17S BMS for LiFePO4?

Darren Orange

Solar Enthusiast
I can't seem to find a good solution to this problem, so perhaps it does not exist. For my application it would be helpful to find a good 17S BMS as my control a MPP LV5048 can charge up to 58.4V which is the max ideal voltage anyway for each cell. To keep long life and max out the battery voltage range I would like to put together at 17S battery.

Any help would be great, thank you!
 

MisterSandals

Participation Medalist
to find a good 17S BMS as my control a MPP LV5048 can charge up to 58.4V which is the max ideal voltage anyway for each cell.
You should control your charging voltage with your charge controller NOT a BMS. The BMS is a safety switch for the limits of the battery (2.5V - 3.65V for example).
 

Darren Orange

Solar Enthusiast
You should control your charging voltage with your charge controller NOT a BMS. The BMS is a safety switch for the limits of the battery (2.5V - 3.65V for example).
I think I should clarify.

The LV5048 has a max charging voltage of 58.4V. If I use a 16S that means each cell would be at 3.65V which is fully charged. I don't want to fully charge the cells, I plan to use about 90% of the useful capacity. So by adding a 17th cell that puts me at ~3.44V with a pack voltage of 58.4V Which is right around 90-91%.

The BMS will still limit the voltage and protect the battery but by finding a BMS that can support a 17th I will effectively increase my capacity without any real draw back to me in the real world.
 

MisterSandals

Participation Medalist
If I use a 16S that means each cell would be at 3.65V which is fully charged. I don't want to fully charge the cells, I plan to use about 90% of the useful capacity.
So you set the CHARGE CONTROLLER (get it?) to control how high to charge your batteries.
The 3.65V safety limit that the BMS imposes is a safety cutoff not a charge manager.

You set your CHARGE CONTROLLER to stop charging at your desired voltage. It is exactly how they are designed to work. It is extremely common for folks to customize the CHARGE SETTINGS to match your desired charge profile.

A BMS is NOT a charge controller. By continually disconnecting at stress levels, it will quickly fail.
 

Darren Orange

Solar Enthusiast
So you set the CHARGE CONTROLLER (get it?) to control how high to charge your batteries.
The 3.65V safety limit that the BMS imposes is a safety cutoff not a charge manager.

You set your CHARGE CONTROLLER to stop charging at your desired voltage. It is exactly how they are designed to work. It is extremely common for folks to customize the CHARGE SETTINGS to match your desired charge profile.

A BMS is NOT a charge controller. By continually disconnecting at stress levels, it will quickly fail.

So my charge controller can only charge to 58.4V that is 100% SoC for this chemistry 3.65V in 16S. So I'll get some 2000 cycles charging to full every time. So I want to only charge to about 90% to increase the battery life.

90% SoC is about ~3.44V for this chemistry, which means if I am using a 16S battery the charge controller would be set to 55V.

Now lets change this to a 17S battery. that means I can set my charge controller to 58.4V and the battery over all SoC would be about still 90%.
However I would gain the added useable capacity of that extra cell at 90%.

The BMS is for safety, hence why I am trying to find one for 17S it has nothing to do with charging the battery but if I can't find a 17S BMS I can't do what I want to do safely. I simply am trying to explain my use case.

Maybe what I want to do is not normal, I'm simply trying to make out my MPP LV5048 capabilities.
 

Darren Orange

Solar Enthusiast
I understand what you're trying to do but it's just not really a thing to my knowledge.

I could be wrong though.
Yea I'm starting to realize that. I don't know how often I would fully charge the battery anyway, so it may be mute point. If it gets fully charged only 1/3 to 1/2 of the year does it really make any difference, it is still going to last nearly 10 years to 80% I would think.
 

Scph9002

Solar Enthusiast
58.4v is not full. 58.4v is just a safe over voltage to push current faster into your battery until it is full. you can charge a battery with as little as 3.4 volt per cell and get it to 99% SoC albeit not as fast as if you would charge it at 3.65v per cell.

But yes in any case, a 17s would be better and can easily not only charge to 90% but even to 99%. with 58.4v although with a relative slow speed
 

Scph9002

Solar Enthusiast
also, i forgot to aswere your question lol.

here is a 17s daly bms. it sys liion but that should work fine with lifepo4..just remeber to change the default settings in the bms from lion to lifepo4 voltages

Im using a "lifepo4" bms to charge a li-ion pack :p

 

Short_Shot

Photon Sorcerer
also, i forgot to aswere your question lol.

here is a 17s daly bms. it sys liion but that should work fine with lifepo4..just remeber to change the default settings in the bms from lion to lifepo4 voltages

Neat.
 

Darren Orange

Solar Enthusiast
58.4v is not full. 58.4v is just a safe over voltage to push current faster into your battery until it is full. you can charge a battery with as little as 3.4 volt per cell and get it to 99% SoC albeit not as fast as if you would charge it at 3.65v per cell.

But yes in any case, a 17s would be better and can easily not only charge to 90% but even to 99%. with 58.4v although with a relative slow speed
Yes so my Bulk would be 58.4V and float would be 56V I believe for full charge. I think for future proofing if I needed to expand the pack staying 16S would be smarter.
 

Darren Orange

Solar Enthusiast
also, i forgot to aswere your question lol.

here is a 17s daly bms. it sys liion but that should work fine with lifepo4..just remeber to change the default settings in the bms from lion to lifepo4 voltages

Im using a "lifepo4" bms to charge a li-ion pack :p

Thank you for the help!
 

MisterSandals

Participation Medalist
I think for future proofing if I needed to expand the pack staying 16S would be smarter.
You are going to need to use a "user-defined" battery type to turn the equalization off because it would kill your LiFePO4 battery.

You might as well just set the charge voltage settings to those recommended for LiFePO4
while you are in there and then you can have the charge profile you seek.

Seriously, this is what a charge controller is made to do. The SCC you have is specifically made with lead acid and AGM charge profiles but the designers had the foresight to allow for future proofing with the user-defined battery type. This is perfect for what you are doing.
 

dRdoS7

Solar Enthusiast
Hi,

I can't seem to find a good solution to this problem, so perhaps it does not exist. For my application it would be helpful to find a good 17S BMS as my control a MPP LV5048 can charge up to 58.4V which is the max ideal voltage anyway for each cell. To keep long life and max out the battery voltage range I would like to put together at 17S battery.

Any help would be great, thank you!

If you're still looking, I have one of these:


I have 18 cells, but it can handle up to 24 cells, and down to 4 cells with a 12v booster (so I have read). My MPP 5048 can charge to 64V, so I wanted to use that. Gives me 2 spare cells in case of failure, I can drop back to 17, or 16 cells, if needed, until I can get replacement/s. Also, slighly higher capacity in the meantime.

dRdoS7
 
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