DEXT connection to Solar Panels

[Allen Tindall]

The following is an answer you gave me which relates to my existing installation using an Optocoupler and three DSSR 20's to connect to my solar panels.  I am currently working on the diagram to replace the Optocouplers with a DEXT.  In another thread you stated to use the DEXT 4S connections for the Solar panels.  Can you provide the best way to connect DEXT 4S to the DSSR 20 RCN and RCP?  

Allen,

The diagram looks OK except for the DSSR20 you need to disconnect the RCP you will not use that at all just the RCN should be connected in your diagram.

The RCP inside the DSSR20 will go to PV panels positive trough some resistors so it is not doing anything other than powering the RCN but since you already apply +12V that is sufficient and you do not want to involve the RCP that can be higher voltage so that RCP connection remains unused.

[Dacian Todea (electrodacus)]

You have older version of DSSR20 the v02c ?  That is based on the fact that you mention RCn and RCp

In that case all you do is connect one of the terminals of DEXT 4S to RCp and the other one to RCn. 

The DEXT can handle up to 400Vdc (not a typo 400V) so it is no problem to handle the RCp as supply no matter what your panel open circuit voltage is.    When you used those Optocouplers those were only rated at 30V and could be damaged by the RCp thus the reason I recommended to use +12V and a resistor with those.

You can of course continue to use the +12V and resistor instead of RCp but is not needed with DEXT so you can simply connect 4S to RCp and RCn.

[Allen Tindall]

Thank you.  That makes connections simple.  I have DSSR20 version V03d if that makes any difference.

[Allen Tindall]

Please provide the part numbers for the 4 connection and 3 connection plugs that come with the DEXT.  I need purchase a pair of 2 connection plugs so I can connect ADC 2 and ADC3 after the SBMS is powered on.  

[Dacian Todea (electrodacus)]

Allen,

Unfortunately a pair of two connection plugs will not properly fit in the 4 connection connector. I just tested and if you force them they will get in at a bit of an angle.

Just search for "3.5mm pluggable connector" and you will find versions from many brands but also different variants.

Here is a two connection one with connections on top and screws on the side as I provide with the DEXT  https://www.digikey.ca/en/products/detail/adam-tech/EBKA-02-A/9830661

But there are also variants with connections on the side and screws on top     https://www.digikey.ca/en/products/detail/molex/0395037002/4480319

And there are also spring terminals as the 2x8pin I provide on DEXT but a bit more expensive  https://www.digikey.ca/en/products/detail/phoenix-contact/1952267/2071461

You can test plugin a 3 connection in to a 4 and next to it one pin from another connector to understand the limitation and why they do not fit great. 

[Allen Tindall]

Attached is my latest diagram to allow replacement of 2 opto couplers with my new DEXT.  In the middle of the diagram is a 6PDT switch.  In the event of an EMERGENCY in which the Lithium Battery System fails, this switch allows switching the entire electrical system in my Motor Home from Lithium Battery to Engine Battery.  As shown the switch connects SBMS0 to DEXT for EXI03 +, EXI04 + and EXIO5 +.  When switched, the SBMS0 + wires are disconnected and the DEXT + wires are connected to the DEXT – wires allowing 3A to 5S to be closed and 5D to be opened when connected to the Engine Battery allowing normal operation of devices.

 Do you see any problem with the installation of the 6PDT switch in the wires between the SBMS0 and the DEXT?

[Allen Tindall]

New copy of DEXT Switch drawing as a Word File in case it doesn't open

[Dacian Todea (electrodacus)]

Thanks for the .doc file. I can open the .vsd file but the text is not quite where it should be so it is harder to understand.

I do not see how what you want will work with the current diagram.

Say Lithium battery is empty and you want to supply everything from your starter battery. You will first need to isolate the Lithium battery by say removing the 400A main fuse and the 50A solar breaker (also remove that 8AWG wire from the battery side of the 50A solar breaker).

 Now that you done that you should be able to switch that 6PDT in the other position and supply your loads from the starter battery.

But if you fail to isolate the Lithium battery first before switching the 6PDT you will be soon in trouble as the Lithium will bring down the Lead Acid battery and if the solar is still connected to this and forced ON by the 6PDT (no more SBMS0 control) that will overcharge and damage the battery or batteries and likely damage some of the equipment that can not handle the PV array open circuit voltage.

  

Maybe I do not fully understand what you want to accomplish.

[Allen Tindall]

I discovered an error on the original diagram and also changed some wire colors so I attached a new copy.

 

In the Lithium Battery mode as shown, the third switch connects EXIO5 + between the SBMS0 and the DEXT.  Just above the 6PDT switch shows DEXT connections 5D and 5S.  The 5 amp inline fuse connected to the 400 amp Main Fuse connects 12 volt + from the Lithium Battery to DEXT +  and to DEXT 5S.  EXIO5 is set as TYPE 5 which under normal operation should close 5S connecting the 16 awg Red wire to the upper Blue sea RBS 7713 closing the RBS 7713 and allowing everything to work.  In the event of OVLK or UVLK or switching the 6PDT switch to the Engine Battery position, 5S should open and 5D should close connecting the 16 awg Red wire from the RBS 7713 to ground switching the RBS 7713 to open circuit leaving the Lithium Battery disconnected.  The first two switches of the 6PDT switch operate similarly to allow normal operation of the Battery Protect and the Power Inverter in both the Lithium and Engine Battery configurations.

 

The 4^th switch of the 6PDT switch allows operation of the Emergency Start Switch in the Lithium Battery mode and engages the lower RBS 7713 to connect the Engine Battery in the Engine Battery mode..

 

When in Lithium Battery mode, Switches 5 and 6 are off.  In the Engine Battery Mode, they double up to carry more current through the 8 awg wire to connect the Solar Panels to the Engine Battery.

 

I realize that this is very complicated, but allowing use of the Engine Battery in an emergency is very important in this Motor Home.  The bed drops from the ceiling and needs 120 VAC to run.  I am mainly concerned about switching the positive wires between SBMS0 and DEXT.

[Dacian Todea (electrodacus)]

The first 3 connections of your 6PDT switch is between the SBMS0 and the DEXT. The switch is shown in normal position where SBMS0 has control over EXT IO3, IO4 and IO5

But when that 6PDT switch is turned in the other position EXT IO3, IO4 and IO5 are shorted at the DEXT input meaning that anything that is controlled by those is ON (close circuit at all times).

This means DSSR20's controlled by EXT IO4 will never stop getting to whatever your PV array open voltage is and damaging any battery and device that is not able to handle that.

All loads will be ON controlled by EXT IO3 since IO3 is shorted by the 6PDT maybe this is the only part that is OK as you want to force your loads to stay ON

And EXT IO5 that you have it set as type 5 will be permanently enabled so 5S close circuit 5D open circuit.

The DSSR20 can not be used without the SBMS0 controlling them.

You do not want the solar panels charging your engine battery as it will overcharge it and damage equipment and battery.  There is no logic inside the DSSR20 is just as the same suggest a solid state relay + ideal diode no way to stop the current (charging) other than trough the EXT IOx control with SBMS0 being able to measure battery voltage and take the decision when to turn OFF the DSSR20.

If you need solar in an emergency to charge your engine battery you will need to add a Lead Acid solar charger in between the DSSR20 output and your battery. 

So for EXT IO5 do not connect the EXT IO5- to the 6PDT switch but directly from SBMS0 to DEXT that way when you disconnect the EXT IO5+ between SBMS0 and DEXT the DEXT will see an open circuit at the IO5 input and then have the 5S open circuit and 5D close circuit.