Li batteries at 48vdc

[2oldman]

After much deliberation and questions, I'll likely be purchasing the 48v Lithium battery pack instead of 4-12v. I liked the idea of 12v batteries for weight and ease of handling, but the possible cell-balancing issues are a deal-breaker. Looks like the 48v pack will be around 130lb. I'll just have to find a couple guys to get it in there. Once in, it shouldn't ever have to come out... at least not in my lifetime.

According to the techs at Relion, cell balancing issues can occur if discharged below 80%. And if I only went with 100a of total capacity, that's a possibility.

Relion company is redesigning their 48v 150ah pack (which I think would be more than sufficient), so I'll be waiting to see what they come up with.

[time2roll]

Any updates on performance or other issues?

[Itinerant1]

2oldman I wish I could help you. With mine they are only in absorb for 0.1 hours than go to float. Besides some of the setting in pt100 controller it has the battery type, absorb as linked with the cpu of the lithium is attached.

[Itinerant1]

N8GS wrote:


So if I am reading this correctly you have a 5p4s system and the BMS is wired to every cell rather than just monitoring each 3.2 volt group.

Sorry for the delay I've been in a poor cell area and moved to the next boondock location.

That's correct. I purchased it through Starlight and he installed it. You might have checked his system this is the make up of it.
www.starlightsolar.com/RV_lithium_battery.html

[N8GS]

2oldman wrote:

N8GS wrote:
Looking forward to getting back there for New years eve. If you are there maybe our paths will cross.

BTW microwave draws 132 amps, voltage drop under load is 0.12 volts on my 12 V system.

I won't be there NY, but I do pop in and out on occasion.

Wow. Mine drops 1 volt.

True but you are at 4 times the voltage. Take your 1 volt divided by 4 and you have 1/4 volt drop at equivalent voltage. Also are you looking at drop from resting voltage or a light working voltage when the heavy load is applied?
Is that as clear as mud or what?

[2oldman]

To be clear, I personally did not ask for it to be built. It is a stock product. I'm not clear on whether any Li's are designed for RV use.

[MrWizard]

Yes..
But that was not the statement or the question

N8GS bought drop in 12v batteries designed for RV use

2old man bought a special built 48v pack
Not marketed as RV drop in

[mapguy]

MrWizard wrote:
No not drop in, his is special order
Not too many RVs use 48v system

Sold as a drop in 48v battery pack comprised of cylindrical cells and battery monitor system.

[MrWizard]

No not drop in, his is special order
Not too many RVs use 48v system

[mapguy]

2oldman wrote:

mapguy wrote:
Floating or storing LifePo4 cells -pouch, prismatic, cylindrical, at 90-100% is harmful to long term life.

Yeah.. it's quite the problem when the mfr recommends a float voltage.

That is why I asked about the data sheet for the cylindrical batteries used within your battery pack. It is these components that need the proper discharge and charge procedures. Pack level volts are secondary to individual cell volts in regard to knowing if you are properly charging/discharging within the knees of the voltage curve.

Sometimes you have to read between the lines - if Relion said "no float", their battery pack is not truly a drop-in replacement for the RV market.

There are white papers that quantify the capacity degradation done by floating at full or nearly full.

[time2roll]

mapguy wrote:
Sorry don't want to sound like a broken record on the float issue....

Floating or storing LifePo4 cells -pouch, prismatic, cylindrical, at 90-100 percent is harmful to long term life.

I believe the float voltages being used are under 90 percent capacity.

[pianotuna]

Hi 2oldman,

He has 12 volt--you have 48. So in watt-hours his bank is 20% larger than yours.

2oldman wrote:

N8GS wrote:
Looking forward to getting back there for New years eve. If you are there maybe our paths will cross.

BTW microwave draws 132 amps, voltage drop under load is 0.12 volts on my 12 V system.

I won't be there NY, but I do pop in and out on occasion.

Wow. Mine drops 1 volt.

[2oldman]

mapguy wrote:
Floating or storing LifePo4 cells -pouch, prismatic, cylindrical, at 90-100% is harmful to long term life.

Yeah.. it's quite the problem when the mfr recommends a float voltage.

[mapguy]

2oldman wrote:

N8GS wrote:
You might want to quiz your supplier as to the need to float..

They say it's not necessary. I cannot set its duration.

Sorry don't want to sound like a broken record on the float issue....

Floating or storing LifePo4 cells -pouch, prismatic, cylindrical, at 90-100% is harmful to long term life.

Harmonizing charging sources is the great challenge "right now" to implementing a LFP system. Typical RV is going to have at least 2 charge sources and could have 4 or more. All these charge sources need to be controlled properly to ensure a long service life without severe capacity degradation.

Look at this link for some info in layman's terms. This is a marine electrician that has been doing LFP on boats, including his own, for a while now.
http://www.pbase.com/mainecruising/lifepo4_on_boats

[time2roll]

Outback must have thought you wanted continuous absorption voltage. 😞