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BMS help

timselectric said:
Most BMS's have passive balancing.
Click to expand...

I have an active balancer and a BMS with a passive balancer. These are new cells but I understand that even though the voltage is the same on each cell the SOC might be different so I need to top balance them by putting them in parallel and charging until full? I nearly bought a JK BMS which has an active balancer built in, but I don't have a bench power supply with a high enough voltage for it so I bought a Daly.
 
Compression! I have Eve cells and the data sheet seems to suggest compressing the cells. I have watched a few videos were there are differing opinions on it. Any thoughts? Im nervous about overly compressing them as the casings aren't exactly bullet proof. My initial thought is do them up hand tight (ive made a thing with threaded bars based on YouTube) and then a few turns on the ratchet, making sure they are equal. The cells are meant to expand a bit anyway when charging so that would increase the compression a bit more I guess.
 
Charger voltages. What would be the absorption and float volts for Eve 24v battery pack? Thanks.
 
slowbutsure said:
Charger voltages. What would be the absorption and float volts for Eve 24v battery pack?
Click to expand...
I will give it to you in per cell voltages so it is universal for everyone regardless of pack size. These numbers are my preferences based on stopping charging to approximately 90% SOC for longer pack life.
Contstant Voltage (Absorb) 3.45 volts per cell or 8*3.45 = 27.6 volts
It is not recommended to Float Lithium for a long period but use a setting of 3.3 or 3.2 volts per cell so that the solar keeps them full until the sun goes down if the load in the afternoon is enough to discharge them below the voltage they settle at. Do not Float if using a powered charger that is always on.
 
Thanks that’s really helpful. It seems so hard to find this kind of information, like it’s a secret. It’s not in the data sheet.

I have a Victron shunt and I have to set the voltage for when the battery is charged. Would that also be 3.45 x 8? At 90% charged? I don’t want to go above 90.

Thanks.
 
slowbutsure said:
I have a Victron shunt and I have to set the voltage for when the battery is charged
Click to expand...
Presumably that is the voltage where you want the shunt to reset the Coulomb counter to 100 percent. My inverter automatically does that but my BMS also has a Coulomb counter and if I recall correctly it does have a setting to reset to 100 percent. Of course 100 percent is really only 90 percent and if there is a setting on your shunt for battery size I make that smaller to compensate and give my cushion at the bottom. My inverter automatically connects to the grid at 50 percent and my low voltage disconnect is 40 percent or a voltage that I estimated is approximately that SOC. I trust the Coulomb counter more than voltage if it has reset recently because if it has not reset it can drift and then voltage is a stopgap measure.
 
Ampster said:
Presumably that is the voltage where you want the shunt to reset the Coulomb counter to 100 percent. My inverter automatically does that but my BMS also has a Coulomb counter and if I recall correctly it does have a setting to reset to 100 percent. Of course 100 percent is really only 90 percent and if there is a setting on your shunt for battery size I make that smaller to compensate and give my cushion at the bottom. My inverter automatically connects to the grid at 50 percent and my low voltage disconnect is 40 percent or a voltage that I estimated is approximately that SOC. I trust the Coulomb counter more than voltage if it has reset recently because if it has not reset it can drift and then voltage is a stopgap measure.
Click to expand...
Yes, exactly. I’m just confused as to what to set the shunt charged setting to, whether it’s the same as the absorbtion or different.
 
slowbutsure said:
Yes, exactly. I’m just confused as to what to set the shunt charged setting to, whether it’s the same as the absorbtion or different
Click to expand...
I don't know your shunt so I was just guessing. As far as I know the shunt does not control anything but if it is communicating with the inverter or BMS then my assumption could be flawed. Take notes and make observations and that will give you a clue. If you set it lower by 0.1 volt it can't hurt anything.
 
Sorry Slowbutsure, had a family crisis and been driving up and down the coast.

Where are you up to with this? You said you have a desktop charger coming so have you top balanced your cells yet?
 
