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Darknight

Need some help with Growatt 3KW settings

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Hi Guys,

I have a Growatt 3kW 24v inverter. I currently have 4 x 330w panels (however, I've bought 2 more to add to it.). I have 2 x 200ah Narada 12v batteries. From what I've read and been told from other members here (thanks @Coulomb and @Jaco de Jongh), the firmware on the Growatt is similar if not identical to that of an Axpert.

Anyway, after some help from you guys and some research during the early stages of my solar installation, I finally understood how my inverter was operating and I've been able to get it to work more or less the way I was hoping it would. This leads me to my current predicament, with which I'm hoping you guys would be able to help me out with. I live in Zimbabwe, and the utility provider (ZESA) have increased their tariffs dramatically and so I'm trying to reduce my utility bill as much as possible which is why I'd like my batteries to charge only on Solar. My current settings are;

01. OUTPUT SOURCE PRIORITY - SOL

02. MAX CHARGING CURRENT (UTILITY CHARGING CURRENT + SOLAR CHARGING CURRENT) - 50A

11. MAX UTILITY CHARGING CURRENT - 20A

12. SETTING VOLTAGE POINT BACK TO UTILITY - 23v

13. SETTING VOLTAGE POINT BACK TO BATTERY - 27v

14. CHARGER SOURCE PRIORITY - OSO

19. BULK CHARGING VOLTAGE - 28.2v

20. FLOATING CHARGING VOLTAGE - 27v

21. LOW DC CUT-OFF VOLTAGE - 21v

Through my inverter I'm running 2 freezers, lights, modem, and TV. During the day, there's enough sunlight to power my load and keep my batteries charged. My load on the inverter is less than 50%. At around 5pm, my inverter starts powering my loads with utility while the little sun-light available charges my battery. Once the evening has set, my battery is no longer being charged or used. What I've noticed however, is that my battery SOC dips from 100% to 25% in a matter of 30mins as the evening sets in around 6pm. From 6pm to 7am, my battery SOC dips from 25% to 10%. My battery voltage however, never dips below 23v during this time and my inverter never signals any alarms.

I thought that if setting 14 - OSO was active, the battery would be charged to 100% by the evening and would only dip to maybe 50% by the morning wherein the solar would kick back in to charge it back up to 100% but that is not what is happening. This obviously leaves me with a problem if utility power is cut in the evening. Maybe some of my settings are wrong? Any help is greatly appreciated.

 

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Sadly, it sounds like your battery is shot. When you switch to utility power at sunset, there should be little load on the battery, something like 25W. The SOC display on the inverter is probably inaccurate like an Axpert's, but not too bad for a lead acid battery. It certainly should not plummet to 25% in half an hour, and 23 V by morning is pretty much dead flat. My guess is that you have a weak cell, so you lose about 2V soon after charging. But the other cells are probably not far behind.

You might get some extra months from it by carefully charging one of the battery modules with a good 12V charger, but I think you need to invest in a new set.

The Growatt firmware is similar to but not identical to Axpert firmware. I don't know if the Growatt firmware has fixed the premature float bugs that they would have inherited. If so, you need some workaround to not murder the next battery. Does your firmware have timed absorb or equalisation settings?

When your battery is sorted, you can change your output source priority to the equivalent of SBU on an Axpert, and use stored solar energy to power loads in the evening and perhaps the night. Consider raising your back to utility voltage to preserve battery life.

If you can't get a new battery for a while, your present settings are about all you can do.

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13 hours ago, Coulomb said:

Sadly, it sounds like your battery is shot.

Well that sounds depressing. I only got the batteries about a year ago.

13 hours ago, Coulomb said:

Does your firmware have timed absorb or equalisation settings?

Nope, not that I could find in the inverter manual.

13 hours ago, Coulomb said:

Consider raising your back to utility voltage to preserve battery life.

Does 24v sound good for this? 

13 hours ago, Coulomb said:

23 V by morning is pretty much dead

For a 24v battery bank, how do you know what voltage is 100%, 50%, 0% etc? I can't wrap my head around this.

