diy solar

diy solar

New DIY 12V Build - low battery voltage from BMS issue

The cell in cell position 1 looks to be the weak link.
I noticed that all the wired chit always happens to cell 1 so I recommend swapping cell 1 with 3 (what appears to be strongest) to see if that helps. Maybe the weak cell 1 moves to cell 3?

Of course labelling your cells with something other than numbers (I use letters A, B,…) will help you keep good notes and talk about them more clearly.
 
I have just finished installing a 500 Ah LFP-bank in my boat. It works fine, the Android BMS also (after dealing with the decimal komma issue).
But I found something that puzzles me: I was testing the temp sensor. It works and close the charging at the defined temperature. Doing this, the APP reports 13,2V, but measuring the output I get 12,5V. A voltage drop similar to what a diode will give. This is the same if I close the charging manually on the APP or the low temp sensor kics in. No big deal, not often I need to discharge the battery in so low temperatures. And once I (or the temp censor) open the battery for charge, the voltage out from the BMS rise to the normal 13,2V, but do anyone have an explanation for this?
 
do anyone have an explanation for this?

Mike
 
Thank you mikefitz and upnorthandpersonal !
Good explanation (and I think I understand it :) )
As I suspected, the lower voltage measured is lost in the mosfet.
I also understand that it is not good to discharge too much when the BMS has stopped the charging.
I have a 120A BMS. How much can I discharge and still be on the safe side?
 
understand that it is not good to discharge too much when the BMS has stopped the charging.
I have a 120A BMS. How much can I discharge and still be on the safe side?
as the explanation suggests once the current is above a certain level (1A?) the BMS switches on the discharge fets so there are no losses.
I use the same BMS, under normal conditions and regularly pull 100 amps for long periods.

Mike
 
Yes, you can say harsh. I'm a novice and working on my learning curve.

And yes, the BMS says 99% full and 13.6V.................................but at the terminals that will supply power to my camper the voltage reads 11.9V. This is low and the original problem I posted about. Why?
I'm not a big fan of the bolt passing current through the wood on the negative side.
 
understand that it is not good to discharge too much when the BMS has stopped the charging.
I have a 120A BMS. How much can I discharge and still be on the safe side?
as the explanation suggests once the current is above a certain level (1A?) the BMS switches on the discharge fets so there are no losses.
I use the same BMS, under normal conditions and regularly pull 100 amps for long periods.

I Discharging 100A even if the charging is disabled and the voltage out is reduced to 12,5V ?
 
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