peak load. I just edited my last post to correct that

OK you have lost me. You are having trouble finding small 48 volt Inverters because they are intended to be much larger than than 300 watts. You are in 12 volt territory.

[Bigbus]

They have a 350 and 700 watt 48 volt inverter (SE350-148 and SP700-148.)

Since those only have two normal outlets, how would I use it to power all my outlets and lights?

[jflorey2]

Since those only have two normal outlets, how would I use it to power all my outlets and lights?

You are going to have a LOT of trouble finding a 300 watt hardwired inverter for 48 volts. Some (like the Prosine) can be rewired via the manual. Some can be rewired anyway, but I wouldn't recommend that. You are likely going to end up with a ~1000 watt inverter that accepts hardwiring. Such inverters often have search modes that reduce quiescent current consumption so that could be an option.

[SunEagle]

Since those only have two normal outlets, how would I use it to power all my outlets and lights?

You would not. You are looking for a larger inverter that can be legally "hard wired" to a breaker panel.

[Bigbus]

You are likely going to end up with a ~1000 watt inverter that accepts hardwiring. Such inverters often have search modes that reduce quiescent current consumption so that could be an option.

Sounds good! Anyone have a specific model recommendation

[ButchDeal]

Since those only have two normal outlets, how would I use it to power all my outlets and lights?

How many outlets and lights do you have?
I am having a hard time understanding how you have only 300W peak load with all my outlets and lights