diy solar

diy solar

BMS common port vs seperate port

The split port has a charge port and a battery port. The BMS can cut off Charge separate of battery (Load). The common port the load and charge port are together. If the split port sees high voltage It can shut off charging. If it sees low voltage, It can disconnect load.
 
The big problem with separate port BMS is the current is extremely limited. Not uncommon for a 100a separate port bms to have a charge line that can only handle 8-15 amps. If you are building a system for solar, use a common port for your loads, and connect the SCC directly to the battery.
 
unnamed.png

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
 
I appreciate thw info guys and thanks for the diagram Will. That's what I was looking for on Google but couldn't locate. I have 5 (soon to be 7) 60ah lifepo4 banks in 8S (24v) total 420ah with 330ah usable. Problem is I set my MPPTs at 26.6 (80% charge) but still find 3-4 cells somehow hitting 4..4 and 4.5 on 2 occasions. Don't know how this is possible. The rest of the cells are 3.2-3.3 as designed. Thought I would implement a BMS on the charge side to see if it fixes the problem. Also, I use aluminum bus bars (+/-) which everything connects to. Not sure how one would seperate charge and load with the BMS in such a design. Any suggestions would be helpful. Thanks.
 
I'm working on a very small system using a Separate Port BMS. I use a relay to disconnect the PV when the BMS does the High Voltage Disconnect.
The relay can handle much bigger amps than the BMS.
 

Attachments

  • Fotovoltaic-v2.png
    Fotovoltaic-v2.png
    197.8 KB · Views: 1,424
I bought the 100A Daly BMS with separate port, and the description on the actual BMS says 20A charge current, 100A discharge current.
I spoke to Daly Official Store on aliexpress, and apparently they checked with the engineer and it can charge up to 100A.

Not sure if there is a language barrier where he doesn't understand my question...
 
I bought the 100A Daly BMS with separate port, and the description on the actual BMS says 20A charge current, 100A discharge current.
I spoke to Daly Official Store on aliexpress, and apparently they checked with the engineer and it can charge up to 100A.

Not sure if there is a language barrier where he doesn't understand my question...

Yea I would be wary of that.
For it to offer both charge and discharge at 100A it will need twice as many MOSFETs as a similar rated common port BMS. I would compare the price between the common port version and the separate port version. If it really has double the amount of MOSFETs, then you should see a significant price difference.
 
  • Quick react
Reactions: GWM
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.

When you say loads do you also include accessories such as power to my Morningstar GFDI, Battery Capacity Shunt, etc? I had originally planed to run my battery negative lead to a grounded bus bar with the BMS in between them. From the (-) Bus I would have connected the Charger, Shunt, GFDI, and the Main Load. Now I understand I shouldn't use the BMS to disconnect the MPPT Charger. So should I connect the charger directly to the battery bank and then have the BMS between the Battery and (-) Bus (Disconnecting the load and all accessories)? Or should I connect the BMS between only the (-) Bus and my Main Load?

Thanks your input!
 
  • Quick react
Reactions: TyR
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
What was the amp rating of the separate port BMS that only provided 10 amps of charging.
 
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! :(

What was the amp rating of the separate port BMS that only provided 10 amps of charging.

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

Will, Did you mean to say "Considering the UNlikelihood of over voltage situation from most high quality mppt, "...
 
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
Word!
 
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

Will,

I am scared to go w/o a BMS. I posted previously about a Victron parasitic issue , (like you to look at in reviews going forward)

-Tim
 
I bought the 100A Daly BMS with separate port, and the description on the actual BMS says 20A charge current, 100A discharge current.
I spoke to Daly Official Store on aliexpress, and apparently they checked with the engineer and it can charge up to 100A.

Not sure if there is a language barrier where he doesn't understand my question...
i noticed that any question they go to the engineer, smiles who is that engineer?
 
I bought the 100A Daly BMS with separate port, and the description on the actual BMS says 20A charge current, 100A discharge current.
I spoke to Daly Official Store on aliexpress, and apparently they checked with the engineer and it can charge up to 100A.

Not sure if there is a language barrier where he doesn't understand my question...
Ditto
 
Are any of you guys know can I use the BMS with separate ports, same like a BMS with common Port, Just use only the load connection ? or bridge the charge port with the load port? I ask because i order it wrong but i think whats can be the different ? So i think maybe the load port can use too for charging bt the over Voltage Protection is not working on the load port. Just under load protection. but i can setup the inverter lower example to bulk only 4.0V it should be ok. And i can protect the battery with a relais too if the voltage is higer than 4.19 V. I think use a pi zero with adc differential...
 
Last edited:
Curious, What kind of BMS did Battle Born or Relion or others engineer into their batteries? Could this offer direction cuz they support both high charge and discharge rates.
Will took apart a BattleBorn and although the BMS isn't a Daly, there doesn't appear to be a separate charging charging port on that BMS.
 
When you say loads do you also include accessories such as power to my Morningstar GFDI, Battery Capacity Shunt, etc? I had originally planed to run my battery negative lead to a grounded bus bar with the BMS in between them. From the (-) Bus I would have connected the Charger, Shunt, GFDI, and the Main Load. Now I understand I shouldn't use the BMS to disconnect the MPPT Charger. So should I connect the charger directly to the battery bank and then have the BMS between the Battery and (-) Bus (Disconnecting the load and all accessories)? Or should I connect the BMS between only the (-) Bus and my Main Load?

Thanks your input!
I am worrying over 4p 8s BMS set up my self. That is to say 4 BYD 24v batteries in parallel. After I bought all this stuff I seen a video Will made, and he said I might be asking for trouble if I go over two or three 8S in parallel. I also will be using 4 separate port BMSs. If you find out any good data please share. Thank you in advance.
 
Back
Top