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Tail current??(BMV702)


gpigeon
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This is my first post on this forum. I am impressed by the overall content of the forum generally.

I have asked this same question on our local solar forum but did not get a reply so I will try here as I see that the Victron BMV702 gets quite a few mentions.

My basic setup is :

Schneider XW8548+ inverter.

Schneider 80/600 charge cont. x 2

Sonnenschein 2RPG1410 batteries x24.

My question....what is the "tail current" mentioned in the Victron manual? I see from other posts that the default is 4% but some say that should be reduced to say 2.8%. Mine was 10% (not sure how it got to that) and I reset it yesterday to 4%. I can't really see that it would have any influence on the charging regime in my case because the BMV702 does not interact with the charge controller in any way. The BMV is merely a "fuel gauge"???/Correct?

Merry Christmas to all of you.

Cheers.

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12 minutes ago, gpigeon said:

what is the "tail current" mentioned in the Victron manual?

Hi gpigeon. Welcome and a Merry Christmas to you too.

"Tail current" is basically the current the bank will absorb at almost fully charged. It is used in the following situation.  

As your batterys charges it "Absorbs" less and less current. The 702 will indicate 100% charge after looking at the following three conditions. Once all three conditions are met, the BMV will indicate the bank as 100% charged. 

  1. (Setting 2)  Bank voltage at "Float Voltage" or higher
  2. (Setting 3) Tail current at less than 4% (In my case 2.8%) of the total Ah rating of the bank
  3. (Setting 4) For a set time of ?? Min. (In my case 30min) 
25 minutes ago, gpigeon said:

The BMV is merely a "fuel gauge"

Yes you can call it that, but for it to know when its full, it will look at the above conditions. 

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Mornin' Jaco,

Thank you for the prompt and informative reply.

I think that this solves one of my other queries I had with the BMV702...it was showing 100% charged whilst the XV8548 had only 3 or 4 of the five LED's lit. Five is fully charged!!! That meant that the BMV702 was indicating full charge too early. Not that it mattered all that much in the overall scheme of things. I will monitor the system and see exactly what has changed now that I have reduced the setting from 10% to 4%.

Cheers. You have a good day.

 

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On 2018/12/24 at 10:46 PM, gpigeon said:

This is my first post on this forum. I am impressed by the overall content of the forum generally.

G'day Mate

On 2018/12/24 at 10:46 PM, gpigeon said:

I have asked this same question on our local solar forum but did not get a reply so I will try here as I see that the Victron BMV702 gets quite a few mentions.

My question....what is the "tail current" mentioned in the Victron manual? I see from other posts that the default is 4% but some say that should be reduced to say 2.8%. Mine was 10% (not sure how it got to that) and I reset it yesterday to 4%. I can't really see that it would have any influence on the charging regime in my case because the BMV702 does not interact with the charge controller in any way. The BMV is merely a "fuel gauge"???/Correct?

You're correct in that the BMV is a fuel gauge and what you are trying to do with the various "end of charge settings" is get a more accurate 100% SOC. Quite often it will jump from 95% to 100% and although acceptable is not entirely accurate. If you battery bank's charge drops below the tail current and remains there for the period specified in Setting 4 it will go to 100%. If you play with Settings 3-5 (I did over several months) one can get the BMV to reflect the SOC accurately.

One of you compatriots helped me in the early days check out the video he made for me.

 

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Hi Chris....thanks for the reply. I did change the tail current seeting to 2.8% and yes, it made the SOC reading more accurate. In the overall scheme of things it doesn't really change the performance of the system. It just makes the SOC reading on the 702 a little more in line with the SOC shown on the XW8548.

Cheers for now. Take care & all the best for 2019.

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