Pierre
Somewhere down South
- Joined
- Dec 21, 2019
- Messages
- 1,122
So maybe the Daly 7S is the answer.
BMS common port vs seperate port
- Thread starter Newenough
- Start date
I know but the 8th module could give me another 400+Wh
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
If the Common port BMS sees a condition that disconnects the battery from its output won't that cause the SCC to be disconnected from the battery and allow the solar panels to damage the SCC? If you make a secondary connection directly to the battery bypassing the BMS connection that will assure a power source to the SCC so as not to damage the SCC from a solar panel connection without power to the battery connection of the SCC, but won't that also allow the solar panels via the SCC to supply a charging current to the battery even if the low temp cutoff of the BMS activates? Seems to me you are either risking damage to the SCC if the BMS disconnects power or you are risking damage to the LiFePO4 battery if the temperature drops below 0 C and you have a direct connection from the SCC with no protection from the BMS. Is this correct or am I missing something here?
KBWaldron
Solar Enthusiast
Having read all the above discussions and looked at my setup, which includes an All-In-One SCC/Inverter, I've realized something. There is no way to isolate the charging versus inverter load current with an All-In-One, short of buying a separate inverter. There is only one connection between the All-In-One and the battery which serves both for charging and discharging through the inverter. Any BMS that is used in this situation is going to disconnect the battery from the All-In-One.
DC and separate Inverter could be isolated, but having to buy a separate inverter defeats the purpose of the All-In-One.
So, I'm left with the conclusion that I need to run my batteries within a safe SOC zone. Now that safe zone could be made broader I there was a BMS that aggressively balanced cells. Is anyone aware of which BMS is the best at balancing cells quickly?
Second, it seems from the discussion that using a relay to cut charging is not good for the SCC. Having observed my SCC's operation that makes sense. It does not just suddenly jump from absorption to float charging but rather ramps down over about a minute. This can be seen by observing the current and voltage as this change occurs.
DC and separate Inverter could be isolated, but having to buy a separate inverter defeats the purpose of the All-In-One.
So, I'm left with the conclusion that I need to run my batteries within a safe SOC zone. Now that safe zone could be made broader I there was a BMS that aggressively balanced cells. Is anyone aware of which BMS is the best at balancing cells quickly?
Second, it seems from the discussion that using a relay to cut charging is not good for the SCC. Having observed my SCC's operation that makes sense. It does not just suddenly jump from absorption to float charging but rather ramps down over about a minute. This can be seen by observing the current and voltage as this change occurs.
Nigelkdx200
New Member
- Joined
- May 16, 2020
- Messages
- 7
The Electrodacus bms does continuous battery balancing while charging. (Cell balancing is done as soon as there is more than 300mA of charge current and delta between cells is higher than 10mV)
Using a relay to cut charging between SCC and battery can be problematic. However if you put the relay on the solar panel feed then you can just disconnect the panels from the SCC which effectively turns off charging. Also with lifepo4 absorption or float are not required so can turn off charging when voltage reached.
Hi Will,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
So you would still use a Daly BMS for an inverter (1000 watt Pure Sine)?
Hi guys, i'm a bit confused here, if i use a separate port BMS on an electric scooter with regen, will the BMS accept the regen charging via the P- port?
Or do i need to use a common port BMS?
Also just to make sure, in case a common port BMS shuts off the common port from undervoltage, it will still accept charging via that same port right?
Or do i need to use a common port BMS?
Also just to make sure, in case a common port BMS shuts off the common port from undervoltage, it will still accept charging via that same port right?
Pierre
Somewhere down South
- Joined
- Dec 21, 2019
- Messages
- 1,122
Depends on the BMS. (1) You can charge via the P or C ports. On the one dual port BMS I have I charge via the P port as the C port charging is limited to 10 amps.
(2) As long as the voltage on the P port is higher (i.e. from a charger ) than the reset voltage for the LVD condition , it will accept a charge.
(2) As long as the voltage on the P port is higher (i.e. from a charger ) than the reset voltage for the LVD condition , it will accept a charge.
John Frum
Tell me your problems
- Joined
- Nov 30, 2019
- Messages
- 15,233
Ok. Thanks. In this project i'll be using a Daly 150A. Separate port is it then.
The peak current the scooter takes is 150A for maximum 3 seconds and the max continuous is 120A (and only at full throttle all the time). A 150A daly is enough i guess. Any thoughts?
