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moinois avatar image
moinois asked

REC ABMS + Victron MultiPlus 12 / 3000 / 120 = Oscillating SoC

As I set up my sailboat with Winston lithium batteries, I have seen that the Multiplus charges to 100% SoC, and then will not supply any current for my DC loads. The result is that the battery is supplying the DC power down to 95% SoC, then it starts to charge up to 100% again as the ABMS has a SoC hysteresis of 5%. I sent REC a support request, but they said it was the charger that needed configuration. So here I am.

What I can see is that the REC ABMS Parameters Charge Voltage Limit (CVL) is set to 14.2V, the Charge Current Limit (CCL) is set to 0A and the Discharge Current Limit (DCL) is set to 250A when the SoC is above 95% and there is no charging.

My expected behavior is that the REC ABMS should remove the CCL and set a CVL whenever the battery is at 100% SoC. To my understanding, the CCL is not just limiting the charge current to the batteries, but also the current that should be off loading my DC loads from the battery.

So my questions are:

  1. Is anyone else with REC ABMS + MultiPlus seeing this behavior?
  2. Is it expected to work like this?
  3. Will it harm my batteries in any way having them cycle between 95-100% SoC a few times per day?

Attaching an image from my VRM portal to illustrate the issue at hand. You can see how the ABMS sets the charge limits while charging and how it doesn't remove the CCL = 0A in the end, and in the second widget you see how my batteries are slowly drained to 95% SoC (13.3V approx) and then charges again.

1612786452942.png

Multiplus-IIbattery chargingBMScharge current limit
1612786452942.png (295.7 KiB)
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Justin Cook avatar image Justin Cook ♦♦ commented ·

Moved to Modifications Space for non-Victron-supported systems (REC BMS supports Victron, but Victron does not support REC BMS) to increase the likelihood of useful input - cheers!

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moinois avatar image moinois commented ·

I just wanted to get back to this topic as more people might see and have the same issue that I had. I got a new firmware from REC that resets the CCL when the charging is done and now it works as I would expect it, that is the Multiplus is feeding the DC loads directly, instead of letting the batteries take the load until 95%SoC when they are charged to 100% over and over again.

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jw1971 avatar image jw1971 moinois commented ·

Thanks for getting back - can you advise who you spoke to at REC? Tine or Primoz to request this revised firmware?

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2 Answers
Daniël Boekel (Victron Energy Staff) avatar image
Daniël Boekel (Victron Energy Staff) answered ·

Hi @Moinois

Your BMS says 'stop charging' so it stops charging...


Why would you program the BMS like this?


I'd set CVL to a safe limit (I prefer 14 volt, LFP cells are fully charged at 3.5V / cell), and only lower CCL to zero when the battery is out of balance (say a single cell reaches 3.7-3.8 volts)

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moinois avatar image moinois commented ·

Yes, that is my question as well. Why does it do like this? I asked them, like a wrote earlier, and they pointed at the MultiPlus configuration as the culprit. But I can see that the BMS is setting CCL during charging to make sure the batteries are charged slowly at the end so that the BMS can balance the cells and not overcharge them. I can't find anything in the manual about this, no settings, no comments on the behavior.

http://www.rec-bms.com/datasheet/UserManual_ABMS_Victron.pdf

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moinois avatar image moinois commented ·

I have had a conversation with REC, and they proclaim the SoC hysteresis is there to protect the batteries as they doesn't like to be at 100% SoC all the time. I'm not sure if holding the batteries at a certain level or jogging them 5% up and down all the time is the least harmful method, but I just have to accept that their product is doing this. Unfortunately.

How I expected it to work was that it would charge to 100% SoC and then limit the voltage to a specific level and removing the CCL (ie float mode) to let the MultiPlus support my DC loads directly, rather than going through the battery, having it charge/discharge all the time. The source of the charge doesn't matter, so it will be like this even when not connected to shore power and only using solar to charge.

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Daniël Boekel (Victron Energy Staff) avatar image Daniël Boekel (Victron Energy Staff) ♦♦ moinois commented ·

Hi @Moinois

that sounds strange...the battery manufacturer (you) should be able to define the settings. and LFP doesn't mind being kept at 3.45 volts / cell

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moinois avatar image moinois Daniël Boekel (Victron Energy Staff) ♦♦ commented ·

I'm not sure I'm able to get through to them. It seems as if the support person I'm dealing with has no intention to even open up for that it might be that I want their product to not constantly charge/discharge my batteries rather than letting the charge source (either solar or MP) take the load. I'm not sure how to convey that their settings will reduce the usability of their product as it will effectively make it impossible to directly run a water heater or a water maker from the solar instead of letting the battery bank take the hit until it drops down below te charging point.

I'm currently testing a new scenario, I pulled down the charging point to 3.2v per cell but still have a charge hysteresis at 5% SoC. I just want to see what the charging would look like. An interesting observation I made is that there is much less ripple on the discharge amperage and also it seems to pull a little more amps. It seems as if the MP was still giving some charge, albeit very low, even if the CCL was set to 0.

1613409400078.png

You can see that I set the charging voltage to 3.2v/cell at 10am and at the same time the amperage being drawn from the batteries got smoother as it dropped a bit.

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1613409400078.png (136.4 KiB)
edvanz avatar image
edvanz answered ·

As far as I'm aware it is because REC doesn't think it is good to keep your cells at 100% SOC. I have changed my hysterics down to 70% SOC. So it doesn't cycle as often and keeps the cells more often out of the higher knee. When in a marina, for a longer time, on shore power I set it to 40% SOC and change that back to 70% SOC the evening before I leave. I have the same issue as you have with my free solar power and waste sometimes free energy but not often as during the night the cells have dropped below the 70% SOC and charging is allowed again. If you are wondering why 70% SOC it is that we have a motor yacht and when underway we would be charging like being connected to shore power and 70% is the minimum I want to have in the cells when going on anchor.

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