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Batteries: Your thoughts please


Jakes
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Guys

My system consists of the following:

  • 15 x 250W Renesola panels
  • 100A MicroCare charge controller
  • 12 x 12REXC200 Narada lead carbon batteries. (They are 165AH at C10)
  • 3 x HAO2 battery balancers
  • 5kW, 48V bi-directional MicroCare inverter

The system has been running for nearly 700 days. We are off the grid.

I recently noticed that the battery voltage might not be what it should be. I realize that voltage is not the best way to determine the state of charge or health of the batteries, but  surely it must give a good indication.

While charging (in "Boost" mode), the system would indicate a battery voltage of 55.4V. It would go to "Float" in the afternoon on a sunny day like it should, indicating 54V.

I started suspecting that something might be wrong when I saw the voltage dropping more that expected after the sun has gone down. It seems that the battery voltage would go down to 51V within an hour after the shadow has moved over the panels. It would drop to 50.5V during the evening and be at 49.5V in the morning. In the evening it works lights in the house (all LED's), one 10W LED throughout the night, makes some tea, works an electric blanket and works 3 x A++ fridge/freezers and a bar fridge.

I have taken individual strings of batteries out of the bank to see how they behave. Immediately after isolating a string the voltage will be at 52V, reducing to 51V within an hour, stabilizing at 50.5V, where it will stay for 72 hours.

The voltages of the different strings test very close to each other. Testing all the batteries individually also indicate the same voltage, even after disconnecting the balancers.

According to Narada, 47V would indicate 0% capacity and 52V 100%.

This means that the batteries in my system would drop to 80% capacity soon after the charge is removed, then down to 70% where they will remain.

I tried getting hold of the Narada importer to get their input, but have not had any success yet.

I am concerned about the health of the batteries, but it could also be that I've got some settings wrong.

I'll appreciate your opinions.

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Difficult to say. The only way to know is to put a known load on and see how it behaves. I wouldn't be concerned really if my batteries ended up at 49V in the morning, that would be a kind of victory in my book :-)

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25 minutes ago, DeepBass9 said:

Also voltage tells you squat about SOC.

No quite. If you know what your load is a discharge voltage can give you an approximation of SOC. The table below is for rested voltage (which never happens unless you disconnect your batteries). 

 post-23-0-04112900-1434977542.jpg.40323bedb15cb18fef893a4be520c0f2.jpg

Charging voltage is as you say tells you squat about SOC.

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For assessing battery condition on a budget: If you don't have one already get a cheap multi meter and actually measure the battery bank voltage and the individual battery voltages as well. the 1kw 48V mc i had was out by 2 volts if i recall, this is obviously important to ensure that it charges up to the correct voltages.

you can do some basic checks, immediately after a full charge remove all load, switch off inverter and check each batteries voltage, apply a stable load that doesn't change like inverter on and run all lights, nothing else. check each battery again. write all these values down as you go along. By looking at the amount of drop each one gets you can evaluate if you have imbalances and anything severe should be fairly obvious.

nice thing about this is that if you apply yourself and measure at 2 different stable loads you can calculate the internal resistances for each of the batteries. i usually use this method when i assess a bank to get a rough idea. but to be truly absolute and nerdy you need to do this several times over the course of a few months each time at the same full state of charge with the same loads, then plot out the increase in internal resistance over time in excel, add a trend line in the plot and estimate when the batteries will die :D haha

should maybe post a tutorial on doing that if anyone is interested. none the less its the cheapest way, cheapest is usually more effort right :P

PS get a BMV..

  

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Thanks so far.

I'm concerned about the batteries coming down from 52V to 50(or so)V in less than an hour, without any load.

I have made notes of different readings, but I'll try and report back with more and better information.

What is your feeling about testing a battery with a heavy load? I see the Hawkins tester can apply a 600A load to a 12V battery for 15 seconds. Won't this shorten the life of a battery that is not in a 100% condition?

