Brand new Multiplus II 6k5 Dc short in 3 hours lifetime, with no load

[The (Paco)]

Hi. One week ago I was installing a brand new Multiplus 48 II 6K5, but not connected yet to the house electric system, because I want it to work in AC Coupling with a Gen 24 fronius, and to do that, first of all I need to upgrade the electrical pannel. So once installed, the batteries are connected and the inverter works fine, 230Vac out, and 0,6Amps DC with nothing connected on AC out1 or AC out 2. Yesterday we continue, to include the CERBO and set up the system, but the two (brand new too) Dyness DL5.0C PRO were at 27% and decided to connect the AC IN in order to charge, and works fine as i expected. First with a charge current limitation of 10Amps, and then to 20Amps because I wanted to stay on the gen24 production at the moment. Well, I did try to disconnect AC In and connect again, to restart charging (it works OK), and do the same but with the (1-0-II) Switch, and it did work well too. So yesterday ends with the batteries at 37% and all the night the inverter had 48V pressence, but stopped on the (0) switch possition, and without AC IN. No power consumption from the inverter, but the CERBO.

Today when the GEN24 was producing enough energy, with no AC IN yet, 37% batteries and I pressed the switch to (I) , the show beggins. CERBO goes OFF inmediately, strong noise and alarm from the batteries. The BMS was protecting and retry every x seconds. Open fuses from booth batteries, and the next retry they work fine. I did open the CERBO fuse (I wan not draw current), close the Precharge circuit, and measure at the VICTRON DC input, and the voltage was not increasing as the capacitors bank charges, because it is a shortcircuit.

I was in shock, because this inverter had no the oportunity to work, today I was planning to test it with a real load when I had the batteries fully charged, but..

This is the schematic. I always put individual protection on the battery side, so you can see two fuses instead of one.

When I first connected AC In to charge Batteries and passing from 10A to 20 Amps charge.

The VICTRON electrical pannel it’s not connected yet. there is a By-Pass and the inverter output protection.

The batteries.

I’m still with the pocker face.. Anybody has experienced some like this? The inverter is on the box, waiting to do a dealer call next week.

Thanks

[nickdb (Nick)]

Am I seeing it correctly- your precharge circuit appears to be wired across the positive and negative battery terminals?

Never a good idea to use connection points as busbars.

[mac]

@The

Today when the GEN24 was producing enough energy, with no AC IN yet, 37% batteries and I pressed the switch to (I)

Was the fronius on the ac-in or ac-out? Was the grid connected to the AC-in?

[The (Paco)]

Hi Nick.

Those wires you are locking at, are the CERBO supply, and yes, is not the best place to make a connection, but that’s not the question I’m asking for. The pre charge circuit is “by-passing via two paralel resistors with a switch” the main battery fuse holder , else it will not work. The diagram is clear about it.

Thanks.

[The (Paco)]

Hi Mac.

As I said, there is nothing connected to AC Out 1 neither AC Out 2, even when the picture indicates 41w consumption on AC Out. The inverter is not connected excerpt AC In, when I was charging. You can see in the schematic. So we could say the victron is working in paralel with the fronius, but only it was yesterday. Today I had not the oportunity, because the DC short when started the inverter via the I-0-II switch.

Thanks.

[fredvduin (Fredd)]

Are you aware about the recommendations

[chrigu]

The only voltage that was present before starting the MP was 48VDC, and as soon as you flipped the on/off switch it created a short on DC? The 48V was present on the DC input during the whole night without an issue?

[lxonline (LX)]

@The

the voltage was not increasing as the capacitors bank charges

Are you sure your precharge circuit didn’t fail? That would be how i would interpret a lack of voltage rise with a precharge in place.

BTW. The perspective of the picture makes it appear as though there are two wires coming out of the top of the precharge and it looks like they go up to the battery terminals when following them in the picture.

I would expect at least 2 connections on the battery positive terminal side if the cerbo and the precharge was connected there. (Or again the picture is not clear did you stack it on the top of the fuse block as it is in the diagram)

@The

because it is a shortcircuit

Determined how?
Pre charge failed on dc would appear like a shortcut.

[The (Paco)]

Hi Fredd. Thanks for remind me, but this has nothing to do with the problem I have. I don’t want this unit to work at full power, in fact the maximum output I expect from it, is about 3Kw, maybe 3,5Kw. so 35mm2 it’s enough even, the wire lenght it’s less than meter and a half.

Thanks for the help.

[The (Paco)]

Hi LX.

