Battery Monitor SOC

[svinshallah]

Regardless of the availability of the "state of charge" function on many battery monitors, in the real world the function simply doesn't work as advertised. Rather than spend a lot of time explaining why SOC functions are useless, I'll refer you to the www.smartgauge.co.uk website that was referenced earlier. They have way more detail about why trying to measure amp-hours in-and-out simply CAN NOT give you a usable SOC reading.

If YOU manually watch the voltage and current, you can tell when the batteries are supposed to be fully charged (i.e., 100%). But you don't know what value that 100% represents as the real capacity of the batteries gradually decreases with use.

If you have to use the SOC function, charge the batteries fully, then reset the SOC to 100%. And do it often.

[sailinglegend]

Originally Posted by noelex 77

The battery return amps is normally set a little below the absorption threshold. 0.2v less is usual.......

I don't understand how this will work for most people because if the battery is at or very near full then any regulator will have shut down to a float voltage long before this. Maybe you have programmed you regulators to only drop to float when they are full - but I fear most people don't/can't do that. It would be good if we could set the reset point at 0.2 volts below float and set the reset % to 90% or less.

[noelex 77]

Smartguage have got a good website, but they are trying to sell an alternative to the battery monitor so read the advice taking this into consideration.

Many people would argue a good battery monitor is essential for a cruising boat. Smartguage does not monitor or measure current and is not a replacement.

A battery monitor must be installed and adjusted correctly. If it is not working correctly there is nearly always a fault here. NASA battery monitors use a smartguage type measuring procedure in addition to also measuring current, but my advice would be to get a good traditional battery monitor.

There is a good article here on how to install a battery monitor. It is worth reviewing if you are having problems.


Installing A Battery Monitor Photo Gallery by Compass Marine at pbase.com

[noelex 77]

Originally Posted by sailinglegend

I don't understand how this will work for most people because if the battery is at or very near full then any regulator will have shut down to a float voltage long before this. Maybe you have programmed you regulators to only drop to float when they are full - but I fear most people don't/can't do that. It would be good if we could set the reset point at 0.2 volts below float and set the reset % to 90% or less.

The primary function of measuring battery return amps is to drop down to float voltage at an appropriate point. This is better than just using a set timed absorption time which can over, or undercharge the batteries depending on the conditions.

It does require a shunt near the battery, or communication with a battery monitor, so it is a level of sophistication that is not present in most boat systems. The simpler timed absorption phase works reasonably well and is probably the most cost effective answer for most boats.

Most battery monitors reset to 100% at this stage. This annoys some purists who argue, correctly, that the real charge level is more like 95%. In practice the 100% reset works well. The small discrepancy does not have much practical impact and on most cycles the discrepancy is corrected because the batteries recieve some float voltage whle the level remains at 100%.

However I agree a reset to a chosen battery percentage at the end of the absorption phase would be a nice addition, but as far as I am aware no one does this.

[sailinglegend]

Originally Posted by noelex 77

Smartguage have got a good website, but they are trying to sell an alternative to the battery monitor so read the advice taking this into consideration.....

Someone posted the link to the Smartguage with no other comments. Their site is full of very useful and informed information about all things electrical - and some very interesting words on trying to measure SoC with Specific Gravity readings. All those who say that SG is the only way to tell if a battery is fully charged should read that.

I have a SmartGuage monitor and a BEP battery monitor which gets more and more inaccurate as the batteries age.

Even with a correctly installed Battery Monitor and shunt all the original settings like Ah capacity, Charge efficiency, and Peukerts constant change with age, as does self-discharge which isn't adjusted for by most BMs as far as I know. So a Battery Monitor is always going to get more and more inaccurate, but a SmartGuage is always getting more and more accurate because it learns what your batteries are doing and adjusts its algorithm but reading the battery voltage over one thousand times a second.

I've seen so many wrongly installed shunts or installations - often caused by extra equipment that has been added by "engineers" that don't know or can't see a shunt is installed, so it is not surprising that Battery Monitors are not always accurate.

When SmartGuage first came out people said it couldn't work - including the man at Merlin who finally bought the company. His clients in the UK Military were demanding a more accurate BM and are now very happy with the SmartGuage. Recent tests done by Odyssey batteries showed it had an accuracy of 0.1% - too good for most of us.

I agree an ammeter is essential so my recommendation is always that a digital one should be bought along with a SmartGuage. This will give you the best and cheapest Battery Monitor setup.

Back to the original OPs problem - I agree with a previous post that solar panels that just can't deliver enough current, but can deliver a high voltage, are probably a major cause of a lot of problems. If solar is your main charging source disable the auto reset function by setting the volts to reset at above 16+ volts (which it will never do) and reset manually only when you "know" that the batteries are full. The only true test for this is an absorption voltage of 14.4v approx with a current that is 0.5% of the service bank capacity. There are large (expensive) Solar Regulators that also have a shunt and act as Battery Monitors so they will be the only type to give you an accurate reset to 100% when fully charged.

