Using Contactor/Relay to connect/disconnect load (inverter)

[WorldwideDave]

Hello and thanks for reading.
I have a tyco (?) brand contactor that I use a Victron Cerbo GX to open and close a contactor.
The negative ground cable of my inverter passes through the contactor (see photo). It works great:


When SOC gets to 10%, I have it breaking the connection between the ground cable, thus killing the inverter, and shutting off the 120V loads the inverter runs (pool pump and heater). I can here the contactor click and kill the power, and then re-connect it once a high SOC returns. It works great.
Today was my first field test.
SOC was at 100% SOC.
Fired up pool equipment.
When the SOC hit 10%, it killed power to the inverter.
SOC climbed back up for a few hours, and at 90% SOC, the contactor connected the inverter back up.
Nothing happened.
My old inverter - a renogy 2000W 12V inverter - would not run the pool pump, let alone run it with the pool heater. The surge was too much for it. I sold it for what I paid, and got a Giandel 2000W 12V inverter, which has been great. It is not programmable, however, and it is also not a victron. But they are $250 USD at amazon right now, and has been a very good inverter for the past year.
But here's the problem - some of you know where this is going...
the giandel has a soft switch on the chassis that you have to press and hold to get the inverter to start.
The inverter also has a remote that came with it - 4 wires on a telephone style cord - that you must also press and hold to get the inverter started.
I thought the inverter was like my renogy, that had an 'on / off / remote' switch. It does not.
So I opened up the remote switch, and here's what I see:



According to chat GPT - which many of you here hate - there is a way to wire it to start up automatically by modifying the cord itself. Some of you have done it - but cannot find that post.
I am using Relay 1 on the Cerbo GX to handle the on/off of the contactor based on SOC.
I have relay 2 free.
If there is a way to either wire something into relay 2, or connect this phone cord to the contactor somehow, or a way to bypass the contactor to get the inverter to turn on and off?
Photo of giandel:

Model is PS-2000SDR. $229 on amazon right now.

Link to manual --> https://www.giandel.com/pages/user-manual-ps-2000sdr

Some screen shots from manual:






I've gazed through the entire Giandel product line and it appears that there is no inverters that have anything but this press and hold switch lately to turn them on and off.

Please advise.
If it turns out I could have done something else vs. wire up a tyco contactor, I'll be fine with that - I have other inverters and batteries and systems I can use the tyco on.

 

[WorldwideDave]

Saw my prior thread in 2024 when I started looking into this; Adam De Lay said he built this, and the advice was to do similar:



That being said, he indicated that when connected to relay 2 he had to manually turn the relay on, wait a few seconds, and then turn it off.

is there a way to do this in the Cerbo GX automatically, like a 5 second relay on then off?

Also confused what the generator helper relay setting is/does and if that could help me here.

Bottom line - should have gone with a victron vs. saving money. Now I'm spending more money and more time for less features. Learning, fun, but getting frustrating.

 

[justgary]

Maybe you can wire a second low-current relay across the bottom two terminals of the connector on the remote board (you can see that the switch goes directly to them). Use small wire, a decent soldering iron, and good flux-core lead solder and it should go well. I suppose you could crack the case on the inverter and do it there if you prefer.

It might be best to delay a few seconds after your main contactor provides DC voltage, then close the relay for one or two seconds. If you do the job right the button will still work also.

 

[WorldwideDave]

As the system is built right now, I will shut down inverter at low SOC but at high SOC the inverter will be connected, but not on, so can't run loads. Update on the project:
Victron Relay: I saw that on the advanced VRM reports that generator runtime was 24 hours. Meaning, the contactor was not flowing current for a total of 24 hours, or about 12 hours per day, for the past 2 days. I didn't like how this looked in reports or when manually stopping and starting, as it was always reversed. I switched the contactor leads through the relay from 'normally closed' to the 'normally open' side, meaning that when there is a low state of charge, it would break the connection in the contactor shutting off the inverter and report it as the generator is off. I know that my inverter is not a generator. However, for reporting purposes, now when it says that the generator is running that means that the inverter is running. I like that better. Makes more sense. I can see generator runtime as how long the inverter was on and inverting vs. the inverter being off.

