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Small offgrid system - need oppinions and suggestions
#1
I'm in the middle of planning the construction of my off-grid tiny house, and came to the conclusion it's better to plan the electrical (and water) part first and then build the frame around it.

What I have in mind right now is a 12 or 24V solar-system using the Electrodacus SBMS120 (http://electrodacus.com/) with a small DIY 18650 powerwall.
By my understanding this way I don't need a separate BMS-system, and can still charge the battery-packs from the grid with a 12/24V powersupply through the SBMS120?

I will include a 240V inverter as well, but I'm not sure about the size quite yet (2kw?).

I have little to no experience on what is most efficient to run on 12/24V and what is better to run on 240V.
Neither am I sure on how big battery-bank I'll need.

I live in Finland so I'm guessing I won't be able to get enough solar power for staying off the grid under the winter months.

All suggestions/advise and help on this project is more then welcome!


(Had trouble to find the right section for this topic, mods are more then welcome to move the thread as they see fit)
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#2
Hello, welcome on the forum. It is important you start with being clear to yourself what your true needs are. This exercise in turn will generate what scenarios are available to you (based on cost, time available, urgency....). The technical details come later.
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#3
The inverter needs to be as big as your load is going to be. If you don't know that yet, then you have to figure that out first. Same with your battery bank, will depend on load and needed runtime.

Solar panels and batteries provide DC so it is always more efficient to run a device directly on DC, either straight from the solar or battery or via DC-DC conversion which is more efficient than AC-DC conversion. Some devices operate on their own AC-DC power supply. For these it might be better, efficiency-wise, to power them directly from the DC part of your system. AC is better though if you want to cover longer distance because of higher voltage and lower amperage. And you probably won't find a DC version of every device you need.
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#4
Hi and thanks silverse2m6!

Thanks for the advice, however it doesn't help me much. Hence my personal needs are rather minimal.

I guess my question is, what is the power consumption and needs of an average person.

We can exclude heating of both space and water, I've got it covered by other methods.


The things I've come up with that would be better/easier/cheaper to run on 240V would be TV, washingmachine and phonecharger.
For this an 2kw inverter would be enough, right?

The whole point of this project is to show the masses an alternative way of living, it would also help if it would be as easily maintained and affordable as possible.

Isn't it better to run a larger inverter then the max load? Or is there any disadvantages beside cost and size?
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#5
Welcome. I run my camper off of 7s li-ion (29V full charge) and I have about 70Ah of storage right now and generally only use about 20Ah per day @ 12V I have a old UPS for my AC needs but it chews 1.5Amps with no load so I don't leave it on.

I have all LED lightening, a furnace that when running uses about 3 Amps, and Fans the biggest uses 3 Amps. Other than charging cell phones and a radio that is on all day long my power usage is really minimal. I charge with 5 older 60W panels that only output about 30W each due to age. run that via a MPT-7210a charge controller (boost) to my battery bank.

My Power wall is usually charged by 11am and I am limiting power to my wall in the summer. I am designing a Water heater to use up the excess solar power when there is too much sun Wink but that's for next summer
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#6
Thanks Jdeadman! Are you running any kind of balancing system?

I'm rather concerned over safety since the packs would have to be inside the house.
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#7
Yeah sure, if the inverter is too big it is just a matter on money, but apart from that it is fine. Phonecharger and TV uses very little power, 2kW for the washing machine is maybe not enough. Look at the specs of your machine, it will tell you the power requirements. Could be 2,5kW to 3kW, depeding on the model.

Yes, you need some way of balancing and monitoring the packs if you plan to leave them unattended. The Electrodacus system you have linked seems like it would be able to do the job, I haven't read thoroughly to the details yet though.
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#8
Yes but just a really small drain RC style equalizer. I keep a close eye on it but with using "repacker" on this site I got my cells really close so it needs very little balancing.

https://www.google.ca/url?sa=t&rct=j&q=&...t0AsEehXBA
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#9
For us to answer on how much energy you use is "impossible" For instance some people use 0.3kWh per day and some use 15kWh or even 20kWh... So its quite a difference Smile

Meassuring is knowing. Basically check your current bill for instance or buy your self e meeter Smile
Follow me! >> YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
Upcomming: 14S 18650~30kWh | Automatic trip breakers, and alot more
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#10
I am thinking I might try to reach back in time, and try to build a pack that can store 1.21GW.
Cell Tracking Website: Under Construction - trackmycells.com
Battery Status: Collecting Cells
Bms: Batrium 14s
Battery Charger Controller: SMA Charge Controler SIC-40
Inverter: Pending (SMA Sunny Island 6048-US-10)
Solar Panels: Soon™
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