REC Q BMS wiring when adding new batteries

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ThirdEyeSamuel

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Jul 27, 2021
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I’ve currently got a perfectly operational system using the REC Q BMS and an 8S4P configuration.
--- right now connector pin 1 is at the main negative terminal of the original battery configuration, and bms connector pins 2 thru 9 are attached to the 8 different cell positive terminals, lastly connector pin 17 is on the master positive of the original battery configuration.

I am doubling my battery capacity by adding on a second 8S4P battery configuration.

Am I able to just remove pin 17 positive and then add the new 8 positive cell wires into connector pins 10 through 17?

Does the bms require that each cell connector pin increases by a single cell’s voltage in series or can this second battery be added in the above manner?

Thank you!
 

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floydR

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Aug 23, 2017
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1,279
Just from reading
REC Q BMS connecting 9-16 (wire10-17) would raise the voltage at the bms even if the cells are paralleled.

Connect the cells in parallel with the first pack. This could be done by 1)extending the length of your bus bars 2x length for each bar 2) by making a separate pack and extending the balance leads. and paralleling the main Positive and main Negative wires of the pack 3)make jumper wires large enough to handle the max A of system and connect each section of bus bar with same busbar on the second pack works too and is probably the best option. You would need to have the cells at near the same voltage. Always confirm voltages with a multimeter.
Later floyd
 

ThirdEyeSamuel

New member
Joined
Jul 27, 2021
Messages
3
Just from reading
REC Q BMS connecting 9-16 (wire10-17) would raise the voltage at the bms even if the cells are paralleled.

Connect the cells in parallel with the first pack. This could be done by 1)extending the length of your bus bars 2x length for each bar 2) by making a separate pack and extending the balance leads. and paralleling the main Positive and main Negative wires of the pack 3)make jumper wires large enough to handle the max A of system and connect each section of bus bar with same busbar on the second pack works too and is probably the best option. You would need to have the cells at near the same voltage. Always confirm voltages with a multimeter.
Later floyd
Thanks for the great input Floyd.

decided to balance the batteries with 4/0 cable four times in each parallel module then double up the wires in each ferrule for the bms once done with balancing

will tie in new battery at shunt and main positive battery fuse
 

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prepared1

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Jan 17, 2021
Messages
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ThirdEyeSamuel: hey, really nice setup! May I ask what your experience has been using the Victron Autotransformer? And, your impressions of the REC BMS?

Thanks!
 

ThirdEyeSamuel

New member
Joined
Jul 27, 2021
Messages
3
ThirdEyeSamuel: hey, really nice setup! May I ask what your experience has been using the Victron Autotransformer? And, your impressions of the REC BMS?

Thanks!
Thanks!

I've used the autotransformer to grant me both 220 and 110v power supply for my residential mini split AC (220) and then the 110 for appliances like induction cooktop, blender, water heater and so on.

Fortunately my experience has been a peaceful and positive one.

REC BMS has done what it's advertised, balancing and disconnecting beautifully, while offering bluetooth and now wifi connection keeping my entire system online for me to monitor and configure from my phone anywhere I am.

Great when you've got a dog and AC in the van while on a trail.

I recommend the REC BMS and am continuing to grow in their ecosystem, I also recommend the autotransformer if you need both 110 and 220.

I am still learning how to do all of these things safely, I've got no experience in any of this except for the last year of research and execution. Safety is the priority.
 
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