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BMS common port vs seperate port

An other question I can't find the answer for is, I have a Victron Multiplus. It is a inverter and charger in one. So a Load and a Charger. Then I use solar when on the road. The question is, do I use a Common or Seperate port BMS? And where do I mount the Victron Multiplus on?
 
Echo, On the split port, does current back feed on the discharge side?
 
Svetlana said:
... the BMS cut off the supply to the load but it also cut off from the Solar Charge Controller. Most people that i talked to said that when you cut off the batteries from the Charge Controller while the solar panels are connected will surely damage the controller....
Click to expand...

I do not at all understand that the SCC can be damaged by an open circuit condition on the battery. This can be caused by many many things (i.e., a blown fuse, a BMS cutting of the battery, etc.). This makes no sense whatsoever. If the SCC can be damaged by lack of a battery connection this is simply poor (VERY POOR) engineering. I know many switching power supplies (which a MPP SCC is) require a minimum load to operate PROPERLY, but they don't get damaged, they simply output a perhaps not very controlled voltage. So this could in theory damage other components down the line (i.e., if the SCC outputs too high of a voltage it could damage a 12 V radio). So yes, in principle there could be a problem but not with the SCC. I guess that having a separate port is safer then.
 
Disconnecting the SCC from the battery under moderate to heavy load i.e. like pulling a plug may cause some arcing and possible damage to the SCC but normally it is advised to connect the SCC to the battery first and then PV to SCC. This just helps the SCC to determine the correct battery voltage as most SCC are multi voltage units. If PV is connected first before the battery it may take a few seconds before the battery starts charging.
 
I was told by Redarc manufacturer that they tell their clients to jumper a external 12v source to the battery terminal to restart their solar controller.
Their new combination dc to dc / mppt controller will repower it self from a solar or vehicle 12v power source without 12v from battery.
I have a question that i can't find a clear answer so far on the forum.
With a common load/charge connection BMS in low voltage disconnect, will the BMS allow the battery to charge.
And will the BMS allow the battery to discharge when high voltage disconnect is activated.
I'm referring to most BMS's and particularly to the
Overkill Solar 12v 4S 120A BMS
That will Prowse has on his web site.
And this one
DYKB smart BMS 4S 12V 60A 80A 100A 120A Li-ion LifePo4 Lithium Protection Board balance High Current Bluetooth APP software GPRS
you can get on Aliexpress they look the same.
For us in Australia, freight it way too expensive from USA so have to source from CHY NA.
 
grey nomad said:
I was told by Redarc manufacturer that they tell their clients to jumper a external 12v source to the battery terminal to restart their solar controller.
Their new combination dc to dc / mppt controller will repower it self from a solar or vehicle 12v power source without 12v from battery.
I have a question that i can't find a clear answer so far on the forum.
With a common load/charge connection BMS in low voltage disconnect, will the BMS allow the battery to charge.
And will the BMS allow the battery to discharge when high voltage disconnect is activated.
I'm referring to most BMS's and particularly to the
Overkill Solar 12v 4S 120A BMS
That will Prowse has on his web site.
And this one
DYKB smart BMS 4S 12V 60A 80A 100A 120A Li-ion LifePo4 Lithium Protection Board balance High Current Bluetooth APP software GPRS
you can get on Aliexpress they look the same.
For us in Australia, freight it way too expensive from USA so have to source from CHY NA.
Click to expand...
My experience with the JBD BMS ( same as Overkill but sourced from CH ) :
The unit has 2x FET control indications displayed , so answer to both questions is ‘yes’ . If any of the FET’s indicate ‘red’ , that function will not be allowed and conversely if any of the FET’s indicate ‘green’ that function will be allowed.
I am a firm believer in the JBD BMS and for the price and functionality it makes a great buy.
I reviewed this unit some time ago in the BMS Section.
https://diysolarforum.com/threads/dgjbd-bluetooth-bms-a-short-review.5290/
 
Last edited:
My BMS (Ji Kong JK BMS) is a common port, but it has separate control for charge and discharge protection. When it goes into under volt protect mode, it will not pass current out from the battery to the load, but if there is charge current coming in, it will still allow the current into the batteries to raise the voltage. And on the flip side, if the voltage goes too high and hits over volt protect, it will go open and not accept any more charge current, but if will still supply current out to the load. I have not tested the over current protection, but I would assume it works the same way. Testing the over and under volt was easy, I just adjusted the trigger voltages to make it switch off and on in each case. I was concerned it would be a problem switching off to stop an under volt, and then not being able to charge, but they thought of that and it works great.

