Battery capacity setting for IP40 Charge Controller

[Solar40]

Hi, does anyone know if the current BCAP setting - 660Ah - is correct?

48v battery bank (24 x 6 PVV 660 - BAE Secura PVV Cell solar)
Charge Controller (Plasmtronics PL40)
Solar panels ( 24 x 60w)

My concern is that it should be set to the C20h setting of 596Ah.

Thanks

[Sunking]

C/20 charge current is way too low for a solar application. Typically if designed properly the charge rate will fall between C/12 on the low side up to C/8 on the high side for flooded batteries. So for a 48 volt battery system with 660 AH battery minimum panel wattage required is 2750 watts with 55 amp charge current.

Only way to see a charge current of C/20 on a solar application is if you are using 8 or more days of battery autonomy. But for 5 days C/12 to C/8 is where it falls.

[Solar40]

Thanks Sunking, are you suggesting that the solar system at 1.44kw isn't adequate for the 660Ah batteries?
We are having some problems with this system.

[mapmaker]

are you suggesting that the solar system at 1.44kw isn't adequate for the 660Ah batteries?
We are having some problems with this system.

In a properly designed 48 volt system with a C/10 charge rate you would be able to push at least 66 amps into those batteries.

If your panels were producing 1440 watts (rare event) and your charge controller were 100% efficient (it's not) and your batteries were up near absorb (about 58 volts), you would be pushing only 1440 ÷ 58 = 24.8 amps into the battery.

--mapmaker

[Solar40]

Thanks Mapmaker, indeed, at best these panels only bring in 15 - 20 amps.

The system was installed 23 years ago. We've had it for the past 16 years and have only used it occasionally. Soon we'd (two of us) like to live in it full-time.

We're off grid and run 2 medium sized fridges, tv, lights, 24hr 71w air pump for sewerage, water pump to pump from rainwater tank, 24hr inverter, so our power consumption isn't over the top.

We're coming into winter here (Sydney Australia) and get about 4-5 hours sun on the days of least light.
It would be great if the fully charged batteries supplied enough power to last 7 days without having to crank up the diesel generator.

What would you recommend?

[mapmaker]

The system was installed 23 years ago. We've had it for the past 16 years and have only used it occasionally.

That was typical back then... batteries were cheap and panels were dear. Now that has been reversed. Living off grid is all about keeping your batteries happy.

Soon we'd (two of us) like to live in it full-time.
<snip>
What would you recommend?

Design a system on paper and then figure out how much, if any, of your current system you can use.

We can help with the design, but engineering is about hard numbers. We need to know your loads, climate, resources.

If you asked me which pickup truck to buy I would ask you to tell me your load (how many lbs you intend to carry or tow). Same goes for power systems... what are your loads?

To know your loads, you must know your daily kwh use, your peak wattage draw, and the time of day that you draw these loads. Give me numbers and I will give you a plan.

--mapmaker

[Solar40]

Thanks again Mapmaker, I'm in the process of determining KwH/day usage. It will take some time.

In the meantime, could you hazard a guess as to why if the batteries are fully charged and then the clouds set in for days, we only get 2 days battery power before needing to use the generator?

These batteries are only 2 years old (gel type - 24 x BAE 2v 6 PVV 660 Secura solar) and I would have though with our moderate usage (general indications in previous post), and the large 48v battery bank, we would get more than 2 days worth. Any thoughts?

[mapmaker]

These batteries are only 2 years old (gel type - 24 x BAE 2v 6 PVV 660 Secura solar) and I would have though with our moderate usage (general indications in previous post), and the large 48v battery bank, we would get more than 2 days worth. Any thoughts?

Generally speaking, gel batteries are not suitable for solar applications, but these specific ones are an exception... they can handle the higher currents that are needed in RE. I don't know much about your batteries, but the specs seem to require a minimum of I₁₀ for charging current. I don't know what I₁₀ means.

Regardless, as has been mentioned, you don't have enough solar panel to charge those batteries.

could you hazard a guess as to why if the batteries are fully charged and then the clouds set in for days, we only get 2 days battery power before needing to use the generator?

Why do you think the batteries are fully charged? I'm not saying they're not... I just don't know and I wonder how you know.

--mapmaker

[Solar40]

What does 'RE' stand for?

