Small Cabin

Small Cabin Forum
 - Forums - Register/Sign Up - Reply - Search - Statistics -

Small Cabin Forum / Off-Grid Living / My head is melting about Batteries!!
. 1 . 2 . >>
Author Message
# Posted: 1 May 2019 12:18


I am new to the forum and new to the off grid world, but have learned a lot be reading on here for several weeks

My build should start in maybe 6 weeks once I have the land and permits finalized – so that is all in hand (up state NY)

I am struggling badly to work out/understand my solar batteries needs and looking for a little bit of help

I will be using the camp in the main for 2 days per week over the summer/fall and maybe on the odd occasion 5 days at a time; but mainly 2 days per week (very little use over the winter due to the snow levels and the roads being blocked

Main use at camp will be;

• LED lights
• Charge cell/laptops
• Hair drier (I know, I know…………..but my wife would kill me otherwise…………..and I HAD to compromise!!)
• Maybe a small toaster

I know the last 2 items are big users

Water Well, fridge, stove will either be Propane or Generator

Daily Watt use I calculate on these items to be around 700Wh max based on average usage times (or 1300W if I connect the Well pump - which would be great if i could do that also)

Based on some of the camps around me, my initial thought is the following;

• 6 x 100W panels
• Charge Controller
• 1000W inverter

What would you recommend in terms of Trojan 105 Solar batteries for say 2 or 3 days charge capability (say 2100Wh for 3 days, or 3900Wh with the well pump)

How many would you recommend to store the charge for 2 or 3 days in a worst case scenario?

The 105 is 6V at 225Ah

It cant be as simple as 6 x 225 = 1350Wh and therefore I would need 4 batteries to give the 3900Wh for 3 days……………that seems too simple!!

Can you help at all?

Nate R
# Posted: 1 May 2019 13:11

You said well is on generator, and then talk about it being on the batteries? Which is it?

If I were you, use a cooler (not fridge) with ice. GOOD cooler. Fine for 2-day trips.

Use a generator for larger loads. Toaster, hair drier, well pump. (Probably use a smaller tank in building w/ 12V/24V pump for feeding faucets)
Propane for stove.

Then get 600W of panels, a small inverter, run 24V of the T105s and maybe a Morningstar Prostar MPPT 40 controller.

REALLY though, I'd go cheap for now and see how you actually NEED and USE power before you spend the big bucks. Get a small/cheap battery and inverter, and recharge w/ generator if needed, and see what your actual loads/uses are once oyu have a place.

Maybe 2-100W panel, a 100 AH battery, a cheap PWM charger, and a battery monitor, and some cheap inverter.

Yes, to size solar, batteries, etc all properly, you need to know your loads. I think the trick is many people don't REALLY know their loads ahead of time. You ened a way to figure that out first, and THEN install/invest in the more expensive stuff.

# Posted: 1 May 2019 13:56

First recommendation, spend the $20 on Amazon and get a kill-a-watt meter. Actually run those loads and see what your usage really is. Run the hair dryer for 15 minutes and see what it is and then you don't have to guess. Same with the fridge for 24 hours, etc.

Cheap investment to help size things properly.

Second don't forget you don't want to discharge your batteries past 50%. My math says you'd want 6 batteries at least.

# Posted: 1 May 2019 14:03

Thanks for the reply

The cooler is a good idea since it is only for 2, maybe 3 days at a time

Even a small Propane fridge is coming in around $800………..I could get 3 good coolers for that price

As this is a new build, I was trying to set it up to run what I want/need from the outset, rather than 12 months down the line needing to change too much

So far, based on guys in the area, using it similar to how I will use it, they seem to have 4 solar panels (300/400W) and 4 or maybe 8 x T105’s…………… was trying to set up something similar

In terms of the Water Well

It looks like everyone in the area powers from their generator – I was simply wondering if I could have the well on solar, if I had the 6 panels and sufficient batteries……………..but cant figure out what that number of batteries should be

Based on all the different solar calculators I have tried and entering all the items I may use, I would estimate 700Wh per day/1300Wh per day if I connected the well

To be honest, I would rather have more power than needed and not have to worry every time I switched on a light or a fan, etc

# Posted: 1 May 2019 14:36 - Edited by: zorro

jhp - thanks for the recommendations

That kill-a-watt meter sounds good!

In terms of the fridge, that will be propane (unless we go the cooler route)

Batteries - this is where I am struggling a little

Estimated Power use

700Wh (without well)
700 x 1.5 (contingency) = 1050Wh per day

3 days = 4200Wh

T105 Batteries

6v x 225ah = 1350Wh
1350 x 0.5 (max drain) = 675Wh maximum

4200/657 = 6 Batteries

So 8 as a contingency

Are my workings correct……………..or am I wrong…………..that is where I am struggling a little!