Pool pump and scheduling problem: The issue I had was that when the inverter is on and running, and a low SOC condition is met, the contactor is shut off and the current stops flowing to the inverter and kills the pump. This is as expected. But when a high SOC is achieved, and the contactor is re-connected and the current flows to the inverter, and I pushed the button to turn on the inverter, the pool pump wouldn't always run. The reason was because the pool pump has really 4 modes it runs on: 1.) off mode; 2.) manual start mode (push button); 3.) automation mode (controlled by expensive Pentair gear), and 4.) schedule mode. To the best of my ability and after reading the manual and asking around online, there was no way to tell the pump to default to turning back on and running the pump. It is a variable speed pump, and is not super basic model, and has 3 built-in schedules you can customize, but there was no "if power comes back on, start the pump" mode. So, I got creative. I created a schedule that starts at midnight and runs for 24 hours at 3100 RPM. That way, when power is restored to the pump, the pump looks at its clock, sees that it is 9 AM or whatever time the SOC is high again, then looks at its own programmed schedules, sees that there is a schedule that started before 9 AM at midnight, and then checks the duration of the schedule (24 hours), sees that the schedule is not completed, and starts running again. Brilliant. The schedule will never run for 24 hours because the batteries will die way before then, so it will always be scheduled to run, and never stop. I am testing this now.

on to the harder problem that I have not solved:

Wiring Giandel: Using Adam de Lay's photo as a guide, I turned off the contactor, killing power to inverter. Then removed the remove display. About 12" down the phone cord (4 wire), I stripped back the insulation and found the 4 wires. I stripped the black and the red and separated them. In VRM I then told the generator to be 'on' meaning connect the contactor and flow juice to my inverter, which turned the inverter on, but the pool pump did not start and had no power because of the soft start button on the side of the inverter. Using the two stripped red and black wires, I touched them together for 2 seconds, then let go, and the inverter clicked on, the pool pump got power, and the schedule ran to start the pump, which is running right now. This is great news, but not done yet.

I saw where someone said to connect these two leads to 'relay 2' on the side of the cerbo GX. Here's the problem I am having:
Is there a way to get relay 2 to turn on and then off seconds later when relay 1 (generator) starts and stops? I don't think there is.
Some rule that says "if high SOC, turn relay 1 on, then wait a few seconds (or a minute - don't care) and turn on relay 2, and when relay 2 is on, shut it off 2 seconds later"? I don't need a rule like that for when there is a low SOC because that just kills power to the inverter completely. Though maybe it would be better to kill the inverter with the soft start button instead.
Another option would be to skip using the contactor all together. I could connect the soft start button wires to the cerbo GX relay 1 instead of relay 2. Then when a low SOC condition is met, I could turn on relay 1 for a few seconds (simulating a button push), then turn relay 1 off. That would be the soft start button push simulation that would put the inverter in the standby mode.
I know that the inverter being in standby mode would still drain the battery some, but at least it would not drain it completely until the BMS cuts off the battery.
Then when high SOC is reached, it would also perform the same action - turn on relay 1 for a few seconds, then turn relay 1 off.
I'm thinking there has to be a way to do this.

 

[ricardocello]

I saw where someone said to connect these two leads to 'relay 2' on the side of the cerbo GX. Here's the problem I am having:
Is there a way to get relay 2 to turn on and then off seconds later when relay 1 (generator) starts and stops? I don't think there is.

Only if you are willing to program under the hood.

NodeRED is a graphical programmers interface that can be installed on the Cerbo, using the "large image".
It probably can be made to do that. And can probably use the SoC condition as well.
I'm not a NodeRED guy, however.

Using MODbusTCP, you can programmatically write a 0 or 1 to Unit Id 100 (System) Address 807.
1 meaning relay #2 is closed, 0 meaning the relay is open.
A Python script could implement your pushbutton for the remote switch.
But you would have to run it somewhere and also read the SoC to trigger it (at address 843).

 

[29597342]

I do something similar but instead of using a 'huge' relay to interrupt the power in/out of my inverters I use a 'small' relay to toggle the on/off switch's on the inverters - which are low voltage/power. My AIMs and SPG have explicit external on/off ports you can plug an RJ45 jack into for this and publish the wiring for this.

