What voltage to charge at to get to 90%?

[jarossamdb7]

I've got a home made bank of these 230ah cells: https://www.aliexpress.com/item/33017301036.html?spm=a2g0s.9042311.0.0.2ae54c4d6m16pP
I've got a Daly BMS, Victron Solar charger, battery to battery charger, BMV and Smart Battery Sense. I had my BMS and Vicron stuff all set to charge to 13.4v/3.35v per cell. But this only got them to 3.28v or so when all the chargers were off. When people say "charge to 3.35v" does that mean your chargers are set at 3.35v? Or your battery is at 3.35v when all charging is complete? I now have my system set to charge at 3.6v and when it settles, after I turn off the chargers it seems to be around 13.4xx/3.37v/cell. Is this on point? Also, should I have the same settings for the Daly and all the victron stuff, or should I have the Daly set at higher, "just-for-safety" levels? I would like my batteries to last as long as possible, but most importantly, I just want to be safe!

 

[Pierre]

One needs to compensate for the volt drops in the closed circuit. Make sure all your voltage sense ( balance leads ) are connected with the least amount of resistance. Compare the reported cell voltages with your own taken with a good quality DVM. Most BMS’s have a ’cell voltage calibrate’ function and if you are confident that your meter is accurate enough you can re-calibrate the cell voltages.

 

[MisterSandals]

I would like my batteries to last as long as possible, but most importantly, I just want to be safe!

Can you describe your use of your battery? I recommend different settings for the different ways batteries are used.

 

[kuranaga]

please submit your CV first

 

[time2roll]

14.4 is virtually 100% charged and yes it will settle. Really need to set voltage based on what the battery monitor tells you is 100%. If you keep coming in at 80% bump the voltage by 0.1 each week until you hit the target. Or work from the top down by decreasing each week. Never going to be exact and will depend on usage and charging etc. Mine is set to charge to 13.80 as a guess to be in the 90% zone and I have no monitor.

When people say "charge to 3.35v" does that mean your chargers are set at 3.35v?

Yes. Although it could still vary based upon how long the battery is held at the target voltage. At 3.35 (fairly low) it will make a difference if held 2 minutes or 2 hours.

 

[Diysolar123]

I've got a home made bank of these 230ah cells: https://www.aliexpress.com/item/33017301036.html?spm=a2g0s.9042311.0.0.2ae54c4d6m16pP
I've got a Daly BMS, Victron Solar charger, battery to battery charger, BMV and Smart Battery Sense. I had my BMS and Vicron stuff all set to charge to 13.4v/3.35v per cell. But this only got them to 3.28v or so when all the chargers were off. When people say "charge to 3.35v" does that mean your chargers are set at 3.35v? Or your battery is at 3.35v when all charging is complete? I now have my system set to charge at 3.6v and when it settles, after I turn off the chargers it seems to be around 13.4xx/3.37v/cell. Is this on point? Also, should I have the same settings for the Daly and all the victron stuff, or should I have the Daly set at higher, "just-for-safety" levels? I would like my batteries to last as long as possible, but most importantly, I just want to be safe!

there are a few things going on here that you need to think about...
Your BMS is to protect your battery, thats its only real job.
You should have you BMS to disconnect at 3.65 because that is the limit it should be working at.

Now, the fun part, when you say the chargers were "off", do you know what your voltages were when that charging stopped?
Is there a chance the BMS actually turned off the charging fets?
You cells do, and should, quickly settle once the charge voltage has been dropped (unless you are float charging of course).
Do you have a daly bms that will allow you to track the voltage/currents over time so you can really see what is going on?
Do you have an accurate volt meter (fluke, etc.) that you have checked with a voltage reference? (precision voltage references are amazingly cheap now and definitely can make sure you are at least reading things in the mv range correctly).
The greater the charge current you allow the greater the voltage "error" due to line losses you will see; this has to do with your wiring.
When trying to make sure things are accurate to within 10mv or so, it can be tricky.

I charge at 3.4V/cell so that means that is the voltage my charger is set at, and I just let it set there; there is no current flowing beyond a few milliamps for self-discharge, a status led and the BMS in active mode.