I don't know what I10 means either but I'm looking into it.
I have found this -
Charging current: unrestrained, minimal charge current should be > 10 h
What does > 10 h mean?

The system has a Victron Energy BMV 501 battery monitor. When the SOC reads 100% and the volts are up in the low 50s, I believe the batteries to be fully charged.
This occurs when the system has no load on it and there are many days of sunshine. For example, when no one is using the system and the 24 x 60w solar panels are left to do their thing in the sunshine.
SOC 100% can also be reached by using the generator.

[Solar40]

What I've found so far-

Charge current - unlimited, the minimal charge current has to be I10

Charging current - unrestrained, minimal charge current should be > 10 h

Charge current may vary from 5 x I10 down to 0.01 x I10

Have emailed the company from where we bought the batteries to see if they can shed some light.
So far no response....

[mapmaker]

What does 'RE' stand for?

Renewable Energy. When charging a battery from the grid, there are all sorts of charging protocols that can be used.... you have unlimited time and power. In RE systems the charging source and loads are coming and going... that creates limits on how you can charge the battery.

The system has a Victron Energy BMV 501 battery monitor. When the SOC reads 100% and the volts are up in the low 50s, I believe the batteries to be fully charged.

Don't believe it. I think your battery is chronically undercharged and quite possibly permanently sulfated. You need to understand the limitations of a battery monitor.

A battery monitor is often compared to the gas gauge in your car, but that is not a good analogy.

The gas gauge in your car actually measures the level of gas in your tank. A battery monitor doesn't measure the level of anything. It is more like the odometer in your car. The odometer counts miles and the battery monitor counts ampHours.

Suppose you have a car that gets about 25 mpg and has a 15 gallon gas tank. Suppose also that your gas gauge does not work. What do you do? You use your odometer. For example: After a fill up you drive 150 miles and you expect that you have used 6 gallons and have 9 gallons remaining in your tank.

If you fill up the tank again you can, as above, use your odometer to estimate your gallons remaining.

But what if you do not completely fill your tank. For example, starting from a full tank you drive 150 miles and then you add 3 gallons to your tank and then drive 100 miles and then add 4 gallons to your tank and drive 150 miles and then add 5 gallons to your tank and drive 100 miles. At this point you estimate that you have 7 gallons remaining in your tank, but that estimate is not too accurate because your mileage is not ever exactly 25 mpg. The only time you know exactly how much gas is in your tank is when you have just filled it up (or when you run out of gas).

So it is with your battery monitor. The only time it is exactly accurate is when you fully charge your batteries and reset the battery monitor to read 100% full. It can be very accurate counting the amphours in and out of the battery, but it can only estimate the state of charge based on what you tell it about the battery capacity and the battery efficiency. It can count (amp hours in) up to 100% before the battery is fully charged.

The other way some battery monitors reset to 100% is based on criteria that you set. For example, you may have decided that your batteries are charged when the voltage is at least 58 volts and the current is below 6 amps for a minute. But is that really when your batteries are charged? (those numbers are examples... I don't know what the settings should be for your batteries)

If you're going to train your monitor how to recognize a fully charged battery, then you yourself must know when the battery is fully charged. With a flooded battery this is done with an hydrometer or refractometer to measure SG (specific gravity). You cannot do this with gel batteries. That is probably the main reason that non-flooded lead acid batteries are so problematic in RE systems.

One way to know if a sealed battery is fully charged is to use a shunt based current monitor to watch the current into the battery during absorb charging. The charging current declines during absorb to a level called 'end amps' or 'return amps'. The manufacturer should be able to tell you the value for your batteries. The problem is that once sulfation has occurred, end amps is not reliable. Also, you would need to know the actual, reduced capacity of your batteries in order to tell the battery monitor what value to use for capacity. In the car analogy, this means your gas tank is smaller than you think... even if you fill it up, you don't know how much is in it.

Bottom line: the longer its been since a complete charge, the less you can trust your battery monitor. And you can't trust it at all if its not set up correctly. That said, battery monitors are valuable tools in estimating your SOC, but you have to understand their limitations.

Be sure that your next batteries are flooded, and make sure you have adequate resources to charge them.

As far as your current batteries are concerned, I think they are sulfated. I don't know enough about those particular batteries to know if there is any hope of recovering them.