Nate R
# Posted: 1 May 2019 15:20 - Edited by: Nate R

1050 x 3 = 3150WH.

I like to figure I'd go down to 40% SOC for an extreme case, not daily. (3 days, no charging at ALL, and you're not cycling these batteries DAILY....)

So, figure 3150WH needed AC..... There will be losses due do inverter inefficiency, etc. Figure 85%? so now we're at 3700 WH for 3 days. Need 6KWH of battery go draw 3700W down to 40% SOC. 6 T105 batteries should be fine if you run a 36V system.

6Vx225 AH = 1350WH/battery. 6 batteries would get you 8100 WH available total. So running 3700 WH out over 3 days still leaves you above 50%.

# Posted: 1 May 2019 16:02

Thanks for pointing out my math error - missed that!!

And thanks for confirming my initial thoughts of 6 batteries and if I can afford it, maybe go a little higher



# Posted: 1 May 2019 18:35

If you are up to six T105 type batteries already switch to a 24 volt system and go with eight in two parallel dtrings of 4 in series. 4S2P. If you are using lead-acid batteries you should have as few parallel strings as possible to get best battery longevity.

# Posted: 1 May 2019 18:38

Well pumps often have a huge startup surge, requiring a big inverter, which is wasted all the rest of the time. Inverters that are way oversized for the normal loads waste more power sitting there powering a few LED's and a phone charger. That is why many people use a generator to pump a few hundred gallons into a tank they use a small RV type pump to supply water to the cabin.

# Posted: 2 May 2019 08:13

I almost wouldnt bother with a huge solar system in this area, NY. We get on average 3hrs of useable sun a day. Let the generator run all the 120v appliances. You can charge a cell phone with a portable battery bank. You dont need a fridge for 2 or 3 days, a cooler will work fine.

Have you calculated the pay back time on solar vs a generator you will alreaty need, so the price of fuel?
For me it wasnt worth solar. Much less hauling back and forth a huge battery bank in the fall/spring....or the contual maintence and checking of battery water levels, SOC, solar input, wattage used.

Il just burn a few gallons of fuel a day and change the oil every year.

# Posted: 2 May 2019 10:11

Thanks for the suggestions on generator v’s solar

Thanks also for the tips on linking up the batteries in a 4S2P configuration - never realized that, so thanks

I have also taken on board the suggestions about the refrigerator v’s cooler and having spoken to my wife, the cooler is the agreed best option for us – can get really good big coolers for less than $300

I may be wrong, but I thought solar panels did not need perfect sunshine and can still charge when it is cloudy/overcast?

The other issue is honestly, I don’t want to spoil the peace and quiet of the area; my plan would be to use the generator as little as possible and really only for the water/shower

This is in “pre-build” stage, so at the moment, I don’t have any solar system/batteries and will need to build it out from scratch; this will be a long term ownership/use of the cabin, so happy to spend a little more up front to try to get it to what I want from the outset, accepting things do change over time

So at the moment, we will likely go with;

• Cooler (no fridge)
• Stove – propane
• Well – generator
• Power – solar with generator back up
• Heat – wood burning stove

We will be putting in a septic and need to drill the well

# Posted: 2 May 2019 10:57

I have planned for 750wh per day and my system is solar - Eastern Canada so same sun as probably upstate NY - and I only get it in the mid-morning to late afternoon but with MPPT CC. I have solar, propane fridge and stove, and wood heat. The solar is only 12 v with two panels pumping about 510 watts in total to keep the batteries (2 - 6V at 370 AH - L16's) up. I have a 1,000 watt pure sine inverter and the whole system works fine - 4 years now. I would suggest to use the generator with the larger draw items such as the well. I have tried the cooler thing and personally did not like it. If I were you (my spoiled opinion), I would beef up the solar a bit and run a small electric fridge. Use the genny to run the hair dryer and toaster. The Killawatt meter is a good idea. Make sure you ground the system properly!

# Posted: 2 May 2019 10:58 - Edited by: offgrididaho

It seems like you're well on the road to sorting this out, and there are some good suggestions above.

A few general things to contemplate as this percolates around in your head:

1) If you're anything like me, don't get too settled on this plan right now, let it evolve. I spent the whole winter tinkering with ideas and massaging my setup, you seem to have some time yet so don't commit until you definitely have to. I look at my version 1 (I ended up with what I call version 4.2) and it's amazing how different it is.

