Overkill bms useless

[brb58]

If the Overkill/JBD BMS is at all accurate, how come my to batteries that are identical have wildly different SOCs? It's not even consistent. Sometimes one is higher than the other and neither match up to my Victron BMV-712.

There is no high current shunt resistor on the BMS like what the Victron Shunt has.

 

[brb58]

What do you mean it has no idea what SOC is?

The Daly I have definitely cuts off charge based on SOC and other parameters BMS will deactivate charge/discharge for.

You can prove this by manually setting soc to 100% at like 25.6 volts (8s pack) and it will shut the chargemos off.

It knows 100%...that's it. It has no idea what it is less than that accurately. In the settings, it it requires to to put in cell voltages for various voltages for various SOC percentages. It is doing a crude approximation based on voltage and current somehow which is no way accurate.

 

[Quattrohead]

It is doing a crude approximation based on voltage and current somehow which is no way accurate.

Has it occurred to you that you may have one cell in one battery that is skewing it?
Make sure each BMS has all of the exact same settings and run them all up to 100% and hold them there for half an hour. Look at your cell voltages then and then use the batteries and check all of your cell voltages at around 50% charge and see where they're at.

 

[brb58]

Has it occurred to you that you may have one cell in one battery that is skewing it?
Make sure each BMS has all of the exact same settings and run them all up to 100% and hold them there for half an hour. Look at your cell voltages then and then use the batteries and check all of your cell voltages at around 50% charge and see where they're at.

LOL...exact same settings. All are perfectly balanced. Some times one battery will be 10% different than the other and then the other battery will be that much higher so it's not even consistently one battery that is higher.

I basically ignore them. I use the Victron BMV-712 to figure out SOC.

 

[Quattrohead]

Mine have spread out again, 1 at 63%, 2 at 64% and the other at 70%.
All 4 batteries at 53.1 V and all cells are very close, 3.324 V highest to 3.317 V lowest across 64 cells.
Good enough for me.
There might be a calibration in the PC software, I will have a look one day when I remember.

 

[brb58]

Mine have spread out again, 1 at 63%, 2 at 64% and the other at 70%.
All 4 batteries at 53.1 V and all cells are very close, 3.324 V highest to 3.317 V lowest across 64 cells.
Good enough for me.
There might be a calibration in the PC software, I will have a look one day when I remember.

So...you see differences too! Having a one BMS 7% from another is not what I would call accurate.

 

[42OhmsPA]

Wish I could get mine that close.

 

[justgary]

I'm asking because the Daly shuts off charge and discharge based on SOC so as the SOC reading drifts, you end up in a situation where it cuts off charge or discharge prematurely.

Among other things.

I want to replace it with something that doesn't have this point of failure.

I don't want to stray the thread to Daly, but your BMS settings should be beyond the settings on your SCC and load control (probably an inverter). The BMS should not be switching off unless the other devices are not doing their jobs.

 

[740GLE]

I have 6 Overkill BMS's and none of them can keep a battery pack balanced. For that reason alone I would not recommend them to anyone.

I actually have purchased 12 of them because I bought 6 for me and 6 for my dad (RIP) when he was building his solar system. His has yet to be used yet. I got them hooked up but no current has gone in or out of them yet.

If you’re not happy with them, hit me up I might snag one off of you. My charge parameters seems to keep my cells in balance and you can never have enough BMS

 

[PreppenWolf]

To reset the Ah, use the Overkill App (not the xiaoxiang) and click this reset button.



The BMS isn't meant to track Ah, it's just a reference calculation. The BMS is tracking voltage. The BMS takes the voltage, references the % chart and the current voltage to create a Ah reference when you alter settings. It then attempts to track this using amp in/out. This was clearly a poor programming decision, but the BMS is there to protect cells via voltage, not track power.

A shunt for the overall system is the correct approach.

 

[Checkthisout]

To reset the Ah, use the Overkill App (not the xiaoxiang) and click this reset button.

View attachment 191723

The BMS isn't meant to track Ah, it's just a reference calculation. The BMS is tracking voltage. The BMS takes the voltage, references the % chart and the current voltage to create a Ah reference when you alter settings. It then attempts to track this using amp in/out. This was clearly a poor programming decision, but the BMS is there to protect cells via voltage, not track power.