--mapmaker

[Solar40]

Wow!, thanks Mapmaker, much obliged.

I think your battery is chronically undercharged and quite possibly permanently sulfated.

Does anyone know the minimum charging current for this type of battery?
Gel type - BAE 2v 6 PVV 660 Secura solar

I've emailed the sales company (nothing back yet) and will email the manufacturer.

So it is with your battery monitor. The only time it is exactly accurate is when you fully charge your batteries and reset the battery monitor to read 100% full. It can be very accurate counting the amphours in and out of the battery, but it can only estimate the state of charge based on what you tell it about the battery capacity and the battery efficiency. It can count (amp hours in) up to 100% before the battery is fully charged.

Understood. With the BMV 501, < and > buttons are pressed for 3 seconds to reset the monitor to 100%.
But, indeed, how to know when the batteries are really charged??

From the battery monitor manual, the battery capacity setting '...must be the capacity at a 20h discharge rate and 20 deg celsius'.
The battery specs put this at 596Ah.
For the last 2 years the battery monitor battery capacity setting has been 400Ah when in fact it should have been 596Ah.
What effect do you think this would have had on our ability to read the batteries health credibly?

If you're going to train your monitor how to recognize a fully charged battery, then you yourself must know when the battery is fully charged.

At present, I guesstimate that the batteries are near to fully charged. Dubious, I know. Today is cloudy and I've had the generator on for 3 hours. The battery charger is outputting 44amps into the batteries and the average cell voltage of the batteries is 2.2v.
I'm thinking that if the batteries were near to fully charged, the amps would be a lot lower than this?? Any comments?

One way to know if a sealed battery is fully charged is to use a shunt based current monitor to watch the current into the battery during absorb charging. The charging current declines during absorb to a level called 'end amps' or 'return amps'. The manufacturer should be able to tell you the value for your batteries.

I'll email the manufacturer.

As far as your current batteries are concerned, I think they are sulfated. I don't know enough about those particular batteries to know if there is any hope of recovering them.

Does anyone know more about these batteries? Gel type - 24 x BAE 2v 6 PVV 660 Secura solar




Off grid, 24 x 60w panels, Gel type batteries - 24 x BAE 2v 6 PVV 660 Secura solar

[Solar40]

As a follow-up, this is from the battery monitor BMV 501 manual.
Am I mistaken or is it possible that the battery monitor can automatically synchronize with the batteries thus giving a SOC of 100%?

Synchronizing the BMV-501
For a reliable readout of the state of charge of the battery, the battery
monitor has to be synchronized regularly with battery and charger. This
is accomplished by fully charging the battery. When the charger is
operating in the ‘float’ stage, the charger considers the battery full. At this
moment the BMV-501 must reckon the battery as full too, so that the
Amphour counting can be reset to zero and the state-of-charge reading
set to 100.0%. By precisely adjusting the charged-parameters in the
BMV-501, the battery monitor can automatically synchronize with the
charger when the ‘float’ stage is reached. The range of the charged parameters
is wide enough to adjust the BMV-501 to most battery
charging methods.

When the BMV-501 can’t be adjusted to the charging algorithm of the
installed charger, the user can always synchronize the battery monitor
manually when the battery is fully charged. This is achieved by pressing
both < and > selection keys simultaneously for three seconds. By
manually synchronizing the battery monitor, the CEF will not be
calculated automatically. When the supply voltage to the BMV-501
has been interrupted, the battery monitor must always be
synchronized in order to operate correctly.

Please note that regularly (at least once per month) fully charging your
battery not only keeps it in sync with the BMV-501, but also prevent
substantial capacity loss of your battery that limits it’s life time.

Charged-parameters
Based on increasing charge voltage and decreasing charge current, a
decision can be made whether the battery is fully charged or not. When
the battery voltage is above a certain level during a predefined period
while the charge current is below a certain level for the same period, the
battery can be considered fully charged. These voltage and current
levels, as well as the predefined period are called ‘charged-parameters’.
In general for a 12V lead acid battery, the voltage-charged-parameter is
13.2V and the current-charged-parameter is 2.0% of the total battery
capacity (e.g. 4A with a 200Ah battery). A charged-parameter-time of 4
minutes is sufficient for most battery systems. Please note that these
parameters are very important for correct operation of your BMV-501,
and must be set appropriately in the corresponding Functions.

