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Alistair Warburton avatar image
Alistair Warburton asked

5kVA Multiplus and Welder?

Hi folks,

I have a 5kVA Multiplus, wrapped up in an easy solar package but I dont think that matters in this context.

It is hooked up to a 13.8kWh BYD pack, all installed as it should be.

I am looking for opinions about doing a limited amount of welding, using a modern inverter based welder.

The welder would only require a single 13A supply and would probably only need to be set at about 80%, possibly less, of its maximum output.

Obviously load isnt an issue, but I am interested to know if I should be considering anything else or even if there is some technical reason that some load are not advised.

Thanks,

Al

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Murray van Graan avatar image Murray van Graan commented ·

I have installed a system a few years back, Multiplus 5kva on an off grid site. When we got there a few days later (still a construction site) we found another contractor happily welding the perimeter fence after plugging in his extension cord. He was using an inverter welder. I’m no welding expert, but the system coped just fine with that setup, it was a 200A welder.

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petajoule avatar image
petajoule answered ·

If you say "modern inverter based welder", I assume you mean a DC-welder yes?


Let me get this straight:


You have a 13.8 kWh BYD battery. I assume 48V?

A 5kVA Multiplus.

You intend to use a welder in a way that:


Battery -->DC-->Multiplus-->AC-->Welder-->DC-->weld


You know, there are videos on YouTube where you can weld directly with a battery. ;-)

Or otherwise: https://www.instructables.com/id/Golfcart--Welder/

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klim8skeptic avatar image klim8skeptic ♦ commented ·

"You know, there are videos on YouTube where you can weld directly with a battery"

You can do this, but you would have to know what you are doing.

Problem with stick welding from a battery is that the arc is blown away from the working point by the constant direction of the magnetic field produced.

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petajoule avatar image petajoule klim8skeptic ♦ commented ·

Doesn't that depend on the polarity? And yes, one certainly has to know what they are doing, but it's perfectly feasible.


For sure you need an arc stabilizer, but for that you could take one of the torroidal trafos if you happen to have some spare part around


;-)

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klim8skeptic avatar image klim8skeptic ♦ petajoule commented ·

"Doesn't that depend on the polarity?"

Still the same problem. Reverse the polarity, you reverse the magnetic field. The arc blows the other way.

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Daniël Boekel (Victron Energy Staff) avatar image
Daniël Boekel (Victron Energy Staff) answered ·

Hi @Alistair Warburton

Welding shouldn't have to be a problem for the inverter...

But..

With all welding jobs, no matter on inverter or not: please take precautions on any communication wiring / any sensitive equipment. welding can generate big fluctuating magnetic fields, and fluctuating magnetic fields can generate electricity in coils and wires running close to it.

And when doing tig-welding: HF arc start is a very high voltage, capable of destroying electronic devices close by (laptops....)

Generally, when grounding clamp on welded object is close to weld location, no crazy things should happen, but keep the precautions in mind.

When welding on a vehicle: disconnect battery / batteries to power down as much sensitive devices as possible.
(I've killed a VFD on my boat by welding close to comms cables)

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Alistair Warburton avatar image
Alistair Warburton answered ·

Thanks folks...

Yes 48V and no I didn't think it was particularly important.

Yes DC welder, nothing special.

Interesting comments/links on directly mucking about with batteries to weld, thanks, but way beyond the scope here and certainly nothing I am going to play with on the new BYD kit.

The items to welded are steel columns for a mesanin, so standing on the ground, well away from the inverter, but not connected to the electrical system. At least not until they are installed and bonded. I understand RFI and inductive coupling but I appriciate the heads up.

Essentially I just wanted to make sure that the inverter would cope with the welder. I assumed it would, given the output transformers, but I am no expert in that regard.

Load isn't an issue because the capacitors on the DC side of the welder will deal with striking and the rest of the thing will essentally soft start.

Welding will be MMA... There isn't much, perhaps 3 or 4 of single filet overall, most of it in place.

I can weld, positionally, fairly well, with a good rod, it is simple to organise and the kit is cheaper than MIG.

Al

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