Two MPPT's, one on each 12v battery of parallel bank of 2.

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alexmisty asked Apr 13, '24

Two MPPT's, one on each 12v battery of parallel bank of 2.

So, I have looked through the Victron Community and have not found my particular situation.

I have 2 x Victron AGM's 230Ah, in Parallel. BUT, each is on opposite sides of the small yacht, 1.5m apart. The Starboard battery is the home of the DMV shunt.

I also have each Solar panel driving one MPPT 75/15 and each separately, and directly, connected to port and starboard batteries.

Now this has worked fine, but now I notice that there is a slight discrepancy with the battery voltages (obviously because of the 1.5m connection 25m2 wire) but why? each battery is being charged 'separately' even though connected together.

Also, the MPPT's don't give the same 30 day yield (202KWh starboard and 230KWh port)

that is close and after all they are two different panels, shaded maybe differently.

This got me thinking about the shunt being only on one side only, capacity might be wrong.

we are in South Africa and it is very sunny, so no worries, the battery bank is pretty full all the time, but what happens when we sail in days of clouds?

I want to know if my setup is good. redundancy and all, but I I doing any harm?

As I finish this post I see batteries at both 12.90V

thanks for help

Alex

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battery charging mppt state

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Answer 1 · 2024-04-24T21:43:05Z

offroadflow answered · 4 days ago

If both batteries are in parallel then they must have the sane voltage in standby.

If you charge on one side more then that side will have a bit higher V during charging. The opposite for discharging.

Just check the electrical connections in between both batteries and you'll be fine.

Happy sailing!

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Answer 2 · 2024-04-25T01:11:40Z

kevgermany answered · 4 days ago

Assuming that DMV is a typo for BMV.

If the MPPTs are connected direct to the batteries, no way the shunt/BMV can work properly.

Unless the batteries share a common negative connections and the charge current and loads go through the shunt to the common negative, the BMV can only measure the SOC of one battery. The other battery can be monitored for voltage only.

Different voltages on each could be due to cabling with points of high resistance, unequal charging. Or because there is no common negative.

It would help if you checked the reported voltages with a meter at the battery terminals. Also draw up a wiring diagram.

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