13 hours ago, Coulomb said:

If you can't get a new battery for a while, your present settings are about all you can do.

I saw in another person's post that you had advised him to lower his max charging current from 40A to 20A. Do you think I should do the same?

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9 hours ago, Darknight said:

For a 24v battery bank, how do you know what voltage is 100%, 50%, 0% etc?

It's really hard, because it depends on the battery type (gel in your case), temperature, and charge history. Most charts specify 25°C, and require the battery to be at no load for several hours, which is not practical for a home energy system. Do a search for lead acid voltage state of charge (images), and you will see many conflicting tables. They all quote 12V nominal batteries, so double or halve voltages as needed for 24V. Most agree however that at 25°C rested, 50% SOC is 12.06 or 12.05 V, and 0% SOC is 10.5 V. 11.5V varies from about 10 - 20%.

So your settings (adding a little for the effects of load) are about 20% for back to utility, and say 5% for cutoff. Those SOC figures are very low, and will kill a battery in about a year. That's the hassle with lead acid, you should only use about 20% of capacity most of the time, and 50% rarely. You can use 80% in an emergency, but only once or twice in the battery's lifetime. So you can never use 20%, rarely the next 30%, and most of the time 80% is unused.

The near impossibility of gauging SOC from voltage is why many users opt for a battery monitor like the Victron BMV. It also takes into account your the peukert factor, where large loads deplete a lead acid battery quicker than light loads. 

10 hours ago, Darknight said:

Does 24v sound good for this? 

Yes, though 24.5V would be better for battery life. But you might find that runtime is too short with 24.5V.

10 hours ago, Darknight said:

I saw in another person's post that you had advised him to lower his max charging current from 40A to 20A. Do you think I should do the same?

You should reduce it to 30A (15% of Ah capacity).

If you find that premature float is badly affecting your system, it looks like you'll need an external solar charge controller.

Sorry to be the bearer of bad news.

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1 hour ago, Coulomb said:

If you find that premature float is badly affecting your system, it looks like you'll need an external solar charge controller.

Or maybe you could try @8321's idea: set the float voltage (setting 27) to 28.0 V. That's 14.0 VPC; enough to charge the battery, and yet under the 14.4 V per 12 V module required for gassing (except in extreme heat, perhaps). You don't want gassing for long in a gel battery, because most of the water can't be replaced; only a small amount of it can be replaced by recombination of 2H₂ and O₂. It might even get a little more life from your present battery.

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Thanks for the feedback @Coulomb

9 hours ago, Coulomb said:

You should reduce it to 30A (15% of Ah capacity).

I'm a little confused on how this max charging current setting works. According to the inverter datasheet the max solar charging current is 50A.

In the settings there's setting 02 - max charging current (UTILITY CHARGING CURRENT + SOLAR CHARGING CURRENT) and setting 11 - MAX UTILITY CHARGING CURRENT. If I lower setting 02 - max charging current to 30A, does that mean that I'm using less solar power to charge the battery since 20A of the 30A is from utility?

Or does that mean that during the day, when my batteries are being charged through solar, 30A of solar power will charge the battery and in the evening when there is no solar, 30A of utility will charge the battery. In this scenario, that would mean that in the event that both utility and solar are charging the battery together, the max amount of power charging the battery will be 30A?

At the moment, my setting 11 - utility charging current is set at 10% of ah capacity which is 20. My setting 02 - max charging current is set at 50A. Should I change both setting 02 and 11 to 30A or just one of them?

8 hours ago, Coulomb said:

Or maybe you could try @8321's idea: set the float voltage (setting 27) to 28.0 V. That's 14.0 VPC; enough to charge the battery, and yet under the 14.4 V per 12 V module required for gassing (except in extreme heat, perhaps). You don't want gassing for long in a gel battery, because most of the water can't be replaced; only a small amount of it can be replaced by recombination of 2H₂ and O₂. It might even get a little more life from your present battery.