Weasel, I recently saw that my charge controller "overreads" by 1V. I would have probably bought diffent equipment if I knew about inaccuracies like this. One hears good things about a product and you base buying decisions on that. Somehow I expected more from MicroCare.

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33 minutes ago, Jakes said:

I'm concerned about the batteries coming down from 52V to 50(or so)V in less than an hour, without any load.

Again, that is equivalent to a 12V battery that comes down to 12.5V when left on its own, which is still a very healthy battery.

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41 minutes ago, Jakes said:

Thanks so far.

I'm concerned about the batteries coming down from 52V to 50(or so)V in less than an hour, without any load.

I have made notes of different readings, but I'll try and report back with more and better information.

What is your feeling about testing a battery with a heavy load? I see the Hawkins tester can apply a 600A load to a 12V battery for 15 seconds. Won't this shorten the life of a battery that is not in a 100% condition?

Weasel, I recently saw that my charge controller "overreads" by 1V. I would have probably bought diffent equipment if I knew about inaccuracies like this. One hears good things about a product and you base buying decisions on that. Somehow I expected more from MicroCare.

According to Narada's data sheet at 10.5v ( 42v for 48v bank ) the battery is dead

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1 hour ago, ibiza said:

According to Narada's data sheet at 10.5v ( 42v for 48v bank ) the battery is dead

Yup, but that's out of circuit/at rest. A 10.5V battery that is presently doing work isn't empty (although it's not in a particularly enviable position either, it's likely to be damaged if you continue).

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1 minute ago, plonkster said:

Yup, but that's out of circuit/at rest. A 10.5V battery that is presently doing work isn't empty (although it's not in a particularly enviable position either, it's likely to be damaged if you continue).

Right, I can't agree more.

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On 7/20/2017 at 1:06 PM, Jakes said:

Guys

My system consists of the following:

  • 15 x 250W Renesola panels
  • 100A MicroCare charge controller
  • 12 x 12REXC200 Narada lead carbon batteries. (They are 165AH at C10)
  • 3 x HAO2 battery balancers
  • 5kW, 48V bi-directional MicroCare inverter

The system has been running for nearly 700 days. We are off the grid.

I recently noticed that the battery voltage might not be what it should be. I realize that voltage is not the best way to determine the state of charge or health of the batteries, but  surely it must give a good indication.

While charging (in "Boost" mode), the system would indicate a battery voltage of 55.4V. It would go to "Float" in the afternoon on a sunny day like it should, indicating 54V.

I started suspecting that something might be wrong when I saw the voltage dropping more that expected after the sun has gone down. It seems that the battery voltage would go down to 51V within an hour after the shadow has moved over the panels. It would drop to 50.5V during the evening and be at 49.5V in the morning. In the evening it works lights in the house (all LED's), one 10W LED throughout the night, makes some tea, works an electric blanket and works 3 x A++ fridge/freezers and a bar fridge.

I have taken individual strings of batteries out of the bank to see how they behave. Immediately after isolating a string the voltage will be at 52V, reducing to 51V within an hour, stabilizing at 50.5V, where it will stay for 72 hours.

The voltages of the different strings test very close to each other. Testing all the batteries individually also indicate the same voltage, even after disconnecting the balancers.

According to Narada, 47V would indicate 0% capacity and 52V 100%.

This means that the batteries in my system would drop to 80% capacity soon after the charge is removed, then down to 70% where they will remain.

I tried getting hold of the Narada importer to get their input, but have not had any success yet.

I am concerned about the health of the batteries, but it could also be that I've got some settings wrong.

I'll appreciate your opinions.

I assume as it's 48v that you have 3 strings of 4 batteries each?

First issue is too many strings of batteries. How are these wired?

Second issue is per your explanation above the absorb voltage is to low @ 55.4v for an AGM unless its very hot.

Third issue is you many be under paneled for the depth of discharge of the battery bank.

I am not familiar specifically with Narada batteries specs, so am speaking in general terms. Batteries should reach absorb voltage per the manafacturer specification and stay there for several hours to ensure full charge. Is this happening? 