A shunt for the overall system is the correct approach.

What's the point of linking it to an inverter charger if it isn't sending accurate soc data to the equipment?

 

[Quattrohead]

I'm assuming we're talking about the 100 amp BMS that do not communicate with inverters.

 

[42OhmsPA]

I think it's the JBDs in general.
I'm currently charging @5A, ~275W. Only 1 BMS reads current, 86W.

 

[PreppenWolf]

I'm assuming we're talking about the 100 amp BMS that do not communicate with inverters.

I am talking about the 100A BMSs. My system is running 8 of them and they've been great.

 

[Bob B]

I only have one JBD BMS. It came as part of a pre-built 100AH battery I bought ..... so, those of you who have 5 or 6 or more of these have more experience with them than I do.

When I first got the battery, I did a LOT of experimentation with it. The SOC tracking via coulomb counting was very inaccurate .... and I was complaining to the Alibaba seller I bought it from. This was at a time when these "smart" Bluetooth BMS were first coming onto the market.
I was using the XiaoxiangBMS APPP at that time and I discovered the calibration settings ...... I carefully calibrate the current in, out, and zero. Subsequent testing of this battery showed that the Coulomb counting SOC is now VERY accurate. I didn't mess with the voltage calibrations since they were already very close to correct. Once calibrated, the SOC has remained very accurate and I haven't had to mess with it again. It now tracks very close to another external shunt I have.
The Overkill Solar App also has the calibration settings and I would recommend that anyone having trouble with the SOC tracking give that a shot .... and make sure your pack has reached the battery full setting which triggers it to start doing coulomb counting.

It's impossible for the Coulomb SOC to be accurate if the BMS isn't accurately reading the current.

For anyone doing a DIY pack, I would consider the BMS current calibration being just as important as a proper top balance.

 

[featherlite]

Once calibrated, the SOC has remained very accurate

Mine too.

 

[Pierre]

I only have one JBD BMS. It came as part of a pre-built 100AH battery I bought ..... so, those of you who have 5 or 6 or more of these have more experience with them than I do.

When I first got the battery, I did a LOT of experimentation with it. The SOC tracking via coulomb counting was very inaccurate .... and I was complaining to the Alibaba seller I bought it from. This was at a time when these "smart" Bluetooth BMS were first coming onto the market.
I was using the XiaoxiangBMS APPP at that time and I discovered the calibration settings ...... I carefully calibrate the current in, out, and zero. Subsequent testing of this battery showed that the Coulomb counting SOC is now VERY accurate. I didn't mess with the voltage calibrations since they were already very close to correct. Once calibrated, the SOC has remained very accurate and I haven't had to mess with it again. It now tracks very close to another external shunt I have.
The Overkill Solar App also has the calibration settings and I would recommend that anyone having trouble with the SOC tracking give that a shot .... and make sure your pack has reached the battery full setting which triggers it to start doing coulomb counting.

It's impossible for the Coulomb SOC to be accurate if the BMS isn't accurately reading the current.

For anyone doing a DIY pack, I would consider the BMS current calibration being just as important as a proper top balance.

i had to do that on the first JBD’s I bought about 4 years ago. The later ones circa 2023 are much more accurate without recalibration.

 

[42OhmsPA]

i had to do that on the first JBD’s I bought about 4 years ago. The later ones circa 2023 are much more accurate without recalibration.

This explains a lot.
I'll try calibrating them. Anyone have any tips and tricks for the JBD PC software?

 

[SeaGal]

Anyone have any tips and tricks for the JBD PC software?

With a bit of trial and error, I increased the cycle capacity to more than the cells actually hold, which makes my (Overkill) JBD pretty accurate. Currently set to 320000mAh for my LF280K's.

 

[42OhmsPA]

With a bit of trial and error, I increased the cycle capacity to more than the cells actually hold, which makes my (Overkill) JBD pretty accurate. Currently set to 320000mAh for my LF280K's.

Interesting. I'll try this as well. I currently have them around 90% of cell rating.

Here's what the packs looked like this morning before I flipped back to battery.

Here's how they look now.


I will get this figured out...