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REC and WS500 User Forum

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controlling CERBO GX with REC BMS hibernate switch?

I've just built a power system for a 45' sloop:

  • 12V @ 560AH LFP battery; REC Active BMS
  • Balmar XT250A alternator controlled by WS500 CAN regulator
  • Victron Multiplus II inverter charger VE.BUS
  • Victron MPPT charge controllers VE.Direct
  • Victron CERBO GX network hub
  • VE.BUS to NMEA2000 gateway to instruments and chart plotter

The CERBO GX is a fabulous device - this is my first use.  With Victron's VRM Portal, I can monitor everything in the system both on the boat and remotely.

Right now, the power to the CERBO GX is controlled by the boat's main Battery switch, so I have to have everything ON if I want CERBO GX data.  The CERBO GX is a very low power device so I want to change this so that power to the CERBO GX is 'switched' with the REC BMS 'hibernate' switch: when the BMS is ON, the CERBO GX is ON, regardless of the position of my main Battery Switch.  That way, when I leave the boat, the Battery Switch is OFF, I can still monitor everything remotely through Victron's VRM Portal.

I believe Victron BMSs have a 'power out' port to do this easily but I don't see the equivalent on the REC Active.  I expect that I have to set up one of the RELAY or OPTO ports to provide CERBO GX power.  If you've done this, please share your configuration.

For anyone setting up a similar system for the first time, once you understand the CERBO GX and VRM Portal, you will want this capability.

If you turn off most of your loads at the DC distribution panel, a few hundred watts of solar should allow you leave your DC electrical system "in service" while you are away.  The only loads in service would be the Victron equipment, BMS, Wifi/Cellular, and bilge pump.   Myself and several buddy boats have systems just like yours and this approach works well.

Hi Rick - thanks for your response.  I'm running things the way you describe right now.  The 'parasitic' load from the BMS/CERBO GX and relays is only 500mA or 6W so the 160W solar array is keeping up, even with the boat on the hard with a plastic cover over it!!  If I leave the Victron Multiplus on, that adds another 50W so I turn that off when I leave the boat.

In a Victron system with a VE.Bus BMS, you power it through the 'load enable' output of the VE.Bus BMS.  So power is provided when the BMS is turned ON and it's cut-off in the event that the battery becomes depleted.

The way my REC-BMS system is configured now, when the main battery switch is OFF, the BMS can be ON but the main contactor (150mA) and the CERBO GX (500 mA) are not energized to limit the parasitic load on the 560AH LFP battery.  Now that I know what the CERBO GX can do, I view it as a critical part of the BMS and I'd like to move the CERBO GX to be powered by the BMS.  I believe I can configure RELAY DCH output as 'load enable' to provide REC BMS controlled power to CERBO GX when main battery switch in the OFF position (disconnect when battery is depleted).  Does that sound right?

I'd like to compare notes in more detail.  E-mail me at steve@imcontracting.ca and I'll send you my system schematic.

Thanks again.

Hey Steve,

Your email kicks back as not found but you can send me your wiring diagram here.

Its an interesting design consideration,



Hi Rick - thanks for your reply.  Sorry, e-mail is steve@imlcontracting.ca.

I'll send system schematic shortly

Got the drawing.  Nice work!

I like your idea of using the the second relay as your interlock to power your mission critical low power loads like the Cerbo direct from the battery pack.  By default it should be set up to disconnect loads on a low voltage so it is likely already configured to work for your application.  And if you set it to trip around 2.9 volts it will give you low voltage cutout protection for those loads as well.

Please let us know how this works out for you.

Oh, I also want to do this, but I have a system with a REC Q BMS already in service. Can that be setup to do it as well? I guess the REC WiFi module would also fit into this.

Hey Adam,

If your opto output is not being used you should be able to add a small interposing relay and set it as a low voltage cutout for these loads.   By default it is set to disable non-smart inverters at 3.6 volts but I recall something that Tine mentioned about being able to use it for low voltage cutout as well, but I could be wrong.  I will copy head office on this one to get clarification.

Tine, is it possible to use the Opto output on a Q-SI Series BMS for low voltage load disable?





From Tine at REC BMS head office:

It is programmed as a charge control, but we can custom re-program it for a small fee of 25€.