BMS common port vs seperate port

[grizzzman]

Thats just moderator crap Art . They know it all.

Hey the problem I have found with drop in 12v LFP's when you use them and charge them they start switching off at lower voltages . 14.6 is the max for 12v 4 cell examples and they start switching off at 14.4v and then 14.2 v even down to 14v.

Opening them up you always find one cell has gone over 3.65v and discharging it fixes the problem . You lose any warranty of course as soon as you open them up.

If you look at a cell charge /discharge graph you will see that between the knees is about 3.4 v to 3.0v so if you keep to those values your cells last. I've been working on Lithium since 1992.

Well I will say one thing. You speak your mind.

 

[Gazoo]

Hey the problem I have found with drop in 12v LFP's when you use them and charge them they start switching off at lower voltages . 14.6 is the max for 12v 4 cell examples and they start switching off at 14.4v and then 14.2 v even down to 14v.

What drop ins are you referring to? I don't believe Battle Born has this problem and my Valence batteries definitely don't because they still function perfectly given their age. Both Battle Born and Valence do use cylindrical cells. A drop in using prismatic cells shouldn't have this problem either if the BMS is working properly.

 

[Dzl]

Thats just moderator crap Art . They know it all.

I'm disappointed you feel that way since I'm honestly trying to understand the point you are attempting to make.

If you spend more time calmly and clearly explaining your ideas, and less time criticizing others I think everyone (you included) will benefit.

 

[ArthurEld]

I was just trying to explain why other people might think it is ok to set the BMS limit higher than 3.65.
I don't set mine above 3.65.
It seems to me that it doesn't hurt to think outside of the box. Especially with these cells.
Nothing fits the rules exactly. And to say it does trips people up too.

 

[Bob B]

Thats just moderator crap Art . They know it all.

Hey the problem I have found with drop in 12v LFP's when you use them and charge them they start switching off at lower voltages . 14.6 is the max for 12v 4 cell examples and they start switching off at 14.4v and then 14.2 v even down to 14v.

Opening them up you always find one cell has gone over 3.65v and discharging it fixes the problem . You lose any warranty of course as soon as you open them up.

If you look at a cell charge /discharge graph you will see that between the knees is about 3.4 v to 3.0v so if you keep to those values your cells last. I've been working on Lithium since 1992.

It seems to me that you are the one taking the attitude that you know it all and nothing anyone else has to say has any value and it offends you to answer a direct question from those who are so ignorant that they don't deserve an answer.

Most of us like to use a BMS where we can monitor individual cell voltages and see a problem before things go too far wrong. Seems like you are using pre built batteries that can't be monitored.

 

[ArthurEld]

Just wondering if you have a reference that can back that up with data? I had one of my cells accidentally go over 3.7V and the plastic casing around it is now permanently bulged (GBS cells). I don't have data of how much above 3.7V it went or how many times.

My guess is that you spent a long time charging at 3.7V which allowed the cells to absorb the whole 3.7V. And I think many people have messed up cells that way.
You saying that you don't know how long or how much above 3.7V leaves a lot of possibilities. Lol

 

[Bob Steel]

What drop ins are you referring to? I don't believe Battle Born has this problem and my Valence batteries definitely don't because they still function perfectly given their age. Both Battle Born and Valence do use cylindrical cells. A drop in using prismatic cells shouldn't have this problem either if the BMS is working properly.

You probably are aware that most BMS's don't actively balance as the charge comes up . They are usually passive balancers in that when a cell gets to a set point ,say 3.55v maybe the BMS bleeds off some of the charge current to earth to allow the lower cells to catch up. Now the fact is that even with 4 cells in a 12v system they often have one cell that goes over the high voltage of 3.65v.

When that happens in a closed dropin what do you do? Gradually the high cell will drop and hopefully the battery switches back on . Many don't and need interference to flatten the high cell somewhat.

The fact that you have not yet experienced this tells me your settings are such that the charging cuts out a good margin lower . Cylindricals or prismatic has no bearing on the matter.

 

[Gazoo]

Now the fact is that even with 4 cells in a 12v system they often have one cell that goes over the high voltage of 3.65v.

But the BMS should cut off the charge when the highest cell reaches 3.65 volts unless it's a crappy BMS. I do agree passive balancing is pretty much worthless with high capacity cells because the voltage jumps quickly at the top and the BMS doesn't have the time to balance. I have seen that for myself with my 8s pack. I am keeping the cells between the knees so I am not concerned.

The fact that you have not yet experienced this yet tells me your settings are such that the charging cuts out a good margin lower . Cylindricals or prismatic has no bearing on the matter.

