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stacy-t asked

14.4 Volts when Master switch is off but MPPT wired to Lynx Distributor

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I have wired my trailer almost identically to this diagram. I am finding with the master switch off I am still getting a reading 14.4V on the lynx distributor via a voltmeter unless I disconnect the solar array to the MPPT via an isolator, which means the batteries wont charge if the system is off. Any suggestions of how I may remedy this issue? I would like a single quick disconnect that shuts down the batteries but allows for solar charging of the batteries. Would I need to wire the cables coming from the MPPT to a fuse then directly to the batteries? Thank in advance. I scoured the posts and youtube and could not find the answer.

MPPT Controllerswiringlynx distributor
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pwfarnell answered ·

On boats the solar is sometimes wired direct to batteries with its own fuse and isolator on a lead acid battery systems. This works fine. If you have a lithium system as per the diagram then you also need to power the BMS direct from the batteries which then powers the Cerbo GX, you can not have the solar alone otherwise it is not protected from overcharge etc. The shunt should be powered direct from the batteries as shown so this will keep track of the SOC.

However, one has to ask, if you have a lithium system as shown and are turning off all loads, do you need to keep the solar working as if you turn off with say 80% SOC the batteries should remain charged for a significant period with just self drain and the SmartShunt running.

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stacy-t answered ·

pwfarnell:

You make a great point. There will be long periods of time the trailer will sit, but I forgot the glaringly obvious point you make. My bigger issue is having to disconnect two switches versus one. If I were to connect the mppt directly to the battery bank, would my negative and positive go on the first battery for each polarity, just as in wiring in parallel?

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pwfarnell avatar image pwfarnell commented ·

You have to leave the MPPT negative connected to the negative bus bar in the Lynx Distributor otherwise the SmartShunt will not measure the charge from the MPPT. You only put the MPPT positive directly on the batteries so it does not really matter which battery as the charge current will be small and you should have good interconnects.

One thing you should think about is each day the MPPT will start with an absorption charge at 14.2V then go to float, your batteries will have very little use, the BMS, Cerbo, SmartShunt and battery circuits. The Lithium charge algorithm may not be ideal for this case as the absorption is 2 hours. It would be better to only float charge until the SOC is 50-70% and then have an absorption charge as a one off. The Lynx BMS can be configured for this but not the VE Bus BMS, it will need some manual intervention.

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