 

[WorldwideDave]

There must be another way.
Example: I'm sure an external relay that exists that has a timer on it, momentary contact for a few seconds, then off.
but I don't know that I could get the VRM device to run the relay with two conditions - low SOC and a high SOC - looking into that next. Any tips appreciated, thank you.

 

[455dan]

These little guys have quite a few timer and one shot etc trigger in / outputs and they are about $8 each. Used to be 16 now 32 programming options- very versatile .

Look through the list of functions Dave one of them should/ may get you the fit you need.

Pardon Our Interruption...

 

[ricardocello]

There must be another way.
Example: I'm sure an external relay that exists that has a timer on it, momentary contact for a few seconds, then off.
but I don't know that I could get the VRM device to run the relay with two conditions - low SOC and a high SOC - looking into that next. Any tips appreciated, thank you.

OK, these DIN relay timers are excessively confusing because you have to read and understand the timing diagrams.

Amazon.com

Option F should do what you want (Single Shot).
Set the timer for 10 seconds, 20% to get a 2 second pulse.
You have the Cerbo relay feed the S (switch) input. Turn it on and leave it on.
The DIN mount relay will only stay on for 2 seconds, then turn off. It doesn't matter what the Cerbo input is after that.
Unless you reset it and reactivate it, which will "push the button" again.

There are lots of others on the market that may be cheaper and not have all of these functions.

 

[WorldwideDave]

Is it not possible to use this new functionality?

 

[WorldwideDave]

I just can't find a lot of documentation on this feature. says a 'control signal' and more. I have a hard time believing I'd be the first person to use that feature to push a button via the relay connector for a few seconds. I can find SO LITTLE about this new feature. It also sounds like (?) that if you have a larger quattro or multiplus already connected to an actual generator, you can then use the cerbo to tell the generator to stop/start.
If I had a larger inverter that wasn't a giandel, I wouldn't be trying to get this to work

 

[WorldwideDave]

OK, these DIN relay timers are excessively confusing because you have to read and understand the timing diagrams.

Amazon.com

Option F should do what you want (Single Shot).
Set the timer for 10 seconds, 20% to get a 2 second pulse.
You have the Cerbo relay feed the S (switch) input. Turn it on and leave it on.
The DIN mount relay will only stay on for 2 seconds, then turn off. It doesn't matter what the Cerbo input is after that.
Unless you reset it and reactivate it, which will "push the button" again.

There are lots of others on the market that may be cheaper and not have all of these functions.

Watched video. Option F looks like power is always on, and you press a button (which I would do from the victron relay) and then 5 seconds (adjustable) later, it would 'click' the button (making contact with those 2 wires I have - black and red, which would in turn would turn the inverter on or off.
I think that would possibly work.
would be better if it would work in conjunction with the contactor I already have.
Requires a lot of thinking power that I don't have available right now. Open to suggestions.
Also open to a cheaper option than $35 USD, which, coincidentally, is what I paid for that Tyco contactor through BatteryHookup.com. Retail was over 350 or something crazy.

 

[WorldwideDave]

Saw that ebay link - wow that's so confusing to me. Looks like you run power and ground to the timer itself, then wires from the cerbo GX to that device, then the wires from the inverter (black and red) to tell it what to open and close? It's just not in my wheelhouse - would need to get my uncle from nasa over again to help me with that. Just not an electrical engineer. I want an easy button where there does not seem to be one.
if people who owned giandel and other inverters knew that to get their inverter to turn on and off on a schedule they would need both a 3rd party device and a cerbo GX to get it to work on a schedule, they would likely choose a victron inverter to skip all that nonsense. I know I would have. Usually Sunshine Eggo would have chimed in by now

 

[WorldwideDave]

Oh no - did not work!
I got a low state of charge alarm.
Went out and saw pump was running.
I am not sure if it kept running because the soc cannot turn the relay off or if it’s because I told the generator to manually start which bypasses the soc rule?