2) Starting small and building up as needed is a good call, with a few caveats. One big one is it's not usually a great idea to add batteries without swapping out the whole bank (i.e. if you start with 4 batteries, adding another 4 new batteries to that bank of now used batteries two years from now isn't recommended). If cost isn't a huge constraining factor if you're over-batteried (for lack of a better word) at first that's not the end of the world, they'll last a long time because you won't be drawing them down very fast. Also, if you can settle on what voltage you're going to standardize at that helps with wire sizing etc both now and down the road (I ended up going 48v, I'm very happy with how it's working, but it does seem like the jump in terms of product pricing and capacities is big going from 24v->48v so 24 might be the way to go for you).

3) Don't forget the inefficiencies of FLA batteries (not a bust on FLA, that's what I went with, couldn't afford the lithium route, just reality). You have a 1.2 inefficiency factor with FLA (i.e. whatever you think your total battery bank size should be you need to increase it by 20% to accommodate the power in and power out inefficiencies). Another efficiency factor is high draws on small banks essentially make them "smaller". The T105 is rated at 225ah at a 20 hour rate, that means it will deliver a total of 225amps if you draw 11.25amps or less per hour. But if you draw more amps per hour than that (which high draw items like toasters and well pumps and hair dryers do) then you won't get 225ah, you might get more like 185ah (the 5 hour rate). Not a huge difference but something to consider.

4) Read up on bulk, absorption and float for charging your batteries. FLA are only happy and last longest when they get fully charged to 100%, meaning you bulk fill the batteries then go through absorption phase where last few amps are packed in there before going to a float (maintenance) charge. Getting that absorption charge is a nightmare with a generator because the charging amps are tapering to almost nothing and you're big burly generator is thumping along noisely for hours putting out 100 watts because that's all the charger wants (make sure you're getting a good quality 3 stage charger). So if you're not going to have that much solar and plan on charging your batteries regularly with the generator, run the gen early in the day to bulk charge your bank and have enough solar that your panels can do the absorption phase for you throughout the rest of the day.

5) Just a thought, but since you're planning this whole thing out, you might at least investigate / consider 12v (or 24v or 48v, but meaning off your batteries) for your fridge. Or even an energy efficient 120v fridge run off an inverter. I have propane fridge now but wouldn't buy another one as they're expensive and I have never had great experiences with them (maybe it's just the ones I've dealt with). You could go with a small RV style fridge (like a dorm cube fridge, but they draw ~36w when running and only run about 1/2 the time unless it's really hot), you could build it into an already insulated box and it would be a pretty efficient way to go. I've also used Engel 12v coolers on our boat and they're awesome and very power efficient.

6) Not sure what your budget is but investigate combined inverter/chargers too. I was a little reluctant at first not having used one before (and fearing what I'd do if the whole thing died), but I really like how the Victrons (and I'm sure others) work both in charging, and inverting, but also supporting each other. The Victron has "power assist" that boosts your generator output by using battery power so if you're running your gen to charge your batteries and you plug in a load in the cabin that's bigger than the generator can take the Victron will stop charging the batteries, put all the gen power to the cabin, and add additional power from the batteries to support the load. Downside on these is they're not cheap and they do have a decent size dead load when they're just sitting there idling along.

-- Bass

# Posted: 2 May 2019 12:32 - Edited by: NorthRick

Quoting: Nate R
6 T105 batteries should be fine if you run a 36V system.

I would recommend against setting up a 36V battery bank. You will be very limited on what you can buy that will work with that. Think 24v or 48v. As stated already you don't normally want more than two parallel trains of batteries. Also, as stated above stuff for 48v is generally for larger systems and the components are more expensive.

If you stick with the 6v batteries you should think either 4 in series (4S) for 24v or 8 batteries in two parallel trains of 4 (4S2P). Both ways get you a 24v bank with one obviously twice the capacity of the other.

Quoting: zorro
6 x 100W panels

I'd look at fewer larger panels too. They tend to be cheaper on a dollars per watt basis. Fewer connections too.

# Posted: 2 May 2019 12:54

Quoting: NorthRick
I'd look at fewer larger panels too. They tend to be cheaper on a dollars per watt basis. Fewer connections too.

Generally true, only exception might be if you can get smaller panels with free shipping. My 315w were only $225 apiece but shipping was $315. And best I could tell that's what shipping would have been if I had ordered 1 or 2 panels, since I got 6 the shipping cost was spread across more panels and not so bad, but if you're only looking for 600 watts it's possible smaller panels with free shipping would be cheaper, albeit with the more connections noted above.

