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Working up design -- multiple questions

  • H
    I am preparing to install a LFP battery on a sailboat and am trying to pin down a BMS.  REC seems to be the best.  I have multiple charging sources that are fairly "dumb" with no CAN controls or even "disable" controls (Balmar regulator, wind generator, towed generator).  My solar is all Victron and so is my inverter/charger (MP2), but I do not have (nor want -- a lot of money for not much use for me) any GX devices.
     
    I intend to have one main contactor (the Blue Seas 7713).  All charge sources will be direct to the main bus, and tripped by control wires (inverter, solar, and 270A of alternators) or in-line contactors (probably Victron Battery Protect).
     
    My sequence of voltages (specific numbers to be determined) are:
    *  HVC (open main contactor)
    *  HVA (alarm and disable charging sources)
    *  Charge source setpoint
    *  Working region
    *  Inverter internal cutoff
    *  LVA and disable inverter
    *  LVC (open main contactor)
     
    My questions:
    1)  Can the HVC and LVC be controlled by a single relay, or do I have to run the control through both BMS relays?  Seems a waste to consume both onboard relays to control one contactor? Are they "dry contacts" so I can run through them in series?
    2)  By ABYC, a pre-alarm is required for any disconnect.  There are 4 outputs (2 relays and 2 optos), and my design uses all 4.  Unfortunately, the HVA would also be the "charge enable" opto coupler, resulting in many alarms (or I configure all charge sources below the HVA and lose the ability for the BMS to control charge sources -- not necessarily bad)  Ideally, I could recover the HVC relay, and use it for a HVA.
    3)  Is it best to run the BMS on the load side, or the battery side, of the main disconnect?  Since there is very little chance of the main disconnect ever opening in the life of the battery, it's probably academic, but how does the BMS handle a loss of power (does it loose, for instance, SOC?).
    4)  I will be using the WiFi adapter.  The LCD does not appear to be available (is that correct?  Every time I try and build an order, I can't find it anywhere).  I will be retaining my ancient but excellent LINK 2000, which will still give me Volts, Amps, and its version of SOC (probably 99% of what I'll ever want to know).  Am I OK using the Link for day-to-day monitoring, and the WiFi when I want details?
    5)  The manual talks about a "Discharge Algorithm" that slowly dials back discharge.  Given that all loads are a set value, how is this accomplished?  An inverter is on or off (the microwave draws a fixed amount!).  Same with DC loads -- I can't control the amount of power the chart plotter draws.  Is this unique to some specific use-case (say, grid-tie systems)?  Can this be disabled, or is this just ignored and has no impact on systems that don't have controllable/variable loads?
     
    Thanks for any input!
     
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  • R

    1)  Yes, a single relay is the standard way to go now "since many loads are now smart and the Active BMS comes configured for that operation, leaving 1 relay and 2 optos for additional customer configuration.  If you want to break out your charge and discharge busses and run two contactors in parallel off the one output that should be fine, depending on the contactor selected.  You can always add a small interposing relay to drive them too if you like

    2)  The REC BMS has an internal alarm that may provide some of the ABYC needs but I would just use the one relay and the two optos with the optos configured for low-temp-volts and high-temp-volts and maybe a few of the available alarm parameters that can be configured

    3)  BMS always goes on the battery side, or else it would never turn on, and it will drop out completely in a very low voltage situation

    4)  The LCD parts are no longer available so the Wifi with a browser is best.  There is talk of a new version next year

    5)  Smart and relay connected loads disconnect in sequence before the main contactor does a hard disconnect so it is more of a stepped discharge

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  • H

    Rick,

     

    Thanks so much.  I was hoping you'd answer.

    1)  If the single relay is standard now, are there any diagrams?  The manual still shows two, and talks about HVC and LVC relays (actually, RelayDCH and RelayCH) and shows running to two contactors.

    3)  The lack of a display is troubling.  With my AGM and LINK, I frequently look at the display for SOC, and when charging at the Amps.  With my intent to keep the LINK, that may solve my curriosity.  Using a cell for several-times-a-day status checks is a non-starter.  "Next year" is awfully far in the future for decision input.  What a connundrum.....

     

    Thanks again!

     

    Harry

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  • H

    Wow.  Now I'm even more confused!

    A)  There appear to be two completely different firmwares -- with Victron/Wakespeed, and without.  I thought the differences were simply setpoints, but they are different firmware.  Which leads to the question -- which do I want?  I won't be using ANY CAN -- I have nothing to connect it to.  Does this make the non-Victron version better for me (but then, it seems I'm stuck with two outputs for my main disconnect).

    B)  Throughout documentation and here on the forum, there is sporadic reference to "Tasks" which may be very helpful to implementation.  It seems like this allows a selection of if/then to control all 4 outputs (two relays, two opto's).  But I can't find any manual/discussion/screenshots on how to use Tasks and just what they do.

    I think I'd be happy if I could

    *  Set the LVC to activate on both Low and High volts (and high temp too).

    *  Set the LVA to activate ONLY on Low volts and high temp (advance warning of disconnect)

    *  Set the HVA as a charge control, backup to the internal charge controls.  Also disable charge on low temp.

    *  Reconfigure the HVC to be an actual alarm, maybe .02V above the charge enable setting, warning of impending disconnect on HV.

    All of the above may well be configurable with a robust "tasks" routine.  But I have no idea.  Worst case, I can do it as originally intended (but I'll get an alarm every time the charge enable toggles).  I assume I must specify NON-Victron firmware, right?

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  • R

    Now that we have the WiFi module there are new features available that allow you to custom configure the second relay and two opto outputs so this is how it goes:

    1)  PC software only and two relay configuration requires 2.9.X-2 firmware(PC softwre does not support tasks feature that is built in to the WiFi module)

    2)  WiFi module and one or two relay config can use standard 2.9.X-1 firmware and you just use the Tasks page on the Wifi module to set it up

    All North American sold REC-Active BMS's are sold with both Victron and WS500 drivers

    I will try to grab some time this week and set up my Active Demo and get you a bit of info on it.  Its pretty handy!

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  • R

    and here is a link to a sample single relay Active BMS wiring diagram that might of interest

    https://rec-bms-na.com/download/31/rec-active-bms-sketches/1290/rec-active-bms-wiring-diagram-rec-active-bms-2p4s-1-relay-precharge_3_0.pdf

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