I am setting my inverter/charger voltage limits to always stay inside of the BMS limits, so it never should go into protect, but the BMS will always be there as an extra safety factor.
 
Will Prowse said:
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! :(
Click to expand...
I just got a 4s seperate port was rated at 20 amps for charge and 100amp for discharge
I think you have to ask them to send a 20amp version though (At least thats why I did)
 
Another member mentioned that Daly can make a separate port charge input up to 50A. Nimi the sales rep from Dongguan Daly Electronics has comfirmed this on Alibaba
 
Ok, I am wondering why you couldn't put in a low voltage cutoff in the load line? If low voltage would be the primary reason in a warm area that the the BMS would cut off. Use a programmable board in conjunction with a 100 amp relay. As long as the voltage is high enough the current flows, but if the drops then the relay cuts off the flow. With the only draw being the MPPT controller. When voltage rises above the predetermined level then the current flows once again.

Likewise, a relay could be used to switch the MPPT over to a very small lead acid battery when the BMS switches off. This would keep the MPPT connected to a battery and preserve the MPPT.
 
If I have a seperate port 150Amp Daly BMS, can I just not use the the center port and use it like it's smaller brother?

There is no lead hooked on to the center post.

Also, tried to hook it up with 2 120Ah cells in series and 4 sets in parallel for 240Ah 12V, but the BMS won't activate. Tried the normal "reset" jumper.

Lithium Charger is 50 amps. Ideas?

Will, it would be great if you would do a short video on the separate port...I know I'm lost.
 
jpc333 said:
can I just not use the the center port and use it like it's smaller brother?
Click to expand...
Sure, why not?
I am not sure whether the "center port" is the charge port or load port but surely there will be times (many!) that they are not being used (not charging and/or no load) so it makes no difference whether its physically connected or not.
 
Depending on how the MOS FET's are laid out, it is possible the load port might not like current going backwards during charging. And the charge port probably won't like load current going out. Without a schematic, it would be hard to know for sure what effect it would have. But my fear is it would go pop like charging through a Victron battery protect. Though on an E-Bike, I know they can push charge power back from the motor with dynamic braking, So.... it might work, but.... I wouldn't try much current in the wrong direction.
 
jpc333 said:
If I have a seperate port 150Amp Daly BMS, can I just not use the the center port and use it like it's smaller brother?

There is no lead hooked on to the center post.
Click to expand...

Can you clarify what you mean here.

The 'center port' is the P- (loads)?
1599946315968.png
And when you say "use it like its smaller brother" are you referring to using it as a common port BMS running everything through C- (charging)?
 
I think you have to use one lead for charging and the other for discharging if I remember right

P- is discharge
C- is charge
B- connects to the battery btw
 
Most on here are referring to a 24 volt system. So I am assuming you are using a inverter for most of the load. It looks like you could just set the low volt cut out on it to disconnect before the bms sees the lowest cell. In my RV I have the inverter LVCO at 11.5 volt I have tested and not seen bms on any of the 12v 200ah. I don’t want to get down into the discharge curve very far away. Most Mppts recommendation on PV volts. 12 volt system is around 75 volts. 24 volt is around 100 volts and 48 system is 150 volts. This is for conversion efficiency. So on a 24 volt system or lower you are not going to see a spike of 50 plus volts from battery disconnect. If you were on 48 volt system and pv strings at the full 150v. I would be more worried about spikes in volts from the sun coming out from behind a dark cloud. I have had my 48 volt system. Alarm on pv over volt and drop pv for a short time. Schneider Mppt 60-150. I am fairly new with lithium. My home system is rolls surrette 880 AH 48 volt. My RV I have 2 200AH 12 volt parallel.
 
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