I think I am ready to buy... analysis paralysis

[xy74]

Looking for thoughts on this system.

900 sq ft cabin, off grid. Recreational use a couple weekends a month with an occasional weeklong stay. Main load would be a residential fridge using about 1 kwh per day. The rest will be pretty minimal, lights, maybe an occasional microwave for a minute, a box fan at night if it's hot, phone charging, and occasionally charging a 12V battery that runs the "outhouse". Doubt there will be a TV, but even so that is minimal. We are used to off grid with an RV, so have no problem with only using what we need. I would turn off the system while we are gone. If for any reason we show up and the system doesn't work, then we live out of the cooler for a weekend and use battery powered lights like we do now and have a good time.

I read through the "can't afford tier 1" thread, pretty good discussion that made me rethink what I want/need. Or just made me more indecisive! I won't say price is no object, but these options are within the budget. I did look at a Sunny Island, that is out of the budget!

Today's plan is an EG4LL 48v battery, a Victron Multiplus II 3kva, Victron MPPT 150/70, and possibly a Global link 520 (if it will turn the system (MPPT) off or on remotely???) Comes to about $4400. Looking at a pallet of used panels from Santan (DIY pergola like structure next to cabin to mount on) (2500 watts or so) for $1250 delivered. Aside from wire and a combiner box, is there anything else I need for a system?

The less pricey alternative would be just get an EG4 or MPP 3K for 1600 less. (original plan A lol)

So does the Victron option seem worth it for my needs? I am ASSuming it would be much quieter in operation?

Is there something else I should be looking at?

 

[DIYrich]

Think about your battery. If it gets below freezing, you need to disable charging.

 

[n2aws]

I know you mentioned not being interested in a "tier 1" system, but being that this cabin sounds like it would be unattended for decent periods, what is the impact should the system fail for an extended period of time? Do you intend to keep the fridge unstocked unless you're visiting the cabin, etc?

If done right, these budget systems can be rock solid and reliable. but, if you are trying to stay budget friendly, sometimes sacrifices have unintended consequences. Just something to consider (I'm not saying budget systems aren't reliable. but I AM saying to factor in that possibiliy) Additionally, I'd consider the system "unproven" for a period of time after it's initial install. Meaning, even if you intend to stock the firdge full time and such, I wouldn't do it at first (just in case)

 

[E. Cho]

That all should work just fine with consideration of previous suggestions. You may need a larger Solar Charge Controller for 2500 watts of panels and cold sunny days? I have a 150/85 and 2280 watts. Have you run your panel calculations through a SCC Mfg calculator?

I live full time on a very similar set up and run all appliances, tools, etc.. I do have a high quality back up generator but don't often need it for charging.

- Add a wire T Class Fuse at the battery.
- add positive and negative bus bars for connections of components or a Victron Power In
- a DC disconnect breaker (& box?), direct battery On/Off switch if EG4 doesn't have one.
- Make sure your battery BMS has active balancing, a smartphone App and Bluetooth connection for set up, modifying settings and for monitoring the battery CELLS balance !!!!!!!
- A Pre Charge Resistor and or switch, if your battery does not have one built in, for restarting the inverter if you shut the system down when away and or for initial start up.
- Hardy backer fire resistant board for mounting components to your wall.

Nice extras could be? A Victron Smart Shunt, Victron Carbo GX for remote monitoring, if you will have internet running full time. I am not familiar with what a Global 520 is.

 

[Mattb4]

Your use case of needing power at irregular periods of time (a few days out of the year) might mean that LiFePO4 batteries will take some special consideration over lead acid. You do not want them to sit fully charged each day and you also have to be worried about freezing temperature effects on them.

One other issue that could be problematic in having a remote cabin solar setup is it might lead to breakins, theft and vandalism.

 

[xy74]

We plan to turn everything off when we aren't there. Doing more reading about the GlobalLink and it doesn't seem you can actually change anything remotely, just monitor. So we would also turn off the MPPT and restart it all when we show up. Need to read more about what the ideal state of charge would be to leave the battery in. I also have a pair of Honda EU2200i generators and will run them as needed if the weather is dark.

We will use the cabin year round, but it won't be that often we show up when it is below freezing. (southern Ohio) When it will be real cold, we will stay home. Same in the summer, real hot we stay home. My understanding is you can draw power from the battery when they are cold, just not charge them until they warm up. Heating system will be a wood stove.

 

[Watts Happening]

Don't let my post steer you in any direction you're not comfortable with, but, I literally have most of what you're wanting to buy listed for sale in the classifieds. It's all darn near brand new, totally functional and will cut that price gap quite a bit. I have the Multiplus-II 48/3000, a 150/85 and even a CCGX if you were so inclined.

