Building a 16s 280ah bank for an off grid house. I don't know.. what I don't know. What am I missing.

[ZColorado]

My Mom has an 2,800sq/ft offgrid house up in the Colorado mountains. Her lead acid bank (48v ~340ah) is about dead. She needs a replacement by Christmas (parts should arrive in time). I am hoping you all can tell me what I may be missing since I am under a bit of a time crunch and don't have my usual months long research cycle to get up to speed.

Already Installed:
SCC - FlexMax60 (FM60-150VDC)
Inverter - Magnum Energy 4400watts (MS4448PAE)
EDIT: 9 qty SCHUCO 235w panels from 2011 - 2.1kw (She probably needs to plan on increasing this)

LiFePO4 ordered - Thanks Jenny Wu!
16 EVE 280ah cells
Daly 16s 200a BMS - From Current Connected

My assumptions/questions

1. Programming the SCC to 3.65 max and 2.5 min according to the EVE battery details
2. Programming the BMS to the same values above? or different? - should this not come pre-programmed?
3. I need to compress/tape the cells together because that helps with long life? - I think all-thread would be my preferred method. (0.21c charge rate)
4. Wiring will be the proper gauge of welding wire with hydraulically crimped ends (I have the tool and experience for this)
5. Do I need additional DC fuses/breakers? - if so what do you suggest?
6. I don't believe I will fry the SCC if the BMS cuts the cells? - anyone have experience with the outback solar flexmax doing this?
7. Can I add another 16s battery bank in parallel to this bank in the future? - I'd assume this would be with an additional solar array and charge controller in parallel as well.
8. Do I need to top balance the cells when I receive them? Can I skip this step if cell voltages are close (how close)

I feel like I have huge gaps of knowledge on physically building the bank and the various techniques and benefits there. Lots of youtube videos on this though.


My google skills are pretty good, but I don't know, what I don't know.

 

[sunshine_eggo]

My Mom has an 2,800sq/ft offgrid house up in the Colorado mountains. Her lead acid bank (48v ~340ah) is about dead. She needs a replacement by Christmas (parts should arrive in time). I am hoping you all can tell me what I may be missing since I am under a bit of a time crunch and don't have my usual months long research cycle to get up to speed.

Already Installed:
SCC - FlexMax60 (FM60-150VDC)
Inverter - Magnum Energy 4400watts (MS4448PAE)

LiFePO4 ordered - Thanks Jenny Wu!
16 EVE 280ah cells
Daly 16s 200a BMS - From Current Connected

My assumptions/questions

1. Programming the SCC to 3.65 max and 2.5 min according to the EVE battery details

No. 3.65V will likely cause the Daly to trip. Set to 3.45-3.55/cell. 3.45V maximizes cycle life but has absorption times like lead-acid. 3.55V will get you charged pretty quick with a relatively short absorption time.

1. Programming the BMS to the same values above? or different? - should this not come pre-programmed?

Defaults are often at 3.75 & 2.3 or slightly outside of cell specs. Setting to cell specs is fine.

1. I need to compress/tape the cells together because that helps with long life? - I think all-thread would be my preferred method. (0.21c charge rate)

Works. Just don't over-do it.

1. Wiring will be the proper gauge of welding wire with hydraulically crimped ends (I have the tool and experience for this)

?

1. Do I need additional DC fuses/breakers? - if so what do you suggest?

Only the ones you should already have protecting the wires already present. Fuse/breaker between battery and inverter and fuse/breaker between SCC and battery. 1.25X wire capacity.

1. I don't believe I will fry the SCC if the BMS cuts the cells? - anyone have experience with the outback solar flexmax doing this?

Few MPPT suffer from this. Mostly just PWM. Not a big concern, but setting your normal operation INSIDE the cell limits helps.

1. Can I add another 16s battery bank in parallel to this bank in the future? - I'd assume this would be with an additional solar array and charge controller in parallel as well.

Yes. No. You could simply double the bank with a second battery in parallel. This behaves like one big battery. Connect in accordance with Victron Wiring Unlimited in Resources section. No need for separate charge controller/array. You just have a bigger battery now.

1. Do I need to top balance the cells when I receive them? Can I skip this step if cell voltages are close (how close)

Absolutely, positively, without any doubt or hesitation, top balance them using the guide. If you choose not to, 99.999% chance you will experience BMS trips due to cell runners and realize that you now have to break the battery back down and top balance it. Even TINY differences in SoC (0.2%) can cause runners and premature BMS trips.

