Newbie- Off Grid Cabin c/w gen support - What size bank 24 or 48

[bigdoughball]

Just starting to put together a small off grid system. I have purchased 8 of 6 volt batteries fRolls S-550, that are 428 AH capacity each. Was told to do two strings of 4 and parallel them to configure a 24v battery bank, that gives me 856 ah. I purch. a 110 vac, 24 volt CC at 40 amp capacity rating, as per installer recommendations. After researching company battery site, they recommend CC should be 10 percent = 85 amps. Am I missing something here!!

I have not used the CC and can exchange it for a higher amp model. I have purchased nothing, but the batteries and CC.

I purchased the Cabin, and it had a 6500 watt diesel gen 120/220 capacity. The cabin is wired for 220v. Reason, it has two 1500 watt base board heaters & electric water heater. Only other source of heat is wood stove. All fine with me, and won't be using the BB heaters / water heater when on inverter, LOL. I have breakers turned off.

The well pump is 110vac that draws 12 amps when started up.Cabin has propane fridge and stove, but want to remove PP fridge, and go with AC fridge. This will save on propane, as I will be able to shut of supply when not at cabin. I will then purchase an energy efficient AC fridge and Inverter. Shut down fridge until I can charge battery bank with solar and then wind. Still need propane, as cabin has propane stove, and will be installing a propane on demand hot water heater.

I removed the electric hot water heater.

The cabin was powered only by generator, but I want to install a solar supplement system with AC Inverter. This will allow me to watch TV at night with some LED lights, and keep the AC energy saver fridge running, while at the cabin, and run the well pump. I might have a need to keep fridge going for 28 days when I am at work. I could shut it down and remove items back to my house if that becomes a problem. And that's my delima right now, have no solar / wind charging ready to go. Don't want to do a AGS, as I won't be at the cabin, and don't like the ideal of a gen running unattended.

So, for now, will shut down inverter when not at cabin, until I install solar and then wind.

Plan to use the generator when needed and to keep my batteries charged after using, for the time being. I will install solar panels in the very near future / 6 months. Also will look at a wind gen too.

I am considering now going to 48 volt system, but really don't know if that is needed. After reading info on this site, it appears to be a wise decision, and will allow me to expand if needed. This cabin is remote, access only by boat/plane/argo/skidoo. Can't drive vehicle, and no grid power.

I will only be using battery bank to power TV/Sat Receiver/Stereo - 300 watts/Energy Efficient 10 cubic fridge/LED lighting inside and out/110 vac well pump.

The time being away from cabin is apox. 28 days and could be 42 one a year. I will do a solar array to at least keep a trickle charge on batteries. Will always top them up before leaving with gen.

So, is it best for me to do a small 48 volt system now and go with a 4k inverter? I have purchased only batteries and can exchange the CC for a 48volt!!

I can easily configure the batteries to 48 bolt and that would only be one string. More efficient/effective to charge and maintain in the long run.

Appreciate your advice, as I am really just getting into this, but eh, KISS, and do it right the first time, money saved and well spent.

Tony

[littleharbor]

While I'll leave the detailed responses to the pros here I would like to comment. If you decide to go with a 24 volt system and 2 strings of batteries (which aren't too difficult to keep a balanced charge on), If you have a battery go south on you , you still can operate on one string while you find a remedy for the other string. If you go 48 volt and lose a battery you are screwed until you can remedy / replace the sick battery.

[bigdoughball]

So true, as I had a good friend who is a tech tell me the same thing. He even suggested putting a battery isolator between the two banks, so the weak cell would not take down the second bank. Don't know if that's a good ideal, as would the isolator interfere with the charging? Not up on the electronics enough, but if it's a good ideal I certainly can do that. Done it before with an atv using a aux battery.

[Logan5]

Why not purchase all DC powered appliances, 24 volt refrigerator freezer, 19 volt big screen TV. Solar or Hybrid well pump and or reserve tank. if your cabin is small, you may not need to run an inverter at all or just to pump water into reserve tank.

[bigdoughball]

Interesting suggestion. The cabin I purchased was already wired for generator AC power, and had two BB 1500 watt heaters and 110 volt hot water heater - 30 gallon. The well pump was already installed using a 110 volt 13 amp AC motor. I removed the hot water heater to install Propane on demand. Keep the darn BB heaters for the winter while waiting for wood stove to kick in, and running gen. The solar dealer suggested I get a DC fridge to replace the propane one. I want to remove the propane one, as cabin is remote and using two 100 lb tanks becomes cumbersome to get back and forth. But will keep two tanks just for the stove, that way I can shut the propane off when leaving.

I will investigate the DC fridge versus low AC fridge. The cost I am assuming is greater for DC than AC, and I do need inverter for the lights and TV that are in the cabin now. Also the darn wiring is all AC coming from the gen shed to the cabin, about 100 feet.

But interesting concept, thanks.

