question

chrichri avatar image
chrichri asked

Battery switched off: Grid fuse blows when Multi Plus powers on

I have a severe problem.

Multi Plus II in combination with Cerbo GX and Plyontech 2000C

Case:

Grid Power lost, MultiPlus 2 continues running on inverter mode, Multi Plus switches off due to low charge state, Cerbo GX still continues to drain Battery, Plyontech battery finally switches off into safe mode.

Once a time (for example one month later):

Grid Power gets back on:

Battery is off ! Multi Plus starts up and Grid fuse blows. It is a 10A and I cant change it because its the grid Supply at the harbour.

How can I avoid this?

Multiplus-II
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3 Answers
Jason - UK avatar image
Jason - UK answered ·

@chrichri When you turn on the Multiplus, it pulls a lot of power to initially charger the capacitors. I have the same issue at home with my Multiplus II 5kVa GX tripping a 63amp MCB. My solution (albeit not the best solution) is to keep resetting the breaker, each time I'm getting a little more charge into the Multiplus capacitors, normally after 3 resets, the breaker doesn't trip. That's the problem when the batteries go so flat they cant keep the inverter powered because the inrush form AC is too much for most MCB;s. Best solution is solar panel, even just the one on a MPPT to the batteries. Helps maintain the minimum voltage needed to power the Multiplus


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chrichri avatar image
chrichri answered ·

Hi, Ok, there is the way to reset the fuse, but I'm not there to do it in this case.

Concerning the MPPT, exactly this is the additional problem.

I explain: My first idea was to simply put a relais on the 48V side. If the relay is off the remote of the Multi Plus is off and will never start up. So, no fuse problem anymore.

But then I had the great idea to add a MPPT to the system. In a rare case that the battery switches off, the MPPT still puts 48 to 50 Volt . The relay will be on, the grid comes and fuse blows.

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Jason - UK avatar image Jason - UK commented ·
@chrichri so if the relay makes the Multiplus’off’ by breaking the DC connection, what keeps the capacitors charged? You would be better off using the relay to control a aux2 connection and set up an assistant to stop the inverter if Aux2 Vdc drops below a set value, in short, relay switches from NC to open, breaks signal therefore dropping to 0Vdc, and stops inverter by using relay control assistant. That way you’ll keep the inverter live and therefore prevent that inrush of current wach time you then turn the unit back on.

What Multiplus do you have because 10A appears very low breaker capacity to have on the ACin. I have a 63Amp MCB on the supply to my 5kva Multiplus and even that trips if i try and power up the Multiplus on AC before Dc and the unit has been off for a while. Obviously im grid connected.

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chrichri avatar image
chrichri answered ·

Hi, thanks for your reply.

First, the MCB amperage I can not decide on that. It is depending on the installation at the various harbours. (Inverter on boat).

Second, i'm wondering why in any case this can happen.

Asuming Battery is off. Grid is off. Sun is shining. MPPT has 48V at BATT because sun is shining. (This should have charged the capacitors)

As grid gets on, still the fuse blows.

I think there should be a program in the Multi that at startup slowly charges the capacitors and then gets full on. There is absolutely no reason to put full on emediately. The hardware would allow for that.

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