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Rec BMS charge and discharge disable


Thanks for putting this forum up. I'm interested in the REC BMS for a future boat install using a Victron and Wakespeed based system. Understand that the primary charge/discharge control will be via Canbus to the inverter and regulators.

From reviewing the Rec BMS documentation, I'm a bit confused as it only shows a single relay to shut-down the inverter/charger.

Can I set up the Rec BMS with one of the guessing MOSFET switches be charge disable and the other be a discharge disable?  In other words separately control charging and discharging similar to other BMS solutions out there? I would like to control some non CAN controlled chargers and load sources via a few Victron battery connects.







Hi Robin,

Early on in the BMS era we needed to have separate UV and OV circuits to protect our systems.  With the advent of "Smart devices" using CANBus it becomes less of an issue.

As you mention the devices talk with each other and the BMS effectively acts as the Master battery protection device on your network.  It will throttle back your WS500s, your MPPTs and your Victron or SMA inverter and chargers to maintain a safe system, with a single disconnect as a fail-safe mechanical disconnect.  In addition the opto output can be used to disable the charger on an older charging device.  You can even add an interposing relay and have it shut down your alternator field, battery charger, MPPT, wind, etc but keep in mind these methods are old binary control technology and do not lend themselves to a nicely regulated self compensating control system.

That all being said, if you would like to split your charge and load buses that is fine too.  You just need a quick firmware swap that can be uploaded from either your wifi module or PC software.  Just send us a quick email with your order number and BMS serial number and we will have head office set you up.

Hope this helps!!

Robin Wessel has reacted to this post.
Robin Wessel

Thanks from user Ben, who reminded me that with the WS500, unlike older external regulators, you would disable it or remove its power instead of using the field wire.

Hello, I'm looking at the Rec Q BMS for my existing 24V system in my van.  The title of this thread just mentions REC but it is in the REC Q subforum so I hope this is the right place.

I have a 24V DIY bank, Victron equipment including a 24V Multiplus, and am planning to add the 24V Wakespeed/Nations alternator.  I am trying to understand the non-CAN charge/discharge control capability of the REC Q BMS.

I know I could control my Multiplus, MPPT, and the Wakespeed via CAN.  However, I also have DC loads controlled by a Victron BatteryProtect, and a Victron DC-DC charger--neither of which support CAN.  Thus, I also need binary charge and discharge control, in addition to CAN.

Looking at the REC Q manual, I see only one charge relay control, no discharge relay and no optocouplers--unlike the REC Active BMS.  Rick's response above speaks to binary control of chargers--but not control of discharging into DC loads.  Is there a way that I can control both my non-CAN DC loads and my non-CAN DC-DC charger with the REC Q BMS?

The Q Series actually includes an Opto relay for interlocking manually with a non CAN charging device.  On a rise in cell voltage the BMS first toggles the opto relay, then if the voltage continues to rise it then disables the main contactor on either an OV or UV condition.  I have attached a sketch similar to what you are describing for your reference.  There are also more PDF examples as well as diagrams.net XML drawing files and libraries available here.

REC North America Downloads link:    https://rec-bms-na.com/downloads/

And we have created a 20 minute tutorial on how to create your own drawings using our symbols libraries and the free online tool diagrams.net

Tutorials link:  https://rec-bms-na.com/tutorials/

Uploaded files:
  • REC-Q-Series-BMS-with-Victron-and-WS500-Diagram-REC-Q-24V-with-PreCharge.jpg

Thanks for the reply.  But again this just addresses charge control, but not discharge control.  Is there a way to control my Victron BatteryProtect to disable DC loads if the battery gets too low?  I need both binary charge control (based on OV) for my DC-DC, and also binary discharge control (based on UV) for my DC loads.

I think that REC may have a solution for that later this year.  I will post something when I get more details.

Thanks, please do.  What would be ideal is a REC Active BMS that supported 8s.  The Active BMS is a nice unit and seems well suited for the needs of vans, RVs and boats with a mix of charging sources and loads.  But unfortunately I'm already at 24V and can't change at this point.

Rick-admin has reacted to this post.


Wondering if there have been any updates on this.

Thank you!

There is another thread similar to this one where they want to use the SI-Q BMS opto output for discharge limit disable of loads, in this case to isolate the Cerbo and only have it disabled on a low voltage  We are just waiting for feedback from REC head office on how to do it.


I have setup multiply REC Q BMS 24V system with one discharge relay and one charge relay.

REC can supply you from a firmware that the opto output controls the Charge relay.
The relay output controls the Discharge(load).

In general the setup is describe in the RECmanual, NON Victron setup.

Ask REC for firmware, Qbms, ""separated relay version"" version including Victron CAN support.

You can not download this from there website, because for the Qbms, the firmware has the serialnumber for your bms in it.

This means I can not share the firmware I use.

But your dealer can supply you from this firmware, or ask REC directly.

On the opto output I use a SSR to control the main relay.




Eran Rundstein has reacted to this post.
Eran Rundstein

Nice, thank you. I will contact them when closer to doing my install.