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Cells read 14V but BMS negative reads 10V

sonny93

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Dec 17, 2020
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Hey guys! Very excited to finally wire all my batteries up. Using a Daly "Smart" BMS
I have 4 cells wires in series @ 280aH or so.

Cell 1 negative to the positive after the fuse reads 14V DC
However, on the BMS P- to positive of the fuse, I am reading 10.28VDC

Any ideas why this is? I've only just connected the batteries, not sure if the BMS needs configuring.
 
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Okay, I launched BMS tool on windows 10 and suddenly it changed to to 14VDC
Can anyone tell me why the SOC is reading 0% in the software? How should I setup the software? I havent calibrated anything yet.

1617103473974.png
 
Had to hit the Scan All button on the Info page.

Lonely thread but I'm sure it will help someone one day!! Am I okay to connect this to my inverter or should I change some settings?

Info page
1617104097628.png

System
1617104141467.png

Charge
1617104190158.png

Discharge
1617104209106.png
 
Under voltage should be 2500 mV (2.5v). Over voltage should be 3650mV (3.65v). To get battery voltage multiply by 4 for 4s 12v or 8 for 8s 24v batteries. I didn’t go over all the settings. I suggest forum search to find sane BMS settings.
 
Under voltage should be 2500 mV (2.5v). Over voltage should be 3650mV (3.65v). To get battery voltage multiply by 4 for 4s 12v or 8 for 8s 24v batteries. I didn’t go over all the settings. I suggest forum search to find sane BMS settings.
Is there a battery voltage setting ? where is that? I have 4s 12V which would be 3650mV * 4 = 14,600mV

I adjusted the under and over voltage as per suggestion. What about the Under voltage release?
1617106084364.png
 
I have not used that BMS, but I was thinking the same thing. Those values look like Li Ion, not LFP settings. 3650 mv is the highest they should ever go. The low side cut of 2500 mv is an absolute limit as well. That is good for the BMS cut off as you don't want that to trigger unless something is wrong. Your charger and loads should shut off between those values. The Charge under temperature should also be at 0C or 32F, not -40. Discharge can o a bit colder, but -10C is still about as cold as LFP should go.

The State of charge may take a few cycles to calibrate. It probably sets the 100% when it detects a full charge cycle. Reaching float voltage with the current tapering down. That is the "Charge End" Volts and current.

Under voltage release would be a little higher than the trip voltage. Over voltage release should be lower than the trip point.
 
Charge end voltage should be about 3400 and Discharger end voltage should be about 3100

You will probably want to change all of the settings I recommended after you understand what they do.

edit: I don't know your BMS either so there might be other settings that could damage your cells. So like was already recommended, find the manual and understand what all of the settings do
 
Under voltage release should be larger than 2500. I would start with 3100
Over voltage release should be about 3400.
Cool, I adjusted to suit this. How do the pictures below look?


I have not used that BMS, but I was thinking the same thing. Those values look like Li Ion, not LFP settings. 3650 mv is the highest they should ever go. The low side cut of 2500 mv is an absolute limit as well. That is good for the BMS cut off as you don't want that to trigger unless something is wrong. Your charger and loads should shut off between those values. The Charge under temperature should also be at 0C or 32F, not -40. Discharge can o a bit colder, but -10C is still about as cold as LFP should go.

The State of charge may take a few cycles to calibrate. It probably sets the 100% when it detects a full charge cycle. Reaching float voltage with the current tapering down. That is the "Charge End" Volts and current.

Under voltage release would be a little higher than the trip voltage. Over voltage release should be lower than the trip point.

I adjusted as per your instructions. Could you double check the temperature release settings on discharge and charge are okay? I don't really understand what this means.
1617106907463.png
 
Also the batteries are rated at 272aH, so I adjusted these two settings. Is this correct?

1617110101428.png
 
Charge end voltage should be about 3400 and Discharger end voltage should be about 3100

You will probably want to change all of the settings I recommended after you understand what they do.

edit: I don't know your BMS either so there might be other settings that could damage your cells. So like was already recommended, find the manual and understand what all of the settings do
Those numbers are very conservative for over and under voltage release.

I didn’t go into all the details because I’m just not willing to fully read the post or type it all up. That’s work I won’t do unless I’m being paid ? (not that I’m offering or trying to sell my services). I’m here to learn what I need to learn, and happy to try and help others who are willing to help themselves. Pay it forward, so to speak.
 
Also the batteries are rated at 272aH, so I adjusted these two settings. Is this correct?

View attachment 43083
Full charge capacity should be the capacity you’ll get depending on the charge limit voltage you set your chargers to and the bottom limit you set for gen-start or inverter cut-off.

3.65v x 4 = 14.6. But you don’t want that to be your charge limit voltage. 14.4 would be better (BMS shouldn’t be tripped on every charge and discharge). Hopefully this gives you an idea how that works (or sparks specific questions).

i‘m a newb when it comes to this stuff so others will be able to explain more and a lot better than I.
 
Those numbers are very conservative for over and under voltage release.

I didn’t go into all the details because I’m just not willing to fully read the post or type it all up. That’s work I won’t do unless I’m being paid ? (not that I’m offering or trying to sell my services). I’m here to learn what I need to learn, and happy to try and help others who are willing to help themselves. Pay it forward, so to speak.
I like to start conservative. That way I know everything works.
That's better than finding out something doesn't work when it breaks. :p
 
I like to start conservative. That way I know everything works.
That's better than finding out something doesn't work when it breaks. :p
Me too, just wasn’t concerned with being overly conservative with the reconnect voltages. Whats the usable AH between 3 and 3.1v?
 
Me too, just wasn’t concerned with being overly conservative with the reconnect voltages. Whats the usable AH between 3 and 3.1v?
If I'm not paying attention I don't want the BMS to reconnect so I put in a number it will never reach.
Then when I get to it, I adjust the reconnect number so it will restart when I'm watching it.

There are many ways to adjust the numbers but the way I said is the way I do it.

My BMS doesn't have charge end voltage and discharge end voltage. The numbers I gave are probably wrong but it's a place to start.

Ah between 3 and 3.1V is a pretty good amount. I don't remember exactly. But since most people are top balanced the cells can start to diverge early at the bottom.
 
Those temp values look good. The trip temp is where it will shut down, and release temp is when it will turn back on. A few degrees difference keeps it from switching off on off on off. Same with voltage and current trip and release levels. The larger the difference, the longer it will take before it comes back on, but too small it can keep switching up and back.
 
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