Would this not risk overcharging the battery? According to the battery sticker, the float is 2.25vpc which is 13.5v per battery module. If I set the float to 28v, that would mean 2.33vpc. Is this difference safe enough to charge the battery without damaging it?

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27 minutes ago, Darknight said:

I'm a little confused on how this max charging current setting works. According to the inverter datasheet the max solar charging current is 50A.

OK, but that doesn't mean that it's good for your particular battery. 50 A is C/4, which is generally too high for gel lead acid batteries.

27 minutes ago, Darknight said:

If I lower setting 02 - max charging current to 30A, does that mean that I'm using less solar power to charge the battery since 20A of the 30A is from utility?

Only if you are utility charging during the day, which would be on rainy or cloudy days, and only if you enabled utility charging. Otherwise, you'll get 30 A of solar charging, if available, and if that won't exceed the absorb/CV or float battery settings (depending on what stage the charging is at).

27 minutes ago, Darknight said:

Or does that mean that during the day, when my batteries are being charged through solar, 30A of solar power will charge the battery and in the evening when there is no solar, 30A of utility will charge the battery.

No, because you set the maximum utility charging to 20 A. So 20 A at night.

Quote

In this scenario, that would mean that in the event that both utility and solar are charging the battery together, the max amount of power charging the battery will be 30A?

Yes. The 30 A limit is to protect the battery.

Quote

At the moment, my setting 11 - utility charging current is set at 10% of ah capacity which is 20.

There is no need to limit the utility charging to a fraction of battery capacity. Setting 11 is there mainly for generators, so you can set a limit and hopefully not overload the generator (whether you actually overload the generator depends on your loads as well as charging power).

Quote

My setting 02 - max charging current is set at 50A. Should I change both setting 02 and 11 to 30A or just one of them?

The important one is setting 02, so definitely change that one. Presumably you're happy drawing 30 A from utility at night (around 750 W plus losses, just over 800 W), so you may as well increase setting 11 as well.

39 minutes ago, Darknight said:

Would this not risk overcharging the battery?

Yes, it's a bit of a desperation measure, but saves outlay on another solar charge controller. But I believe it's fairly safe; once fully charged, the battery merely draws little current, and little harm is done (there is a little extra heating, which is not good for lifetime). If the battery gets hot (around 40°C), then 14 V per nominally 12 V module is a gassing voltage, so you might have to be careful in summer, and perhaps reduce the float voltage setting a little. In another topic, @plonkster has claimed that 14 V is a gassing voltage (even at 25°C I think), just with less volume of gas. My understanding is that it's a pretty much binary thing; at a certain voltage, the gassing starts, and at lower voltages, it's pretty much not happening, and a sealed battery (such as your gels) should cope with it happily. I'm no lead acid expert however, so do your research.

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1 hour ago, Coulomb said:

gassing voltage

Sealed batteries can recombine the hydrogen into water, as long as you don't boil them (in which case the pressure valves open and you hear that whistling sound).

I also would not say I am an expert with lead acid... certainly less so these days. I'm working from the knowledge that Storage Mode in the Victron inverter/charger goes down to 13.2V per 12V increment, and their documentation states that this is below gassing voltage, but does not fully prevent self-discharge and therefore the charger will do an absorption cycle every few days. So what I can tell you is 13.5V is a "slow" gassing voltage and 13.2V is not. But as Coulomb points out, its temperature dependent too.

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7 hours ago, Coulomb said:

The important one is setting 02, so definitely change that one.

I've changed the setting 02 this evening to 30A. I'll monitor it during the day tomorrow.

I think my batteries are definately shot. Reason being that today I allowed utility to charge my battery fully. The inverter showed 100% SOC on the battery icon. This evening I changed my charging priority to OSO and the SOC% immediately dropped to 50% with the battery voltage sitting at 25.8v. Within about 90 minutes the SOC dropped from 50% to 25% with the voltage sitting at 24.6v. After that, I decided to change the charger priority back to CSO which started charging the battery with utility. The voltage immediately shot up to 28v.

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So just an update on the situation and an insight into how some of these solar equipment companies over here are operating. 

