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Bill avatar image
Bill asked

Stopping my MPPT from charging around 80% SOC while the RV is in storage

I have seen other questions like this but the answers were more about folks NOT wanting to do this. I am trying to find out how to do it. I am assuming maybe by changing the voltage, I tried lowering the float voltage to 13.5 from 13.6 and it had no visible effect. Instead of trial and error I am hoping to start in the correct area as my storage facility is far away. (I monitor it via VRM)


PS. I want to do this, so I don't need any info on why folks don't think it needs to be done, I have read all that and still want to do it anyway to lower the cycle count on my older LI batteries.

SOC
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3 Answers
bunya-solar-pl avatar image
bunya-solar-pl answered ·

Could you let us know what gear you've got please?

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Bill avatar image Bill commented ·

Currently have 2 Smartsolar 100/50 controllers, CerboGX, BMV712 and SBS, SOB 8kw LiFePo4. I would like the 100/50's to bring the Lifepo4's to 80% max while the motorhome is in storage, then 100% while traveling. I am thinking I could setup two profiles, but I have not yet figured out what values would need to be changed. I tried lowering the float voltage in two steps, but it appears to have done nothing at all. -Bill

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derrick thomas avatar image derrick thomas Bill commented ·
You could probably achieve this with os large and node red
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justinford avatar image
justinford answered ·

You could use a Battery Protect connected to one of the solar charge controllers that it would shut down the power from the solar array when your SOC reaches 80% with the relay control in the BMV 712. Use a separate battery protect for each controller or just shut one controller off when in storage. When traveling just disconnect the relay control.

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Bill avatar image Bill commented ·

I though I read you cannot leave the controller connected to the PV panels if the battery is disconnected from the controller? I am getting the impression I cannot setup the controller itself to stop charging at some voltage that is close to 80%?

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justinford avatar image justinford Bill commented ·
The battery protect would disconnect the array not the output of the solar charge controller. But the specs would need to be met. The battery protect is capable of 36v DC. But the Cytrix 24/48 400a can go to 76V. Some of the 150 series charge controlers have a built in remote on/off


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Bill avatar image Bill justinford commented ·
Crap, I run my array at ~90 volts.
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djsmiley avatar image djsmiley Bill commented ·
Or just use a regular relay, and use the BMV's relay output to switch on a certain SOC. The small BMV relay will switch the bigger relay which would work as a PV disconnect relay, thus disconnecting the panels.

You also can use a relay output of the Cerbo for this


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Bill avatar image Bill commented ·
Yes, there are things running on the batteries, a few cameras and a cellular router. Ah, so battery connect disconnecting the Solar Array instead of the batteries.
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djsmiley avatar image
djsmiley answered ·

I would manually set it to 60% SOC or so and disconnect the battery. (Assuming its a LiFePO4). Most vendors recommend 50-60% SOC as optimum for storage of the batteries. Self-discharge is almost zero, so no MPPT or charging required, unless you need to run some applications while in storage


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