Off-grid system - currently have generator to start when SOC is below 30% and stop when SOC goes above 75%. However, recently had a total shut down of the batteries during a bms firmware update where the generator did not start. I looked at the Cerbo settings and only see SOC autostart enabled. Which additional condition should I enable so if there is total loss of AC from either the batteries or the PV inverter that will start the generator?
does the generator has its own battery?
I think you need to program this condition, eighter via "Assistants" in your charger / inverter or via Node-Red
the gen has its own battery to start it.
I was just thinking about this - but if the batteries were to go offline and shut down the system, including the cerbo gx, how would the generator know of the power failure and be triggered to start from the gx?
To cover a system shutdown you would need an external relay fed from the same DC supply as the Cerbo that it held in the open position when there is battery voltage. If that voltage is not present, the relay would close and trigger the generator.
This would be wired in parallel to any trigger from the cerbo for low SOC start.
This would however mean that the relay is drawing power 24/7, even if only a few mA.
Are there any products recommended for this solution? The cerbo is powered by the bms so it does not have independent power.
Why not just use a fail-safe relay contact, IE relay on inhibits generator start, you could always add a manual switch to the circuit to inhibit manually.
Doing that, the default condition for the generator is running so if all control, at the Victron end, is lost the thing will just run... If you add a motorized changeover, loads to Gen / Inverter, and inhibit that auto function with a second fail safe relay on the GX, when the GX is up, the changeover will not operate but if the GX is down, or you manually ask for an inverter bypass, the changeover will see the Gen AC and connect the loads to it.
Simple, cheap, easy!
Just power the cerbo from the generator battery
The spec sheet states 8-70V, 2.8W at 12V without the screen, so if you want an always on system then power it from all batteries via a bunch of diodes. Better yet, give it a battery of its own, a cheap 12V or 24V Gel, which you could just float, from everywhere, via diodes, and a boost converter, would be ideal as Lead Acid chemistry doesn't need a charging algorithm unless you want to charge quickly, or at least not slowly. Almost all power backup systems just keep the battery on permanent float, think alarm panels and emergency lights...
I have my home automation system, a Raspberry Pi, all my network equipment, including the 4G connection to the world, and the Cerbo, running from my 24V pack which is set, in the Victron kit to shut down the inverter at 95% DOD, ish. The end result is if everything fails and the system go's dark, from a power point of view, I still have circa 24 Hrs of connectivity, to trouble shoot, even when that means using VRM as a way to see what is going on.
BTW I don't normally cycle to 95% DOD, that is just the point at which any remaining stored energy will only be used to keep the controls/comms up, pick whatever point at which you are comfortable, the batteries internal BMS, and/or low voltage cutoff in the critical circuits PSU, will protect the cells. The PSU I use and a diode for 2 power sources
Appreciate all the suggestions, but I am not a electrical engineer so I am looking for off the shelf products that can solve this in the simplest terms. If I power the cerbo by the gen battery, what will charge the battery when it gets low (assuming the gen doesnt operate often). Other than setting the gen to auto run monthly etc, I fear the battery will die powering the cerbo and screen - although that sounds like the simplest method and the gen is behind the wall the cerbo is mounted on.
The power requirements are modest but you are correct you would need to have a maintenance charge hooked up to the Gen battery, although arguably you should be doing that anyway.
The Cerbo requires a minimum of 8V so it is possible that cranking a heavy cold generator would brown it out. In general using a cranking battery to supply a control system is something you would want to avoid if you can. Yes I know literally every car, and almost all generators, use the same battery for control and cranking but they all contain kit designed to cope with the voltage swings.
If by 'this' you mean your original question, IE make the generator start if the Cerbo is down, see my first answer it cant get any simpler than that and you already have everything you need to set it up, with the possible exceptions of an additional switch and or AC changeover, if you decide to add them.
Modifying the Cerbo power supply circuit, and doing that with an off the shelf unit as oppose to a couple of diodes...
Buy a small, or even large, battery, literally any chemistry, power the Cerbo with it and add a maintenance charger. Victron do a range of DC-DC chargers designed to, amongst other things, maintain a vehicle battery from a system battery, you would essentially be creating a UPS for your Cerbo, and you should still probably rewire the generator control to make it run by default.
I already have a UPC in the tech space powering CCTV - so plugging the cerbo into this would be easy. Will investigate further... TIA
