Old DYI Off Grid guy but totally new to the LiFePO4 battery scene.

[Jake59]

We have had an off grid cabin going on 21 years. I started in 2003 using a Trace SW5548 inverter with 8x Trogan T-105 batteries and 8x 60w solar panels plus a Trace C40 charge controller. After 6 years the Trogans were done, so I located some even larger locomotive batteries from Dyno Batteries here in Seattle. These massive 2.2 volt 500 ah have served us very well for 15 years as I never abused them for the first 10 years but the last 5 have seen them dipping well below the 45 vdc minimum voltage desired.
So now it is time to break into the new age of LiFePO4 batteries. I am looking at 16x 304 ah units from the 18659 Battery Store. I am comfortable in wiring these all up but I am not understanding the sizing of the BMS. My SW has a 5.5 kw inverter so the input could be >100 amps. OK their JK BMS B2A24S15P is rated at 150 amps continuous but I do not understand is the need or the sizing values for active balancing. Is 2 amps better than .6? Is active balancing even desired or needed as some Daly brand BMS units requires an additional components?

We use the cabin 2 weekends per month on average (more in the summer and less in the winter but do enjoy the wilderness year round) so there can easily be several days if not a week or more that we are not there. The biggest hitter is out 1/2 hp shallow well pump and then the occasional power tool. I have upped the solar collection to 1200w and we have a Yamaha 6600 genset for bulk charging if needed.

Moving forward I will be updating the charge controller to a mppt unit and do plan to top balance charge these LiFePO4 batteries before installing. I have created a battery location that will maintain temperatures above 32 f except maybe for the 2 crazy 15 below days we experienced last month.

Once this system is up and running I have the additional desire to move to a LiFePO4 100 or 150ah house battery for our 87 VW Westfaila but for now we need to get the cabin setup and running.

TIA

 

[sunshine_eggo]

For quality cells that are reasonably well matched, passive should be fine. Active current affects how quickly the active balance can correct any imbalance.

Your cells are good for 304A, so the BMS should be that or less.

IMHO, avoid DALY.

 

[OffGridForGood]

The biggest hitter is out 1/2 hp shallow well pump and then the occasional power tool.

8x 60w solar panels

Trace SW5548 inverter

The well pump will have a high start up current (in rush) but this will last only a few seconds, or less, then settle down to normal operating current.
The inverter you have - SW5548 - is this 5500W max output? (not very familar with the Trace units) does the Trace output 120 v only or is it 120 /240?

you don't tell us much about the loads side of the existing system. With only 480W of PV it would take a long time to charge up a 304Ah 48v pack (15.5 kWh pack / 0.48kw PV = 32hrs (sunny hours) to charge up this pack. you said Seattle - PNW is not known for a lot of sunny hours generally)

I ask since it may be your planning to expand the PV side, and the battery will make sense, or if it takes two weeks to charge up is ok since you visit a few times per month, more often during summer - but more sunny skies in summer. If the 15.5kWh battery will supply all you need for a visit, maybe the small PV makes good sense, since it doesn't need to supply the loads on demand.

For a DIY pack, I like my JK BMS's and I have several of them.
A 5500W (assumed) max output inverter will draw from the 48v battery 5500/48 = 114amp at max output. I expect your jet pump will not require full capacity of the inverter. An in-rush meter would tell you the peak on start up to know for certain.

 

[Jake59]

The well pump will have a high start up current (in rush) but this will last only a few seconds, or less, then settle down to normal operating current.
The inverter you have - SW5548 - is this 5500W max output?

Yes I understand that a motor load has a high inrush load to start it. I have searched for a lower hp or even a DC with a soft start but my well is too small at 3" diameter for a submerged pump. We have had this setup for the last 20 years and it works OK matched with the SW5548 which is a 5.5kw at 120v inverter using a 48v battery bank. I have also increased our solar panels to 1200w, still not much but we have time (days) between visits to allow the batteries to recharge.

Again my question is the sizing of the BMS and the need for active balancing. With our low frequence use of the cabin would a lower .5 amp balance be more advantageous vs a 2 amp balance? Does the active balance stay active (and at what ampage?) even as the cells come in to a balanced range?

 

[sunshine_eggo]

IMHO a 1/2 hp pump is likely not going to surge beyond about 3500W, and that's if it's very, very inefficient.

Again my question is the sizing of the BMS and the need for active balancing.

Again, you size based on the cells you're using and the needed current.

With our low frequence use of the cabin would a lower .5 amp balance be more advantageous vs a 2 amp balance? Does the active balance stay active (and at what ampage?) even as the cells come in to a balanced range?

If this doesn't answer the question, please tell me where I'm failing you:

For quality cells that are reasonably well matched, passive should be fine. Active current affects how quickly the active balance can correct any imbalance.

