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Top and Bottom Balance for EG4 12V

EARVS

New Member
Joined
May 12, 2022
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This is my first posting here on the site. I am new to working with LiFePO4 (nearly so).

I purchased an EG4 12V rack, first rack I've owned. I thought I was having issues but I think
it was the settings on my Victron Shunt. I needed to make sure there were no draws at all
and reset the current base (I'll call it). Now it reads "okay" I let the unit charge up with a
Victron IP65 and a bit confused on making setting right (for now). I got the EG4 monitor
software installed and could see some things ... and from here are my questions, some general
and others likely basic too.
1. I have read where people top balance (okay) but the bottom balance and not sure how that
works and how to do it. I have turned off the charger and just using the unit and am guessing
that sooner or later it will shut off automatically. Then completely full charge the unit until the
Victron charger goes into Float or Storage. I am assuming this is doing a bottom balance
and top balance. How often would I do this and/or is it okay to just leave a charger on and
let it keep management of it as I use it? 2. I've had it running a day or so, lights, radio etc. and the Shunt
reads 94% but the BMS EG4 software said 91% ... So I am thinking synchronization or that I didn't
have right true state of charge at reset of current and percentage when reset. 3. The four sensors
reading the "cells" in the EG4 software shows three at 3.28 and one at 3.18 ... each cell I am
sure is four individual cells that their BMS doesn't read individually. Is this a good or bad
differential... remember too, I am using down the battery for now. Had he battery on line about
4 days.

Later, I am planning on connecting and using the Victron Multiplus II 12V and a bit trepidations
based on what I've been reading on this site. Apparently the 12V version of the EG4 doesn't
communicate with the Cerbo GX, but 24 and 48 do ... I am told.

Any tips, tricks or comments that may help are welcomed. Have a great day. pb
 
1. Top balance if you will be recharging your battery daily to near full.

Bottom balance if:
you will regularly deplete the battery to 0%
This is an EV application where heavy discharge currents pose a risk of driving an imbalaced cell too low.

NEVER both.

99.99% of folks running solar power systems would want a top balance only.

Accounts of testing make it look like folks are trying to do a top balance, but they're just testing capacity after a top balance.

2. You can't trust a BMS SoC until the battery has been fully charged in accordance with the battery charging parameters.

You can't trust a shunt SoC until the battery has been charged to the 100% charged criteria for the shunt, AND those criteria are accurate.

3. 0.1V differential in the working range is not good. You have 3 cells in the working range, and one just below. This suggests that your reported SoC is inaccurate.

Recommend you reconnect the IP65, charge to 14.4V and hold 14.4V until the current drops to 5% of capacity, i.e., 5A for a 100Ah battery.

As the charge approaches full, you should look for outlier cells higher than the others. You may need to hold the battery at 14.4V to force the BMC to engage balancing to pull the high cells down.
 
1. Top balance if you will be recharging your battery daily to near full.

Bottom balance if:
you will regularly deplete the battery to 0%
This is an EV application where heavy discharge currents pose a risk of driving an imbalaced cell too low.

NEVER both.

99.99% of folks running solar power systems would want a top balance only.

Accounts of testing make it look like folks are trying to do a top balance, but they're just testing capacity after a top balance.

2. You can't trust a BMS SoC until the battery has been fully charged in accordance with the battery charging parameters.

You can't trust a shunt SoC until the battery has been charged to the 100% charged criteria for the shunt, AND those criteria are accurate.

3. 0.1V differential in the working range is not good. You have 3 cells in the working range, and one just below. This suggests that your reported SoC is inaccurate.

Recommend you reconnect the IP65, charge to 14.4V and hold 14.4V until the current drops to 5% of capacity, i.e., 5A for a 100Ah battery.

As the charge approaches full, you should look for outlier cells higher than the others. You may need to hold the battery at 14.4V to force the BMC to engage balancing to pull the high cells down.
Wow, ... this is the best most clear and to the point information. IP65 Charging. Thank You.
This EG4 -LL 12V is a 400Ah system. You suggested 14.4V charge for a 100Ah battery to get the BMS to balancing?
After I do this and can verity it with the pc software, then I would set/reset the shunt (right?). At that point, then I can
just let the charger manage it and maybe set it to 4 amps rather than the 15 amp option.
The only thing I need to do is get the accurate data for the EG4 12V Rack ... they say charge at 14.5V, recommended
bulk 14.25V , recommended float 14.1V and absorption 14.1V. Victron has bulk, absorb, float and storage. I can go in
and do some custom settings but it is interesting the nomenclature is different from Eg4. thanks again.
 
