Sparking when connecting Venus GX

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Enrico Zanolin asked Dec 29, '19

Sparking when connecting Venus GX

My system (MultiPlus II 48V 5KVA + Venus GX ) recently stopped reporting stats and was no longer reachable which meant I had to restart it.

In my setup the Venus is plugged directly to the batteries (as seems to be recommended) which makes power cycling it a bit tricky. The easiest way for me to do this was to disconnect the the M8 eyelet connector from the MultiPlus DC input where it is installed. This lead to fairly heavy sparking on reconnection.

As far as I am concerned, the Venus does not have a huge power draw and I cant imagine there is a large inrush current when connecting it. During installation I actually connected the power by plugging the green terminal block connector into the Venus. This caused a spark at the terminal block and a very significant spot weld. The practical upshot is that the block connector is no longer removable due to the spot weld which is why I have to disconnect on the MultiPlus side.

Is this kind of sparking to be expected? The fuse is not blown and the Venus seems to be working fine after the restart. If the sparking is expected can someone explain why this is the case?

The Venus is essentially an off the shelf consumer grade RPI thingamajig (beaglebone I think) that has been hardened and extended. As far as I can tell it has its own power supply to convert the wide range input voltage down to something the board can use, and has an add-on board for all the Victron communications busses. Finally the whole thing is conformally coated to protect it (nice!). I mention all of this because similar consumer grade product generally do not spark like this and I was pretty disappointed by the spot welded terminal.

I am just trying to understand if I am possibly doing something wrong or if there is some technical explanation that explains what I am observing.

Thank you.

Venus GX - VGX installation

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kai ♦ commented · Dec 30, 2019 at 01:48 PM

It does sound like capacitor inrush as others have said. The welding action is highly dependent on the electrical conditions and the contact physics. I'd guess that you got unlucky.

As you indicated for the 48v DC MP input, the inrush for any other device can also be managed with a limiting resistor (and/or a switch that is suitably rated).

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Daniël Boekel (Victron Energy Staff) answered · Dec 30, 2019 at 11:10 AM

Hi @Enrico Zanolin

I can confirm there is a little spark when connecting, due to a (small) capacitor on the input, but have not seen a 'big spark' that welds the connector. do you still have the 3.15A fuse inline with the input?

I'd check the current use of the unit once connected, should be way below 0,1A on a 48v system.

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Enrico Zanolin commented · Dec 30, 2019 at 12:48 PM

Thank you for your response, yes the fuse is currently inline and working. Perhaps I am not used to the amount of sparking to expect at these voltages.

My experience was definitely colored when I connected the batteries to the MultiPlus for the first time which had a large inrush draw to fill the MultiPlus capacitors and next time I am going to use a current limiting resistor for the initial hookup which will hopefully avoid it.

Perhaps I am being overly paranoid, its good to know that some sparking is to be expected.

Thank you

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Daniël Boekel (Victron Energy Staff) ♦♦ Enrico Zanolin commented · Dec 30, 2019 at 01:16 PM

What I do when connecting a Multi: turn it on so it charges the DC bus, than close battery breaker. You'll get a low battery warning, but it will start 'charging'

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Answer 1 · 2019-12-30T00:59:41Z

JohnC answered · Dec 30, 2019 at 12:59 AM

H Enrico. This sparking is typical of a Multi 'filling it's caps'. With 48V especially, it can be frightening when unexpected, and can indeed damage terminal threads and lead to the stainless steel galling.

It's part of the reason why a rugged battery isolator is recommended. Rugged because the sparking will still happen within the isolator and may even cause damage in there too if done regularly.

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Warwick Bruce Chapman commented · Dec 30, 2019 at 04:05 AM

But how does connecting the Venus GX draw current to fill the multi caps?

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