Overkill Solar Bluetooth app vs victron smart shunt
- Thread starter moonlitsouls
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If the BMS is calibrated then it will be more accurate. I know the mv's on mine are off by a few compared to my DMM. And I am sure the current is close to being accurate but the only thing I have to compare with is a DROK meter that uses a hall sensor. There is a few amps difference between them. So I haven't bothered calibrating mine.
ScoTTyBEEE
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There’s no reason why you can’t adjust the calibration settings and get the readings identical (providing you’re sure smart shunt is more accurate)
I got a response from Overkill. They said it will take a few cycles for the BMS to calibrate. They also said that the Victron will always be more accurate than the BMS.
A got some sun this weekend, and was able to nearly charge the battery. The BMS reached 100%, but the voltage per cell was still 3.4v and it was still accepting high charge current. The Victron was showing about 85% at that time. Battery should reach 100% today. Anyway, it is clear the BMS doesn't use voltages as I originally thought, or it would know that the pack was not at 100%.
The Victron is a much more sophisticated meter than what the BMS presumably does. The Balmar meter is probably the only meter that is more sophisticated than the Victron, and the Balmar probably only has an advantage with Lead Batteries. I doubt the BMS takes into account a Peukert effect, or charge efficiency. It might be possible to make them match, but it would be by sacrificing the Victron accuracy. FWIW, the Victron and BMS both report the same current and voltage, so I trust that is correct. The BMS just doesn't do as good of a job figuring the SOC from them.
A got some sun this weekend, and was able to nearly charge the battery. The BMS reached 100%, but the voltage per cell was still 3.4v and it was still accepting high charge current. The Victron was showing about 85% at that time. Battery should reach 100% today. Anyway, it is clear the BMS doesn't use voltages as I originally thought, or it would know that the pack was not at 100%.
The Victron is a much more sophisticated meter than what the BMS presumably does. The Balmar meter is probably the only meter that is more sophisticated than the Victron, and the Balmar probably only has an advantage with Lead Batteries. I doubt the BMS takes into account a Peukert effect, or charge efficiency. It might be possible to make them match, but it would be by sacrificing the Victron accuracy. FWIW, the Victron and BMS both report the same current and voltage, so I trust that is correct. The BMS just doesn't do as good of a job figuring the SOC from them.
If you don't need bluetooth, the AiLi shunt monitor works very well and it's much cheaper than the Victron Smart Shunt.
AiLi Voltmeter Ammeter Voltage Current Meter
It is very small, but it is there.
Yes, but it's negligible and can be safely ignored. LFP batteries provide 95-100% of their rated capacity at 1C, and they don't behave liked lead-acid batteries. Peukert doesn't apply.
There is capacity remaining in a FLA/AGM/GEL that is run higher than its C20 rating to termination, e.g., if you run at a C rate that yields only 60% of C20 capacity for LFA/AGM/GEL to "empty," a good portion of that 40% C20 capacity still remains in the battery and can be used at lower C rates. This is not at all true with LFP. There will be negligible capacity remaining following a 1C discharge to 2.5V/cell even at lower current draws.
I agree and disagree. The error might be small, but in a case where you might not be able to get to 100% often for the meter to resync, a small error will add up over time.
Lithium battery suppliers do not consider it negligible. They give a Peukert value (1.05) to program into the Victron and other meters that can account for it. It is small, but it is there. It might be negligible to you, but it is measurable and real.
So yes, it can be safely ignored, but you do get more accuracy by not ignoring it, particularly with higher loads if you go long periods and many cycles without charging to 100%.
Please provide a reference for a Lithium supplier recommending a Peukert value of 1.05. To my knowledge, that recommendation starts and ends with Victron.
Reliance on current counting to consistently establish 100% is folly. Victron indicates a battery must be taken to true 100% (based on voltage and tail current) at least a couple times a month to maintain accuracy.
How To Configure Victron BMV-700 with LiFePO4 Batteries
Click here to read about the Victron BMV-700 and watch our instructional video on how to configure it with our Battle Born LiFePO4 batteries.
battlebornbatteries.com
Interesting that battleborn suggests charge efficiency of 99%, and Lithionics 98%. But both have the same Peukert exponent of 1.05.
I do realize that coulomb counting will not consistently establish 100%. Assuming that any single SOC meter is going to be correct without sanity checking it against something else is a good way to get into trouble. But, I believe it will come closer to it with Peukert taken into account. In practice, I monitor the BMV-712, the MPPT controller, and the BMS, and use some personal judgement. This is a new Lithium install for me, but I've been doing it with lead acid for a long time(which at times can be quite difficult). And I am really looking forward to it being *much* easier because Peukert has so little effect. But for now I am not considering it negligible, and will leave it programmed in my 712.
Kennedyma
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I can confirm this is what I've seen as well. I have both the shunt and the BMS. When they go out of sync, which they do, a charge up to 100% will reset them and they will stay in sync then. I haven't figured out what makes them go out of sync yet, but sometimes I'm 20-30 amps off.
With that said knowing what I know now I wouldn't have bought the Victron unit for my 100ah battery. The BMS works great for me.
If I had a single battery, I might have skipped the Victron BMV-712 also. What the BMV does give over the BMS (through the app) is a quick way to check the state of charge. My wife is OK with looking at the BMV panel, but opening the BMS app isn't going to happen.
I have two 4s batteries, so the BMV is appropriate in my case. I don't have to access two BMS devices to get the state of charge. It could be argued that accessing just one of the BMS and doubling what it sees would be good enough. But the BMV provides other benefits like low temperature communication to the Victron MPPT and an audible alarm that the BMS doesn't provide.
Kennedyma
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Actually I asked Steve at Overkill Solar, and he said there is a shunt current monitor in the BMS they sell. Apparently it does not computing state of charge by voltage only, as you say.
Yes, I learned that.
