Battery Monitor SOC

[sailorboy1]

Originally Posted by s/v Jedi

Did you miss my posts Don?

no. I already had read the manual more than once and all I had asked is if anyone else thought maybe disablng the reset was worth thibking of

[sailorboy1]

Originally Posted by JayH

I have a Victron BMV. My own experience is that when plugged into the dock, the automatic sync feature works fine. But away from the dock and charging from solar panels, the sync happens prematurely.

I think this is because the solar has limited capacity and when there are loads (refrigeration, etc) that match the charge current, the BMV sees high voltage but low net current, which triggers the sync.

Perhaps the solution is to raise the "Vc" setting. The Victron documentation says “Make sure the voltage-charged parameter [Vc] is always slightly below the voltage at which the charger finishes charging the battery (usually 0.1V or 0.2V below the ‘float’ stage voltage of the charger).”

In the meantime I have disabled the automatic sync feature on my BMV. Waiting for a better answer...

This is pretty much what I think. Has disabling the auto sync caused any issues with the rest of the monitor functions?

[noelex 77]

Originally Posted by Don L

so maybe just change the time delay, I have it currently set for 5 minutes but don't know what I may have had set at last year

5 mins at the absorption voltage (or just below) with return amps at 1% means the batteries must be close to fully charged (normally reported as 100%, but in reality probably 95%)

It is important to reset the battery monitor at this stage to preserve its calibration.

There are arguments whether it should be reset to 100% or 95%, or 90%, but as long as its consistent it is not very critical.

This is a reliable point of reference that should be used to reset a battery monitor.

If it is causing problems there is something else wrong. Battery return amps combined with voltage should be one of the most accurate (electronic) reference points in establishing the SOC of a lead acid battery.

[s/v Jedi]

Originally Posted by Don L

no. I already had read the manual more than once and all I had asked is if anyone else thought maybe disablng the reset was worth thibking of

Okay, good luck. I wouldn't have mentioned the battery issue if I wouldn't have thought it was related.
Saves me time and effort this way.

[JayH]

Originally Posted by Don L

This is pretty much what I think. Has disabling the auto sync caused any issues with the rest of the monitor functions?

My SOC and CE drift south after a few days and quickly become useless until I manually sync. I've messed with the CEF and PC settings, but I haven't been able to keep them accurate. I think syncing regularly is pretty important to the proper function of these devices.

[btrayfors]

You didn't say what kind of batteries you have and their age.

IF they are flooded batteries and IF you are in New England, then 14.1 or 14.2VDC is WAY TOO LOW.

Trojan recommends their T-105's be charged at 14.8VDC. I routinely charge my 10 T-105's at that voltage, and that in 60-70 degree ambient temperature. In colder climates, 14.8-15.0VDC would be appropriate.

With a "battery full" threshold of 14.2VDC, the battery monitor is going to declare the batteries full way before they actually are.

And, Jedi's right about intermittent exercising and kicking the voltage up to absorption levels. My Victron MultiPlus is programmed to do that every other day for 30 minutes.

Higher charging voltages are generally good for the batteries. You just need to keep an eye on the electrolyte levels. HydroCaps or WaterMiser caps are a good investment, too, to lessen water loss and frequency of re-filling.

Bill

[noelex 77]

The battery return amps is normally set a little below the absorption threshold. 0.2v less is usual.
The reason for this is the absorption voltage is a target. In practice the battery voltage will fluctuate slightly from this as the inputs and loads vary.

A cutoff criterion that used the full absorption voltage for 5mins would likely never be reached because within the 5min the voltage will briefly drop slightly below the absorption voltage as a load kicks in and the controller fails to compensate rapidly enough.

The voltage is not very critical for the return amps setting. A battery bank that is at 14.2v with a net input of 1% is it at a similar SOC to one at 14.5v with a net input of 1%.

[btrayfors]

Originally Posted by noelex 77

................

The voltage is not very critical for the return amps setting. A battery bank that is at 14.2v with a net input of 1% is it at a similar SOC to one at 14.5v with a net input of 1%.

Well, not unless you think that somehow Ohm's law doesn't apply to battery charging :-)

As you raise the voltage, the return amperage will increase too, as the increased voltage overcomes the battery's internal resistance.

Of course one can debate what's really a "full charge".

Bill

[noelex 77]

Originally Posted by btrayfors

Well, not unless you think that somehow Ohm's law doesn't apply to battery charging :-)

As you raise the voltage, the return amperage will increase too, as the increased voltage overcomes the battery's internal resistance.

Of course one can debate what's really a "full charge".