[mapmaker]

Am I mistaken or is it possible that the battery monitor can automatically synchronize with the batteries thus giving a SOC of 100%?

The manual gives three method of reset. The "automatically synchronize" means that when your battery charger or solar controller goes to float, the battery monitor will reset. You must program the battery monitor to recognize float.

Basically, in this mode your battery monitor is not doing an independent audit of your battery's SOC... it's just letting your chargers decide when the battery is 100% SOC.

btw, how do your charge controller and your battery charger know when the battery is charged and that they can go to float? There are many ways to do this, some much better than others. If those charger settings are wrong, all the solar panels in the world won't get your battery charged.

Getting back to the manual... the "charged parameters" method of reset is the 'end amps' method that I described in an earlier post. Many folks consider it the most reliable method, but as I mentioned previously, if the battery is not brand new and fully charged, the manufacturer's specs for those numbers are not useful. If the battery is sulfated, the end amps will be reached too soon and if you stop charging because you (or your charger) thinks the battery is charged, you will get even more sulfated... downward spiral.

btw, many charge controllers can use end amps to manage the daily charge. There are two ways this can occur.

1) Some charge controllers measure their own output and assume that it is the battery current. When it declines to end amps, they know the battery is charged. Of course, if you have other loads or other chargers connected to the battery, the battery current will not be the same as the controller's output. Many grid-powered battery chargers work this way... they assume you are not driving the golf cart while you are charging it.

2) Some charge controllers use a shunt so they know exactly what's going into or out of the battery. When end amps is reached, they can go to float. It doesn't matter what else is connected to the battery.

btw, your victron battery monitor uses a shunt, so it knows what's going on. of course, your monitor is not a charger.

Getting back to your batteries... you need to try and recover them. I don't know enough about those batteries to give you advice. One thing you should know about sulfated batteries... they behave like regular batteries, but with reduced capacity. They take a charge, they approach end amps, etc. If you are to use your battery monitor or any charging scheme that depends on knowing the SOC, it's up to you to set the battery capacity accurately. Your batteries are not, at the moment, 596 ah.

btw, my batteries are 25° F cooler in the winter than the summer. I tell my battery monitor to use a reduced capacity in the winter, because cold batteries have reduced capacity. I've read about some systems where the battery monitor can take into account the temperature.

At present, I guesstimate that the batteries are near to fully charged. Dubious, I know. Today is cloudy and I've had the generator on for 3 hours. The battery charger is outputting 44amps into the batteries and the average cell voltage of the batteries is 2.2v.
I'm thinking that if the batteries were near to fully charged, the amps would be a lot lower than this?

me too. keep an eye on the temperature.

Do you have a digital voltmeter? It's a good idea to measure the voltage across each of the batteries while current is flowing. If you are pushing 44 amps into the batteries while you measure, you can look for discrepancies among the batteries. You might find one battery is an outlier... If you try to recover your batteries by a long, controlled overcharge, you may be greatly overcharging all the batteries in an attempt to recover that one weak battery. Sometimes it's best to separate the batteries and try charging them in isolation.

--mapmaker

[Solar40]

Today I ran the generator for 6 hours.
Here are the results-

After 2 hours -
Charger output: 44A
Average cell voltage of the batteries: 2.20v
Battery monitor volts: 54.40

After 3 hours -
Charger output: 40A
Average cell voltage of the batteries: 2.34v
Battery monitor volts: 55.20

After 4 hours -
Charger output: 38A
Average cell voltage of the batteries: 2.36v
Battery monitor volts: 55.99

After 5 hours -
Charger output: 34A
Average cell voltage of the batteries: 2.37v
Battery monitor volts: 56.10

After 6 hours -
Charger output: 26A
Average cell voltage of the batteries: 2.37v
Battery monitor volts: 56.25

Note: From the manual, the Float charge (float voltage) is 2.25V/cell +or- 1%.

What do the above results say about the state of the batteries?
If I do this again tomorrow, is there any danger of overcharging the batteries?



Off grid, 24 x 60w panels, Gel type batteries - 24 x BAE 2v 6 PVV 660 Secura solar, Ip40 Charge Controller, BMV 501 Battery Monitor