LiFePO4 Battery Bank in Series (48V or 60V) balancer

[Thingol]

Hello folks,

I intend to series-connect four or five 12V Lithium batteries to make a 48V or 60V bank for my residential solar project. From my reading here and here, I understand that keeping the four/five units in balance is critical. Note that each of these units already have an internal BMS, so unit-level balancing is taken care of. I found that one way to balance out a series bank is with a Victron battery balancer. However these are going for USD 65/- a piece or so and do not appear to have such great ratings . For a 48V bank (four 12V batteries), one would need 3 balancers. Should a balancer cost that much ?? I am looking for better alternatives in terms of price and compactness, preferably ones that come as a single unit for 48V banks (four 12V batteries) or for 60V banks (five 12V batteries). If anyone has dealt with this before, please share your experience and recommendations, many thanks.

 

[snoobler]

I use these on my 12V:

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You would need one for each 12V.

 

[Ampster]

I would also look carefully at the specs of inverters and chargers/controllers with respect to their maximum voltage. Also low voltage cutoffs might not be safe for five 12 volt batteries in series. Depending on chemistry Lithium batteries in nominal 12 volt packs can reach in excess of 70 volts when fully charged.

Here is another thread discussing the issues in detail:

Changing from 2-48v banks to one 60v

Hello folks, semi newbie here. Were completely off grid in rural New Brunswick. Three years in and a few beginner mistakes, we seem to have a few batteries nearing their lifespan. We've run two banks, 8 6v batteries for most of the time. It appears after the worst 6 week run in weather We've had...

diysolarforum.com

 

[Thingol]

I would also look carefully at the specs of inverters and chargers/controllers with respect to their maximum voltage. Also low voltage cutoffs might not be safe for five 12 volt batteries in series. Depending on chemistry Lithium batteries in nominal 12 volt packs can reach in excess of 70 volts when fully charged.

Here is another thread discussing the issues in detail:

Changing from 2-48v banks to one 60v

Hello folks, semi newbie here. Were completely off grid in rural New Brunswick. Three years in and a few beginner mistakes, we seem to have a few batteries nearing their lifespan. We've run two banks, 8 6v batteries for most of the time. It appears after the worst 6 week run in weather We've had...

diysolarforum.com

Hello, thanks a lot for making this point. I intend to use the Victron Easysolar 5000VA charger/inverter unit. I just revisited the datasheet and see that the 150V/100A charger it comes bundled best works with 24V/48V banks, which it will auto-detect. I see no mention of 60V banks in there, only 12v, 24v, 36v and 48v. The absorption, float and equalization charges listed here in the datasheet would then be for the bank voltages I just mentioned. It appears that it would be easist to perhaps drop down to a 48V bank, but I'll first try to find out if the unit is indeed configurable for a 60V bank-do you know? Many thanks.

 

[Ampster]

-do you know?

I looked but did not see any default settings as high as 70 volts. What did you find?

 

[snoobler]

My 48V Quattros have a hard limit of 66V. Appears EasySolar does too. They likely have nearly identical guts:



I am not aware of any Victron hardware that works with 60V nominal. If you plan to use the stated unit, you must use 48V.

 

[Thingol]

I looked but did not see any default settings as high as 70 volts. What did you find?

I found the same thing @snoobler posted up above. I checked with my supplier about swapping out the 1 battery for extra solar panels but that may not be possible since the order has been prepared already. I also checked the SMA Sunny Island specs (see 17.3 DC Connection for Battery) and found that they all run with max 48V banks, even the Sunny Island 8.0. Not sure what I can do to incorporate the fifth battery without incurring extra cost..Any ideas?

 

[Ampster]

Any ideas?

Lithium does not self discharge so you could keep it as a spare. The cost would be insurance that your pack lasts a long time. I have some spare cells that I configured into a 12 volt pack and purchased a small inverter that I take to my sister's house during power outages to keep her refrigerator/freezer running. She has several outages a year. If you choose to store it and not use it then it should be discharged to about 50%. The exact percentage is not as important as the concept of not storing it fully charged.

 

[Thingol]

Lithium does not self discharge so you could keep it as a spare. The cost would be insurance that your pack lasts a long time. I have some spare cells that I configured into a 12 volt pack and purchased a small inverter that I take to my sister's house during power outages to keep her refrigerator/freezer running. She has several outages a year. If you choose to store it and not use it then it should be discharged to about 50%. The exact percentage is not as important as the concept of not storing it fully charged.