The peak current the scooter takes is 150A for maximum 3 seconds and the max continuous is 120A (and only at full throttle all the time). A 150A daly is enough i guess. Any thoughts?
UnderVoltage*Protection i guess
Pierre
Somewhere down South
- Joined
- Dec 21, 2019
- Messages
- 1,122
Yes indeed. I changed it to LVD
Sorry Joey.
apctjb
Solar Enthusiast
- Joined
- Jun 16, 2020
- Messages
- 456
Only one positive and negative connection to the MPP Solar all in one inverter which means if the the BMS (or fuse, circuit breaker, etc.) disconnects the battery the built in MPPT controller is in an open circuit condition and the array goes to Voc. I am going to guess (perhaps someone with an all in one can verify) that disconnecting the battery does not damage the built in MPPT controller, as that is a likely condition at some point.
With an all in one seems unnecessary to have a BMS with seperate charge and discharge disconnects, one is all that is needed.
Dauntless
New Member
- Joined
- Feb 14, 2020
- Messages
- 43
I just recemy bms which looks exactly like yours with one label being different.
I love the size, weight and large cables.
It states Discharge 200A, Charge 100A. That works for me.
One question, why the dual cables for each?
Do they provide any benefit? How?
John Frum
Tell me your problems
- Joined
- Nov 30, 2019
- Messages
- 15,233
They double up smaller cables because they are more flexible and fit the solder pads better than 1 large cable.
What gage and temperature rating are the cables?
Also if this is a commodity BMS you should derate both the charge and discharge current by .5.
Dauntless
New Member
- Joined
- Feb 14, 2020
- Messages
- 43
Cables are 6 awg, 200°C
Any reason I shouldn't use them both on different posts of the battery?
John Frum
Tell me your problems
- Joined
- Nov 30, 2019
- Messages
- 15,233
2x 6awg is equivalant to 1x 3 awg.
200 celcius gives it even more legs.
That may be possible depending the exact configuration of your pack.
I will defer to others on that point.
Dauntless
New Member
- Joined
- Feb 14, 2020
- Messages
- 43
That all depends- the MPP solar units will cut charging if the detected voltage reaches the pre programmed cut off point. It will also pass the load off to line (or just disconnect load)if the voltage is below the set point. In general, while fuses are good, they technically should serve no purpose as the wire gauge should be able to carry more than the MPPsolar unit can draw or charge at.
The unit however cannot detect when a cell is falling being or getting ahead of any other cell, and it cant manage charge distribution.
You can I think in theory manage that with an active cell balancer.
However if you have more than 1 battery in parallel, the MPPsolar unit doesnt know. It just detects the voltage on the string.
The two batteries would try to balance out , since their parallel. But this balancing is outside the control of the MPPsolar unit.
If battery 1 is at a higher SOC, it will force it to battery 2. How battery 2 processes the power, would depends on if your using a BMS, an active balancer, or nothing at all.
If you use nothing at all, the battery would just take it where it can, just like regular charging. It may go out of balance, it may not, or it may be very little.
If you have a bad cell, or a dying cell, there's no way to know. It will try to push the voltage no matter what. On a 24V battery, it doesn't care if 1 of the 7 cells or 1 of the 8 cells is dying. It will shove it into the rest of the cells, damaging them.
If you had a BMS, it would disconnect due to over voltage to an individual cell.
In short, I'd say the BMS should be programmed to a higher boundary than the MPPsolar- BMSdisconnects should be lower than the MPPsolar setting, and over voltage should be higher than the MPPsolar settings. This would ensure that the only reason a disconnect would happen is if something got out of wack (i.e. dead short cell) .
Will it hurt the MPPTcontroller? That Im not certain. I will tell you that my LV2424 wont' even turn on without a battery at a minimum SOC. (15v?16?) So if the battery disconnects, the unit gets a hard shut off. If you have more than 1 battery in parallel, even if one battery disconnects, the MPPTcontroller will only charge until the voltage of the remaining batteries come up.
The only time this setup becomes problematic is if load demand or charge current exceeds what the remaining batteries's BMS can handle.
The other "gotcha" of this is when you have more than 1 MPPSolar unit in parallel. I haven't had time to setup my second one, so Im not sure what happens.
Similar threads
