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Recommend me some batteries for solar to replace existing lead acid deep cycle


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Hi there.

 

Yes you can run them in Parallel but not series. Bian will be able to give you more info but there are people who have build their own batteries and run 3 sets in Parallel.

He will be able to give you advice on custom builds. 

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Just be aware that the Pylontech US3000 (3.5kWh) is a 48V battery and your inverter runs on 24V. You would require the Pylontech UP2500 (2.84kWh), which is the only 24V model they offer

@Lindsay check in here https://lithiumbatteriessa.co.za/ and speak to @Bain Viljoen 

Yeah different BMSes have different expectations of the hardware connected to them. Some BMSes get very upset and disconnect their DC protection relay/FET easily if you don't stop charging quickly aft

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@Bain ViljoenThat 6kwh 24V unit looks good. What are the interface options on it, can it talk to the Axpert inverters or does the BMS have USB/serial comms?

You guys aren't based in Cape Town as far as I'm aware, so what would it cost to ship it down and what are the support options down here if there are any issues or problems installing it?

Thanks!

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@Lindsay At the moment the smart battery has coms to Victron inverter and possible SMA.

Growatt, Goodwe and Sunsync support are coming in about a month or 2.

They can Parallel upto 16 units together.

I have sent the guys at @ICC information with my protocol for integration and await their response.

Voltronics/Axpert are not willing to play ball and answer any of my emails. So unfortunately no integration with them any time soon.

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@Bain Viljoen If one has a Victron BMV7XX connected to a Raspberry Pi running ICC-Pi, why would there be a need for the BMS to communicate with the RPi and ICC. The BMV7XX would determine absorb and float voltages accurately and ICC would control the inverter's chargers accordingly. Of course if the BMS does communicate with ICC, one would save the cost of a BMV7XX, not an insignificant amount. At least that is how it appears to me or am I missing something.

If my perception of the matter is correct, one would be able to use any LiFePO4 battery with an inverter controlled by ICC provided you also have a BMV7XX installed and feeding relevant information to ICC. The issue of connecting a BMS to an inverter has cropped up several times in the past but the reason for the connection has not been clarified. Perhaps someone will explain and contribute to my understanding of the purpose. 

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The bmv is design actually to be use with lead acid based batteries by using the  Peukert's law to work the state of charge of battery and discharge. With the lithium and lifepo4s busy taking over the market slowly, Peukert's law don't really work with them. 

A bms is Battery Management System that actually keeps a eye on every sell in you lithium / Lifep4 setup and works out the stage of charge and deside if it needs to shift volts over to other cells "active ballancing" or if there cell run away that it stop the sell from run away by stopping the charge toe the batteries and start moving the extra of the over charge cell to the other cells. 

Now if you bms got comms, it will  inform the inverter to say to it "Hi , stop charging, we got some problems that we need to sort out, we will inform you to start charge again" . So the inverter will wait for the responds back. 

Now some bms don't have comms so the guys use bmv to help with charging and discharging info. There is fine line of working this out with the guessing game of the Peukert's law. We use between 1.00 and 1.05 for this in lithiums.

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2 hours ago, Gerlach said:

The bmv is design actually to be use with lead acid based batteries by using the  Peukert's law to work the state of charge of battery and discharge. With the lithium and lifepo4s busy taking over the market slowly, Peukert's law don't really work with them. 

You can  however configure the Peukert factor on the BMV to make it work with LFP batteries. Just set it to 1.05 (or even to 1.00 to disable it), instead of the usual 1.2 or 1.25 for lead acid.

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@plonkster Thank you for your explanation which clarifies the issue. If I were to replace my FLA batteries with LiFePO4, of  course I would include preferably the ANT BMS and most likely use @Bain Viljoen's cells. However since I already have a BMV700 and ICC on a RPi, I could not figure out the need for communication between the BMS and the inverter. Clearly it is essential if one does not have a BMV7xx and ICC control. Furthermore I would expect that the BMS would terminate charging when the cells are fully charged, irrespective of whether solar or the inverter mains charger still supply current, at least that is my perception after considerable research. 

@Gerlach thanks for your explanation. My point however was that Axpert users with similar installations to mine and who wish to switch to LiFePO4 cells with a BMS, would not have to wait for communication between the BMS and inverter to be implemented. @plonkster's explanation has in my view confirmed that. 

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2 minutes ago, ebrsa said:

terminate charging

Yeah different BMSes have different expectations of the hardware connected to them. Some BMSes get very upset and disconnect their DC protection relay/FET easily if you don't stop charging quickly after it has ordered you to do so.

In my experience, if you keep your battery voltage BELOW the voltage where the BMS activates its protection features, and if you have a large enough battery so that constant charge current interventions is not necessary, then you don't need communications with the BMS. If anything bad happens, the BMS shuts off the power and the entire house goes dark. Oops... let's not do that again 🙂

There is however one very useful feature that comes from BMSes that can do comms, and that is that they track SOC. If you already have another way to track SOC (eg an inverter that has this built in, or a BMV), then you don't need to use the BMS for that. SOC is always an estimate, and even the BMS gets it wrong (I have examples of use cases where a BYD battery gets it spectacularly wrong), so using your BMV-7xx is really not a bad alternative.