You have 600ah of battery storage and 3700watts odd  in panels. This is ok if your under 20 -25% DOD nighly. 

Otherwise you could battle to put back the used energy during the day with other loads etc. 

Hard to say not knowing where your located as sun hours, average daily loads etc all play a roll.

Load test - charge batteries per manfacturers spec, and hold vlatgae for 3-4 hours or when battery tail current reaches c/1 (i.e 6 amps).

Now apply a C10 load of battery rating i.e. 60 amps @ 48v 2900 watts odd. Battery voltage should not drop below 49v odd. If voltage drop significantly more than this, you have fading battery/s.

 

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Hi LivSol

I'd like to learn.

1. You're correct - it is a 48V system. The 12 batteries are arranged in 3 strings of 4 each. 4 batteries in series make 1 string and the 3 strings in paralel make the pack. How should I reduce the number of strings? I'm keen to learn.

2. Read about the Narada lead carbons. They don't run the same voltages as other lead acid batteries. I can supply some information, but there are values that I haven't got.

3. The "production" figure of the charge controller seems to be at an average of around 8-10kWh/day. With a mountain to the east and to the west our sun day is shorter, but I doubt that it would be too short. Normal sunny days the system goes into float sometime in the afternoon. If the panels were insufficient, that would not happen?

4. Yesterday I isolated the panels from the system. The battery voltage soon goes down to 51V. I switched on 2 kettles (3550W in total) for 45 minutes, refilling with cold water once they boil. The voltage was at 49.5V, after the "test". (We could now make coffee for a compound).

Your views please.

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22 minutes ago, Jakes said:

Yesterday I isolated the panels from the system. The battery voltage soon goes down to 51V. I switched on 2 kettles (3550W in total) for 45 minutes, refilling with cold water once they boil. The voltage was at 49.5V, after the "test". (We could now make coffee for a compound).

Your batteries are still good. They may not be after a 45min test. My failing  batteries cannot keep the microwave going for 5 min.

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On 7/25/2017 at 7:36 PM, Jakes said:

Hi LivSol

I'd like to learn.

1. You're correct - it is a 48V system. The 12 batteries are arranged in 3 strings of 4 each. 4 batteries in series make 1 string and the 3 strings in paralel make the pack. How should I reduce the number of strings? I'm keen to learn.

2. Read about the Narada lead carbons. They don't run the same voltages as other lead acid batteries. I can supply some information, but there are values that I haven't got.

3. The "production" figure of the charge controller seems to be at an average of around 8-10kWh/day. With a mountain to the east and to the west our sun day is shorter, but I doubt that it would be too short. Normal sunny days the system goes into float sometime in the afternoon. If the panels were insufficient, that would not happen?

4. Yesterday I isolated the panels from the system. The battery voltage soon goes down to 51V. I switched on 2 kettles (3550W in total) for 45 minutes, refilling with cold water once they boil. The voltage was at 49.5V, after the "test". (We could now make coffee for a compound).

Your views please.

Okay. A couple of things.

The load test I set out should only last a short time about 90 seconds or so. 

Whilst the C10 load is being applied you monitor the battery voltage. The voltage should not sag past a certain voltage. 49v wold the the minuim in my view. 

However, wet cell, AGM and gels will all be different due to their respective design, age etc. it's a quick indication test to where you are.

also, you can check the voltage of each battery as well during this test, to see if there is a battery or two dropping more than the others during the C10 load test.

Taking C10 out the batteries for 45 min won't hurt them. Theroretically, you should be able to run that load for 5 hours and would then be at 50% dod.

LivSol.

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  • 11 months later...
On 2017/07/21 at 2:16 PM, plonkster said:

A 10.5V battery that is presently doing work isn't empty (although it's not in a particularly enviable position either, it's likely to be damaged if you continue).

exactly what happened to one of my 250ah units - even when it still was able to pass a couple of seconds on the hawkins load tester; it stayed in the green for 5 seconds at 500amps... cf thread 'midpoint panic'

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