Nate R
# Posted: 2 May 2019 13:08

One way around the shipping MIGHT be: V-Boat-Back-Up-System-Off-Grid-Application-RNG-300D

Ship to a Home Depot for free and pick up there.

# Posted: 2 May 2019 13:29

Thanks for all the info guys – really appreciate all the help

I need to spend some time going through all the info, especially around the 24/36/48V issues

I think I am likely to go the T10’5 at 6V batteries as they seem to be pretty common, though crazy heavy

I also never realized it was better to have fewer panels – I was working on the basis that if I had 6 and 1 was damaged due to trees or wind, it was less expensive to replace

But I will look at the Home Depot site – even Amazon has the option to order with no shipping – and yep, I also had a quote of $350 just for shipping…………………….I am not paying that to anyone for shipping

I will also pick up the batteries, even if that takes 2 trips cause again, shipping quotes are crazy

# Posted: 2 May 2019 13:34

For batteries also check out the Deka GC15, you can order to store for free pickup at Lowe's (get their credit card and you get 5% off also).

# Posted: 2 May 2019 13:48

Since you are in the planning stage, here is my $.02

Requirements: Run a Hair Dryer, Led Lights, Charge Cell Phones and Run well Pump.

Wire your cabin like a house, use a panel with breakers. Wire in a generator feed and an Inverter feed. Plan for a battery storage area or generator shack and run 220 volts to the cabin main panel. Buy a generator that will run your good pump and hook it up to the main panel and go from there. You will be more efficient running 120-volt outlets and lights than 12 volt or 24 volt.

After you really find out what you need and want, you can build out your solar system to meet those needs.

I bought a cabin that had no power, and went the 12 volt route, than 24 volt and now I run the whole thing off 120 volt AC with an inverter off my battery bank. I use my generator for the hairdryer, vacuum and power tools. Works great.

# Posted: 2 May 2019 14:07

If you want quiet you can spend alot of money on a inverter type generator or build a small shed and run 100+ft of 240v line.

I built a shed for mine and plan on running it 200-250ft from the cabin. The shed is alreaty built and ready to go to the property. I dont even have a driveway at the moment but i also didnt want to hear a generator running for hours on end.

If you find your self useing the generator for small loads you can also use an inverter/charger connected to a battery bank powered by your generator.

Do you have trees on the property? Any shade and that 3hrs of average useable sun can really drop. There is a useable sun for solar web site. It really needs to be calculated into any system. Upstate NY dosnt have alot of sunny days fall/winter/spring.

# Posted: 2 May 2019 14:23

I started with a cabin that was already wired 120v, so it was easy for me, but I did the same as redwolfguild and brettny. Cabin is all 120v, power comes from batteries and inverter (or generator) in shed away from the house, can't even hear the generator in the house, and all my normal 120v stuff runs without issue.

The cost savings on the generator can be substantial. Instead of an EU2200i (1800w continuous) very quiet generator I got an EG2800i for same price (2500w continuous)... a little louder but not noticeable since it's away from the house.

When sizing generator best practice seems to be to find something that can run your charger at its max rate (some higher end chargers can be throttled down a little bit, but not too much) without running at over 80% of generator's rated power.

# Posted: 2 May 2019 14:31

The generator and "mains" set up also sounds interesting - used to be confused, now I am getting lost

The Deka GC15 - is it this version;

If so, that is a good price - can also get a 10% coupon from Ebay - so 8 would be $1036 plus tax

A $324 saving over the Trojans

Are they just as good batteries - reviews seem to be good?

# Posted: 2 May 2019 15:06 - Edited by: silverwaterlady

I might get flack for this idea. It sounds like you don’t need a lot of solar.
Check out the Goal Zero “generators”. It’s a self contained lithium battery that you can charge at home and at camp use the solar panel to maintain the charge. I have the small and medium size.
The small I use outside to run my rv pump for my shower and small tools. The medium I use inside for battery charging and kitchen appliances that don’t heat up.
I needed something simple and easy. Lightweight and portable. Batteries I didn’t have to leave at camp on a trickle charger. The batteries can be replaced too. They are perfect for me.
Goal Zero also has led lights. You can string together two sets. Might light your entire cabin.
Shawn James on YouTube lights his off grid cabin with those lights.

You will need a generator. This will be for your wives hairdryer. Lol and your toaster (toast bread on a griddle or use a camp toaster that sits on your stove burner). Buy a quiet Honda.