 

[fafrd]

I've got a home made bank of these 230ah cells: https://www.aliexpress.com/item/33017301036.html?spm=a2g0s.9042311.0.0.2ae54c4d6m16pP
I've got a Daly BMS, Victron Solar charger, battery to battery charger, BMV and Smart Battery Sense. I had my BMS and Vicron stuff all set to charge to 13.4v/3.35v per cell. But this only got them to 3.28v or so when all the chargers were off. When people say "charge to 3.35v" does that mean your chargers are set at 3.35v? Or your battery is at 3.35v when all charging is complete? I now have my system set to charge at 3.6v and when it settles, after I turn off the chargers it seems to be around 13.4xx/3.37v/cell. Is this on point? Also, should I have the same settings for the Daly and all the victron stuff, or should I have the Daly set at higher, "just-for-safety" levels? I would like my batteries to last as long as possible, but most importantly, I just want to be safe!

What size wires are you using from SCC to battery? Have you measured voltage from SSC output to battery terminal when charging at max current?

I suspect you’ll be surprised to see how much voltage is being lost (meaning when SCC believes battery has charged to 3.6V it’s probably well below that voltage in reality).

 

[jarossamdb7]

Can you describe your use of your battery? I recommend different settings for the different ways batteries are used.

I am full-time in my van. I have a fridge that uses about 3a when the compressor is running. my interior lights are about 1.5a. I have a 25amp, 12v hot water heater which I usually run on a 2 hour relay maybe 3 or 4 times a week, but I'd like to run it more when I can. I have a evaporative cooler which runs at around 10amp max. With my inverter, Sometimes I will vacuum (500w) briefly and If I am driving (thus my 30amp Orion is running) sometimes I use my 700w instant pot. When I had my 220ah AGM setup, id rarely go below 85% soc.

I plan on running a 25-60ah 12v air conditioner come summertime, I currently have that 230ah lifepo4 bank, but I plan on adding another bank of 4 240ah lifepo cells and if I need to, I will upgrade with a 3rd 240w solar panel and switch from my 100/30 Smart Charger to a 100/50.

 

[jarossamdb7]

What size wires are you using from SCC to battery? Have you measured voltage from SSC output to battery terminal when charging at max current?

I suspect you’ll be surprised to see how much voltage is being lost (meaning when SCC believes battery has charged to 3.6V it’s probably well below that voltage in reality).

for my battery to battery, I have a short run from my vehicle battery, then about 6ft of 1/0gauge. I have not measured with a DVM, but I have my Smart Battery Sense, connected directly to the bank of the 4 cells.

 

[jarossamdb7]

14.4 is virtually 100% charged and yes it will settle. Really need to set voltage based on what the battery monitor tells you is 100%. If you keep coming in at 80% bump the voltage by 0.1 each week until you hit the target. Or work from the top down by decreasing each week. Never going to be exact and will depend on usage and charging etc. Mine is set to charge to 13.80 as a guess to be in the 90% zone and I have no monitor.


Yes. Although it could still vary based upon how long the battery is held at the target voltage. At 3.35 (fairly low) it will make a difference if held 2 minutes or 2 hours.

Held? you mean like setting an adaptive or limited "absorb" time on my victron stuff? Should I do this? how much time is good?

It seems like my battery monitor needs to be configured correctly and calibrated. Because it seems to get confused. Its only as good as the parameters I feed it to go off of, yes?

 

[jarossamdb7]

please submit your CV first

When all is setteled, it seems that the current voltage (thats what you are asking for, yes?) is 3.47. Which is a little higher than I would like, so I am slowly lowering what I have the chargers feeding it

 

[MisterSandals]

I am full-time in my van

I plan on running a 25-60ah 12v air conditioner come summertime, I currently have that 230ah lifepo4 bank, but I plan on adding another bank of 4 240ah lifepo cells

It sounds like you have good experience with your cells. I think you are be a little over conservative with your charging profile than you need to be.
I am a conservative charger too but since you have these in use 24/7/365, they can be safely charged to 14V and floated at 13.4V. If you find you need to squeeze a little more out of your batteries, 14.2V and 13.6V would help.
These are still well within what the battery is designed to handle.