You have to get the pack charged high enough for the BMS balance to kick in and hold it there for a while to give it time to balance. The EG4 balancer is SLOW so it can take a long time to get the pack well balanced.
This isn't something you need to do all the time, the pack is fine with some drifting of values over time and it will not even be apparent if you aren't fully charging and discharging at the ends of the scale regularly.

You can't really bottom balance the EG4 since it's built in balancer only works at the top, and the cells are welded together so you aren't really able to discharge them independently.
If you open the top of the pack, you'll see that the pack is made up of (4) 4-cell packs, so the cell reporting is on the (4) pack basis. Top balancing will help you get them all back in line, it just takes a LONG time.

For charging
14.4 is the normal recommendation, EG4 says 14.5 in their specs, that's why there is a discrepancy. You will need to choose what you feel is best for you. I've found that my (3) packs need 14.6/14.7 to actually fully balance over time.

I have (3) Eg4 12V and I only occasionally charge them all the way to 100% as I don't need the entire pack capacity on a daily basis. So I keep it about 85% as the top and rarely let it get below 20%. It's connected to a set of Magnum inverters and they handle the majority of the charging, but I do have the 15amp Victron IP65 for getting them in balance since it's very easy to manage.

If you add a custom profile, then turn on the advanced settings, you can really tune the IP65 for your charging needs then save the profile for later use. It's incredibly flexible and useful.
Plus the built in graphing and monitoring will give you a ton of data. You can watch the charging amps tail off near the top so you know when it's almost completely full.

The external shunt is the best way to track the overall pack values, but it WILL NOT include the consumption of the BMS in the calculations, so it will begin to vary from the pack's SOC over time. This is normal and expected. There is very little useful energy in the very top or very bottom of the pack anyway, so just mentally remove those ends from your SOC and it's easier to live with.
 
You have to get the pack charged high enough for the BMS balance to kick in and hold it there for a while to give it time to balance. The EG4 balancer is SLOW so it can take a long time to get the pack well balanced.
This isn't something you need to do all the time, the pack is fine with some drifting of values over time and it will not even be apparent if you aren't fully charging and discharging at the ends of the scale regularly.

You can't really bottom balance the EG4 since it's built in balancer only works at the top, and the cells are welded together so you aren't really able to discharge them independently.
If you open the top of the pack, you'll see that the pack is made up of (4) 4-cell packs, so the cell reporting is on the (4) pack basis. Top balancing will help you get them all back in line, it just takes a LONG time.

For charging
14.4 is the normal recommendation, EG4 says 14.5 in their specs, that's why there is a discrepancy. You will need to choose what you feel is best for you. I've found that my (3) packs need 14.6/14.7 to actually fully balance over time.

I have (3) Eg4 12V and I only occasionally charge them all the way to 100% as I don't need the entire pack capacity on a daily basis. So I keep it about 85% as the top and rarely let it get below 20%. It's connected to a set of Magnum inverters and they handle the majority of the charging, but I do have the 15amp Victron IP65 for getting them in balance since it's very easy to manage.

If you add a custom profile, then turn on the advanced settings, you can really tune the IP65 for your charging needs then save the profile for later use. It's incredibly flexible and useful.
Plus the built in graphing and monitoring will give you a ton of data. You can watch the charging amps tail off near the top so you know when it's almost completely full.

The external shunt is the best way to track the overall pack values, but it WILL NOT include the consumption of the BMS in the calculations, so it will begin to vary from the pack's SOC over time. This is normal and expected. There is very little useful energy in the very top or very bottom of the pack anyway, so just mentally remove those ends from your SOC and it's easier to live with.
Thank you. I have been trying to set the IP65 and I can't seem to find, even in custom, advanced and expert where to set their "bulk" to 14.4 or whatever. Absorption, Float an Storage is what they have and let be adjusted. I will download and read the IP65 manual this evening. Off to wErk I go... thanks again... have a great day.
 
kind of old thread but anyone know what i am doing wrong. trying to use the EG4 PC BMS software to see status of my packs by cell. i cannot get it to connect. i used an rj45 ethernet cable to the RS485 then an adapter to UCB C on laptop. shows on port 4 but no luck after 10 min of scanning...Screenshot 2023-09-09 094420.pngScreenshot 2023-09-09 094516.png
 
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