All 16 voltages could be exactly the same out to an absurd decimal place, e.g., 3.2999743V, and that tells you NOTHING about whether they need to be top balanced or not. They need to be. Always.

I feel like I have huge gaps of knowledge on physically building the bank and the various techniques and benefits there. Lots of youtube videos on this though.


My google skills are pretty good, but I don't know, what I don't know.

If it's an option, set Daly to only balance during charge, above 3.40V and only when cells are 0.03V apart.

Big house for a wee battery, but the transition to lithium gives her about 75% more USABLE capacity.

 

[Steve_S]

These are in my Signature but many browsers (phone ?) can't see the signatures on the forum. So I'm posting them separately, this will help you out.

Luyuan Tech Basic Lifepo4 Assembly Guide
STATUS of ESS / Storage Cells being purchased. (commodity cells)
General LiFePO4 (LFP) Voltage to SOC charts/tables 12/24/48V
Calibrating Voltage of your system to ensure Optimal Operations. SCC, Inverter/Charger, voltage matching.

 

[JoeHam]

Is the cabin heated 24/7/365 ?

Don’t forget you cannot charge LiFePO4 below freezing.

There are ways to mitigate that but ignoring it does not end well. ?

 

[ZColorado]

Absolutely, positively, without any doubt or hesitation, top balance them using the guide. If you choose not to, 99.999% chance you will experience BMS trips due to cell runners and realize that you now have to break the battery back down and top balance it. Even TINY differences in SoC (0.2%) can cause runners and premature BMS trips.

All 16 voltages could be exactly the same out to an absurd decimal place, e.g., 3.2999743V, and that tells you NOTHING about whether they need to be top balanced or not. They need to be. Always.

Much appreciated info. Thank you. I will dig into the top balancing "guide" I've not seen that yet, but i'd bet its in an easy to find place. EDIT: oh yeah, it's pinned to the top of the section. I missed that little pin icon. Thanks!
Link here: https://diysolarforum.com/threads/top-balancing-how-to.15839/

 

[ZColorado]

These are in my Signature but many browsers (phone ?) can't see the signatures on the forum. So I'm posting them separately, this will help you out.

Luyuan Tech Basic Lifepo4 Assembly Guide
STATUS of ESS / Storage Cells being purchased. (commodity cells)
General LiFePO4 (LFP) Voltage to SOC charts/tables 12/24/48V
Calibrating Voltage of your system to ensure Optimal Operations. SCC, Inverter/Charger, voltage matching.

I will read those, thank you for posting them.

 

[ZColorado]

Is the cabin heated 24/7/365 ?

Don’t forget you cannot charge LiFePO4 below freezing.

There are ways to mitigate that but ignoring it does not end well. ?

It's her full time residence. Battery is inside in a special room.
I have some rudimentary knowledge of these lifepo4 banks from a camper/travel trailer project of mine, but I passed it over because of that fact.

 

[Steve_S]

I will read those, thank you for posting them.

I gave up following threads long ago because it was just too much. I look into threads I have posted randomly. If you have specific questions you can FLAG me by quoting a post or using the @Steve_S and that will send me a notice.

 

[ZColorado]

I don't want to derail this thread but she is under paneled, and under battery banked. Our most likely plan is to add another ground mounted solar array with another charge controller in parallel. I assume that should work?

Currently has 9 qty SCHUCO 235w panels from 2011 - 2.1kw

 

[sunshine_eggo]

I don't want to derail this thread but she is under paneled, and under battery banked. Our most likely plan is to add another ground mounted solar array with another charge controller in parallel. I assume that should work?

Currently has 9 qty SCHUCO 235w panels from 2011 - 2.1kw

I presumed by your .21C it was somewhere in the 2kW range. Your cells can handle 0.5C , so you're good for up to 140A or as much as 140A * 56.8 = 7,952W total.

Simply add arrays with FM60 or 80 as needed. They can be connected to the battery bank as parallel chargers. Given that you are already using Tier 1 hardware, I would encourage you to stick with it and not be swayed by the EPEVER and cheaper MPPT controllers. On any new arrays, make sure your series Voc is not too close to the 150V limit. Given the colder temperatures, panel voltage will go increase, and you'll want to have plenty of headroom below 150V to ensure you don't exceed it. When putting a new array in place with its own MPPT, there is no compatibility concern with the panels of your other array. They can be different size, brand, power, etc.