Tony

[Logan5]

Yes and most are top load, so takes some getting used to. You are attempting to add battery solar power to a cabin originally designed as a generator only set up. Going All DC may not be a good fit for you unless you do work a wood stove. and or if you plan to live full time

[bigdoughball]

Thank you. Yep that's my delima, cabin design for 220 vac gen. But I will take my time and seek good advice, like this forum. From the reading of some post, it's more than helpful advice, it's also the hazards I am being made aware off. Not matching inverters/fuses and wiring for the system I develop. I am a newbie, but have the ability to read and take the advise of others. I do know how to use a meter, taught by my late father-in-law who was an electrician. He helped me a lot, and to respect electricity. Hence, that's why I posted on this forum, a very well knowledgeable base of members who certainly know their stuff.

[Mike90250]

To run the pump, you need a pure sinewave inverter.
But first, you need to work up a power budget, to see what size system you need. Add up the wattage and hours of your gear
10 watt LED light x 4 hours = 40 watt hours
When you have a final watt hour total, then you start sizing the battery bank

[bigdoughball]

Been trying to just that, and this is what I have so far:
Energy Efficient Fridge - Med Size. I think they are around 2 amps per hour. So 2 amp times 120 vac = 240 watts per hour, times 8 hours (avg usage per day) = 1,920 watts per day.
Pump = 13 amps times 120 volts = 1560 watts. Times 30 min per day = 780 watts
Lights = 4 LED at 8.5 watts each = 35 watts times 4 hours = 140 watts
TV = 100 watts times 5 hours per day = 500 watts
Stereo = it's a 300 watt sound bar system, but don't know exactly how much it draws. I haven't figured that one out. It's on when TV is on, so 5 hours of usage.

That should be it for battery / inverter usage in a day. I do have gen to top up the batteries after a day or so usage. So total wattage draw per day is 3,340 watts. Does this seem correct or close to what I can expect?

If so, I am configuring two battery banks of 4 times 6 volt surrette S-550 batteries, that have 428 ah rating for each battery. So that gives me a total of 856 ah when I parallel the two banks. So would that be 24 volts times 856 ah = 20,544 ah battery bank. If so, how do I calculate how long before I deplete 20 percent of my battery bank, using the above watt draw per day? Is it calculated by multiplying 20,544 times 20% = 4,108 ah hours of usage. Would this mean I would get one day of free usage and then have to charge?

This is calculated as if I don't have any solar or wind inputting into the battery bank. That will come later, just doing it a bet at a time, and using my Gen and battery charger to charge back the batteries. I will certainly get a solar panel and CC to supplement the batteries with a trickle charge when not at cabin.

Really don't know if I am on the right track with my calculations, as have been reading a lot and my mind is all over the place, LOL. But please put me back on the correct track. Oh, and what inverter wattage would compliment this system. Was thinking about a 4kw PSW.

I have an 24 volt 40 amp IOTA charger bought too.

Thanks, appreciate the help.

Tony

[bigdoughball]

One other important factor I have to consider, what would be an acceptable depletion level of my 6 volt batteries? Rolls state a 6 volt battery is depleted at 5.25v. I know my batteries are at 6.27 volt now fully charged. All 8 of the 6v batteries read that. So that only gives me 1 volt of depletion, but then the battery would be depleted, and I don't think that's acceptable? Kinda lost at the moment, trying to get my head around how long I can be on battery power, before I reach the better re-charge state. My Battery Charger is pre-set for certain paramiters to shut down, but I think that is not acceptable either. Would like to have control / input over them settings to set a better buffer zone. Maybe I am over thinking this too much!

[Mike90250]

Well, you appear to have started buying gear and locking yourself into a 24V system. Generally, a single series string of batteries is better (more consistent , reliable) than a parallel system.

Fridge. Energy Star rated fridges claim about 300-400Kwh yearly usage, which is roughly 1Kwh per day, give or take. So either your fridge is not a saver, or you are overestimating how much it actually consumes.

Loads, depletion, you measure everything in watt hours. Convert your battery to watt hours 25v x 856 = 21,400 wh (batteries are actually 12.5v, but simply called 12V)

On a daily basis, you only want to consume about 20-30% of the charge. Calculate it in watt hours, and that's how you plan. A battery in use has weird things happen to it's voltage, and you can't rely on voltage as a "counter"

[bigdoughball]

Thanks for the Chart, I have that saved and will print it off. My batteries now are at 6.27 v. Expecting my adapter, for the 5-20p plug on the charger, any day now. Will get them charged up. In my garage with no load, all hooked up, but not being used yet. Will move to cabin later.

Yes, I decided on the two strings and parallel after getting some advice from a few buddies. Basically my cabin is remote and they convinced me to have a parallel 24v instead off one string 48v. Just in case a battery starts to get bad in one of the two strings. I can at least get by until I find the culprit.

Yell, overestimated the fridge. Will be looking for an energy starr fridge. Danby 9.9 model listed for 297 kwh/yr would be the model.