Regarding your BMS settings, it sounds like you match the safety limits to your charging profile. To prevent your BMS from tripping, it should be set at the battery safety limits (2.5V low, 3.65V high). I run inside here as my conservative settings (2.7V and 3.63V).

Does this address some/most of what you are asking?

 

[time2roll]

Held? you mean like setting an adaptive or limited "absorb" time on my victron stuff? Should I do this? how much time is good?

It seems like my battery monitor needs to be configured correctly and calibrated. Because it seems to get confused. Its only as good as the parameters I feed it to go off of, yes?

If the voltage is set a bit low and you are not getting to 90% one option is to extend the absorption time (if available) rather than increasing the voltage. Increase by 30 minutes each week and see if the increased time gets you close to 90%. I would not go past 120 minutes. At that point bump the voltage.

Not going to be exact as the usage cycle varies and may even vary by the seasons. Soon you will be checking it every 90 days instead of every 90 minutes.

I don't know much about configuring the monitor.

 

[MisterSandals]

BMV and Smart Battery Sense

I don't know much about configuring the monitor.

Personally I think the BMV 712 is more hassle than it’s worth. It’s reading seems to drift over time so I found myself checking it against the voltage in my head as a sanity check.
Now I just watch voltage and removed the BMV shunt as it’s an extra layer of complexity. My plan is simple. Charge to 13.8V absorption, float at 13.2V based on my use. At 13V, I think getting low (20%?), at 13.4V pretty full.

If you are seeing absorption time, you are in Victrons “expert mode”. I would tread lightly here and start at lower absorption times and experiment/adjust slowly and carefully. I have not messed with expert mode in over 2 years of using my 100/30.

 

[MisterSandals]

If the voltage is set a bit low and you are not getting to 90% one option is to extend the absorption time (if available) rather than increasing the voltage. Increase by 30 minutes each week and see if the increased time gets you close to 90%. I would not go past 120 minutes. At that point bump the voltage.

After rereading this, I kind of like this more and more. I am assuming this means charging at a conservative voltage (below 14V?) and holding longer.

Since it is expert mode and I don’t have an expert shingle on my wall, I personally would try small 10 min increments if I went that route.

This is going to occupy my thoughts for a good part of the day…

 

[John Frum]

My suggestion is charge the battery nearly full and don't exceed 90% depth of discharge.
Any voltage >=13.8 will get your battery pretty much full.
In order for you BMS to maintain the top balance, its good to charge into the high knee.
Its also good to leave a little room so that your bms doesn't trip on a cell exceeding 3.65 volts.
14 volts is a nice round number to start with.

As for 90% discharge that depends on the cells in the pack.
I suggest you do a test discharge at a current draw representative of your use case until the first cell starts to drop away from the rest.
That is the point where you want your inverter low voltage disconnect to occur.

 

[time2roll]

Currently my solar charges to 13.8 and holds 5 minutes. I assume that is in the 90% zone. Maybe not. I also have my controller set to equalize every 21 days for 30 minutes at 14.2 volts. I expect that will top it up good and allow some balancing.

 

[time2roll]

Since it is expert mode and I don’t have an expert shingle on my wall, I personally would try small 10 min increments if I went that route.

Easy to verify amps as you enter absorption and calculate how much more is needed. If you need 10 more Ah and you are getting 20 amps that would be 30 minutes. Maybe more time due to amps tapering off. All is just a slide rule guess.

 

[MisterSandals]

Easy to verify amps as you enter absorption and calculate how much more is needed. If you need 10 more Ah and you are getting 20 amps that would be 30 minutes. Maybe more time due to amps tapering off. All is just a slide rule guess.

Makes sense to me. I will have to start watching amps at end of charge cycle. It sounds like there is good info there that I am missing out on collecting.

Thanks! I learned something today!

 

[Pierre]

Good advice above. All batteries / packs are not born equal and quite a lot of experimenting by trial and error is sometimes needed to optimise your particular setup.