I contacted the company that I bought the batteries from to inform them that there seems to be a problem with the batteries. They told me that they would send a technician to my house to check the batteries. I had requested for them to send the technician today in the morning so that I could be available for the technician. The tech arrived late but was able to check the battery. The tech told me that one of the batteries had a problem and that his company has been experiencing a lot of similar problems with these batteries as they are intended for cell towers. The tech told me that they would replace the batteries but they did not have stock of these exact models. He told me to ask their sales team if they could provide me the solar compatible batteries they do have in stock if I was willing to pay a topup on what I had already paid for my current batteries. The tech asked me not to mention him when I spoke to the sales team.

I spent the rest of the afternoon trying to contact the company only for them to ignore my calls. Eventually, at around 3.30pm, I got through. I informed the sales person that their tech found that there was a problem with the battery. I asked the sales person if I could top-up money to get the battery that they have in stock, at which point the sales person became irritated. I asked the sales person if he could give me some form of assurance that if I replaced the batteries with the same model, I shouldn't experience the same problem. The sales person became extremely irritated and began to shout at me over the phone. I calmly asked the sales person why he was shouting at me. This made him angrier. I then told him that If he wanted to shout and yell at me, that he should refund my money and take the batteries back as I did not wish to deal with a company that shouts at their customers. I then hung up the phone.

I then whatsapped the sales person to inform him that his customer service was poor and that I did not want to deal with his company. I requested for my money to be refunded. He proceeded to tell me that I was bullying him (even though he was shouting at me on the phone) and that he would not refund my money. I then told him that the only way I would accept the same model of batteries was if they were delivered still in their boxes and with some form of proof that they were brand new (As a side note, when I bought my batteries initially, they were not in boxes. They were simply cling-wrapped). I told him that If he could not do that, I would prefer to be refunded.

The sales person then went on to label me a racist even though I never once insulted him, or his race, or raise my voice. I actually referred to him throughout the conversation as "my friend". I decided to block his number.

So that's pretty much how my search to fix my batteries has gone. I am a service provider by profession and some of my clients sell batteries. Namely the Trojan and Allgrand batteries. However, they are quite expensive and I don't really have the cash at the moment to sink into a new set of batteries. I may be able to get the Allgrand batteries on terms, however I'm not sure how good these batteries are. I honestly don't mind replacing my current batteries with a brand new set of the same model at no cost but I'm not sure how to continue communicating with this company that I bought my batteries from initially after dealing with their sales person.

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Sorry to hear about the terrible experience with the sales person.

Is there no way to speak to a manager or the owner?

 

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4 hours ago, francois said:

Sorry to hear about the terrible experience with the sales person.

Thanks

4 hours ago, francois said:

Is there no way to speak to a manager or the owner?

I'll have to see if there is a manager or owner available. I honestly just don't want to have to deal with this same dude again.

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Hi Guys,

Small update. So I managed to get the company I initially got the batteries from to allow me to get 2 x brand new Narada 200AH batteries by paying a small topup. Unlike the batteries I had previously, these are a different model that come sealed in boxes and are apparently more compatible to solar systems. I happen to know the company that sells them these batteries and I'm able to get 2 more brand new ones to increase my battery bank to 4 batteries. What I'm hoping the guys here could help me with is what values I would have to place on the following settings if I did decide to increase my battery bank to 4 batteries. Obviously because I'm running a 24v system, the batteries would have to be connected in such a way to keep the voltage at 24v while increasing the amperage to 400ah.

  1. MAX CHARGING CURRENT (UTILITY CHARGING CURRENT + SOLAR CHARGING CURRENT). At the moment this is sitting at 30A. I'm assuming this would increase if my battery bank increased to 4. Any idea what the setting should change to?
  2. MAX UTILITY CHARGING CURRENT. Currently this is set to 20A. I'm assuming this would also increase if the battery bank increased. I'm assuming this would increase to 40A (10% of battery capacity).

I'm also assuming that my voltage settings would remain the same since it would still be a 24v system.

Thanks

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