Bill

I think you are confusing the return amps voltage setting with the absorption voltage.
Changing the return amp voltage does not change how much the current the battery is accepting, this is controlled by the absorption voltage.

The return amp voltage only controls when the absorption phase is terminated.

The point is that the voltage rise at the end of charge is reasonably rapid, so if we take a battery that has reached return amps criteria of say
Greater than 14.2v and a current less than 4A (for a 400 AHr battery) for greater than 5mins and instead of terminating the absorption at this stage we allow the battery to continue charging at the absorption voltage until the new criterion of Greater than 14.5v and a current less than 4A for greater than 5mins we will find the battery has accepted few amp hours between these two cut off points.

If we factor in that the battery efficiency at the stage is poor, the overall SOC is similar.

A difference of less than 1% would not be unusual.

[btrayfors]

I see what you're saying. However, it doesn't address my basic point, made in post #21 above, that the absorption voltage setting is WAY TOO LOW.

It follows that if the absorption voltage is set way too low, and the monitor setting for return voltage is 0.2VDC below that (way too low) absorption voltage, then the battery is nowhere near 100% SOC when the monitor decides it is "full".

Bill

[s/v Jedi]

Originally Posted by btrayfors

I see what you're saying. However, it doesn't address my basic point, made in post #21 above, that the absorption voltage setting is WAY TOO LOW.

It follows that if the absorption voltage is set way too low, and the monitor setting for return voltage is 0.2VDC below that (way too low) absorption voltage, then the battery is nowhere near 100% SOC when the monitor decides it is "full".

Bill

And as such we go back to the batteries that never get fully charged. It's all beating around the bush instead of tackling the issue that is at the center of it all. But Don won't accept that I guess. It also doesn't help when people start making jokes when I mentioned this before; it's even understandable that somebody who is not an engineer starts doubting it then. When I write that I expect a "lazy" battery and to give it a couple of deep cycles and fully charge it so that the battery gets to it's maximum capacity for it's age then I'm dead serious. I was forced to study this bloody thing into the chemical processes and every electron and ion involved for four bloody years. Every manufacturer, incl. Trojan, states that even when new, the batteries need a couple of cycles to attain their full capacity. When people ridicule this, they should be ignored, instead of the tech members of CF who just know this because it was part of their professional life. That is the problem on CF, this "it's just the Internet" mentality where complete ignorants make statements like if they are experts and people actually believe that because it is not allowed to write that they are wrong. ("our members don't want to be told they are wrong, even when they are") go figure.

[JayH]

I don't know where the stuff about undercharged batteries is coming from. Is that in another thread?

The OP complained that his BMV was syncing early.

It seems to me the problem is likely that Victron's advice in their documentation (linked below and partially quoted in post #14) is not correct for a boat with solar panels. In this case, the Vc setting should not be below float voltage, it should be below absorption.

They probably assume a charger with enough capacity to offset any loads. This doesn't work when charging from a limited source like solar. My experience is that with Vc set too low, the BMV syncs prematurely when the solar charge current is offset by loads that reduce the net current to the batteries. Raising Vc to just below absorption may fix the problem.

They also say elsewhere in the same document that the "It" setting should be 4% for a LA battery. I think this should be more like 1% (for my batteries anyway). Lifeline says acceptance current 0.5% of capacity is "full".

http://www.victronenergy.com/upload/...%20PT%20SE.pdf

[Kettlewell]

When I write that I expect a "lazy" battery and to give it a couple of deep cycles and fully charge it so that the battery gets to it's maximum capacity for it's age then I'm dead serious.

^^+1^^. Not sure if Don has tried this with his batteries yet, but I have experienced this problem before when I had some batteries that were only cycled very lightly but never getting a really good charge.

[sailorboy1]

Originally Posted by s/v Jedi

. But Don won't accept that I guess. .

Maybe Don wishes you would stop looking for a "problem" to fix other than the question that was asked. I could post a lot about what has been done to the batteries, but none of that was question. I thought you were going to save time and effort!

Maybe Don has a different view of whose answers he may consider "expert" and doesn't feel the need to address the others snide questions.

Maybe Don doesn't like that some people seem to want to suggest he is an idiot in an effort to make themselves an "expert".

Maybe Don wonders why some say what he was asking can not be happening, even though someone posted they have seen the same thing.

Maybe Don thought about whether he was even going to ask the question for 2 weeks because he wasn't sure if it was worth sorting though the answers.

I think I know the answers!

[Jimbo485]

JayH is on the right track. Adjust the parameters and leave it on automatic. Higher Vc and lower Ic.