I have Victron Mp2 and Freedom One 10/8 battery.
When loadshedding starts some of my lights flicker on/off. This does not seem to happen when loadshedding ends.
My PC’s and other electronics stays on and does not seem to be affected.
Should I anyway use a UPS for every PC, or is this power flutter not generally bad for PC’s ?
In my case, when the SOC is high, the light flicker is hardly noticeable.
When the SOC is lower, it is more noticeable.
If there is a big load on the inverter at the time, it is distinct.
It is normal.
PCs have power supplies with large capacitors, you don’t notice anything. as designed.
Lights don’t have that, so you notice the flicker, the 20mS break between Eskom and inverter power, when it switches over.
… in a very non-engineer/scientific explanation.
Let me answer the second part first. Yes, normal that it doesn’t happen when the grid returns. When the grid returns, the Multi can carefully plan the changeover and do it in a manner that causes a very small interruption. It will synchronise it’s frequency and voltage with the grid before switching over, making for a very smooth transition.
When the grid fails, this is not possible. It happens unexpectedly (from the viewpoint of the electronics), and every time is slightly different. If you know a little about AC (alternating current), you have a voltage constantly changing between -325V and +325V (230V is an average), and how things behave is going to be different if the outage occurs at the peak of the wave as opposed to at the zero crossing point.
Also, the Multi doesn’t (in the first millisecond or so) know if this is an outage, or merely a slight dip in the voltage. You don’t want to go disconnecting and reconnecting on every slight dip in the voltage either. It takes a bit of time (think slow motion) to realise, this is a real outage, I need to disconnect the grid and power the load.
During that time, there will be a drop in voltage, and your lights will dim/flicker. Especially incandescent lamps, where the brightness is proportional to the square of the voltage, they show even a small drop in voltage very clearly.
Now with that said, is it bad for the appliances? For most of them… no. Some are even designed to expect it, because most UPSes out there work on the principle that they have 20ms to switch over. The device can “ride through” that 20ms dip.
But, I have heard of very sensitive lab equipment that cannot handle it, and if you have one of those, your only solution is going to be an expensive offline UPS: the kind where there is no switchover and you essentially have an inverter and a charger running at the same time.
Online UPS. 
One can mitigate the changeover on some devices by using cheap/free offline UPS’es, the ones you pick up for free when people throw them away in disgust seeing they cannot handle LS.
Just replace the batts with the cheapest 12v lead acid batts one can find. Or, like I did, DIY ones own small 12/24v Lifepo4 bank and forget about it.
These little UPS’es need to work for less than 20ms at a time. Don’t have the solution for lights though, as I’m not putting lights on a modified sine wave UPS, and Online UPS’es draw too much standby power.
Ugh. I could have sworn it was the other way around. Someone probably went and changed the definition again in the last two decades. Sure, in modern parlance, you want an online UPS.
It used to be called “offline”, because your loads were “off the line”.
Anyway, so it seems online means the inverter is always on-the-line, line-interactive is what a Multi with ESS does, and offline/standby is the cheap kind you buy at your local computer store.
I feel the same way every time a UPS discussion comes up…
Been like that for decades now.
In non-tech terms:
Online means:
AC powers the charger, from AC to DC to power the batts.
The batts power the transformer all the time to supply AC all the time.
100% no break in the power supplied… loads are kept “online”, as the transformer is “online”.
Hence a higher standing load, more losses, like a 2.4kVA APC Online UPS, just sitting there, runs at ±100w with no loads.
You will never see a break in power on like lights.
Always pure sinewave inverters.
Offline
The inverter is actually “offline” all the time, pass-thru the AC, until there is any form of interruption on the AC. Hence much more economical ito standing losses.
Some marketing terms come in like “inline” and all that. As the transformer is “inline” to the AC.
You will see a break in power on like lights.
Tend to be modified/square sine wave inverters.
You get a lot of more marketing jargon to confuse the shiite out of it all.
The key is:
Is the transformer on all the time, or not?
Is the AC pass-thru in normal conditions, or not?
Is the power online all the time, or not?
Let me edit:
The then Online Double Conversion models … Online UPS.
Nice summary:
Thanks, all of that makes a lot of sense. I suppose the “power flutter” that occurs at the start of load shedding is a 20ms dip in power/voltage and not a surge in power.
From an electronics perspective a short power dip is probably potentially less harmful than a power surge…
To mitigate power surges, one has a surge arrestor installed on the main DB.
To protect the main DB … more importantly … to also protect the inverter.
I have a Tripconnect that also has surge-arresting capabilities. I switch off the main DB when the volts drop below 215v (we average 243v) and over 250v. Inverter takes over in any event at wot, 256v.
I did this to protect the house, as the inverter only protects the Critical loads.
What I was asked a while ago by my supplier, was to also install surge protection on the critical loads DB. Why, I asked … it is more for the highveld, for surges from lightning strikes close by, that can cause surges to come from the house, back to the inverter. My inverter basically sits between two surge arrestors.
Pennies on the rand compared to fixing surge damage.