Good day. For two years, we have been operating a three-phase system consisting of 3x Multiplus-II 5K and 4x Pytes V5 batteries (20kW). These each run on a Lynx Power In rail with 70mm² and a maximum cable length of 1.5m. Now the system is to be supplemented with an MPPT 450/200. This is also connected to the Lynx Power In rail with 70 mm² and a cable length of 1.5 m. However, when the batteries are switched on, they now go into ALARM mode because the start-up current of the MPPT appears to be too high. If I first switch on the battery and then add the MPPT using a battery switch (1000A version), the system works. I am sure I read that the MPPT is equipped with a soft start. Question: What am I doing wrong, both in theory and in practice?
DVCC is active – value is 350A. When the master battery starts, it starts on its own. The others follow step by step. And yes, just from the sound of the Pytes battery’s semiconductor switch switching, you can “hear” that there is a good flow of current. The question is, why does the MPPT RS draw so much power when it is connected to the battery—even when it is switched off?
All MP2’s have DC capacitors on the 48V side.
3 x MP2 have a certain total capacitance value.
It seems that the batteries could handle the rush in current of 3 x MP2 capacitance.
Now, adding an MPPT 450/200, which also have capacitors, that add to the MP2’s capacitors.
It may well be the case that the batteries could not handle the total capacitance.
To verify it, take out 1-2 MP2 from the circuit and add the 450/200 and see if behaves the same.
That’s exactly my impression too. When the first battery starts up with 3 MP-IIs connected, there’s a noticeable crackling sound – but it’s been working without any problems for 2 years, during which time I’ve only switched it off a maximum of 4 times for updates. I also suspect that the MPPT, with its additional capacity, is now overloading the first battery to start up. I will try this out by removing the fuses from the individual devices. However, this won’t really help me later on, as the system is set up the way it is—everything is hard-wired.
I don’t understand this bit. As @Meine_Energiewende notes, the batteries should be on when the MPPT comes on. In what scenario are the batteries off but the MPPT on?
It doesnt matter if the MPPT or MP is on, their input capacitors are always connected to the DC input, so they get charged once voltage is applied. If the builtin precharge circuit of the BMS is not enough you can use an external one.
The simplest method is to use a pushbutton with a 33ohm 10W (or similar, anything from 20 to 50ohm would do) resistor in series. Push the button, wait a few seconds, then switch the batteries on.
@chrigu I now understand the issue, partially. I thought the capacitors remain charged for as long as the system remains connected? That would make a pre-charge circuit only relevant when the system, for some reason, shuts down? Did I misunderstand that part?
Hello. First of all, thank you very much for the numerous comments. As @chrigu correctly explained, all Victron devices are always connected directly to the Lynx Power with their capacities (even when switched off). When the Pytes V5 batteries are started, each battery starts one after the other. This means that when starting, the first battery sees the full capacity of all connected Victron devices without support from the others. However, since a V5 can already handle up to 200A load for a short time, the inrush current must be higher. I’m really not quite sure how other users deal with this. Precharging via a resistor would certainly be conceivable, but I’ve never read about this in practice. I can probably rule out a defect because the MPPT works in principle, right?
Okay, thank you for the information. As soon as the panels are installed, I will test the sequence. I’m just surprised that I haven’t come across this problem in forums before. But as we all know, you never stop learning.
