JBD BMS - How to correct inaccurate SOC value ✅

[OTRwSolar]

double post

 

[OTRwSolar]

If I take your example, you charged to 14v and then the battery is now at 13.68v. Imagine if you charged it at 13.6 in the first place, it would drop to something like 13v or less after rest, which is not a 100% SOC.

Not correct. Final resting voltage for a fully-charged 100% SOC 12v lifepo4 battery is slightly less than 13.60v---does not matter if it was charged at 14.60v or 13.60v (or any voltage in-between). It may take a day or so to reach this final resting voltage if the battery was charged at 14.6v, but it will drop. If the battery was charged at 13.60v it takes very little time to drop to the final resting voltage.

 

[squowse]

13.9 seems a bit low since my 100% is at 14.02, no ?
I was thinking about putting 14.5 in the victron app, because after resting it will mean 14v

You can use 14V. I use 13.9V based on looking at the cell voltages. I want to avoid any cell going to 3.5 or above during normal charging. It still gets them to 99% (arbitrary whether this is 100% or 98%).

 

[ramstein]

I got the 14.02v value after 20 hours rest, I thought it finished dropping. According to what you are saying it would have dropped to 13.6v after more time. 20hours seems a lot of rest already, but that's good to know thanks.
So I will use 14v as the max charging voltage then, so when it drops it stabilizes at 13.5-13.6

 

[OTRwSolar]

I got the 14.02v value after 20 hours rest, I thought it finished dropping. According to what you are saying it would have dropped to 13.6v after more time. 20hours seems a lot of rest already, but that's good to know thanks.
So I will use 14v as the max charging voltage then, so when it drops it stabilizes at 13.5-13.6

We charged our 12v 200ah LifePo4 to 14.40v on Friday. It’s Sunday morning right now. Voltage is 13.60v and still slowly dropping. It takes a while.

 

[ramstein]

We charged our 12v 200ah LifePo4 to 14.40v on Friday. It’s Sunday morning right now. Voltage is 13.60v and still slowly dropping. It takes a while.

I didnt know this, since I often see people talking about 30min/1hr rest. Even a known manufacturer (I forgot their name) recommands 1h per 100Ah. That's good to know.
Well 14v max is quite conservative. I don't mind much if the battery gets 3000 cycles instead of 5000 it's stil very good

 

[OTRwSolar]

I didnt know this, since I often see people talking about 30min/1hr rest. Even a known manufacturer (I forgot their name) recommands 1h per 100Ah. That's good to know.
Well 14v max is quite conservative. I don't mind much if the battery gets 3000 cycles instead of 5000 it's stil very good

We abuse our 200ah lifepo4 with repeated .6c (120a), 100-0, discharges. Sometimes charge at .5c (100a). Have almost 75 cycles after two years of use. If we get 500 cycles we'll be more than happy.

 

[ramstein]

We abuse our 200ah lifepo4 with repeated .6c (120a), 100-0, discharges. Sometimes charge at .5c (100a). Have almost 75 cycles after two years of use. If we get 500 cycles we'll be more than happy.

lol exactly my friend

 

[OTRwSolar]

We charged our 12v 200ah LifePo4 to 14.40v on Friday. It’s Sunday morning right now. Voltage is 13.60v and still slowly dropping. It takes a while.

It’s Wed, 5 days after a 14.40v charge to 100%. Battery/pack was completely disconnected after charge. Voltage has finally dropped to 13.42v.

 

[ramstein]

Thanks, mine finally went up from 11.49v to 11.66v after 5 days at 0%. Will charge it now

 

[Vi s]

Thanks, mine finally went up from 11.49v to 11.66v after 5 days at 0%. Will charge it now

Guess not much significant harm to do this briefly once for the sake of science.
I read in studies the longer you leave batteries in a fully charged or -depleted state the more harm is done. Left in a fully depleted state is even more harmful if i remember right.
For example I read fully charged left for a year can cost you more than 10% capacity permanently. Can't remember numbers about the fully depleted state. Sure numbers differ from study to study but the consensus is the same.

A few other possible science projects, how many % capacity get into the battery from:
- 3.40V till 3.45V,
- 3.45V till 3.50V and
- 3.50V till 3.65V
(all without absorption of course).

What's the time difference in % to charge from maybe 3.1V to 3.45V, 3.1V to 3.5V and 3.1V to 3.55V (all tests without- and with absorption if you usually do so)?

Does anyone already have some numbers?
If not and if i can find a single cell somewhere i will do these tests myself because i am curious about it.

 

[Vi s]

How many % capacity gets into the battery from:
- 3.40V till 3.45V,
- 3.45V till 3.50V and
- 3.50V till 3.65V with absorption?

Tested a 5000mAh cell with my Ebc-A05+ tester.

Results:

Voltage while charging with 0.4C	SOC (two test rounds)
3.40V	77.5 , 78.7%
4.45V	94.1 , 94.9%
4.50V	97.6 , 97.9%
4.55V	98.4 , 98.6%
4.65V (Without absorption)	99.1 , 99.2%
4.65V (With absorption)	100%
Voltage while discharging with 0.5C	SOC (one test round)
3.10V	12%
3.05V	6.9%
3.00V	5.2%
2.90V	2.9%
2.80V	1.6%
2.50V	0%

 

[ScottWCO]

So I'm having a related issue with my two packs using JBD 120a 4s BMSs bought from Overkill. These units like to reset their own stats now and again. I had my batteries at somewhere in the low 60s percent SOC the other day, but the BMSs have reset themselves and show 99% and the available amp-hours at an equivalent level.

This isn't the worst thing, I suppose - I've got a Victron system set up and will go by the shunt reporting more often than not - but it's still annoying.

 

[Vi s]

So I'm having a related issue with my two packs using JBD 120a 4s BMSs bought from Overkill. These units like to reset their own stats now and again. I had my batteries at somewhere in the low 60s percent SOC the other day, but the BMSs have reset themselves and show 99% and the available amp-hours at an equivalent level.

This isn't the worst thing, I suppose - I've got a Victron system set up and will go by the shunt reporting more often than not - but it's still annoying.

First download the overkill app and check your capacity configuration settings, especially the 100% to 0% voltage values, if there is anything unusual.

 

[squowse]

So I'm having a related issue with my two packs using JBD 120a 4s BMSs bought from Overkill. These units like to reset their own stats now and again. I had my batteries at somewhere in the low 60s percent SOC the other day, but the BMSs have reset themselves and show 99% and the available amp-hours at an equivalent level.

This isn't the worst thing, I suppose - I've got a Victron system set up and will go by the shunt reporting more often than not - but it's still annoying.

Would be so much better if you could disable the BMS guessing SoC and input it yourself. Really hoping for a firmware update one day