Offgrid Genset Transfer switch

sodamo · Dec 31, 2024

WinterDeere

Doable I’m sure. I actually have 3 individual AC inverters and they are managed via software. My previous system had 4 120v inverters and the system was smart enough to operate safely as normal 120/240. But as for the gensets, that’s a potential headache I’ll avoid.

ponytug · Jan 1, 2025

@sodamo synchronizing gensets prior to transferring the loads has been done lots of ways. The "old fashioned way" is three light bulbs, and a transfer switch or relay. However, that's just for transfer of power.

There are fairly readily available surplus synchronization switches, and that would be my recommendation.

If you want to run two generators, especially two different types or capacity generators, it requires specialized control wiring to ensure that the load is shared equitably and the frequency is kept constant. To do that you need to get pretty deep into electronics, power generation, and control theory. That's not exactly home brew in my book.

Personally, I would rather have the power drop for a few seconds while I flipped a switch rather than have over voltage / over power event from a botched synchronization. That would be very pricey. I don't maintain critical medical loads or radar that require always on power...

All the best,

Peter

hayden · Jan 1, 2025

Just to be sure I'm clear on your power system, and what you are trying to accomplish...

The FX inverters and EG4 are for charging only. So they have AC input only when powered by one of the generators, and the FXs do not have their inverter output's connected to anything. Is that right?

And your goal is to be able to power either the Radian inverters, or the FX+EG4 from either of the 3 different generators?

How do you want it to behave? Gen start triggered off low battery SOC? When that triggers, do you want a generator to start and connect to each of the charger groups? Or just one, and in what priority order? Or should it rotate through them so they both get exercised?

And what about the generators? Always try to start two of the three? Start based on some priority order, or rotate through them so they all get exercised?

I built a somewhat similar system with two generators. When the batteries drop below 25% SOC, one of two generators starts, warms up, then the AC connects to the inverters/chargers. Either generator can be enabled or disabled, and if both are enabled, one always takes priority running and the other only starts if the first fails.

AC power switching is done using industrial contactors, and it's all controlled by a PLC with custom programming. It took a little work to create it all, but it works great.

sodamo · Jan 1, 2025

Hayden, good understanding.
The Outbacks have Automatic Generator Support built into the Mate module and I can set priorities by Voltage ( 24 hour, 2 hour, 2 minute) or by SOC. Yes, want either to have choice of 2 gensets (manual choice) and my ability to set priority of system via Mate.while they share common battery knowledge, Mate control is separate. Only need to run1 at a time. A bit tricky in that LifePO battery voltage is rather flat. I also have the advantage to control via wifi from anywhere I have internet. Handy when traveling as I can monitor and notify housesitter if need be.

Genesets are propane (house tank), diesel, (10g? tank), gas (5g tank. I could chose by fuel, but all hover around $5/g. Been tempted but never figured cost to run. My system is robust enough that the $ are less concern than my motivation. Of course the propane is auto filled and I usually have diesel and gas on hand.

geteh · Jan 5, 2025

sodamo said:
We have been totally offgrid since 2005. Several systems, several upgrades.
Our current house system is pretty robust:
Totally off grid - Hamakua side, Big Island, Hi

36 Trina 280w & 16 Phono 250w in 48 volt array (fixed) 14080w
12 Hyundai 365w (4380) 18460w total
Radian Inverters GG8048A/GS4048A w GSLCs
4 FM 80 charge controllers
Hub 10.3
FNDC w/3 shunts
Mate 3s
OpticsRE - MMKL - Ninole Hi
15 SimpliPhi 3.8 (57kw) (1125 AH)
14Kw Kohler 14RESA (Propane)
Autostrart

Charging Only
2FX3048T Inverters (no ac output)
Hub 10.3
FNDC. - shared shunt feeds from Radian FNDC
Mate 3s
EG4 Chargeverter
10Kw MEP 803a Military gen (diesel)
Honda EU7000i (gas)
Autostart

Starlink w Eero Pro 6e network for OpticsRE
capcut old version
My upgrades have not been kept up todate as far as geneset transfer switching
I hope to rectify that and document a bit in this thread if anyone cares to follow and/or comment.

I have a 1 Victron MultiPlus 48/5000/70 inverter charger 230 volt (not a MultiPlus 2) passing through a Victron Autotransformer and connected to a main electric panel at 110vt on each side and neutral to the neutral bar in the main panel. We now have a new diesel generator 240 volt floating neutral. I would like to power the main electrical panel through a Blue Seas AC Rotary switch 2 sources to 1 (Main electric panel), 2 position and off 65amp 240volt. The main panel is grounded to earth via large copper Rod. Generator to feed 2 hots and neutral to the panel via switch. Question #1. to keep both sources from having any issue with back feeding through the neutral Gen system and solar system could I switch neutrals in the Rotary switch for both systems and connect neutral to the grounding bar in the main panel? Since we use either the generator which is 12.5kw for big load usage including charging solar batteries through the main panel when required or we go through the solar system via the AC rotary switch and to the panel which is maxed at 5000kw. Never at the same time. Question #2 what would be the best solution for connecting these power sources? We are located on a remote Western Caribbean Island with no grid power so we are the power company.
The original installer has grounded the Solar Autotransformer, Inverter/ Charger and PV breaker panel together at a bar and then to a seperate ground rod which is approx 11' from the main Panel Grounding rod. Suggestions and Advice is greatly appreciated.

hayden · Jan 5, 2025

geteh said:
I have a 1 Victron MultiPlus 48/5000/70 inverter charger 230 volt (not a MultiPlus 2) passing through a Victron Autotransformer and connected to a main electric panel at 110vt on each side and neutral to the neutral bar in the main panel. We now have a new diesel generator 240 volt floating neutral. I would like to power the main electrical panel through a Blue Seas AC Rotary switch 2 sources to 1 (Main electric panel), 2 position and off 65amp 240volt. The main panel is grounded to earth via large copper Rod. Generator to feed 2 hots and neutral to the panel via switch. Question #1. to keep both sources from having any issue with back feeding through the neutral Gen system and solar system could I switch neutrals in the Rotary switch for both systems and connect neutral to the grounding bar in the main panel? Since we use either the generator which is 12.5kw for big load usage including charging solar batteries through the main panel when required or we go through the solar system via the AC rotary switch and to the panel which is maxed at 5000kw. Never at the same time. Question #2 what would be the best solution for connecting these power sources? We are located on a remote Western Caribbean Island with no grid power so we are the power company.
The original installer has grounded the Solar Autotransformer, Inverter/ Charger and PV breaker panel together at a bar and then to a seperate ground rod which is approx 11' from the main Panel Grounding rod. Suggestions and Advice is greatly appreciated.

I think I'll need to see a sketch of this system. I can't really follow your description. Depending on how you use the autotransformer, and how you do your grounding and neutral to ground bonding, you can end up with circulating currents in the system. The Victron autotransformers are particularly prone to this because they are asymmetric, i.e. the two halves of the windings are NOT equal, so one side may be 107V and the other side 115V.

sodamo · Jan 5, 2025

Hard for me to follow as well. My old FX system used an autotransformer to make 240 from the 120 inverters. Would hope Victron has documentation. As I recall all the neutrals and grounds were common.