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REC and WS500 User Forum

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Backup Alternator Protection?

I'm getting ready to install the final pieces of my system which includes REC Active BMS with WS500 regulating a Balmar XT-250 alternator directly charging my 840ah of LiFePo. My starter and thruster batteries are charged with DC-DC chargers fed off the main house bank.

Recently, while finalizing the install of our Victron MP3k Inverter/Charger I noticed the BMS was disconnecting the charge bus Victron as the battery was reaching capacity - which was understandable as that is what is supposed to do. Though I did thought the BMS would communicate via CANbus to potentially control the MP3k to lower incoming charge so the battery could be topped off rather than just disconnected from the charger entirely and abruptly.

This behavior raises concerns as the Balmar Alternator will likely be kicking out 2-3 times the charge rate (150-225a) as the MP3k (50-90a), so I imagine this large incoming current could cause the BMS to kick even earlier as the batteries get to capacity. I understand the WS500 + BMS should do a controlled slow down/shut down of the alternator, but I'm concerned what will happen if the BMS just disconnects abruptly - what will protect the alternator.

What is recommended here?

  • Balmar Alternator Protection module?
  • Balmar Transient Spike Protector?
  • Sterling Alternator Protection?

 

Your big variable here is your alternator.  They can not be expected to act instantaneously like a battery charger, or even charge at a specific current, especially as you get near the bottom of the range.  A protection device is highly recommended.  There is a separate thread here on the forum where we go into quite a bit of detail on it and many other good threads on the net as well, but it basically comes down to the fact there is no one single fits all solution and you need to see what best fits your systems design parameters.

Quote from Jamie Reece on March 20, 2022, 9:07 pm

Recently, while finalizing the install of our Victron MP3k Inverter/Charger I noticed the BMS was disconnecting the charge bus Victron as the battery was reaching capacity - which was understandable as that is what is supposed to do. Though I did thought the BMS would communicate via CANbus to potentially control the MP3k to lower incoming charge so the battery could be topped off rather than just disconnected from the charger entirely and abruptly.

AFAIK, this only happens if you have a GX device. In my system, I have a Cerbo GX which listens to the REC BMS and then controls the charge rate of the MultiPlus based on what is being asked. The rate then slowly goes down all the way to zero and the contactor never opens.

Thanks Adam. I have the Cerbo as well, but it doesn't seem to work in the manner you describe. I'll have to go back and check my setup.

 

Do you have any guides on how to setup the REC with the Cerbo?

There is a REC & Victron guide, somewhere.

 

Does the Cerbo GX see the BMS and it's various data outputs?

DVCC must be enabled, as well.

i use a sterling alternator protection device as a backup in case this happens

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