Grid lost - sudden demand on batteries causes dip

Nee some guidance here please guys as I’m seeing behavior that points to a potential issue and need to know how to ascertain where the problem lies and fix it.

The last 2-3 instances where the grid went down, I got the idea that my batteries (4 x 12 V 200Ah AGMs - bought April 2020) may be faulty, or there is a problem on the inverter. (Victron Multiplus II 3 Kva 48V)

When the grid goes down, we are immediately aware of it as my son’s PC and screen shuts down, and the kitchen light dips.

Now this changeover to the inverter power used to be seamless and one was not even aware that the grid went down.

Why I’m thinking it could be the inverter - the kitchen light is only 2 half meter fluorescent tubes which pretty much draws no current. Why on earth would this light dip? Granted, it is a troublesome light that actually consists of 4 tubes, but when all 4 is replaced, the outer 2 lasts a month and then pops.

Why I’m thinking it could be the batteries is because of the more heavy consumers. We can hear the dip in the aircons (two of them totaling about 1800W - fixed speed types) - this was a separate incident. Also to be noted is that my two fridges is on the same circuit as my son’s PC.

Our old 350W plasma energy consuming monster tv doesn’t even phase when this happens. Its only the aircons, the fluorescent light and PC (750W) we have observed does this.

So this never use to happen and the batteries are basically new being less than a year old.

Is there VRM portal data that one can study to see where the issue lies? Or must load tests be done on the battery bank or even individual batteries?

Where do I begin?

The problematic light.

I’ll start looking at the volts/amps of the batteries, to see if it dips substantially at the time.

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We had a power failure last light at around 20h30. So here are the graphs I found for batteries but don’t suppose these are of any help.

and then this one.

Where do I check for this?

I looked at his data for yesterday and I must admit, I am a bit worried about the battery health. The battery voltage dropped with 4 volts with 800watt load, that is normally the start of a not so good end…


Oh no, that’s bad news. 800 is barely a load. Could be only one of the four batteries I suppose?

I would look at the graph for Battery Voltage and Current, like this one:

Wait, I might be a bit hasty here, please switch off the grid and give it a 2kwh load for a few minutes, I just want to check something.

I’ll switch off at exactly 13h30 in 3 minutes time, and warm something in microwave.

Should I do another one? Boiled a cup of water which took about 2 minutes.

Sorry I am not thinking, please switch your PV off before boiling another cup of coffee. Trying to do too many things at once.

Ok PV off and going again in 5, 4, 3, 2, 1…

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I made a mistake, batteries seems fine…

I saw that sometimes gaming PC’s switch off when the GPU is pulling enough power, the same PC will remain on when the GPU is idle, The flicker/dip in the lights will always be there, as will the aircon that runs slower on inverter. Normally the aircon will run at up to 24? Volts, and when the grid fails the inverter creates its own 230VAC, that 15 volt difference can be heard in fans and aircons. You will clearly hear the difference in speed between Grid and inverter.

Do yourself a big favour, change the tubes to LED…

Remove all wiring inside the fitting and take a live and neutral to one end of the new tubes. The tubes are marked at the end where the wires should be.

Thanks for looking at this Jaco, I really appreciate it.

A new kitchen light has been on the to do list for a few months already, but we couldn’t find the time yet.

Ok this is comforting then that all is still within acceptable parameters. I’m just a little worried about that gaming pc. My son bought it a week ago with savings of the past 6 years. It is quite expensive and would hate to see something blow up there. I suppose I must look at getting it its own small UPS.

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It uses a higher voltage to initially “strike an arc”, to ionize the gas inside the tube (which makes UV, which is converted to light by the phosphorous layer on the tube). Once the arc is struck, it runs at low power levels. If the voltage drops (for a short time), the ionization is lost and it has to strike the arc again. So the lamp is not telling you anything different to the PC.

There is always a small interruption time during changeover. This is typically less than 20ms. There will also be a bit of voltage sag because of the load on the battery, and this is obviously worse when there is a large load on it. But mostly, many appliances don’t like a 20ms dip, and that is the worst-case scenario you get with a Multi. Sometimes it helps to replace the power supply of that particular PC.

Thank you Plonkster, and there I’ve learned something again today with regards to fluorescents.

Not following you with the PC’s PSU.

Do you mean I should replace it with a lower watt unit? This is akin to telling my son that I have to sell the PC as it will interfere with his school work. It will not go down well…

Or a better module? This one is bronze rated.

The PSU inside the computer (I assume it is not a laptop, obviously) has a bunch of capacitors in it, and it is supposed to be able to ride out a momentary dip in supply. This is done deliberately, because cheap UPSes also take about 20ms to switch over.

But the capacitors inside the power supply slowly lose their capabilities over time, mostly because they are slowly cooked by the heat inside the computer, and because PSU makers save money by fitting the cheapest one that will make it through the warranty period.

So over time, the PSU’s ability to ride through a UPS changeover becomes affected. And often just fitting a new one (of the same wattage and quality, or better) restores things to normal.

Much obliged!!!

Thank you so much. This PC is actually secondhand coming from Port Elizabeth and we don’t know how long the previous owner had used it or whether it was overclocked. So you may be onto something here.

I even heard electrical components in a PC starts rusting there within 2-3 years. Eeeek!

Some information on the different PSU versions (Bronze, Gold, etc.)