 

[jimf909]

We have had an off grid cabin going on 21 years. I started in 2003 using a Trace SW5548 inverter with 8x Trogan T-105 batteries and 8x 60w solar panels plus a Trace C40 charge controller. After 6 years the Trogans were done, so I located some even larger locomotive batteries from Dyno Batteries here in Seattle. These massive 2.2 volt 500 ah have served us very well for 15 years as I never abused them for the first 10 years but the last 5 have seen them dipping well below the 45 vdc minimum voltage desired.
So now it is time to break into the new age of LiFePO4 batteries. I am looking at 16x 304 ah units from the 18659 Battery Store. I am comfortable in wiring these all up but I am not understanding the sizing of the BMS. My SW has a 5.5 kw inverter so the input could be >100 amps. OK their JK BMS B2A24S15P is rated at 150 amps continuous but I do not understand is the need or the sizing values for active balancing. Is 2 amps better than .6? Is active balancing even desired or needed as some Daly brand BMS units requires an additional components?

We use the cabin 2 weekends per month on average (more in the summer and less in the winter but do enjoy the wilderness year round) so there can easily be several days if not a week or more that we are not there. The biggest hitter is out 1/2 hp shallow well pump and then the occasional power tool. I have upped the solar collection to 1200w and we have a Yamaha 6600 genset for bulk charging if needed.

Moving forward I will be updating the charge controller to a mppt unit and do plan to top balance charge these LiFePO4 batteries before installing. I have created a battery location that will maintain temperatures above 32 f except maybe for the 2 crazy 15 below days we experienced last month.

Once this system is up and running I have the additional desire to move to a LiFePO4 100 or 150ah house battery for our 87 VW Westfaila but for now we need to get the cabin setup and running.

TIA

You're going to love LiFePO4 batteries. Gone will be the days of lengthy absorption and equalizing charges, anxiety of dropping below 50% SOC, checking electrolyte levels, measuring specific gravity, etc.

When you're ready to build a battery for your Westy head on over to thesamba.com to see some LiFePO4 house batteries. I have a 280 ah battery in the basement of the Westy closet. Battery anxiety has ended. (Maybe you've already been camped out at thesamba for 16 years?)

 

[OffGridForGood]

the SW5548 which is a 5.5kw at 120v inverter using a 48v battery bank.

okay 120 only , not split phase.

IMHO a 1/2 hp pump is likely not going to surge beyond about 3500W, and that's if it's very, very inefficient.

He will be fine with the above set up.
If that inverter was split phase 120/240 and the pump 120, then there could have been a problem.

 

[Notes]

Jake59, I have a soft start Grundfos 10SQ05-160 (96160167 ) 3" well pump. 10GPM, 1/2 HP, 115 volts. My Trace SW4024 has no problems. It max out at 1.4kw if I remember correctly. Its soft start and variable speed.

​

 

[sunshine_eggo]

Jake59, I have a soft start Grundfos 10SQ05-160 (96160167 ) 3" well pump. 10GPM, 1/2 HP, 115 volts. My Trace SW4024 has no problems. It max out at 1.4kw if I remember correctly. Its soft start and variable speed.

​

SQ line has no surge whatsoever.

 

[Jake59]

If this doesn't answer the question, please tell me where I'm failing you:

Hey Sunshine! You are by no means failing me. I if anything it is me just overthinking it. I had a 48v Chinese 3" submersible but the pipe ID is also 3" so it is almost like a piston fit. Why the PO only placed a 3" pipe is beyond me.

Thanking you for your support.

 

[Jake59]

You're going to love LiFePO4 batteries. Gone will be the days of lengthy absorption and equalizing charges, anxiety of dropping below 50% SOC, checking electrolyte levels, measuring specific gravity, etc.

When you're ready to build a battery for your Westy head on over to thesamba.com to see some LiFePO4 house batteries. I have a 280 ah battery in the basement of the Westy closet. Battery anxiety has ended. (Maybe you've already been camped out at thesamba for 16 years?)

Thanks Jim, I have been a member of thesamba for many years and there are many many many threads on both solar hacks and house battery hacks. I'm most excited by this group's knowledge of DIY LiFePO4 batteries. By buying the raw cells with an external BMS I hope to place 150 ah pack where one could only best fit 100 and better yet save several $100's doing it.

 

[hwy17]

I'm not sure that DIY and unattended operation go well together. But I maybe have just overcomplicated my own DIY project compared to the popular BMS options.

 

[jimf909]

Thanks Jim, I have been a member of thesamba for many years and there are many many many threads on both solar hacks and house battery hacks. I'm most excited by this group's knowledge of DIY LiFePO4 batteries. By buying the raw cells with an external BMS I hope to place 150 ah pack where one could only best fit 100 and better yet save several $100's doing it.

Good point. I was exposed to many LiFePO4 and solar ideas at thesamba but came here for expertise when building batteries for my cabin and the van.