Buy two coolers. One for beverages and stuff you use often. The other you only open for lunch or dinner. Your ice will last longer and the food will stay fresher a while longer.

We did not buy a bunch of expensive stuff until we got in our cabin and lived in it for a few trips.
I’m glad we did it that way. Saved a lot of unnecessary expenses.

# Posted: 2 May 2019 15:19

Yes, those are the Deka's I was talking about. Seem to be well reviewed, they're US made, it seems like they rank out about as well as the Trojan's. 6v gets you a lot more "deep cycle" type battery. And the 8 I ordered from Lowe's were nice and new, I ordered them in March and they had a March/2019 manufacture date on them so they hadn't been sitting in a warehouse somewhere uncharged for years. That being said, I'm just building things out now so can't speak to their performance too much.

silverwaterlady makes good points, you can definitely start small and build out later, this thread is just giving you the various options (small and large) to try to wrap your brain around. GoalZero makes nice stuff, and it's plug and play, but you do pay a premium for the plug and play aspect.

# Posted: 4 May 2019 09:07

Quoting: beachman
beef up the solar a bit and run a small electric fridge. Use the genny to run the hair dryer and toaster.

A 1200w Victron will run all those loads. Just not all at once.

There are lifepo4 lithium battery packs on ebay. Some very good sellers. Even amz has them now.

The longevity (3-10 times) and the efficiency (instantly increases the size of your system by 20%). Make the value unbeatable. If you don't want to be spending money to upgrade continually. Start with lithium. Reduce the size of the amp hour capacity by 1/2 and you'll have more usable power for decades longer.

In eastern Ontario there is a brilliant (cough cough) lithium battery pack available. smile.

Deep cycle lead is dead. Too heavy. Too toxic. Too inefficient. Some guys already invested in them. But for anyone starting afresh. Lithium is the cheapest option.

# Posted: 5 May 2019 08:11

You can also buy one hell of a old electric vehicle lithium battery off ebay for $1k. Charging is a bit dif but no water to check, no bad off gassing, you can safely use 80* of the capacity and the life is 4x longer.

# Posted: 6 May 2019 12:42 - Edited by: zorro

Ok – started to look at the lithium battery option, which I had not considered before

Cost- 8 x T105’s = $1360 or so

If I was planiing 8 x T105’s (225ah x 6V) = 1350ah x 8 = 10800WH……………….say 50% = 5400Wh

Now if I look at a Lithium battery

Renogy Lithium Iron Phosphate Battery 12 Volt 170 Amp Hour = $1500

Does that actually provide 12 x 170ah = 2040Wh

So would I actually need 2 of the lithium to get me to 4080Wh, still 1000Wh less than the T105’s?
I know they are longer lasting, less maintenance, etc, but if the above is correct, extremely pricey?

# Posted: 6 May 2019 12:55

Others (like creeky) know more about this, but my understanding was best practice was to not drain a lithium battery below 20% SOC, so figure that Renogy battery is good for 1,632Wh.

I think it would take 3 of those to be equivalent (the lead are less efficient so you get a boost of 20% over lead in using lithium) but maybe you could get away with 2.

I'm with you, in the end I couldn't justify the expense. The way this really can play better financially is if you're savvy enough (I wasn't) to buy batteries off eBay and then set up your own BMS, it seems the off the shelf batteries from the big names now getting into it (Renogy, Victron) have a big premium pricewise, although you know what you're getting more so than with an eBay purchase if you're not already pretty knowledgeable about this stuff.

# Posted: 6 May 2019 13:19


I know very little about the whole solar system and am still learning

So if we use 80% for lithium, then that would be ……….

12v x 170ah x 80% = 1632Wh

That is 1/3 of what 8 x T105’s would give for the same cost

I cannot afford to pay 3 x the price for similar power output levels……………….even with the extended life/low maintenance

It would be great having 3 lighter Lithium batteries, will a smaller overall size compared to 8 large and heavy T105’s……………….but that would be $4500 v’s $1360 – that is quite a difference!!

I was at a friends cabin over the weekend and he checked his 6 x T105 batteries for the first time this spring and it took him about 10 minutes in total – I think I can live with that

# Posted: 6 May 2019 15:23

If you're really concerned about the checking you can google "battery watering systems" that allow for quick filling of everything at once. I haven't gone down that road yet.

. 1 . 2 . >>
Your reply
Bold Style  Italic Style  Underlined Style  Thumbnail Image Link  Large Image Link  URL Link           :) ;) :-( :confused: More smilies...

» Username  » Password 
Only registered users can post here. Please enter your login/password details before posting a message, or register here first.