Good to know that with external shunts, accurate readings can be obtained. It’s a bit of a blow if the internal shunts can’t currently be calibrated properly in the software though. ?Yes I did, Sveirge. In fact I tried several times with the same results. However on the bright side, I installed a 300A 75mv shunt and was able to get the current spot on. ( I ended adding 101mv to the starting value of .2500 to get it dialed in.)
I concur. Using charging direct to the battery terminal with iCharger I see no balancing occurring on the BMS, whatever I do with BMS settings. Even enabling “balance on discharge” doesn’t help, which seems odd to me.Been running cycles and found that using an external shunt there is NO balancing. The only time it balanced was when it was on PV charging.
That was me enquiring on Dacian’s forum. I was mainly asking about the automation functionality as I would like to do a little more, or at least have the flexibility to do more than the existing type 1- type 6 automation outputs allow.There was a person in the ElectroDacus forums that wanted Dacian to increase the shunt offset due to his amps readings being to high on his "green" SBMS40. This does look like a flaw in at least the prototype units.The second time I emailed Alex about the problem, I never heard back from him.
I can not in good conscience recommend this unit at this time. The lack of accuracy with respect to amps reading errors and lackluster support.
Did you provide pics around the shunts like Dacian asked?That was me enquiring on Dacian’s forum. I was mainly asking about the automation functionality as I would like to do a little more, or at least have the flexibility to do more than the existing type 1- type 6 automation outputs allow.
An interesting detail which emerged from the subsequent discussion was that even if Dacian releases a new version of his software, it cannot be loaded direct onto the green 3D Brothers edition devices due to the use of a different wifi module on these units (ESP8266 vs ESP32 in Dacian’s original design). This means that any further software upgrades would need to be recompiled and rereleased by Alex / 3D Brothers following Dacian’s release of a new version.
This also brings me back to the issue of the PV shunt accuracy, as based on above I believe it would actually be Alex who would need to modify Dacian’s source code to increase the shunt resistance range, then compile and release this with user instructions on how to upgrade devices. This assumes that this will not be done “in house“ prior to shipping the production versions of these units, which is of course far preferable.
Unless Alex wants to help out, those of us with prototype units may well not get that software update although I suppose we could get a copy of Dacian’s source code and figure out the intricacies of correctly bundling it with the right ESP8266 drivers and settings, etc. That’s beyond my capabilities, but someone with a software background who is au fait with ESP8266 might well be willing to take it on.
I will send over to Alex my thoughts on this and emphasise the importance of modifying that software before shipping his production batch to indiegogo backers, to avoid his users being disappointed.
Yes, via email. He couldn’t be sure but felt that the new design did correctly incorporate kelvin probes.Did you provide pics around the shunts like Dacian asked?
So it’s a been a while since I posted to this thread, but I’ve continued to use the SBMS40 which was performing well, sitting between my 2 parallel connected 160W PV panels and 4S LiFePO4 battery. I say “was“, because today we had a major malfunction
I happened to pass through the room which houses the set up and noticed a bad smell. Glancing at the screen of the SBMS40 my eyes popped out of my head as I saw all four cells at 4.4V and rising....! I quickly tripped the breaker which connects the PV panels, so charging current reduced to zero, and went to add some load to the circuit to bring down the voltages. By the time I got my iPad connected for monitoring, to take the below screenshot, the cells were down to around 3.9V each. Note the SBMS temp reported on the screenshot is 23.2C and the battery temp is the room ambient, a very modest 15C.
On examination I see a blown component, presumably the charge FET, so I guess this has failed short circuit and no longer switches off when commanded by the software. I’ve checked and found that the EXTIO3, used to control external charging sources, does operate as normal, switching from closed circuit to open circuit when cell voltages rise above the “over voltage” set point which I have configured as 3.5V.
On the screenshot you see the PV 1 hour graph showing the charging current up to the over voltage event (when it drops to zero). Charging current was under 20A and had peaked at just over 20A about 20 mins before. I had been warned that this SBMS40 might be more properly named SBMS25 when used without a heatsink, but now I wonder if even that is correct. I’m quite mystified though, as the SBMS40 was reporting an internal temp of just 23C and Alex from 3D brothers tells me they have soak tested at 30A without heatsink.
I could go on using this device to control external charge controllers via EXTIO3, but if there’s no current via the PV port there is no cell balancing function, which makes it a not very useful BMS. I doubt I can replace the failed FET, it’s too tiny. A real shame.
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