My Valence batteries always charge to 14.62 volts. Yes, I know it should be 14.60 volts and my meter could be off a bit. The tail current when the charge is cut off is always 500ma's. It does take quite awhile to get from say 1 amp to 500ma's and I believe that's when most of the balancing is taking place and it is noted in the Valence manual. But then the Valence batteries I have are medical grade and very robust. Still I am surprised how well they have held up given their age. As I recall one of them was manufactured in 2011. I don't know when the other one was manufactured because when I received it the label was missing.

 

[SG-1]

I am looking at a DALY 10s BMS, can I use this affectively on a TESLA battery pack. Reason why I want this one it comes with Bluetooth so can check all settings etc . . .

 

[GXMnow]

I thought most Tesla packs are 6S. Two is series is 12S. So unless you are changing the wiring inside a module, or the BMS can be programmed for cell count, you would want a 6S or 12S BMS. The lower pack voltage on the Tesla modules have caused some trouble. I am using Chevy Bolt modules, and I had to reconfigure them to gt 14S to work well with my Schneider inverter. What voltage system are you trying to run?

 

[SG-1]

I thought most Tesla packs are 6S. Two is series is 12S. So unless you are changing the wiring inside a module, or the BMS can be programmed for cell count, you would want a 6S or 12S BMS. The lower pack voltage on the Tesla modules have caused some trouble. I am using Chevy Bolt modules, and I had to reconfigure them to gt 14S to work well with my Schneider inverter. What voltage system are you trying to run?

24v system, and yes Tesla packs are 6s . The Daly BMS is a smart BMS with bluetooth that I am looking at. I have seen other BMS used higher than 6s but without the bluetooth which is what I want to keep an eye on the pack

 

[Bob Steel]

. Yes, I know it should be 14.60 volts and my meter could be off a bit.

Mmm try buying a LT1021 chip for a few cents and check it.

 

[Hans Kroeger]

There are a lot of variables. I was referring to the over voltage protection limit and assuming the problem would be fixed if the limit was hit once.
There are so many variables that it is hard to give advice.
When I went over 3.65 it was for a short time. There should never be any absorbing or floating or low Amp charging above 3.65.
But if someone sets their OVP to 3.75V and one cell races up to 3.75V and then charging shuts off, it won't hurt anything as long as it only happens once.
But you can't set the over voltage recovery to something like 3.65 because that would cause the charging to repeatedly charge to 3.7V and that would damage the cell. Absorbing, floating, low Amp charging or repeatedly charging above 3.7V will damage the cell.
It is possible to damage cells by floating at 3.6V. So many variables.
Sorry, no backup. Believe me if you want to.

Hi Arthur,
Your thoughts are very much appreciated. I am still not clear what OVP Voltage is ok for LiFePO4 cells without Yttrium. Actual CALB cells are delivered with data sheets, that specify 3,9 Volts for OVP Voltage setting.
Earlier in this discussion I was pointed to 3,75 Volt for OVP.
My BMS system assumes the end of charge voltage to be at, or below 3,6 Volts. With an OVP Voltage at 3,9 Volts there is 0,3 Volts headroom for the balancer to do his job, before an OVP cut off may occurr. I expect, that normal ops will stay below 3,6 Volts. Going up to 3,9 Volts is only the result of something going wrong, e.g. hardware failure.
In my BMS an OVP or an UVP event will be latched, until someone decides to reset the system.....
Any comments?
Regards Hans

 

[ArthurEld]

Hans, I own EVE 280Ah so your specs may be different than mine.

I think you should be fine having your BMS OVP set to the highest recommended for your cells.

My charge limit is closer to 3.4V. There's really not much voltage above 3.4 and I get more cycles if I use about 70% of the available capacity.

My float is set to 3.3V since I am not trying to use all of my capacity now. I think it is bad to set float above 3.4V.

Everyone has their own limits. My limits tend to be wimpy. But I haven't had the need to use my full capacity yet.

 

[Hans Kroeger]

Hi Arthur,
thanks for your reply and confirmation......and yes, setting the float voltage low will help to decelerate calendar aging.
Kind Regards from Bavaria,
Servus Hans

 

[ArthurEld]

Hans, I own EVE 280Ah so your specs may be different than mine.

I think you should be fine having your BMS OVP set to the highest recommended for your cells.

My charge limit is closer to 3.4V. There's really not much voltage amp hours above 3.4 and I get more cycles if I use about 70% of the available capacity.

My float is set to 3.3V since I am not trying to use all of my capacity now. I think it is bad to set float above 3.4V.

