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Small system for cabin

Sfath

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Oct 16, 2021
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Hi All,

I wish to build a small 12v 320Ah 4s solar battery system for my cabin using Eve cells. Is there somewhere where someones done a complete step by step guide build from the solar panels, to charge controller, to BMS to batteries, ect? I also need little help choosing the items with the build too. Appreciate if someone can direct me to where I can learn this.

Sfath
 
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OK, so you need 2 instruction sets then it sounds like. First the Battery Build which Will did a video on that shows you how to build the battery from raw cells, and then the Classic 12v system to take that battery and marry it up with the charge controller and panels and fuses and such.

Really easy, even I figured out how to do it a couple times.


That sort of helps but is there a step by step guide to building a complete 12v 4s system from solar panels to batteries? I kind of need help in sizing up (components) and connecting everything.
 
Like I said, it's going to be a 2 part event. First you need to build a battery, the video guide and instruction page I linked earlier. Then you take that battery and add it to the rest of the parts like the Classic 12v system or the AIO 12v system depending on which way you want to go.



Picking up a copy of his book for about $5 would be a REALLY good idea since it's cheap and tells you so many of the basic things that "Everyone Just Knows".
 
Okay, thanks a lot for your help! That other long video will help!
 
May I ask what amp size for a solar charge controller and a BMS is okay to use on a 12v 320Ah 4s system? On Will's Classic 12v System he uses a 40amp solar charge controller. Is a 100amp solar charge controller okay to use on a 12v 320Ah 4s battery bank? Also, would a 100amp BMS ok to use on that battery bank too?
 
The 100a on the BMS is the rating of the max continuous draw, so a 100a BMS on a 12v battery could feed about a 1Kw inverter before you start stressing the BMS. The 100a on the charge controller is the maximum amperage it could send to your battery bank. There's a difference, and sometimes the BMS will charge at a lower rate than it can discharge, but that's becoming more and more rare. For reference I used a 120a BMS for both of my battery builds just to get that little extra out of them since the BMS's were pretty much the same price between 100a and 120a.

As to the panels, the rule of thumb is Panel Size / Nominal Voltage = Amps of SCC, so 400w of panel / 12v = 33a, so a 40a is plenty. If you wanted more charging capacity you'd need a larger SCC. If you did a 60a SCC for example you could get 720w of panel, or 800w of paneling with inefficiency and imperfect weather would be safe.

With the generic figure of 4 hours of USABLE sun on a 400w array is 1600 watt hours potential generation. 1600 W/h on a 12v system is 133Ah you could theoretically generate. With a 320Ah battery I would recommend at LEAST 60a of charging with 720w of panels (800 for round numbers) which would give you 4hr * 60a = 2400Wh / 12v = 200Ah potential power generation in a day, give or take.

If you really wanted to be able to completely drain and recharge in 1 day the math gets bigger:
320Ah * 12v = 3840Wh. 3840Wh in 4 hours = 960w of panel (call it 1000 for round numbers, weather, inefficiencies). 1000w of panel / 12v system = 83A SCC to feed that. Now, in the Real World you'd be lucky to get 80A to the batteries so a pair of 40a SCC's in parallel to the battery each with its own 500w worth of panels would pretty much max out that system.

Now, if you can live on less than 130Ah or 1560 watt/hours a day then you wouldn't drain your battery any faster than a 400w array could refill it, but if you got multiple days of krappy weather you'd have to spend a lot of time playing catch-up.


Remember, these guides were done when the most common size cell were 100Ah cells so a 400w system could refill a 100Ah cell in an average day. Your battery is 320% larger so the size of the charge controller and panels will need to scale up accordingly.

As for parts for this whole system, the 2 most common ways are:

1: The "Easy" way - An MPP 1012LVM All-In-One inverter, a Class-T 125a fuse, a 120a DC breaker (for disconnecting), inline fuses for panels OR a combiner box with fuses.

Pro's: Cheap, easy to assemble, has all the working parts in a single package.
Con's: About 10% of your battery capacity will go to the AIO unit to exist, only provides 1000w of 120v AC output, only a 40a SCC built in so you'll need another SCC and array in parallel to fully charge the batteries in a day, one part goes out replace the whole unit.

2: The "Custom Way" - A decent quality 1000-1200w Pure Sine Inverter, dual 40a MPPT SCC's, a Class-T 125a fuse, a 125a DC breaker (for disconnecting), inline fuses for panels OR a combiner box with fuses.
Pro's: Slightly less standby power, maxes out the realistic charging capacity of your system, individual pieces can be replaced, more clout on your favorite solar forum.
Con's: Much more expensive than going with the AIO route, takes up more physical space, you'll get good at crimping cables.