[sailinglegend]

Originally Posted by Don L

Maybe Don wishes you would stop looking for a "problem" to fix other than the question that was asked.....

I agree with you Don - thanks for posting that - I hope Jedi gets the message. The trouble is he won't see this message because I'm on his long "Ignore" list, so apparently my posts come up "suppressed"! I guess you are now on his "Ignore" list.

The man clearly has a lot of knowledge - but what we want here is people with immediate practical solutions, not "I thinks" - who don't have to post: "..please wait a bit while I look up the answer in the right manual". Sometimes people get carried away with their "theories" - it is usually the same serial offenders - with thousands of posts - that are the worst. The last time I checked on Jedi he was posting 40 a day.

This is a technical forum not a chat forum. People want to read good posts with suggestions relating to the original posts. The problems is of course we don't know exactly where you are coming from and that you have, of course, already read the manual!

It's a great pity that these kind of posts - and your put-down and mine - can spoil a very good thread.

I think ALL posters should be made to fill in their profile so we can look to see how valuable or sensible their advice might be.

[sailorboy1]

Originally Posted by Jimbo485

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

I agree and have already set my Vc pretty high (something in the 14s) and have the Ic set at less than 1%.

The thing I'm still considering is setting the Vc even higher, like to 14.6. Which would mean that with my current programing of my solar controller would mean that the system has reached absorption voltage, which the controller holds for 1 hour before it will go into float.

While the Victron says to use the SOC display as the main monitoring item, I am thinking the CE (amp-hours is more useful). But of course this means the system can not be reseting early as that makes the CE go to zero.

All I know for sure is that last year the SOC would reset when I know the batteries had no charging, but were 95% charged when I left the boat (on the display as I found that this reseting ended up saying the batteries were 100% when the gravities said they were 50%).

[sailorboy1]

Just as an update for anyone coming across the thread as research:

I didn't change any settings and decided to just see what happened over time.

The boat has been on solar now for a month with the refrigerator on all the time and the controller history says that the solar is putting in 60AH/day on average . The battery monitor says there is -20AH in the morning and as the sun comes up the batteries start charging. The amps into the battery drop to about +2.5 amps right about the same time the state of charge hits 100%, which is also about the same time the system goes into absorption.

I did change the controller from 1 hour minimum at absorption to 30 minutes the other day as the water level in the batteries seems to have dropped more than I would have expected in 1 month.

PS - on a usage item I found that leaving the inverter on in standby uses 40AH/day, which is almost as much as the refrigerator. That seemed crazy just to allow the time on the microwave to be correct all the time. So turned it off!

[noelex 77]

Originally Posted by Don L

Just as an update for anyone coming across the thread as research:

I didn't change any settings and decided to just see what happened over time.

The boat has been on solar now for a month with the refrigerator on all the time and the controller history says that the solar is putting in 60AH/day on average . The battery monitor says there is -20AH in the morning and as the sun comes up the batteries start charging. The amps into the battery drop to about +2.5 amps right about the same time the state of charge hits 100%, which is also about the same time the system goes into absorption.

I did change the controller from 1 hour minimum at absorption to 30 minutes the other day as the water level in the batteries seems to have dropped more than I would have expected in 1 month.

PS - on a usage item I found that leaving the inverter on in standby uses 40AH/day, which is almost as much as the refrigerator. That seemed crazy just to allow the time on the microwave to be correct all the time. So turned it off!

Some/ most inverters have a high standby current. Generally the larger the inverter the larger the problem.

For most inverters it pays to turn them off when not required.

Many appliances can be run directly from 12v, which is generally more efficient

[roetter]

I had the same problem with my Victron BMV.
Setup:
840Ah LA batteries - EXIDE
950W solar with Outback 80

I believe the Outback came programmed to 14V absorption.
I had left the BMV at the default settings. All was fine during the summer in the Med as usually the sun plus the occasional travel under engine was enough to get the batteries fully charged and the BMV synchronized every few days. So there was little drift.

However, we then came to fall with shorter days and more days just on the hook. In the morning the coffee maker running on the inverter caused a low-voltage alarm even though the batteries where supposed to be 80% full. I soon realized that somehow the BMV mistook the amperage from the solar in the afternoon going down as a full battery and it set itself to 100% SOC. I also found that the Outback would remain often in float voltage even thought it should have gone back to absorption voltage.

So I did two things:
One - I played with the parameters that tell the BMV that the batteries are full. i.e. higher voltage, lower amps, longer times - to prevent premature synchronization.
Two - I set the absorption AND the float of the Outback to 14.6V. Somebody on CF said I could have changed the re-bulk voltage to prevent it from staying in float for too long. I never checked if that worked. I never had to fill my battery water, so I was not overcharging.

For a while the BMV never synched but after a while I found the parameters that fit my conditions pretty well. I also on occasion ran the engines or a small Honda generator in the morning to make sure the sun that day would definitely fully charge my batteries that day.