No matter what you do, pony up the extra money for the top tier stuff and you will have many years of reliable power. Saving a few bucks up front is NOT worth forever questioning, tinkering and hoping your system is reliable, I can assure you of that.

 

[Rocketman]

Do you have internet at the Cabin? Or cell signal?

If you have internet- get a GX device- Cerbo.

Also get the Smartshunt.

You will be able to monitor and make changes from home!

Also With Victron mppt and inverter hooked up to a GX, you can tell the mppt to not charge the batteries below ____(user setable)F. Then the bms low temperature becomes a backup.

 

[ChrisG]

What is the reason why you don’t want to leave LifePo4 at a high state of charge for backup reasons, like float at 54.5? Feel there is more risk dealing with FLA, venting, etc. I’ve looked at a few cell manufacturers and don’t see any guidance on leaving these in a high state for backup reasons.

 

[robby]

What is the reason why you don’t want to leave LifePo4 at a high state of charge for backup reasons, like float at 54.5? Feel there is more risk dealing with FLA, venting, etc. I’ve looked at a few cell manufacturers and don’t see any guidance on leaving these in a high state for backup reasons.

It shortens their life significantly if they are left at 100% charge continuously.
Recommended long term storage charge for LifePo4 is typically 40% while with FLA you can store them at 100% without an issue.

 

[ChrisG]

It shortens their life significantly if they are left at 100% charge continuously.
Recommended long term storage charge for LifePo4 is typically 40% while with FLA you can store them at 100% without an issue.

Any idea how much the lifespan is shortened? Having PV helps but really need to keep good amount of reserves for power outages.

 

[rhino]

It shortens their life significantly if they are left at 100% charge continuously.

Define 100% state of charge with LiFePO4.

 

[timselectric]

Define 100% state of charge with LiFePO4.

3.4v per cell, resting.

 

[rhino]

3.4v per cell, resting.

Isn't that why it is better to float at lower voltage like 3.35V then?

 

[timselectric]

Isn't that why it is better to float at lower voltage like 3.35V then?

Yes, but don't leave them there for more than a day or two.
It's important to let the cells get down below the upper knee, occasionally. I wouldn't leave cells that high for extended periods. 3.25v, is perfect for storing.

 

[ChrisG]

Yes, but don't leave them there for more than a day or two.
It's important to let the cells get down below the upper knee, occasionally. I wouldn't leave cells that high for extended periods. 3.25v, is perfect for storing.

So is everyone just using FLA if systems are primarily for grid backup? 100% FLA charge is about equal to 50% LFP so seems like no benefit. For those with Anker or EcoFlows are they only charging to 50% and storing?

 

[timselectric]

So is everyone just using FLA if systems are primarily for grid backup? 100% FLA charge is about equal to 50% LFP so seems like no benefit. For those with Anker or EcoFlows are they only charging to 50% and storing?

I don't know what everyone else is doing.
I only know what I believe that they should be doing. lol

 

[Q-Dog]

So is everyone just using FLA if systems are primarily for grid backup? 100% FLA charge is about equal to 50% LFP so seems like no benefit. For those with Anker or EcoFlows are they only charging to 50% and storing?

I leave our refrigerator and security cameras running on the backup all the time so the battery never sits at 100% for more than a couple of hours in every 24 hour period. That uses up about 15% of our battery capacity during the night.

 

[ChrisG]

I don't know what everyone else is doing.
I only know what I believe that they should be doing. lol

That actually made me lol. I just find it hard to believe that LFP 90-100% can’t be sustained for a long time without damage or shortening life. I just looked at EcoFlows and i can’t find anywhere not to charge and store at 100%.

I have a very specific use case, a very pissed off wife, I’m trying to solve for. Last week we used up 40% of our battery before dawn which ended up a full day of storms so no solar. Then by 9am grid power was out for 27 hours (noon the next day). So had to use a generator. Main concern was deep freezer and fridge. Want to build a small LFP system dedicated to those devices and always be at 100% ready charge.

 

[xy74]

Do you have internet at the Cabin? Or cell signal?

If you have internet- get a GX device- Cerbo.

Also get the Smartshunt.

You will be able to monitor and make changes from home!

Also With Victron mppt and inverter hooked up to a GX, you can tell the mppt to not charge the batteries below ____(user setable)F. Then the bms low temperature becomes a backup.

I don't have internet, but do have a decent Verizon signal. Thus the GlobalLink, but it really doesn't look like it will do what I was thinking it could do. My thought was if we leave and the battery is low, then I would want to be able to leave the charging on until a certain point and then turn it off completely. Doesn't look like that is possible or is it???? So probably not use it at all and just leave it all off when we aren't there. Will look into a Smartshunt.