2 Victron MPPT100/50s, different status's

[Naughty Cat]

I wonder whether someone more knowledgable than me on Victron Solar components can help me understand the following discrepancy?

I have 700a of Gel house batteries for 12v systems.
I have 8 x 100w flexible panels on my bimini leading to a Victron MPPT 100/50 (unit 1) near the rear of the boat.
I have a further 4 x 100w panels on my coachroof leading to a separate Victron MPPT 100/50 (unit 2) by the batteries.
I do not have temperature data but I am assuming that the offset would be the same in any event.

Both have the same settings, including the float setting being set at 13.8v. Here’s the discrepancy:

In the morning, my battery capacity is typically around 75%. I am a catamaran, running a fridge and freeer, currently in warm waters. Both units read bulk. At around 80-81% unit 2 goes straight to float. Unit 2 stays at bulk charge even up to 99-100% battery capacity.

The practical issue is that I am not getting the full benefit of my solar capacity, as the majority should come from Unit 1 but that is sitting at float.

Should I set up a VE Direct network between the two? Would that solve the issue? This is not without complexity because the two units are too far away from each other to speak currently hence I wish to understand the problem first. Or am I misunderstanding the data and the float/bulk status is irrelevant?

Any advice very gratefully received.

[Hartleyg]

I would start measuring the actual voltages on the two regulators - since they have no other input for voltage, each regulator is using its "Battery" terminal voltage to determine charge state. Remember to use the negative post at each regulator, not a "common ground" when taking the measurements.

If you have a dirty (resistive) connection somewhere between the regulator and the battery itself, there will be a voltage drop across it, andthe voltage at the regulator will rise and the regulator will shift to "float" prematurely - exactly what you are seeing.
The other possibility is that the regulator is experiencing some sort of internal setting problem, but this, I think, is less likely.


Hartley
S/V Atsa

[noelex 77]

You can link the controllers over Bluetooth. They will then be both at the same charging stage (bulk, absorption, float or equalisation).

At the moment neither controller is acting correctly. One is dropping to float too quickly, and one too slowly. As well as the good suggestion of checking all the connections also make sure all the parameters are the same on the two controllers (not just the voltage set points). I suspect there is a significant difference somewhere.

I would also order the inexpensive Victron Smart Battery Sense. This provides more accurate battery temperature data. Without this (or a similar device on the Victron network ) the internal temperature of the control unit is used as the battery temperature. As your controllers are mounted in different locations this may account for some (or even possibly all ) the difference in charging performance you are experiencing.

[FlyingScot]

Read the manual. Connect them via so they operate as one. Ve.Smart Networking

[smac999]

you should also connect them to a bvm or smart shunt via smart networking so they are using actual battery voltage instead of controller output voltage.

if they are too far apart to talk bluetooth. you can get a cerbo gx and then plug both into it. but the cerbo doesn't actully syc the charging between mppts like the bluetooth network does. (don't ask me why, but it doesn't) if you add a smart shunt or bvm to the cerbo, and turn on dvcc, it will share the shunt battery voltage to both controllers though.

[Naughty Cat]

So, I have been out of cell range for a few days. Thank you for the pointers. I took some readings this afternoon on another lovely sunny day.

Reading across battery terminals, 13.28v. Batteries at 89% of capacity.

I took 2 readings at each MPPT. The first was across the +ve and –ve of the MPPT, the second was from the +ve of the MPPT to a negative in the DC system close by.

Unit 1 (the one on float) 13.59v across terminals, 13.47v terminal to negative
Unit 2 (the one on bulk near the batteries) 13.30v across terminals, 13.28 to negative

Each unit is set to 13.80v for float and 14.40v absorption. All settings exactly the same for both. There is no apparent degradation of the wiring or connectors, but only from what is visible.



It should be possible to set up a VE Direct bluetooth module from Unit 1 sufficiently close for the two to talk, as it is a remote module. Which one would act as master though? The one that is going too quickly to float or the one that is not going quickly enough?

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[Hartleyg]

OK Cat,


It sure looks to me like your unit #1 has a greater resistance between it and the battery. I suspect if you had examined the voltages earlier (when they were both in Bulk) the difference between them would have been even greater. I also believe that your battery voltage (at the time of the reported measurements) was probably more like the 13.3V that you measured across Unit #2.
What is happening is the the voltage at the output of Unit #1 is rising quickly and is significantly higher than the battery voltage when it is in Bulk (and passing the most current) because of the voltage drop in its leads. When that voltage at the controller rises to 14.4 it switches to float. It is still sourcing some current into the battery, but not what it did in bulk.
You can test this by measuring the voltage drop in the positive (and also possibly the negative) lead by measuring the drop between the MPPT + and the battery + : you may see as much as a volt between the battery and Unit #1 while Unit #2 will be much lower (measure when they are both in Bulk).


Hartley
S/V Atsa

[Naughty Cat]

Thank you for taking the time to respond to these questions and you are absolutely correct in terms of the measurements. Now all I have to do is find out where this resistance is coming from!

[Cpt Mark]

On a different note. Same controllers and ve smart sense. I noticed, in full sun, no shade, that one of my panels (I have 2, each with its own MPPT) was at 0 volts. WTH? No breakers tripped etc. Went into the app and all looked fine. Turned it off then back on and voila, working fine again. Weird.