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Voltronic Tri and Float Voltage


Rick C
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Hi all,

I have a 5KW Voltronic Tri inverter. I was reading in the forum about a charging issue , and my problem is quite different from the one reported a while ago regarding the charging algorithm.

I recently bought four 12V 250AH Ultracell Gel batteries (250AH @ 48V). I noticed that the battery voltage reading spends most of the day at 56.4V. I have 21 275W panels in 3 orientations:  6 facing east, 3 facing north and 12 facing west. All of them in 3-series (37.5 x 3 ,  112 Voc app)


We intentionally oversized the solar for my daily loads , it was designed especially for winter time and also to avoid deep discharges to the batteries. (I live in Chile, there is a lot of sun here)
I use the only solar (OSO) parameter, but very rarely it reaches the float voltage of 54V, (Only when my house is alone and there is no great variation in the loads during the day) But, when I am at home connecting and disconnecting loads it is almost always at 56.4 V.

They also get float stage when I switch to AC charging at night , and the AC charger puts some amps on battery and reaches float in a few minutes at 54V, and stays very pacefully at 54V until the next morning.

My questions are 2 :

1) Could the batteries be damaged by the BULK voltage all day?

2) What is the logic of this wierd algorithm and can it be modified?

As additional information the firmwares are 

76.10 for mains

1.02 for SCC (the same for 3 MPPTS). (I suspect the problem is here)

Thanks in advance. This is a really great forum!

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On 2020/12/17 at 5:48 AM, Rick C said:

1) Could the batteries be damaged by the BULK voltage all day?

Yes, it's possible that they could dry out, converting the small amount of water in them into hydrogen and oxygen, and having the gas vent due to over-pressure before there is a chance for recombination into water again.

On 2020/12/17 at 5:48 AM, Rick C said:

2) What is the logic of this wierd algorithm and can it be modified?

My guess is that your battery has a high internal resistance, so when you have high loads come on, the battery voltage sags. If it sags enough, 4.00 V below the float setting for 10 seconds with no exceptions, or float voltage less 1.00 V for about 30 minutes (using a "leaky bucket" algorithm; excursions above (float-1.00V) leak out of the bucket twice as fast as it fills). With either of these, the charging goes to zero for about 15 seconds, then starts again, and is back at full bulk charging about 30 seconds after that. That would be why you see the difference between not being at home, with relatively constant loads, and being home, with peaky loads.

This behaviour can't be modified. We do change the voltage thresholds associated with these changes in the LFP flavour of the patched firmware, but you'd need the lead acid flavour, which doesn't change these thresholds.

You could check your logs for the 30 seconds of zero charging, and to see if your battery voltage droops enough to trigger these conditions.

One thing you could do is to make sure that you aren't getting significant voltage drops across your battery cables, isolator, and fuses. Your battery cables should be at least 35 mm² (assuming a 5 kVA model).

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Sounds creepy!

I checked how the voltages vary and, even with high loads, the voltages sags very little. (51V-52V)and just for little seconds while the panels supply power to the load (Because I have 21 panels that previously to this high load were working at minimum capacity because the battery is already full ). 

The battery wiring is very thick, actually. So, no problem with voltage dropping.

What I can do? Since I can't change that algorithm, should I buy one or more external MPPTs? and leave the Voltronic just as an inverter?
This one has 3 MPPTs that would be completely useless!
Or leave the smallest solar string connected to the Voltronic in order to automatically go to the grid at night? In this case, two MPPTs would be unuseful!

The fact that it can damage the batteries is not funny to me or anyone. I enlarged the solar field to produce more energy and apparently I am in trouble !!

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12 hours ago, Coulomb said:

The 56.4V it spends a lot of time at is I assume per the inverter itself, not an external multimeter?

What is your maximum total charge current setting, setting 02?

Do you know the maximum charge current set by the battery manufacturer?

The 56.4 is got from the inverter, and also i used an external multimeter... Same volts.

The setting 2 is @ 30A (250AH battery bank. Only Solar charging OSO Mode).

The Batteries are Ultracell, I dont know the maximum (I couldn´t find it) , but I've heard that a charging at 0,1C es safe. Actually when I see 56.4 for hours and hours, the charging current is between 3A and 6 A.

 

 

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15 hours ago, Rick C said:

The 56.4 is got from the inverter, and also i used an external multimeter... Same volts.

The setting 2 is @ 30A (250AH battery bank. Only Solar charging OSO Mode).

That all seems good.

Quote

Actually when I see 56.4 for hours and hours, the charging current is between 3A and 6 A.

My only guess is that with three solar charge controllers all independently trying to stick below a current limit, there is nearly always a time when the total is over 5 A, which is what your current threshold will be (for any maximum charge current under 60 A). Even a short excursion over 5 A will reset the timer that has to see 30,000 measurements below 5 A in a row without exception, before the transition to float stage.

That figure of 30,000 was increased by Voltronic from 500 (a factor of 60!), presumably as an attempt to work around the premature float bug. In patched firmware, where the premature float bugs are fixed, we actually put that figure back to 500, where it belongs.

Sadly, if my theory is right, it seems that this means your inverter is going to be stuck with a sort of "overdue float" bug. Sadly, the latest dual/triple MPPT firmware that I have is 75.31, which seems too old to attempt to use on your inverter. However, it's old enough to have the 500 threshold, so it should be free of the "overdue float" bug. Lightly patched firmware version 75.31a is available if you're willing to try it, against my recommendation.

Your best bet might be to press for an updated main firmware for your model, then (assuming that it doesn't fix the problem) PM it to me for patching. Unfortunately, triple MPPT models are rare, and the firmware for them may not update frequently, so 76.10 might be the latest version available.

Edited by Coulomb
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Coulomb thank you very much for your help. I agree with you. It is not recommended to downgrade the firmware. Besides, in the Australian forum they say that 75.31 patch is only for models under 1.0 PF (Mine is 1.0 PF).

Can i get some help if I send a mil to Voltronic? Or in your experience, they never respond?  

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13 hours ago, Rick C said:

Can i get some help if I send a mil to Voltronic? Or in your experience, they never respond?  

I've had no responses emailing Voltronic Power. You are meant to go via your reseller, even though they ultimately have to go to Voltronic. So email or call them and see how you go.

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