 

[WorldwideDave]

I think the issue is that I want the rule and the relay and the contractor to work the exact opposite way that it is working right now. Right now, when power is applied to the contactor, it finishes the circuitry on the negative inverter cable which enables the inverter to have electrons flowing to it.
I think I want the default to be that when the generator function of the Victron sees that the low state of charge has been met that it applies power to the relay, which then disconnects my inverter.
For now, I have it reverted to how it was yesterday, which means the reports will all be kind of backwards. When it says the generator is on, I will have to remember that that means that the inverter is disconnected.

I feel like I am both stupid close, and stupid. There’s gotta be a way to make this work.

 

[WorldwideDave]

OK, thinking outside of the box now…
Instead of the relaying for a generator, I’m telling the system to use the relay as an alarm. IOK, thinking outside of the box now…
Instead of the relaying for a generator, I’m telling the system to use the relay as a alarm. I have set it to be normally open.
Then using Victron connect, I jumped over to my smart shunt and set an alarm condition that says if it reaches 10% state of charge, to set off an alarm. Wouldn’t reaches 90% to shut off the alarm. Let’s see what that does.

 

[Brucey]

I have a tyco (?) brand contactor that I use a Victron Cerbo GX to open and close a contactor.
The negative ground cable of my inverter passes through the contactor (see photo). It works great

Just be aware you may want to put a pre charge circuit in there to use in conjunction with the contactor. Maybe only needed for higher voltages?

 

[WorldwideDave]

The good thing is it seems to be working with the 'alarm' function.
however setting an alarm from low SOC of 10% to 90% SOC means that the alarm stays on (and the inverter off) until it reaches 90% soc, which may be 24 hours later depending on when it goes off and what the clouds are doing, etc.
The other bad thing is that a silence alarm button appears taunting me to click it. Here's the deal, though...if you click silence alarm, the relay changes position, thus both clearing the alarm and reconnecting the inverter.

 

[WorldwideDave]

Just be aware you may want to put a pre charge circuit in there to use in conjunction with the contactor. Maybe only needed for higher voltages?

the pump has a soft start.
the inverter has a soft start.
it is only disconnected usually from 4 PM to 10 AM, about 18 hours.
It is a cheapy inverter at $230 USD on amazon right now. If it fries, well, victron is my next purchase.
If I add more batteries, the runtime will be longer, and the alarm enabling may be reduced. Charge times may increase, however.
Either way, if you're following along, you'd see that I still haven't figured out how to toggle the wires for the inverter on and off to get it to start even if the contactor is there re-enabling the ground connection to the inverter.
I'd like to solve that without having to buy something, or without having to go to NodeRed or Solar Assistant or something.
Happy to throw money at the problem for $20 that eBay contraption looks interesting.
Just can't wrap my brain around that right now.
Also would like to find a way to use the 'generator' function vs an alarm to enable contactor. I want to look at reports and see 'generator runtime' and have that be the 'inverter' runtime in my head. Not inverter downtime/offline time.
Also would be GREAT if they added some of the features - even if just 'alarm' - to the two Relay 2 options there are today (manual + temperature).
I'm doing all this because of a few reasons:
1.) don't want the battery BMS to be the reason the pool pump shuts off. BMS should be the absolutely last place anything shuts down in my system. MPPTs won't love that. I think BMS low voltage is set to 10 VDC
2.) don't want the inverter undervoltage protection to be the reason why the pool pump shuts off. That is set to 11 VDC I believe. It has shut off many times.
3.) want to be able to manually shut off pool pump from afar. If someone tells me there's an issue, or I'm abroad, or pool cleaner is there and needs help understanding the system, i can just shut it off via VRM.
4.) I want the system to be smarter. If the SOC hits 10%, I want to ensure the inverter shuts down. Other small DC loads will keep going, but after about 5 days of that and idle consumption, the battery will hit low voltage disconnect. With inverter off I will extend this amount of time.
5.) I have a contactor - might as well play with it.
6.) I have a cerbo with 2 relays - might as well learn hands-on something new fun and mildly exciting
7.) best to play on this smaller 2000W 12V system to build confidence before I take on a 15,000W 48V system
8.) hobbies like this make me want to stay home and tinker vs. go out to clubs/bars/etc.