Overkill bms useless
- Thread starter bronxfire
- Start date
Pierre
Somewhere down South
- Joined
- Dec 21, 2019
- Messages
- 1,129
Bleedingblue
Solar Enthusiast
- Joined
- May 12, 2020
- Messages
- 545
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.
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.
Quattrohead
Solar Wizard
I absolutely do not believe that for a moment, mine are all within 5 millivolts.
I was alerted to this when I changed the voltage = charge % parameters in the app. I had wondered why there were even there but ok, better to enter the tables I have. As soon as I saved them the displayed charge level changed significantly. The fact that these are parameters and that the charge state changed when they did indicate that JBD (if not others) is using that table to display a charge state on the dashboard. my understanding is that using cell V for charge state is not dependable except at the very top and bottom.
Last edited:
I did same recently and the % became much closer to what I expected.
It's seems to be coming to light that passive balancing is not going to help much on bigger cells. JBD/Overkill would be wise to promote the reliability of their primary BMS function rather than suggesting that the weak passive balance circuitry is effective.
In looking into the various brands at 200 amps throughput, Daly was easy to eliminate, and Seplos too spendy. JK and JBD seem to be in the goldilocks zone. Still I was concerned about a few reports of JK's firmware issues. These are probably not that common and/or long since corrected, but given the choice between a BMS that balances well but might fail overall vs one that is reliable as protection but can't be counted on to balance, I chose the latter and a cheap active balancer.
Rat's nest of double leads is a con, though. More than the extra circuit board or $15 additional cost.
Confirming that it uses cell V, not current movement for state of charge.
42OhmsPA
What's in a title?
A bit of both I think. The % does not move up and down with the voltage due to varying loads.
It would seem to me the voltage points are a reference to make corrections to the electron count.
Bob B
Emperor Of Solar
- Joined
- Sep 21, 2019
- Messages
- 8,645
The voltage setting are used at initial startup as a SOC guesstimate ..... Once any cell reaches the cell full voltage setting the
SOC will go to 100% and start tracking via amps in and amps out instead of voltage ..... If any setting change is written is starts over like the initial startup.
SOC will go to 100% and start tracking via amps in and amps out instead of voltage ..... If any setting change is written is starts over like the initial startup.
Checkthisout
Solar Wizard
- Joined
- Nov 14, 2021
- Messages
- 4,810
Bms will cut off charging based on SOC.
Wrong...it does it based on voltages. The BMS has no idea what SOC is.
Checkthisout
Solar Wizard
- Joined
- Nov 14, 2021
- Messages
- 4,810
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.
This thread is specifically about Overkill/JBD....
Checkthisout
Solar Wizard
- Joined
- Nov 14, 2021
- Messages
- 4,810
Yes but I hate my Daly and I'm trying to learn
So JBD/Overkill bms is not useful in tracking battery soc and makes no decisions based on soc, its a voltage only device?
TomC4306
Solar Obsessive
No.
There is a shunt in the Overkill BMS that does a fair job of SOC calculations.
I have 2 that I have been watching in Solar Assistant for over 2 years.
They work well.
Gavin Stone
Solar Addict
My overkill is usually around 7% off of the shunt. My JK BMS is fairly close usually. But I know people that have JK’s that are off by around 10%. Honestly I don’t care 
. I have the BMS for protecting and balancing the cells.
Adding a shunt is easy if you want a super accurate SOC.
. I have the BMS for protecting and balancing the cells. Adding a shunt is easy if you want a super accurate SOC.
Checkthisout
Solar Wizard
- Joined
- Nov 14, 2021
- Messages
- 4,810
My overkill is usually around 7% off of the shunt. My JK BMS is fairly close usually. But I know people that have JK’s that are off by around 10%. Honestly I don’t care
Adding a shunt is easy if you want a super accurate SOC.
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.
Gavin Stone
Solar Addict
I haven’t used Daly much. But from what I remember there were voltage options in there. For individual cells and as a pack.
Not really fond of Daly.
