Mitigating Mini-Dips in Off-Grid System

[jestermaroc]

We are living on an off-grid property in Zambia and have recently finished our solar installation, and its running great! We are looking for a solution to help mitigate power dips due to motors starting. There are a couple of boreholes on the property which we plan to run with our solar system, but we do not want to damage our hybrid inverters by subjecting them to constant power dips. We also have a workshop where we are using power tools like grinders and welders. We are seeing significant micro-dips (230 down to 205v) on our isolated grid when powering on pumps, grinders, and a welder.

Would anyone be able to advise what we can install to deal with micro-dips? I have emailed a couple of electrical companies in South Africa with a request for a solution and none of them have responded. What I have seen online is capacitor banks of some sort, but all DIY guides have been focused on lead-acid systems and the dips between the battery bank and the inverters on the DC side. We are hoping to find a solution to install on the AC side.

For reference, our solar installation is 3x Growatt 5kw inverters in parallel, providing a single 230v phase for a combined capacity of 15kw, and these are connected to a bank of 3x Rosen Lithium 7.2kw (150ah) batteries for a total of 21.6kw installed storage.

 

[timselectric]

Does this dip also happen on the DC side?
If so, that's where the issue is. And where a solution should be applied.
Could be as simple as increasing battery capacity.

 

[jestermaroc]

We replaced the 6mm wire supplying the workshop with 16mm wire, and the voltage drop has improved significantly. Its now dropping from 230v to around 220v at the initial stages of welding. I feel this is an acceptable dip.

I did go and measure the DC side, and there is a 0.1v dip (49.9v to 49.8v).

 

[Mattb4]

High starting current loads put a heavy strain on any power system to maintain voltage. The old lights dimming effect can be seen in many on grid setups when you start a big load. It helps to oversize all conductors and connectors as you report.

 

[toms]

I have a setup used to power inductive loads (bore pump and desalination plant, as well as heat pump A/C) and i use maxwell supercaps on the DC side to eliminate voltage sag to the inverter. This has been working well.

 

[Phil.g00]

I have a setup used to power inductive loads (bore pump and desalination plant, as well as heat pump A/C) and i use maxwell supercaps on the DC side to eliminate voltage sag to the inverter. This has been working well.

So is that just a bunch of huge capacitors across the battery?
They look like they are series instead of parallel; what was the rationale behind that?

 

[toms]

There is a 48 and 16V supercap in series to cover the voltage range of a 48V LiFePO4 pack.

The supercap is in parallel with the battery, and eliminates voltage sag to the inverter.