If you're running anything off a DC bus like lights or diesel heaters or the like, you'll need to get a DC fuse block involved, and that's more based on how many slots you'll need than anything else.

If you're working with a tighter budget there are places you can and can't skimp out on to work with that. The SCC doesn't have to be Victron levels of $pendy, a Rich Solar, HQST, or even a PowMr will turn solar DC into battery DC for much less money. The MPP 1012 unit is very cost effective when you look at all the things it includes like the 40a SCC, the inverter, the generator input, the automatic transfer switch, and the convenience factor. The place you DON'T want to skimp are your safety devices like the fuses and breakers. Remember, fuses are (often) cheaper than fires! ;) Having said that, for some reason 120a Class-T fuses are harder to find than Unobtanium or an honest politician so that's going to be a challenge. I personally gave up after months of hunting and just used a good quality DC breaker and took the risk, but YMMV.

Used panels are a great deal if A: you can find them locally and B: you've got lots of space to put them. Shipping costs on panels means that unless you're buying 2 dozen of them, it's getting pretty even on the $/watt scale to new panels from Amazon where you're looking in the neighborhood of $1/w shipped. Lots of people will tell you "I can get used panels for $0.10/watt all day long" but when you start at $400 shipping PLUS panels, that figure falls apart pretty quickly if you're only getting 4 panels or so. Craigslist and FB Market are your friends, but sometimes Amazon is the winner.

Also, know the limitations of your system. A 12v battery with a 100a BMS can't feed more than about 1200w so don't be tempted to buy that Chinesium 5000w 12v inverter, it's junk. Also, spending the money on a Pure Sine rather than a cheaper Modified Sine will pay off in the long run. Sure, it's cheaper now and you can take all that money you saved and put it towards new appliances or electronics that the MSW inverter fried. What a value!

Have you done a power audit yet to guesstimate what your cabin is going to use yet? It'll help give you an idea of what to expect your system to accomplish. Like many of us on here before you, rather than making a system to do what you need, you're starting with a system and seeing what it can do. Not horrible, but there is a "Tuition" fee to buying parts first and hoping you can use them all later.

Don't worry, you're not the first and you won't be the last. ?
 
The 100a on the BMS is the rating of the max continuous draw, so a 100a BMS on a 12v battery could feed about a 1Kw inverter before you start stressing the BMS. The 100a on the charge controller is the maximum amperage it could send to your battery bank. There's a difference, and sometimes the BMS will charge at a lower rate than it can discharge, but that's becoming more and more rare. For reference I used a 120a BMS for both of my battery builds just to get that little extra out of them since the BMS's were pretty much the same price between 100a and 120a.

As to the panels, the rule of thumb is Panel Size / Nominal Voltage = Amps of SCC, so 400w of panel / 12v = 33a, so a 40a is plenty. If you wanted more charging capacity you'd need a larger SCC. If you did a 60a SCC for example you could get 720w of panel, or 800w of paneling with inefficiency and imperfect weather would be safe.

With the generic figure of 4 hours of USABLE sun on a 400w array is 1600 watt hours potential generation. 1600 W/h on a 12v system is 133Ah you could theoretically generate. With a 320Ah battery I would recommend at LEAST 60a of charging with 720w of panels (800 for round numbers) which would give you 4hr * 60a = 2400Wh / 12v = 200Ah potential power generation in a day, give or take.

If you really wanted to be able to completely drain and recharge in 1 day the math gets bigger:
320Ah * 12v = 3840Wh. 3840Wh in 4 hours = 960w of panel (call it 1000 for round numbers, weather, inefficiencies). 1000w of panel / 12v system = 83A SCC to feed that. Now, in the Real World you'd be lucky to get 80A to the batteries so a pair of 40a SCC's in parallel to the battery each with its own 500w worth of panels would pretty much max out that system.

Now, if you can live on less than 130Ah or 1560 watt/hours a day then you wouldn't drain your battery any faster than a 400w array could refill it, but if you got multiple days of krappy weather you'd have to spend a lot of time playing catch-up.


Remember, these guides were done when the most common size cell were 100Ah cells so a 400w system could refill a 100Ah cell in an average day. Your battery is 320% larger so the size of the charge controller and panels will need to scale up accordingly.

As for parts for this whole system, the 2 most common ways are:

1: The "Easy" way - An MPP 1012LVM All-In-One inverter, a Class-T 125a fuse, a 120a DC breaker (for disconnecting), inline fuses for panels OR a combiner box with fuses.