Oh yeah, that's definitely a great idea. I am aware of the SOC~lifeExpectancy relationship. I would have preferred to have it in the bank though- just so that the whole bank ages slower and I have a bit more usable capacity. I will research a bit more on the 60V bank possibility but I was reluctant to look outside of Victron and SMA.

 

[Ampster]

I will research a bit more on the 60V bank possibility but I was reluctant to look outside of Victron and SMA.

My Outback inverter and one of my Orion BMSs have the same limitation. It seems like there is a component cost inflection point that drives that issue. Others with more electronics experience may have details.

 

[Lt.Dan]

Im bringing this thread back because I have a question. How come this isnt more talked about? We drive balancing into everybody's head, but as soon as they are in a pack, its never talked about again. Is keeping entire packs in balance with each other not critical? I mean 4x 12v batteries in series, there could be a pretty big difference between them.

 

[Ampster]

My guess is that most large DIY packs consist of 4 or 8 or 16 LFP cells in series and they are kept in balance or the pack shuts down.

The issue is 12 volt batteries in series is unique to each manufacturer of those specific batteries. Some have communication cables that keep them in balance and others may not recomend putting them in series

 

[Lt.Dan]

The communication cables make sense, how about DIY batteries like with the 280ah cells. Someone could make 4x 12v batteries for ease of mobility but have no way of keeping them in sync?

 

[Ampster]

Someone could make 4x 12v batteries for ease of mobility but have no way of keeping them in sync?

Yes they could but most 48 volt inverters of any capacity are heavy enough that I would not call them mobile. I made some mobile 12 volt packs with inverters to keep my daughter's and sister's refrigerators runnig during power outages.

To modularize a 48 volt pack into 4 cell segments is simply a matter of finding the connectors to run a 16S BMS and disconnect the segments. In fact, to me it is the weight of the cells that would be how I would decide how to modularize them, not the voltage. With the right connectors it could be any combination.

 

[Gadgetnerd]

Hello folks,

I intend to series-connect four or five 12V Lithium batteries to make a 48V or 60V bank for my residential solar project. From my reading here and here, I understand that keeping the four/five units in balance is critical. Note that each of these units already have an internal BMS, so unit-level balancing is taken care of. I found that one way to balance out a series bank is with a Victron battery balancer. However these are going for USD 65/- a piece or so and do not appear to have such great ratings . For a 48V bank (four 12V batteries), one would need 3 balancers. Should a balancer cost that much ?? I am looking for better alternatives in terms of price and compactness, preferably ones that come as a single unit for 48V banks (four 12V batteries) or for 60V banks (five 12V batteries). If anyone has dealt with this before, please share your experience and recommendations, many thanks.

Price wise lifepo4 280ah 3.2v cells are a no-brainer. My 15kwh 48v bank cost 1800usd.

 

[Thingol]

Price wise lifepo4 280ah 3.2v cells are a no-brainer. My 15kwh 48v bank cost 1800usd.

Depends on where you are though. My project site is down in Kenya. Certain things are difficult or expensive to get or ship in without much fuss with customs. Then again, I am yet to get to that gangster level where I build my own battery packs . If I knew a seller that's got such units (your 15KWH) already assembled as such and that would have a clear customs process, I would buy from them...

 

[Gadgetnerd]

Yes, customs in some countries..corrupt, inefficient I'm sure. Building packs with BMS is simple though.

 

[Thingol]

Yes, customs in some countries..corrupt, inefficient I'm sure. Building packs with BMS is simple though.

Yeah, but for Kenya, customs is much improved since they started ending the paper era. Charges, taxes and the clearance processes are clear but the permits you need to bring in what is where the real headache is. Branded, pre-assembled batteries would for sure be easier for an ordinary Joe to bring through than Li cells.

 

[eabyrd]

Pondering the feasibility of using four 200ah Chins/Amphere time/zooms (pick the cheapest at the time) batteries in series. To keep the four balanced I was looking at the balancer below. I have 2 which I have been using on AGM stings since 2019. Any thoughts?

https://smile.amazon.com/Battery-Equalizer-48V-Voltage-Balancer/dp/B07L8WKKC3/ref=sr_1_3?crid=R45N9TVD94P&dchild=1&keywords=taico+battery+equalizer&qid=1632424883&sprefix=Taico%2Caps%2C152&sr=8-3

 

[Gadgetnerd]

Just get a 4-8S 48V BMS, probably cheaper and way better.