Daly BMS - What am I missing?

[TheGriz]

Hello folks...first a little background. I was using the Chargery 8T BMS on a 4S EVE 280 AH LFP pack. I ran into one issue after another, until finally it just simply wouldn't turn on. BUT please I don't want this thread to be a about who has had success or issues with the Chargery. I am moving on and looking at an alternative.

I have been looking several other BMS, of course as the topic suggests, the Daly BMSs. Now I understand that Daly has the smart BMS where the parameters can be set for HVD and LVD. But looking at the "non smart" Daly, the voltage disconnects from what I'm reading in specs are outside safe parameters of LFP prismatic cell. As we know the low voltage limit is 2.5v for LFP, but the Daly LVD is 2.2V. Conversely, the LFP high voltage should not exceed 3.65V and the Daly is 3.7v. So with these Daly specs, I see the the LFP aluminum case prismatic cells being damaged being discharged/charged outside the LFP specs.

Having said that, I see the Daly BMSs being commonly used in many builds of LFP aluminum cased prismatic cells. Please help me understand...what am I missing?

What are everyone's' thoughts on a quality 12V 4S BMS that won't break the bank, and has low-temp protections. I'm hoping for 200-250amp and still have separate ports for charge and discharge.

Also, the mechanical 400A DC Contactors that came with the Chargery are ridiculous energy hogs and get stupid hot. What are other energy efficient alternatives.

Thanks for all anticipated responses,
Mike

 

[snoobler]

"safe" parameters are often over-stated. LFP can technically be charged safely to 4.2V, but there is no benefit to doing so, and it may impact cycle life if done routinely.

3.75 vs. 3.65V is a non issue in that context.

2.5V is the "new" discharge convention. Cell manufacturers used to indicate 2.0V as the floor. Some still do, so 2.2V is not catastrophic.

The BMS shouldn't be activating regularly. Your equipment should be programmed to cut off well before these limits are reached. The BMS is a safety system. If it's activating, something is wrong - could be a design flaw, configuration flaw or component failure. You should know a BMS is there, but you should never "see" it working.

To my knowledge only the "smart" Daly have low temp protection. They get pretty spendy.

Contactors just plain use juice. A certain amount of force is necessary to hold the contacts in place, and that requires power. Even 5W of power generates a lot of waste heat. They just get hot. N.O. contactors carry a penalty that you have to live with.

 

[peterwareing]

I don't know if this will help but I have a cell that rises faster than the others when the bank is getting very near full capacity (full in my view).
I was unsure if the 3.75v quoted for the BMS over voltage was the bank voltage or the cell voltage and also whether the whole bank would be disconnected when one cell got to 3.75v.
The BMS has a safety cut off at 3.75v which did worry me initially - but true to its word the BMS disconnects the single cell at 3.75v and it drops down to 3.55v within a very short period of time and the rest carry on charging.
So under a charging load it does not necessarily mean the cell is holding 3.75v.
I do not have to worry about LVD because the inverter is handling the LVD at just above 3v.
Occassionally I charge any cells that appear to be getting nearer to the 3v limit individually in situe using a small DC bench supply at night - it takes just a few minutes. I may try a similar tactic using a resistor on the run away cell but its not a huge issue at the moment and I monitor them a lot (my babies :D)
I have been looking at getting a smart BMS so I can adjust the parameters but am happy with my current BMS and not really got extra money to throw around.

 

[snoobler]

I don't know if this will help but I have a cell that rises faster than the others when the bank is getting very near full capacity (full in my view).
I was unsure if the 3.75v quoted for the BMS over voltage was the bank voltage or the cell voltage and also whether the whole bank would be disconnected when one cell got to 3.75v.
The BMS has a safety cut off at 3.75v which did worry me initially - but true to its word the BMS disconnects the single cell at 3.75v and it drops down to 3.55v within a very short period of time and the rest carry on charging.
So under a charging load it does not necessarily mean the cell is holding 3.75v.
I do not have to worry about LVD because the inverter is handling the LVD at just above 3v.
Occassionally I charge any cells that appear to be getting nearer to the 3v limit individually in situe using a small DC bench supply at night - it takes just a few minutes. I may try a similar tactic using a resistor on the run away cell but its not a huge issue at the moment and I monitor them a lot (my babies :D)
I have been looking at getting a smart BMS so I can adjust the parameters but am happy with my current BMS and not really got extra money to throw around.

The way you worded that implies that the other cells can continue charging when the BMS activates due to one cell at 3.75V. That is not the case. Once the BMS is tripped, no current flows into any cells until the reconnect voltage is reached.

If you're tripping the HVD, lower your charge voltage until it stops doing it. After a week or two, tick it up .05V and see if it quits tripping. If it trips, move it back down and wait another week. Rinse and repeat.

You should stop mucking with your cell voltages. You're working against the BMS's balancing. Sometimes parents muck about in their children's lives and just make things worse. This is one of those times.

If you routinely DEPLETE your battery and never fully charge it, they should be bottom balanced. If you routinely fully charge your battery but never deplete it completely, they should be top-balanced. Any mucking about that you do likely overrides the BMS balancing function and makes it worse.

 

[peterwareing]

Thanks for the heads up about the bank cutting off until the reconnection voltage is reached I honestly thought it was the single cell.

After reading your post about taking the cells down to 2.0v or 2.2v or 2.5v - I would not consider my 3.09v LVD to be a DEPLETE issue? Any cells that drop below it (could be months) - I monitor then carefully add a little via the bench suppy - I am only talking 3.04v up to 3.07 then monitor and perhaps top up again a few days later.

The higher cell voltage only occurred when my inverter was switched off during a particularly cloudy week where I had switched the inverter off to avoid cycling on/off around the LVD then forgot to switch it back on. I normally charge to around 3.5v only.

Thanks for the good information - I will implement what you have advised and I will consider myself 'told off' like one of the children you refer to - mucking about?

 

[snoobler]

Sorry. "told off" wasn't the intent. I can't speak for YOUR children.