Pro's: Cheap, easy to assemble, has all the working parts in a single package.
Con's: About 10% of your battery capacity will go to the AIO unit to exist, only provides 1000w of 120v AC output, only a 40a SCC built in so you'll need another SCC and array in parallel to fully charge the batteries in a day, one part goes out replace the whole unit.

2: The "Custom Way" - A decent quality 1000-1200w Pure Sine Inverter, dual 40a MPPT SCC's, a Class-T 125a fuse, a 125a DC breaker (for disconnecting), inline fuses for panels OR a combiner box with fuses.
Pro's: Slightly less standby power, maxes out the realistic charging capacity of your system, individual pieces can be replaced, more clout on your favorite solar forum.
Con's: Much more expensive than going with the AIO route, takes up more physical space, you'll get good at crimping cables.

If you're running anything off a DC bus like lights or diesel heaters or the like, you'll need to get a DC fuse block involved, and that's more based on how many slots you'll need than anything else.

If you're working with a tighter budget there are places you can and can't skimp out on to work with that. The SCC doesn't have to be Victron levels of $pendy, a Rich Solar, HQST, or even a PowMr will turn solar DC into battery DC for much less money. The MPP 1012 unit is very cost effective when you look at all the things it includes like the 40a SCC, the inverter, the generator input, the automatic transfer switch, and the convenience factor. The place you DON'T want to skimp are your safety devices like the fuses and breakers. Remember, fuses are (often) cheaper than fires! ;) Having said that, for some reason 120a Class-T fuses are harder to find than Unobtanium or an honest politician so that's going to be a challenge. I personally gave up after months of hunting and just used a good quality DC breaker and took the risk, but YMMV.

Used panels are a great deal if A: you can find them locally and B: you've got lots of space to put them. Shipping costs on panels means that unless you're buying 2 dozen of them, it's getting pretty even on the $/watt scale to new panels from Amazon where you're looking in the neighborhood of $1/w shipped. Lots of people will tell you "I can get used panels for $0.10/watt all day long" but when you start at $400 shipping PLUS panels, that figure falls apart pretty quickly if you're only getting 4 panels or so. Craigslist and FB Market are your friends, but sometimes Amazon is the winner.

Also, know the limitations of your system. A 12v battery with a 100a BMS can't feed more than about 1200w so don't be tempted to buy that Chinesium 5000w 12v inverter, it's junk. Also, spending the money on a Pure Sine rather than a cheaper Modified Sine will pay off in the long run. Sure, it's cheaper now and you can take all that money you saved and put it towards new appliances or electronics that the MSW inverter fried. What a value!

Have you done a power audit yet to guesstimate what your cabin is going to use yet? It'll help give you an idea of what to expect your system to accomplish. Like many of us on here before you, rather than making a system to do what you need, you're starting with a system and seeing what it can do. Not horrible, but there is a "Tuition" fee to buying parts first and hoping you can use them all later.

Don't worry, you're not the first and you won't be the last. ?
Thanks a lot for all that info! :)

With my 12v 320Ah 4s eve battery pack (just ordered on aliexpress) I am going to use these 2 x 300 watts solar panels with one solar charge controller. Are these panels (attached) ok to use with that 4s battery bank and is one SCC okay to use? I prefer to use one SCC to keep it simple. My budget is tight too.

I don't intend to use much heavy loads on the battery. The most would be a 700 watt small microwave. Mainly use it just to run small fridge, lights and watch TV.

May I ask what size "amp" of single solar charge controller would you use with that battery pack? And also what size amp BMS too? As well as what size breakers/fuses would you use there?

I live in Australia, so I will be using 240v appliances.

I really appreciate all your help!
 

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Well, you've got 600w of panels divided by a 12v system so 600w / 12v = 50a SCC. I'd recommend a 60a just to give you a little headroom since nothing likes to be run at 100% all the time. As for the SCC on a budget, anything along the lines of a Rich Solar 60a, or an EPEver 60a is a good choice, but if you're on a tighter budget you can probably get away just fine with a PowMr 60a and it'll still turn Solar DC into Battery DC just fine.

Yes, all my links are US Amazon because that's what I have handy but it gives you an idea of what you're looking for.

I'd spend the little extra on a JBD Smart 120a BMS for the bluetooth features and reliability, plus the extra amperage it gives you. I think you can get them on AliExpress as well and they have a 150a version that buys you a little more inverter. Finding the inverter locally will take some work on your end as the Amazon Australia isn't really giving me any good options and I don't know who your local better suppliers are. About the best advice I can give you is to stick with 1500w or less and LOTS of good reviews.