Sorry to hear that. I started using the desktop charger but calculated it would take about 16 days to charge at such 4 amps. So I have my solar charger charging it. Yesterday was cloudy but it received 4.5kw. So it should be getting there. Once they are fully charged I’ll put them in parallel to top balance. The bms shows they are all very close together in volts. I did have an active balancer but managed to fry it when I was connecting it!

Tiny Movements in volts when charging lithium takes a bit of getting use to when your use to lead acid! Out of interest what do you normally charge up to and discharge to? I’m looking at 90% and 10%
 
slowbutsure said:
Sorry to hear that. I started using the desktop charger but calculated it would take about 16 days to charge at such 4 amps. So I have my solar charger charging it. Yesterday was cloudy but it received 4.5kw. So it should be getting there. Once they are fully charged I’ll put them in parallel to top balance. The bms shows they are all very close together in volts. I did have an active balancer but managed to fry it when I was connecting it!

Tiny Movements in volts when charging lithium takes a bit of getting use to when your use to lead acid! Out of interest what do you normally charge up to and discharge to? I’m looking at 90% and 10%
Click to expand...

Ok well you can always take then up close to the top then use your desktop charger for the last part. When connecting things like your active balancer and BMS, connect all your sensor leads before connecting to the device.

On my caravan I go up to 90 - 95% and have it set for down to 10%. I have never been that low but I did forget to turn my inverter off for a couple of weeks and and they went down to 14%.
 
Tim Tim said:
Ok well you can always take then up close to the top then use your desktop charger for the last part. When connecting things like your active balancer and BMS, connect all your sensor leads before connecting to the device.

On my caravan I go up to 90 - 95% and have it set for down to 10%. I have never been that low but I did forget to turn my inverter off for a couple of weeks and and they went down to 14%.
Click to expand...
What kind of solar charger do you have? Is it a Victron? What settings do you use for absorption abs float?
 
I have an EPEver Triron and dont have the documentation with me nor can I remember the settings i used but they will be the same as listed below.

On page 24 of the link below are the LifePO4 settings that you can use but double them as you are now using a 24v system.

https://www.epever.com/wp-content/uploads/2021/04/XTRA-SMS-EL-V1.3.pdf

I have a few other inverters around but my Triron has been great. I need to buy another so that will probably be an Xtra next.
 
Last edited:
slowbutsure said:
What kind of solar charger do you have? Is it a Victron? What settings do you use for absorption abs float?
Click to expand...

I did see that you were also asking about compression somewhere but couldn’t reply to you. There are those for compression and those that can’t be bothered. I actually compressed mine at first then just simply clamped them up and taped them together before removing the clamps. At between 3000 and 5000 cycles, even if i discharged mine every day I will either be dead, given up playing with solar or the technology with have changed. Plus the cells are not dead at that stage they will just have 80% capacity of their original capacity.

Just an individual choice really.

This guy is funny, just like Will is when he is doing a late night videos and needs matchsticks to keep his eyelids open.

https://www.google.com.au/search?q=...sion&ie=UTF-8&oe=UTF-8&hl=en-au&client=safari
 
Ampster said:
I will give it to you in per cell voltages so it is universal for everyone regardless of pack size. These numbers are my preferences based on stopping charging to approximately 90% SOC for longer pack life.
Contstant Voltage (Absorb) 3.45 volts per cell or 8*3.45 = 27.6 volts
It is not recommended to Float Lithium for a long period but use a setting of 3.3 or 3.2 volts per cell so that the solar keeps them full until the sun goes down if the load in the afternoon is enough to discharge them below the voltage they settle at. Do not Float if using a powered charger that is always on.
Click to expand...

Do you discharge to 10%? If so what is that in volts? Thanks.
 
I am a bit confused with sic at th moment. My cells are at 3.346. But the bms app says it’s at 100%. It’s in absorbtion with no amps going in. Any thoughts anyone? Thanks
 
slowbutsure said:
Do you know this chart to be accurate? I’ve seen different charts with different numbers.
Click to expand...

If you google and look at images you will find many charts exactly the same but remember LifePO4 are different to AGM and lead acid etc so make sure you are looking at the right chart. Remember these figures are approximate.
 
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