What size of solar system

[Jaust]

Thanks for your reply Sunking. If you read my earlier reply it explained my reaction and I did apologize for getting a little ticked. But getting a responce like bringing up a 12v battery each time... That's just a waste of my time. And if there is a problem with my configuration I definitely want to know so I can rectify it. Your latest response makes a lot of sense. if you read my reply just before this one you'll see that I purchased the cabin with this battery and inverter setup already installed. From the research I did it looked like a good setup. I charge the batteries with the Xantrex 2400w inverter/charger powered by my generator and according to the indicator it has gone through all three phases of charging into float mode with the batteries at full charge. That's why I wasn't sure where the problem with this setup existed. I don't know why the previous owner used this setup but I know he did a lot of research before he did this. I also probably misstated the AH of the batteries because I believe they 230 AH. My mistake.

I have been looking into rewiring the batteries to either 24v or 48v setup and getting a new inverter if that's what I need to do. I'm not against losing a couple batteries for the 48v setup. What difference besides cost would there be between the two. Does it matter that the cabin is all wired for 12v. What about all the stuff we have plugged in, (cell phone charger, wife's Christmas stuff, our lamps, etc...)I am still a little confused on how that would all be affected if I have to make a change. Thanks for all your help. It is greatly appreciated.

And thank you mschulz. I just saw your post while I was replying to Sunking. I will get the exact battery specs but I won't be back up to the cabin until Thanksgiving. As for the power usage I know I'm still on the high side but I know we use no more than 4kwh a day. I'll look at getting rid of those lights and for now I'll worry about a solar setup after I figure out my battery setup. Thanks much.

[Sunking]

Thanks for your reply Sunking. If you read my earlier reply it explained my reaction and I did apologize for getting a little ticked. But getting a response like bringing up a 12v battery each time...

No reason to apologize, at least not to me. My skin is to thick to let someone I don't know hurt my feelings. So we are good.

The reason I kept bringing up 12 volts is you did not seem to understand the consequences, and it appears you are now seeing the light. I am more than happy to help you, but what you have is a bit dangerous and I do not want any part of it. So good luck to you and be safe. I am out of this thread.

[paulcheung]

To the OP,

If you are sure you not use more than 4 KWH in three days, that is less than 2KWH each 24 hour period. You don't need that amount batteries. I have a small off grid system run 24/7 is 90 watts about 2KWH a day, I have 675 watts panel and 450AH at 12 volt battery. It working ok for me if I don't have rainy days. I have to use generator to charge the battery when I have cloudy days.

In your situation, you are not use the power 24/7. So it is a bit difficult to assume the high power demand, but I assume the high demand will be in the day or the evening, You can get away with the current 12volts wiring if your highest demand not over 675 watts. you can just use 4 of those batteries wired in 2 in series and 2 string parallel if they are 6 volts 225amps, you can get 2 250watts solar panels and wire them in series and get a 40 amps MPPT charge controller. you don't need more than 500watts panels as you just go there once a while and you have generator to charge the batteries if you need it.

[Jaust]

Thanks paulcheung, I'll wait and figure out tha solar later. I want to make sure I get he batteries set up the best way. I was just asking which configuration would work best. And I didn't mean the cabin was wired 12v but that the wires on the batteries are all set up for the 12v and whether they would have to be chsnged also if I had it wired for 24v. As for the power I'm still high with the 4kwh in a day but when I'm up there next week I'm going to get an exact wattage and better guesstimate of how much time we use everything to get an exact on that.

[paulcheung]

It is all depend on the amount of power you need in 24 hours period. I think 24 volt battery system is adequate for a vacation cabin, still it is the amount of power that matters. When you find out the amount of power you need, we will be able to advise you properly.

[mschulz]

Since you have the batteries, wire them up in 1 series to make 48 volts. Your efficiency will be greatest.

I bet those batteries are 220amp. So useable power =220amp x 48v * .20 = 2112 watt hours. This will draw down your new bank to only 20%.

Now let's find out what draw and charge you need. We are going for c/8 on those.

220amp / 8 = 27.5 amps. This is what you should put in and take out. So your panels and inverter should be no larger than. 27.5 x 48v =1320 watts.

This tells you that if you wire 8 of yor batteries together for 48 volt, yor inverter charger needs to be 1200-1400 watts at 48 volts.

Like I said before, dump all your 12 v stuff and run it off your new inverter.

***note that this does not account for any days of no sun and if you are using the cabin on cloudy days you will need to run your generator each day to charge your batteries. This is an estimate only. Now you need to get the actual size of your batteries and your usage to see if it will work.

[paulcheung]

Since you have the batteries, wire them up in 1 series to make 48 volts. Your efficiency will be greatest.

I bet those batteries are 220amp. So useable power =220amp x 48v * .20 = 2112 watt hours. This will draw down your new bank to only 20%.

Now let's find out what draw and charge you need. We are going for c/8 on those.

It is a vacation cabin, he doesn't use it every day, so 20% for 5 days it is waste of money. He can safely discharge to 50% and still last him few years as the cycle count on each year is less than 50 cycles. Remember battery will die in a few years even you don't use it at all.

also the C/8 rate is also too much as he has the whole month to charge back the battery, the solar power just sit there and wasted, He has generator to charge the batteries if is needed.