Everyone has their own limits. My limits tend to be wimpy. But I haven't had the need to use my full capacity yet.

edit: meant amp hours

 

[Stewfish]

Can someone explain the difference? When would you want one or the other? Benefits?

I like how Rhino sums it up in the Chargery DCC relay post. Sometime I think their should be sticky threads in here and all of us noobs wouldn't be asking the same questions. I just had this same question. I'm not sure if Chargery has the decreased amperage when doing separate port vs common like Will mentions above. That would suck tho

rhino:
After following this thread related to Chargery BMS and it's DCC I will summarize my understanding:

• The BMS should not be responsible for every day high voltage cutoff (this should be configured via your charging source such as solar charge controller).
• The BMS should not be responsible for every day low voltage cutoff (this should be responsibility of your inverter)
• Your charging source and inverter have their cutoff voltages specified for the the entire battery bank. This is why a BMS can be important since one bad cell will likely not be detected by monitoring voltage of entire battery bank.
• Your BMS has its cutoff voltages specified for any individual cell of the battery bank.
• When using the common port DCC from Chargery:
  • You only need one DCC.
  • If the high or low voltage cutoff configured in the Chargery BMS is surpassed then the DCC will trip and the entire battery bank will be disconnected.
  • Physical manual intervention required to get your system back up.
• When using the separate port DCC from Chargery:
  • You will need two DCCs. One that will cutoff only loads and one that will cutoff all charging sources. You will need to make sure the rest of your system has these two systems wired separately.
  • If high voltage cutoff configured in the Chargery BMS is surpassed then the DCC for charging sources only will be tripped. Battery bank will no longer be charged but all loads such as your inverter will continue to operate.
  • If low voltage cutoff configured in the Chargery BMS is surpassed then the DCC for load sources only will be tripped. Battery bank will continue to be able to be charged but all loads such as inverter will be disconnected.
  • System is likely to self-recover and physical manual intervention is not immediately required.
• Any time the BMS did trigger a DCC to disconnect the battery the reason for it disconnecting must be investigated and corrected since that should be considered an error state. This condition is the last line of defense to prevent one or more of your cells in your battery bank from being permanently damaged.

 

[Stewfish]

View attachment 665

Also, I posted this elsewhere sometime ago:

Quick update for advanced LiFePO4 raw cell systems using a Daly BMS:
On my website I recommended using a separate port BMS for over voltage protection for the mppt connection (if common port BMS is used, possibility of destroying mppt during low voltage disconnect).

Well yesterday, a viewer and I finally received our separate port BMS from Daly, and the amp rating was not as advertised on the listing. The separate port can only handle 10 amps!

Considering the likelihood of over voltage situation from most high quality mppt, and the chance of matched LiFePO4 cells going out of balance is rare (and BMS will correct for cell drift over time), and that LiFePO4 can be over charged to 4.2v per cell before electrolyte degradation... I would say its safe to connect mppt directly to the battery bank, and bypass the BMS entirely. We have been doing it this way for years, but people still want to use a BMS.

I would say use BMS for loads, and not for chargers. If you have mismatched cells, and some hit a higher voltage at high SOC quicker than others, drop the upper limit voltage of your controller. 14.0-14.2v is a safe charging voltage that can give full capacity with LiFePO4 12v.

I hope this helps! I bet most people building these systems will figure this out when they see this problem, but if you are a beginner trying to build an advanced level system, then this bit of information will be very useful. Let me know if you have any questions

Makes sense,

I think your next vid should be the Chargery with the DCC and check the separate port amperage. I think because I bought cells from China on Alibaba it would be wise to have the dual DCC on separate ports. I think if Chargery can figure out all their issues then it will be a better system than the daly for large 16s 48v BMSs. The Daly is still limited by its wire guage that it can pull through the circuit board, Overkill Solar tried to fix this with soldering larger guage wires. The new bus bars on the side may help but it's still fet based and I think the weakest link to a system.

With the DCC the consumption seems to only be present while running and its 11ma or .13w at 48v

Please make a chargery area, Daly, etc for BMS

Can you add sticky threads to this forum please. It would be super helpful

 

[Bob Steel]

Could I get you to tell me what a DCC is please?
I see it is a Contactor. DC contactor
A very expensive one at that.

 

[Dzl]

Could I get you to tell me what a DCC is please?

This:

I see it is a Contactor. DC contactor
A very expensive one at that.

More specifically, it is a large bi-directional solid state relay sold by Chargery, the main selling point being its very low idle power consumption and high current ratings.
Chargery DCC (website and manual)
Chargery DCC (forum post)