But ideally you want a BMS that allows you to regulate the voltage and not constantly mess with current limits. If you just aim for 3.45V per cell, it should run like a conventional lead acid bank...

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9 hours ago, plonkster said:

In my experience, if you keep your battery voltage BELOW the voltage where the BMS activates its protection features, and if you have a large enough battery so that constant charge current interventions is not necessary, then you don't need communications with the BMS. If anything bad happens, the BMS shuts off the power and the entire house goes dark. Oops... let's not do that again 🙂

Ok, so if I implemented Pylontech or the ones Bain sells then I gather I'll just have to make sure it doesn't ever go past the maximum voltage amount to avoid it shutting off. I've heard that disconnecting the batteries from Axpert type inverters while there's solar coming in can cause them to blow.

It doesn't sound like there's any essential communication needed that requires the BMS to talk to the inverter. I would however like at least to log the data from the BMS so I can monitor the SOC on my Raspberry PI and check they aren't undercharged (I already log from my inverter and using shunts with my own code, not ICC).

@Bain Viljoen Would you be willing to send me your protocol? Maybe you can also send me an quote for the 6kw 24V one including shipping to CT so I can take a look?

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@plonkster Thanks a lot for you reply. My knowledge of LiFePO4 batteries is limited to what I could learn from Internet research whereas you have the advantage of practical experience. Some things seem to to need little more than logical reasoning based on available information. However practical experience will always trump that. Anyway it all remains a lot of fun, something that is in lamentable short supply these days. 

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  • 3 weeks later...

Sorry to revive my old thread, but assuming I was moving to Lithium batteries, what capacity should I buy?

I only use around 2kWh (80Ah @ 24V) per 24hr cycle, and probably drain 30Ah overnight (unless we in middle of winter where it could be up to 40Ah) at which point they start charging again in the morning. I still have a lot of items on normal mains electricity, and am not planning on moving everything over to solar.

Would 2.8kWh be enough that the DOD wouldn't be too much and the batteries would be ok for several years?

I'm hoping to avoid buying two of these battery packs (Pylon) which ends up a bit pricey.

Thanks in advance.

Edited by Lindsay
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On 2020/09/29 at 6:08 PM, Lindsay said:

Thanks. Sounds like around 3.2kWh would be ideal, but maybe I could just get away with 2.8kWh :)

Worst case I could always switch to charge off the grid on particularly bad solar days.

You Should have a Look at the ZTE 4.8 KW lithium battery not badly priced.

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On 2020/10/05 at 12:49 PM, Lindsay said:

I'm looking for 24V options

Do you use the same amount of power throughout the year or do you have times of heavy usage (like family visiting etc)?

For me that is the one thing that makes lithium batteries not worthwhile at the moment. As a crude example say you use 8kwh daily, you can get a 10kwh pylontech bank and drain it to 80% DOD daily but what happens when family comes around?

For the same price you can get about 36kwh of gel batteries, drain them to 25% DOD daily and when the family comes over you still have well over 20kwh extra capacity to dip into.

Edited by tetrasection
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1 hour ago, tetrasection said:

Do you use the same amount of power throughout the year or do you have times of heavy usage (like family visiting etc)?

For me that is the one thing that makes lithium batteries not worthwhile at the moment. As a crude example say you use 8kwh daily, you can get a 10kwh pylontech bank and drain it to 80% DOD daily but what happens when family comes around?

For the same price you can get about 36kwh of gel batteries, drain them to 25% DOD daily and when the family comes over you still have well over 20kwh extra capacity to dip into.

But what is your guaranteed lifespan for gel batteries at a 25% DOD?

Pylontech you have 10 years at 80% DOD. That is what sells them in my opinion. My 1.5 year old AGM's were struggling to hold load for even 2 hours during load shedding. The LifePo4's are (again my opinion based on experience with both), just much more robust if you plan to cycle them every day

Edited by PhilFM
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33 minutes ago, PhilFM said:

But what is your guaranteed lifespan for gel batteries at a 25% DOD?

Pylontech you have 10 years at 80% DOD. That is what sells them in my opinion. My 1.5 year old AGM's were struggling to hold load for even 2 hours during load shedding. The LifePo4's are (again my opinion based on experience with both), just much more robust if you plan to cycle them every day

According to google Gel batteries should last about 6 years at 25% DOD.

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I agree, if your daily energy requirements are constant throughout the year then lithium is a no-brainer.

However if you tend get visitors over holidays and need extra power for even a day or two you are pretty screwed.

Hence IF you do get visitors and need extra capacity on occasion I'd say Gel batteries are still the better option (or at least more cost effective, compared to buying extra lithium batteries that will only be used a few days a year) and in 6 years time there will probably be cheap sodium batteries on the market.

Edited by tetrasection
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