Again the generator need to start and run for hour or so every month or two, so he can use that to stir up the electrolyte in the batteries.

[mschulz]

It is a vacation cabin, he doesn't use it every day, so 20% for 5 days it is waste of money. He can safely discharge to 50% and still last him few years as the cycle count on each year is less than 50 cycles. Remember battery will die in a few years even you don't use it at all.

also the C/8 rate is also too much as he has the whole month to charge back the battery, the solar power just sit there and wasted, He has generator to charge the batteries if is needed.

Again the generator need to start and run for hour or so every month or two, so he can use that to stir up the electrolyte in the batteries.

Paul - like I said at the bottom, it is an estimate only. We all think differently about cycling as well - what is too much or a waste of $$.

[Jaust]

Ethanol you both for the info. I have learned slot in a short amount of time. I will definitely look into rewiring either 24 or 48. I'm still wondering what is so dangerous about the setup now. The guy that set it up was no dummy. I'm just wondering what is so dangerous that it scared Sunking away. I'm sure he's so used to everyone bowing to him and his knowledge. But after I explained my setup and asking what I can do to make it right that instead of helping he says yor on your own. I'll probably get thrown out of the forum but he can kiss my ass. What kind of a responce is that? I've been on another forum that has given me great advice. I had to laugh when I saw his name come up. They warned me about him. I should have listened.

[Sunking]

I'm just wondering what is so dangerous that it scared Sunking away. I'm sure he's so used to everyone bowing to him and his knowledge. But after I explained my setup and asking what I can do to make it right that instead of helping he says yor on your own. I'll probably get thrown out of the forum but he can kiss my ass.

Your skin is real thin. I will not help you if you intend to use 12 volts. I don't want any part of you injuring yourself, others, or burning your home down. I have taken an oath as a professional to do no harm. Someone else can help you do that and be held liable. Not me. Someone will be around to explain it to you later. Who ever told you it was a good idea or set it up that way is not knowledgeable and did not know what they were doing. If they had would know the dangers of 12 volt high current systems.

I will give you one hint. a 2000 watt inverter at 12 volts takes 200 amps of current. A large luxury home with all the electrical bells and whistles does not draw that much current. Possible if they demanded 48,000 watts, but it never happens. Those houses have much larger service wires than you do. Walmart stores do not draw that much current. Nor does an oil refinery which draws million of watts at a time. They do not do it for 2 reason. Big waste of money and dangerous. That ought to give you something to think about.

[Jaust]

Sunking, I wish you would have read the threads. I've said multiple times that this is the way I bought the cabin. I've asked for your help to help me rectify this problem and you said you want nothing to do with helping me. So I'm asking for help from someone that will tell me what the problem is and to help me. I respect the knowlege you have and wish you were on my side but since you're not I need help. That's all I'm saying. I personally would not tell someone that what you have is do dangerous that I don't want to help you make it safe.

[Sunking]

Sunking, I wish you would have read the threads. I've said multiple times that this is the way I bought the cabin. I've asked for your help to help me rectify this problem and you said you want nothing to do with helping me. So I'm asking for help from someone that will tell me what the problem is and to help me. I respect the knowlege you have and wish you were on my side but since you're not I need help. That's all I'm saying. I personally would not tell someone that what you have is do dangerous that I don't want to help you make it safe.

Read my lips. 48 volts. Loose 4 batteries. 400 watts of panels (grid tie panels, not battery panels) , and a Midnite Solar Kid controller. Buy a 48 volt inverter and run everything off 120 VAC. In addition buy a good Golf Cart 48 volt battery charger to run off the genny. Its that simple.

[Jaust]

How many times can I say I'll worry about the solar later? What's the best battery configuration? You say it's so dangerous with no explanation why.

[paulcheung]

Less than 800 watts inverter you can use 12 volts, 800 to 1500 watts 24 volts, over 1500 watts inverter 48 volts. Those are the best configurations.

When you draw more than 50 amps current from the battery bank, you need some big wires and when you reach to 100 amps it is hard to terminate the end properly unless you have the right tools and experience. many thing can go wrong when you dealing with high current, slack connection can cause fire.

[Sunking]

What's the best battery configuration?

To use all your batteries 24 volts. To extend battery life and efficiency 48 volts

You say it's so dangerous with no explanation why.

Answered that a few times and by others. CURRENT.

1000 watts at 12 volts is 100 amps
1000 watts at 24 volts is 50 amps
1000 watts at 48 volts is 25 amps.

A 1000 watt 12 volts requires a minimum #4 AWG very expensive wire only for short distances. More than 10 feet bigger more expensive wire. It requires special tooling (hydraulic compression) , training, and heavy connectors to . It also requires frequent inspection of loose connections and poor termination on cables. Failure to do those things will lead to a meltdown and or fire.

EV9MeltedTerminal.jpg

The issue is resistance and current flowing through the resistance of loose connections and poor wire terminations. On efficiency side the same issue, resistance. The resistance in wiring causes power losses as heat in wiring and connections. Less current means lower power losses or higher efficiency. 24 volt systems are 400% more efficient than 12 volt systems for a given power level on a given wire. A 48 volt system is 1600% more efficient.