Hi! Does anyone here use JBD BMS? Why it is “only” charging my battery to 41.5V, instead of 42V? Maybe it is some settings?
What’s your charger voltage at?
I measured 42V.
I’ve seen that happen a lot. I wouldn’t worry about it cause you’re only losing like a single percent of battery capacity and it is a bit healthier for the battery to just keep it like that.
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It might have charged to 42.0V.
Every pack will settle back down in voltage a little after charging stops. This is normal and as @Akbrock47 mentioned it’s only a tiny drop for your setup. Your pack is fully charged. 
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Looks like the battery will be decent, but i’d be watching temps on that xt90 while you weld. Xt90 got way too hot for me to be comfortable with, qs8 was MUCH better
Kinda put together spontaneously so likely ill revisit connection out.
Have a float charger too so will hopefully do well. If i end up swapping out to something else later ill get some solar panels for the shed and use it there. Id be pretty happy if i could mostly run my shed off the sun.
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Yep keep the battery fully charged all the time, i leave the charger on even when im welding
The correct float voltage for a lead acid AGM battery is very important to their longevity.
Ideal float voltage is influenced by the battery temperature, state of health, and any loads which might still be on the battery while it is being floated.
Floating too low a voltage will allow slight discharge to occur, even if float voltage is well above resting OCV, and more so if there are still loads on the battery whilst being floated.
When I have floated my AGM’s too low, and then manuLly boost voltage back to absorption voltage, the amperage required to achieve the ~14.4v, and how long it takes that amperage to taper to 0.05c at a constant 14.4v indicates the battery was discharging while being floated, but float 0.15v higher and it nearly instantly tapers back to 0.05c at 14.4v.
Different AGM manufacturers will spec a float voltage, at 25degrees Celsius, from between 13.2 to 13.8v, and lots of maintenance chargers designed for flooded lead acid might only hit 13.1v, and some will be 14v, so double check, and use a dc clampmeter over one of the leads, so you can see how much amperage the battery is accepting at the voltage the charging source provides.
Lead acid batteries are petulant in regards to achieving excellent Longevity from them.
I would have loved to be able to monitor individual cell voltages when living off grid, but with AGMs, one has to rely on voltage, and how much amperage is required to achieve that voltage, and how long it takes amperage to taper to low levels, at absorption(not float) voltages. Judging lead acid performance while discharging is how much voltage it can maintain under the load, and for how long it can do so.
And then, when rechargjng, does it take 106% of the energy it discharged for amperage to taper to 0.05c over 6.6 hours or 125% over 12 hours?
With Lead acid, achieving max longevity, and max performance, requires true 100% recharges, and few ‘smart’ chargers actually can achieve this, but especially so on a deeply cycled hard working lead acid battery.
99% recharges are half as good as 100%, with lead acid, in terms of achieving max longevity.
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Regarding spot welding, I dont have a Kweld, just a cheapo welder on a cheaPo Zee 3s 5.2ah 80c battery. My first practice welds showed the hottest part of the circuit was the fake looking XT60 on the 12awg leads coming off the cells. I’d replaced that with Xt90s and then shorter millisecond pulses were required to achieve same weld but the hottest part of circuit was the 12awg on battery side of XT90.
Xt90s as the inrush current on these cheaPo welders helps them to smoke their mosfets prematurely. I now use a small 22ah agm just to power the welder’s circuitry through xt90s, and the lipo through xt90s for the weld juice.
I tried one cheapo welder with a black circuit board, it proved barely capable of welding 0.15pure nickel at max duration pulse. I then tried it on my pair of 7 year old but still healthy 6v Deka GC-2 AGMs, with about 900CCA (when new) on kts lowest power setting and a 7ms pulse, and it tried to drill a hole through the battery can, machine gun style, as mosfets shorted closed. Brown underwear, and thankful for eye protection.
There is definitely a goldilocks zone on the weld battery with the cheaPo spot welders.
I’ve been surprised how quickly my LiPo depletes from 12.55 to 11.9v when welding 0.1copper 0.1nickel plated steel sandwiches with 70ms pulses, just doing one row on a 10s2p battery. I have been disconnecting my cell meter from it when welding for fear of smoking it, and try to keep lipo in 12.0 to 12.55v range, as going lower requires increasing pulse duration.
I’d love the consistent reliability of a Kweld, but cant afford it.
AGM batteries have much lower self discharge than flooded lead acid 2-3% per month at 25c vs 12-15% for flooded, but they still dislike being stored undercharged, and the lower they sit there and the longer they sit there, the less energy they can store and the slower they can deliver what they can still store.
Getting a petulant mistreated AGM, and to a lesser degree, flooded lead acid back to its max potential remaining capacity and performance is almost the exact opposite of what everybody who has turned a wrench on an automobile , will authoritatively tell you.
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Both look too hot, 0.2 works best at around 48-50 for me. And i printed you a case
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Was a lot easier to remove at 50, some of them left nothing when torn off, popped but didnt rip
Fair enough. Different setups do tend to play a little differently. Remember you’re looking for the nickel to tear and leave spikes. If it just leaves little circles of nickel on the cell, its usually cos its too hot or possibly too much pressure
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Ooh, ill go back down and play with that… thanks
The angle of the probes also affects the welds pretty dramatically too
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50j after breaking the tips in and this is what rhey are looking like.
Frightened shit out of myself by absent-mindedly shorting out a p group on the bench somehow… gotta learn some new habbits for sure
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i’m allowed to laugh because i have the same skidmarks in my undies
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Thank you very much for the kind answer.
The BMS has been running for 7 days, drained the battery by about 10% (bluetooth + balancing). I am going to add a physical switch to turn it off completely when not in use.
All the time cell 3 is a bit weaker than the others, and the best delta voltage I can achieve is about 20-30mV. Is this an acceptable value?
When I am removing BMS and I am trying to balance with my active balancer I achieved 0.009V. Then it goes out of balance a bit when I remove the active balancer.
Two pictures there from the first and last day:
Good idea.
That’s fine. Tighter voltage grouping is a complete waste of charging/balancing time unless you know how the cells match as they discharge. A 30mV spread won’t affect performance IMO.
That’s no problem at all. I regularly balance to a 45mV-55mV spread without worries. It speeds up charging and doesn’t result in any performance issues since I am not trying to run down to low voltages (where imbalances start to show up).
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