As for breakers and fuses, check the BlueSea Wire Ampacity Chart for wire sizes but you'll want max amps + 20% on each end, so:
60a MPPT * 20% overhead = 70 or 75a DC breaker from SCC to batteries (it calls for 72a but nobody MAKES a 72a, so you could go either way)
1500w Inverter wants 125-ish amps * 20% overhead so 150a DC breaker/ fuse
The BMS connects to the battery cells so no fuse there, just Cells -> BMS -> Breaker -> Inverter
If you're getting a DC fuse block involved you'll have to add up all the fuse sizes you're going to have installed and add 20% to calculate breaker and wire size to that.

I also recommend getting a shunt based power meter because you're going to want to know how dead or full your batteries are at any given time. A lot of people use the Aili Shunt Volt Meter as it's a pretty effective piece of kit for pretty cheap. That'll go between the P- on your BMS lead to the Neg- of all your DC stuff including the SCC, fuse block, inverter, and 12v MargaritaMaster-1200. If you check out my cart you can see it right there to the right of the main unit housed in its own box.
 
Well, you've got 600w of panels divided by a 12v system so 600w / 12v = 50a SCC. I'd recommend a 60a just to give you a little headroom since nothing likes to be run at 100% all the time. As for the SCC on a budget, anything along the lines of a Rich Solar 60a, or an EPEver 60a is a good choice, but if you're on a tighter budget you can probably get away just fine with a PowMr 60a and it'll still turn Solar DC into Battery DC just fine.

Yes, all my links are US Amazon because that's what I have handy but it gives you an idea of what you're looking for.

I'd spend the little extra on a JBD Smart 120a BMS for the bluetooth features and reliability, plus the extra amperage it gives you. I think you can get them on AliExpress as well and they have a 150a version that buys you a little more inverter. Finding the inverter locally will take some work on your end as the Amazon Australia isn't really giving me any good options and I don't know who your local better suppliers are. About the best advice I can give you is to stick with 1500w or less and LOTS of good reviews.

As for breakers and fuses, check the BlueSea Wire Ampacity Chart for wire sizes but you'll want max amps + 20% on each end, so:
60a MPPT * 20% overhead = 70 or 75a DC breaker from SCC to batteries (it calls for 72a but nobody MAKES a 72a, so you could go either way)
1500w Inverter wants 125-ish amps * 20% overhead so 150a DC breaker/ fuse
The BMS connects to the battery cells so no fuse there, just Cells -> BMS -> Breaker -> Inverter
If you're getting a DC fuse block involved you'll have to add up all the fuse sizes you're going to have installed and add 20% to calculate breaker and wire size to that.

I also recommend getting a shunt based power meter because you're going to want to know how dead or full your batteries are at any given time. A lot of people use the Aili Shunt Volt Meter as it's a pretty effective piece of kit for pretty cheap. That'll go between the P- on your BMS lead to the Neg- of all your DC stuff including the SCC, fuse block, inverter, and 12v MargaritaMaster-1200. If you check out my cart you can see it right there to the right of the main unit housed in its own box.
That's all a big help!

Are the 'amp" sizes you recommended still the same for me even if I'm in OZ on 240v instead of your 120v?

Do I need a shunt? I thought a bluetooth BMS can tell you the state of charge?
 
Yes, the amps are all on the 12v side so it doesn't matter what the inverter is putting out, just how many amps it's drawing from the battery and watts are watts. Whether you're pulling 1500w from your battery at 12v or pulling 1500w from your inverter at 240v, it's still 1500w. Since your fuses and wires are all on the 12v size, you budget for 12v supply on everything.

Yes, you can log into the BMS with a phone if you want to whip out the phone and pair it every time you want to see what you've got left, or you can have a simple percentage bar you can check at a glance. I'd at least put it on the "Future Upgrade" purchase list.
 
Yes, the amps are all on the 12v side so it doesn't matter what the inverter is putting out, just how many amps it's drawing from the battery and watts are watts. Whether you're pulling 1500w from your battery at 12v or pulling 1500w from your inverter at 240v, it's still 1500w. Since your fuses and wires are all on the 12v size, you budget for 12v supply on everything.

Yes, you can log into the BMS with a phone if you want to whip out the phone and pair it every time you want to see what you've got left, or you can have a simple percentage bar you can check at a glance. I'd at least put it on the "Future Upgrade" purchase list.
That all makes more sense now! You've cleared lots of ? for me! I want to thank you again for all your help!
 
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