I have an Airstream Xe that came equipped with a Cerbo GX. I wired the relay 2 output to a Bosch automotive relay, with built in scrubber and then connected the NO side of the relay to the motorized battery disconnect. I can turn the relay on if the battery disconnect is closed via the existing manual switch or if the disconnect has been recently opened. However, if I try to turn the system on after an overnight, the Cerbo will go into a reboot loop. I thought the relay would protect the Cerbo from interference, but that’s not the case, any suggestions on what I can do to address the issue?
I’m also seeing the same reboot if I close the disconnect using the manual switch and the relay is connected. Pulling the plug to the relay will avoid the reboot.
The use case here is, I want to close the disconnect so that the reefer will start cooling down before I pick up the trailer from storage.
I’m going to try using shielded cabling to the battery disconnect, but not confident that will change anything.
It sounds a bit like a power drop, or fast short circuit during the relay switch. When the Cerbo GX is connected to the same battery, it will react as a short power outage. Did this work ok before, and is the battery in good condition?
You could try to see what happens when you power the Cerbo GX with a different (external) power source.
And maybe a scematic of the relay confiuration you made, would give some extra information.
If you have access to an oscilloscope (handheld scopes are getting very affordable these days), I’d suggest you double, triple check for any issues with back emf spikes originating from the bosch relay. I had a similar issue a while ago with a rPi based automation system that I just couldn’t figure out until I found the secondary (external) was back feeding massive transient voltage spikes to the primary (internal) relay that, even though that internal relay had potential free contacts, still propagated through to the digital interface with the rPi, enough to get it to reboot spontaneously (without permanent damage).
If spikes are indeed the root cause, buy/build a dedicated transient suppression circuit to be wired in between the Cerbo and the External relay.
Or replace the bosch relay with a fully rated solid state relay
Or insert a solid state relay in-between rated only for driving the bosch
But the most elegant solution is likely a dedicated transient suppression circuit.
Batteries are in good condition, and it worked ok before I “improved” the circuit. Batteries are 810Ah of Battleborn lithium and less than a year old. It’s hard to troubleshoot since it’s only repeatable when the RV has been powered off for some period of time. If I try to turn it off then back on, it will work normally, it’s when the power has been off the RV overnight and I power it on the next day that I see the reboots. Doesn’t seem to matter if I turn the power on using the OEM switch or the Cerbo relays, either way it will reboot the Cerbo. Unfortunately, the Cerbo doesn’t allow you to set a power on state for the relay so it will cycle continuously as it loops.
Focussing on the Cerbo GX relay, I can only conclude that it is powering the coil of a secondary relay, nothing to point at there…
If the relay of the Cerbo GX would be overloaded, still then it’s a potential free contact, which at most can burn out, but will not effect the Cerbo GX itself.
I’m still not convinced what the feeding power/voltage towards the Cerbo GX does when switchting. What happends when you pull the relay connector out of the Cerbo GX, does the bootloop stop? And when you activate the relay in the Cerbo GX software/GX Touch screen, with the connector still disconnected?
Where does the Cerbo GX get it’s power from, from the same battery where the relays are connected to? And what voltage do you meassure in the evening when everything works ok, and when you messure the next morging?
The observation that it works OK from one to off to on when rapidly switched but faults if left overnight suggests that what you are seeing may be a transient low voltage due to start up surge current. If you have an inverter then if the input capacitors on the DC side discharge then they have a very high.inrush current. There may be other transient start up loads after an extended power down. Is this possibly affecting the cerbo power supply. Some batteries with built in BMSs can trigger over current protection during start up of inverters, no idea if this could be the case here.
Who knows, maybe it is a scrubber. But seriously, I would not 100% rely on that Bosch relay snubber circuit to be fit for purpose in this specific use case. That Bosch relay was possibly not designed to be driven by a mcu+relay on a single pcb.
As stated before the issue (reboots) seem to point to a local transient spike / EMI issues propagating through the Cerbo relay by electromagnetic coupling. I had that situation myself, it required a specific suppression circuit with multiple components to get rid of it. If I can find it still I’ll upload a picture
But seriously, I would not 100% rely on that Bosch relay snubber circuit to be fit for purpose in this specific use case. That Bosch relay was possibly not designed to be driven by a mcu+relay on a single pcb.