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jacrupi avatar image
jacrupi asked

Rebulk Starts Everyday?

I have a MPPT 100/30 solar charger. It is connected in parallel with a MasterVolt Shore power charger. Everyday, when the sun rises, the solar controllers start a Bulk-Absorption-float cycle that lasts about 1.5 - 2 hours. Lifeline (as well as practical Sailor) says this is not good for the long term health of the battery bank. Is there anyway to stop the controller from rebuking everyday? Also, if I disconnect the panel from the controller will that cause any damage to the panels (LG Panels) or the charger? Any input would be greatly appreciated. thanks.

MPPT Controllers
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Alexandra avatar image
Alexandra answered ·

@jacrupi

Bulk and absorption are the same voltage. So it may look like it is re bulking but may just be in absorption stage as it is not drawing high current to charge.

https://www.victronenergy.com/media/pg/Manual_BlueSolar_100-30__100-50/en/configuration-and-settings.html#UUID-b7b9ed32-6c85-f1b5-73ae-62b40fec3529

You can change when it rebulks by changing the rebulk offset in the settings

screenshot-20210712-211010.jpg


screenshot-20210712-211010.jpg (173.6 KiB)
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jacrupi avatar image jacrupi commented ·
I tried to change the re-bulk offset a few times - it doesn't seem to impact the daily bulk cycle from starting. From what I can gather this is how it is supposed to work based on responses from others on this blog. Have you gotten this setting to work?
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Alexandra avatar image Alexandra ♦ jacrupi commented ·
@jacrupi

I have never personally changed it. Never seen the need. I want my batteries to charge to full everyday as we are offgrid.

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pwfarnell avatar image
pwfarnell answered ·

If you have the absorption stage set to complete on tail current, then if your batteries are full because you have not taken any charge out overnight then the bulk and absorption phase will be very short. I have mine set like this and as soon as the absorption voltage is reached the current is below the tail current setting and it goes to float. Admittedly, having a GX device and BMV shunt with DVCC enabled gives a truer measure of battery current rather than solar output to the battery, but this may also work for your set up.

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jacrupi avatar image jacrupi commented ·

Thanks. I have a MasterVolt Shunt in my system so the Victron cannot read the amount of current going into batteries (vs. other loads) directly. How long does it take your system to a complete a daily cycle from Bulk to Absorption to float. Mine completes in under 2 hours.

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pwfarnell avatar image pwfarnell jacrupi commented ·
If I am off grid and used power overnight then it can be 4 plus hours depending on the use. If I have been connected to the grid and the batteries are full, or i have been off grid but not used power overnight then it will be about 20 minutes from the voltage rising above the float setting before the absorption voltage is reached and the charge current is below the tail current setting of 1% of capacity, at which time it returns to float.


you can use tail current setting with the current exit the MPPT but that also includes any load rather than just the battery charge.

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jacrupi avatar image jacrupi pwfarnell commented ·
Thanks. I will play with the Tail Current. Do you have the "Adaptive Absorption Time" Enabled or disabled?
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rslifkin avatar image
rslifkin answered ·

It will always start in bulk when the sun first comes up. The rebulk voltage only determines when it will go back to bulk during the day after reaching float.

In my setup with a Smartshunt and Cerbo GX, the MPPTs are set to end absorb based on tail current. So every morning while the boat is on shore power, they'll run the voltage up to absorb and then almost immediately drop to float as the current is well below the tail current setting.

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jacrupi avatar image jacrupi commented ·
Thanks. Do you have the "Adaptive Absorption Time" enabled or disabled? I have it enabled, which may be an issue if I want to take advantage of the "Tail Current" Setting.
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rslifkin avatar image rslifkin jacrupi commented ·
I think you can have both enabled, but I have it disabled on mine. Basically, it'll end absorb either after the target time (adaptive or fixed) or when the tail current is reached, whichever happens first.

With a GX device and DVCC, you can have it sense the actual current going into the batteries. Otherwise, tail currently only functions on the current leaving the MPPT, so if there are any loads running, it'll drop to float too late (unless absorb times out).


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jacrupi avatar image jacrupi rslifkin commented ·
Thanks. I will play with Tail Current and Disable the "Adaptive Absorption Time" Have a nice evening.
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pwfarnell avatar image pwfarnell jacrupi commented ·
5hr fixed absorption time with tail current enabled. Hardly ever reaches 5hr of absorption unless I have been off grid and it is poor light the next day. I found that the adaptive was not great for times when on shore power, hence the move to tail current.
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jacrupi avatar image jacrupi pwfarnell commented ·

Thanks. I will give that a try tomorrow. Have nice evening.

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jacrupi avatar image
jacrupi answered ·

Update: Disabled "Adaptive Absorption Time" setting. Short term: Adjust Tail current to match size of battery bank plus anticipated DC Loads. Long term: Add a Victron Smart Shunt to the System so Solar Controllers will only look at current into the House Battery Bank to compare with Tail Current setting. Comments would be appreciated. Thanks.

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pwfarnell avatar image pwfarnell commented ·
Sound like a good plan assuming that you have a Smart MPPT, but I do not know the detail of the Smart Network system as I have the Cerbo, the manual says it shares voltage and current.
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