Victron Battery Protect with Inverter?

[George Mitchell]

The solution I came up with is to use a voltage monitoring relay to control a solenoid that shuts down my inverter when the voltage drops to 12 volts by disconnecting its DC power. I also power the solenoid via the inverter so that a low voltage shutoff is permanent until I manually restart the system by momentarily transferring it to grid power. That way the system is not cycling on and off as the panels try to keep up with the load. I also use an automatic transfer switch so that I can run the inverter into the night and at the moment it shuts down, grid power instantly takes its place and the load is not interrupted. I have using this system for several days now and it has worked flawlessly and requires no smartphone or computer interface to program and function. I have a computer background and for some things I prefer mechanical solutions to automated solutions.

 

[George Mitchell]

After working on the solenoid based undervoltage disconnect for over a month, I have finally come up with what appears to be a sustainable solution by moving from DC switching to AC switching on the feed to the power supply. The problem with DC switching is that solenoids are an inductive load and that means an initial inrush of current on activation and a flyback surge on deactivation. This syndrome led to intermittent and eventual permanent contact failure on the sensors. Until that point everything worked flawlessly. My eventual solution was to short out reverse current on the solenoid itself with a flyback diode and protect the DC output of the power supply which is now connected directly to the solenoid with rectifier diodes. I also have added a relay on the load side of the inverter so that the AC load is disconnected simultaneously with the DC supply, with the purpose of protecting the solenoid contacts and protecting the inverter from DC disconnect under load. This has been a real learning experience but now I hopefully have a system that will be both reliable and durable well into the future AND I appreciate all the helpful comments.

 

[George Mitchell]

read the manual for your inverter. My Samlex 2000W sinewave inverter warns to not switch inverter off while under load.

Thanks for that information. Unfortunately I already learned the hard way. I disconected the DC supply to the inverter under load which resulted in a gut wrenching arching sound from the solenoid. It then occurred to me that this was not likely to extend the life of either the solenoid or the inverter. Fortunately those Giandel inverters are pretty tough and internally protected, but I was not about to take any more chances and immediately installed an AC relay connected in parallel with the solenoid and protected by rectifier diodes that simultaneously disconnects the AC load along with the DC supply. No more terrifying complaints from the solenoid since, so everything seems OK now. But again, thank you so much for the warning.

 

[Factory400]

It is not a trivial task to disconnect a high-current DC load by mechanical means.
MOSFETs are the key element for this task, but at a cost so most inverters do not have this.

A few design options for the inverter design:
Expensive load-break rated mechanical DC contactor which is also fairly big. - Can be switched under load)

Inexpensive relay not rated to break a load which is also small - Will self destruct if switched under load.

Hybrid option is to have MOSFET's switch the load on/off then use an inexpensive relay for air-gap disconnect.

 

[George Mitchell]

Thank you for sharing this. In my case my system is 12 volt so I am using a 300 amp rated continuous duty solenoid which I close before engaging the AC load and which then opens simultaneously with removing the AC load with an AC relay in case of under voltage situation. This arrangment seems to be working with no problems. I have had the solenoid engaged for long periods (up to 8 hours) without overheating it. I am permanently limiting the DC load on the solenoid to 140 amps max. I don't want the inverter left active when the load is removed and figuring out how to do it via the remote switch port is more complex than what I can deal with. But I do appreciate your information. I am familiar with MOSFET's as solid state switches but have never worked with them before. I only wish that there were a reasonably priced product on the market that would fill this void such as a hybrid MOSFET/solenoid combination OR some sort of device that would interface with the remote switch port, but I doubt that remote inverter switches are standerdized. In any case I would not want to shut down the DC supply on my inverter under load anyway knowing what I now know.

 

[Oberon]

There's a guy, Ross Freeman, on the Electrodacus forum, who built a circuit to control this type of inverter - it converts an on/off input to a press/release type output. Only turns the inverter off at low battery, needs to be manually turned back on.

Success! SBMS0 control of Push-Button Inverter Power Switch

groups.google.com

I also have a 24V Giandel inverter and I'll be building this circuit to control it. For someone like me who has very little electronics background, it's non-trivial to figure out exactly which components to buy and how to put everything together. But I'm up for a challenge!