I have one off those counter top ice makers and only use it when on gen, so that's not a problem.

The longest stay in summer will be around 4 days. The winter will be longer stays, as I can skidoo to cabin in about 20 min from my house. Summer time by truck and boat. Not a big deal thou.

The problem with me, I work 28 days on and off. So will have to make certain those batteries are charged up before I leave the cabin. Once I get the install done and re-wired thru a auto transfer switch for Gen and (inverter / batt power), I will install a couple or three solar panels with mppt cc. This will certainly keep the batts up while I am away, and assist in putting back some juice in batts too. For now, by buddy will monitor and start gen for me, if needed. That takes the pressure off getting everything at once.

Thanks, much appreciated. I realize it takes a bet of work to monitor the batts, and keep them in good condition, as to get as much as possible out off them. This is new to me, so learning as I go!!

Tony

[Sunking]

Just starting to put together a small off grid system. I have purchased 8 of 6 volt batteries fRolls S-550, that are 428 AH capacity each. Was told to do two strings of 4 and parallel them to configure a 24v battery bank, that gives me 856 ah. I purch. a 110 vac, 24 volt CC at 40 amp capacity rating, as per installer recommendations. After researching company battery site, they recommend CC should be 10 percent = 85 amps. Am I missing something here!!

Who ever told you to wire them in parallel should be shot and dismembered. Make sure to cut their head off to make sure they are dead and never come back. Go with 48 volts.

Lead acid batteries should be charged with a C/10 current.where C = the battery rated AH capacity. So if you have 850 AH you need 85 amps. Your batteries are 428 AH meaning they need roughly 43 amps. Wire them in parallel and you need 86 amps. Makes no fricken difference as it requires the exact same wattage of 2000 watts. However more expensive to do at 24 volts, because if you use 24 volts means you need a 80-Amp MPPT charge controller for $600. With 48 volts means a much less expensive 40 amp charge controller and smaller wire. Those Zombies who told you 24 volts want to kill you and your batteries, cut their heads off. They are ignorant and stupid.

[bigdoughball]

Thank you Sunking, was hoping you chime in. I can / WILL configure the bank to 48 volts, no problem.

So that's it, you and Mike90250 have told me to go to 48. That's why I am here, to get the advise from experts. So better lesson eh!! LOL. Thanks!!.

I have nothing purchased yet, just the batteries and constructed a box to put them in, so that makes it all easy to re-do the wiring from 24 to 48.

Also the charger hasn't been used, just setting waiting for the darn electrical adapter. Glad I didn't have one, LOL. Will return it and get a 48 volt charger, and make certain it's 40 amps.

I also used the C/10 formula, found it on the Rolls website, and question the amperage of the charger this Solar Installer sold me. He hasn't answered my email yet. But won't have any problems returning it. Will be talking to him tomorrow. He did mention to me about the advantages of going with higher volts, but a few of my friends who have solar, said 24v would be fine. They started out with their solar about 10 years ago, and some have 12 volts while one converted to 24.

I haven't even looked at the cost of solar panels and mppt cc, so thanks for steering in me in the right direction and will save a few bucks in the long run.

And if a battery does pack it in, I can always use the gen to get by until I get another battery to replace it, no big deal.

Many thanks, have a great day!!

Tony

[Sunking]

Tony do not ask the Installer. In other words do not trust him to even know what he is doing. He most likely has no clue. Answer the question yourself with facts, not opinions. If your Controller is a Real MPPT Controller, if not you got screwed. With a MPPT controller:

Output Current = Panel Wattage / Battery Voltage

It is 3rd grade math, you do not even need a calculator to figure it out. Example 1000 watts / 24 volts = 40 amps.

Do not get to hung up on hitting C/10. There is a window of C/6 to C/12. C/10 is just in the middle of the pack. As long as you hit the window, you are OK. You do not size the batteries and charge current to match. Not initially anyway. Battery size is determined by daily watt hour usage and sized for 5 day autonomy which in practices gives you 3 days usable to CYA on short 2-day cloudy spells. So if you need say 4.1 Kwh per day, you need a 20.5 Kwh battery. I only need to know AH after I know how many watt hours of capacity the battery is required to have and what battery voltage is required. If I were to go with 48 volt battery the AH = 20,500 Watt Hours / 48 volts = 427 AH @ 48 volts

The panels are sized to generate your daily watt hour usage worse case. 8 times out of 10 your charge current will fall within the acceptable range for the battery. You only fall out of that range if you live where winter Sun Hours are really short or really long. If that happens then you make adjustments. If your days are to short giving you a C4 charge current you use AGM batteries and eat the cost.

Back to the example if you have a 48 volt 428 AH battery you know immediately you need a panel wattage of at least 36 amps x 48 volts = 1728 watts to meet the C/12 minimum, and up to 71 amps x 48 volts = 3400 watts at C/6 maximum. Hint you need to be 1700 to 3400 watts with your batteries. That is a job for 48 volts. Not even possible with 12 volts.