Cerbo-S-GX, SOC for relay heater control

DIY
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1

I have a Cerbo-S-GX, and have the relay connected to the “remote on/off switch” on a Smart Battery Protect which is connected to a heater. I like to run the heater when the Battery SOC is >90% in order to warm up and dry out my engine compartment and reduce condensation.

I essentially need the same GX Relay control as for the Generator Start/Stop, but inverted. I want the relay to close when SOC is higher than 90% (starting the heater), and to open when Battery SOC is lower than 85% (turning the heater off), or something like that.

Is there a way to do this? I can’t see how. I could also use Voltage, or Temperature, if those are options, but prefer SOC if possible.

Thank you!

2

If you are not using the generator control you could always use that to start/stop a generator and use the opposite contacts on the relay (swap NO for NC or vise versa) to get the heater running when the generator would be stopped. The other alternative would be to install the Large Venus OS image and use node red to drive the relay. There is a node red category if you want to explore this further / ask help etc.

3

Thanks for the quick reply – didn’t think about switching the contacts; that should work for me. Cheers!

4

I’ve tried this, and it sort of works, but something isn’t quite right.

I switched the contacts, so that the Smart Battery Protect remote control is plugged into the NO and Common, so that the heater control logic is:

  • “Start generator” when SOC is lower than 90%
    • [Normally Open] Relay ON = Heater OFF
  • “Stop generator” when Battery SOC is higher than 99%
    • [Normally Open] Relay OFF = Heater ON

If I have “Autostart" enabled, then the heater runs for a short time, then stops, but it restarts again before the SOC recovers. If I have “autostart” disabled, the heater never runs.

Note, I have a thermal cutoff switch on the Smart Battery Protect remote circuit as well, so that if the temperature in the engine compartment gets above a certain level, the heater is turned off even if the SOC is still above 90%. This works and cuts off the heater after about 10 minutes; I just want the SOC to recover fully before it starts again.

Any ideas what I’m doing wrong?

5

What sounds to be happening is the SOC gets to 99%, starts the heater, the thermal switch shuts the heater off after 10 mins while the SOC is between 90% and 99%. In this case the relay remains on so when tje thermal breaker cools the heater restarts. The thermal breaker operating will not affect the relay or generator control

I suggest you trial this without the thermal breaker to see if the heater cycles properly between your required SOC to prove the generator start stop works. Perhaps set start and stop SOC to 95% and 98% to get smaller cycles for evaluation only.

6

I think you’re probably right, and good ideas, I’ll try that.

It’s still mysterious to me that the relay wouldn’t flip back after the SOC drops below 90; that happens and it keeps cycling, was down to 70% yesterday.

In any case I’ll try your suggestion and report back. Thank you!

7

May be I am wrong then in my assumption if it went below 70% SOC. This seems odd because below 90%, the NO terminals should close and the NC terminal should open, stopping the heater.

Do you have the Smart Battery Protect set to operate in lithium mode, which is the mode where the remote input controls the device totally, no interference from voltage settings.