I have a two similar off grid systems using the same opZs 3000 with a smart shunt to control the battery level. I performed the first charge of the batteries according to the battery manufacturer. (They came dry charged). One of the systems is working fine. The other has two problems:
The batteries never go into absorption charge, they jump straight from bulk to float when the SOC is 85%. When they reach 85% bulk is finished and they should go to absorption not float.
The SOC of the smart shunt and inverter are not matching, they give different values.
This is making the system not to work fully and the batteries are not charging well which makes the voltage reach very low levels during the night.
Is there any way to force the batteries into absorption?
Smart shunt settings
@mike I’m not sure of your configuration but the smart shunt OR the multiplus are configured as the “battery monitor”. They can’t both be the battery monitor so it’s not a matter of them agreeing as the SOC is set by the smartshunt.
You may need to provide more information for meaningful feedback.
Hi Trevor,
Thank you for your answer. I have chosen the Quattro as the “battery monitor” but I am also looking at the data the shunts are providing and I wonder why they don’t match. What other information would you need?
@mike that is good information. Please Uncheck “enable battery monitor” on the Quattro. If you have a shunt fitted it would normally be the battery monitor.
Also, when you enable “dynamic current limit” the maximum charge current from the Quattro is significantly reduced.
Also, the tail current on the MPPT is way too high. The MPPT goes from bulk/ absorption straight to float when charge current drops below the tail current. This is set to 38 amps and I would probably set that to closer to 2- 5 amps.
@Yachtbird To calculate the tail current you get 1% of the total battery capacity and then divide that by the number of racks? or just the total battery capacity connected and then get the 1% of that?
The configuration is two 48V racks of 2450 Ah.
Now that I look at it, couldnt it be possible that I get no absorption charge because the tail current is so high that if there is a cloud and the charging current drops a bit it jumps directly to float?
We are using the Quattro as battery monitor because it usually gives a lower voltage reading and we want to be on the safe side.
@mike Once again I am sorry that I am not having a great day! I was confused with “Weak AC” so quite right, Dynamic Current limit does NOT reduce charging current.
@mike the tail current is a percentage of the total capacity. You have quite a lot of capacity so your tail current is quite high, much higher than installations I get involved with. The installations I am used to have a shunt tail current default of 4% so lets say a 400aH bank would have a default tail current of 16 amps.
You are happy to have a tail current of 1% which is fine but with such a large system that is quite considerable current. As pwfarnell quite rightly points out the scale of your tail current is reasonable for the size of your battery bank. If the charging capacity of the solar charger drops below the tail current, that may be accompanied by a reduction of the absorption voltage too, which means the criteria for float has not been met. If however the absorption voltage is maintained and the current drops below the tail current, the charger will go straight to float.
I know you do have the tail current set correctly but by way of experiment, perhaps reduce it much further and see if the charger still goes to float without passing through absorption. It would be interesting to see what happens.
Also, the use of the Shunt as the battery monitor makes sense as it is mounted usually close to the batteries and the voltage reading is right on the battery terminals. The reason the Quattro may read slightly lower voltage is the slight voltage drop of the cables feeding the Quattro so it may not accurately reflect the terminal voltage of the batteries. Also, once again as pwfarnell righly points out the Quattro doesnt “see” the charge current from the solar so it cannot work out SOC whereas the shunt sees all charge and discharge current and therefore is capable of accurately calculating SOC.
Hi @Yachtbird, yes it all makes sense and I think I have all the settings right. However I still dont understand for example why does it go from bulk to float that many times:
I was confused with “Weak AC” so quite right, Dynamic Current limit does NOT reduce charging current.