Here's the NEC guidelines for temperature compensation on PV:

Adjusting Solar Panel Voc for temperature

When designing you solar panel system, it is important to adjust you solar panel Voc for temperature in order to ensure you do not over-voltage the PV inputs of your solar charge controller. This paper shows how to calculate the Temperature...

diysolarforum.com

Also worth confirming your existing array has been properly configured. If they're 60 cell panels, 3S3P array is good.

Lastly, on your FM60, if you have the temperature probe installed, you need to disconnect it. You do NOT want temperature compensation enabled for LFP, and disconnecting it is the only way I know to disable it.

Probably worth considering getting some inexpensive panels shipped from SanTan Solar in AZ. They're pretty good about decent freight shipping prices. You can get an FM80 and another 4kW (18 230W used panels for 3S6P array) for about $1400 before shipping, mounts and wiring. Lots of DIY mount options for not a lot more. Probably less than $2K total for another 4kW. She'll be living in luxury... running around the house, turning on lights like a madwoman giggling maniacally.

 

[ZColorado]

I presumed by your .21C it was somewhere in the 2kW range. Your cells can handle 0.5C , so you're good for up to 140A or as much as 140A * 56.8 = 7,952W total.

Simply add arrays with FM60 or 80 as needed. They can be connected to the battery bank as parallel chargers.

Perfect, that's what I thought I could do, thanks for verifying.

..., I would encourage you to stick with it and not be swayed by the EPEVER and cheaper MPPT controllers.

I work in Industrial maintenance, I hear you loud and clear here. I prefer to do it once, and do it right.

Also worth confirming your existing array has been properly configured. If they're 60 cell panels, 3S3P array is good.

Good point, I will dig into this when I am there. (thanksgiving and x-mas) The PO has done a few things that were odd, so I'd not be surprised to find issues. (She is 3.5hours from me)

Lastly, on your FM60, if you have the temperature probe installed, you need to disconnect it. You do NOT want temperature compensation enabled for LFP, and disconnecting it is the only way I know to disable it.

I will look into this as well. I do believe the probe is installed.

Probably worth considering getting some inexpensive panels shipped from SanTan Solar in AZ. They're pretty good about decent freight shipping prices. You can get an FM80 and another 4kW (18 230W used panels for 3S6P array) for about $1400 before shipping, mounts and wiring. Lots of DIY mount options for not a lot more. Probably less than $2K total for another 4kW. She'll be living in luxury... running around the house, turning on lights like a madwoman giggling maniacally.

Thanks for the link to that vendor. I will check that out. I suspect I will be doubling the bank and adding panels within a few months. She is mostly worried about the short winter days, and possible weather. She is high enough elevation that there is no A/C, just well water and radiant heat.


I very much appreciate the help!

 

[sunshine_eggo]

Good point, I will dig into this when I am there. (thanksgiving and x-mas) The PO has done a few things that were odd, so I'd not be surprised to find issues. (She is 3.5hours from me)

If they've been working, they're probably fine, but it never hurts to make sure things are within spec.

I will look into this as well. I do believe the probe is installed.

You definitely want it installed for FLA/AGM/GEL. Unless you never vary from 77°F much, failing to temp comp for lead means much shorter battery life.

Thanks for the link to that vendor. I will check that out. I suspect I will be doubling the bank and adding panels within a few months. She is mostly worried about the short winter days, and possible weather. She is high enough elevation that there is no A/C, just well water and radiant heat.

How is the radiant heat generated? I hope not from electricity....

 

[ZColorado]

How is the radiant heat generated? I hope not from electricity....

Ha! that would be nuts.
No. she has a large underground propane tank & High efficiently boiler.

 

[sunshine_eggo]

Ha! that would be nuts.
No. she has a large underground propane tank.

Whew.

 

[HRTKD]

If you don't want used panels, CEDGreenTech.com has a warehouse/office in Denver. I bought panels from them last year and it was a very good price and excellent service.

 

[Northernboy]

I'm in northern Alberta and I run the same inverter with a midnite solar classic 150 cc. I just did the same type swap you're doing, my AGMs for a 2p16s battery using 280ah rept cells. The one thing I would add to her system is an auto gen start for the magnum inverter and a standby generator. I set my auto gen start to 48.4v that way my cells will never get below 3v. Set the charge parameters in the magnum the same as your charge controller. Then set your charge amps to 40a and your gen run time to 4hrs and that will give you a 160ah boost till the next day.