For the pre charge to work, CERBO switch/fuse must be open, else it will be a load drawning current in paralel with capacitors, and it turns into a voltage divider and the bank capacitor will never be charged. The first day tests, confirmed that was enough current with the resistors values i did choose, because the Multi don’t draw any current when the ON switch is set to 0 and so, the capacitors are charged in 15 seconds or the like. How I know it? Just measuring in the DC bolts at the Multi, the internal resistance of digital multimeters are in the Megohms range, so it’s not a problem. . Yesterday it was fine, it works fine, all the night the victron had the battery voltage on it’s DC bolts, it was just this morning putting On, that it blowns. LX If we are looking at the same schematic, there is a positive and negative wires going from the Multi to the CERBO via a switch with fuse. And the Precharge circuit, is an R network Bypassing one of the fuse holders in order to limit the inrush current. May be it’s my fault making the schematic, but I think it is clear.

The pre charge circuit is working fine, the multi has the DC on short circuit, my question was about if anybody experienced this with a brand new unit. I have a 24V 1200W working for 14 years night and day without problem, I have the multiplus II 3000 working without problem. We had the old multis on a TV station working without problem, even under severe storms. That’s why I’m so surprised with that, the maximum current on the DC side was 20Amps yesterday charging battery…

Maybe I’m not explaining well, English is not my best.

Thanks for the help.

[The (Paco)]

Hi Chrigu.

Yes, when I finished to work yesterday I left all connected, but the Multi stopped by the switch. Remember there is no load connected to the AC OUT, so when i started it must begin to invert, because it was nothing connected yet to AC IN.

Thanks.

[mac]

So the GEN24 was not connected to the multiplus at all? Was anything connected to the AC in when you turned the inverter on?

[The (Paco)]

Hi mac.

Nothing was connected, in AC IN, ACOUT 1, AC OUT 2. Just batteries feeding all night long the Multi and the CERBO. As I repeated a lot, The Multi was only AC IN connected yesterday, to charge a bit the batteries that were at 27% and were pushed to 37% cause i wanted wait until today to charge at 100% when the Fronius produces enough energy. At this time of year in a sunny day it produces 38Kwh daily, so why pay if I have it for free.

In my work place, sometimes (it’s not common) we found defective series, In power tubes (TV and radio transmitters, even in transistor series bipolar or FET types), amplifiers, power supplies etc. I Know my Multiplus it’s fried, My question it is just because it is a relatively new model and want to know if they are related cases.

The shortcircuit now is ever present , meanwhile it was not until I start this morning, so It has to be with the inverter cicuitry ( IGBT’s or MosFETS, etc) because when Multi is turned On just with battery voltage present, it starts in inverter mode by default.

Thanks.

[cbr]

How did you measure the short circuit? What is the resistance over the 2 terminals with nothing connected on the MP side? What is the resistance over the 2 terminals on the lugs side?

As I remember when you measure if there is a connection between + and - you will indeed measure a connection because the inverter coil is connected in between them in inverter mode, however this should not be a short circuit but a connection with a reasonable high resistance.

[The (Paco)]

Hi CBR,

When the multi is OFF there is virtually no current drawing, because the control circuitry is OFF, so we can say the only thing or the equivalent circuit of the Multi is a capacitor. No other thing is affecting that, even if you see another two wires connected, because is the CERBO supply, and that is open circuit by a fuse and is not on the circuit.

The first tests, when the inverter was working propperly, the pre charge circuit, or the soft start circuit, or the inrush current limit circuit, the name is not important, limits the charge capacitor on a rate well defined by the resistors (405 Ohms) and the capacity. 15 seconds was enough to the voltage to rise to the battery voltage. So I press Precharge, measure at the lugs and waitt to have the battery voltage, then close the fuses. (with a light bulb it’s easier, but I haven’t got one)

After the fault, there was no more “voltage ramp” when precharge is On, but a flat 1,8mV at my multimeter. 0V if the precharge is OFF.

If we have virtually 0V, it means there is not resistance at the measured point because there is passing aprox 130mA (52V/405 Ohms) and 0V/0,130A= 0 Ohms.

Even if I measure with the multimeter the ressistance between the DC input is a clear and static 0 Ohms. If there was not a problem, you will nottice resistance increasing with time, according to the capacitor charging. voltage rise, lowers multimeter current, so it thinks the ressistance it is rising.

Furthermore, If two 100Ah batteries in parallel beggins to alarm, and make strange noises every time they try to start, and cut …

Thanks for your help.

Today i did call to the dealer, and this week the inverter returns to them.