I mainly change my battery via solar panels, but I would also like to have the option to charge it from another 12v battery. Main reason for doing this is to top up the battery during cloudy days. 

So I'm thinking of getting an inverter and connect it to the grid input on my inverter and charge my battery that way. 

 

My current system looks like this:

1 x RCT-Axpert 5K inverter

6 x 250watt panels 

1 x US3000C PylonTech battery 

Not grid connected. 

 

Would a 1000w inverter be able to do the job, or do I need something bigger? 

 

Edited July 22, 20222 yr by TheOracle

1 hour ago, TheOracle said:

I mainly change my battery via solar panels, but I would also like to have the option to charge it from another 12v battery. Main reason for doing this is to top up the battery during cloudy days. 

So I'm thinking of getting an inverter and connect it to the grid input on my inverter and charge my battery that way. 

 

My current system looks like this:

1 x RCT-Axpert 5K inverter

6 x 250watt panels 

1 x US3000C PylonTech battery 

Not grid connected. 

 

Would a 1000w inverter be able to do the job, or do I need something bigger? 

 

What size 12V battery do you want to use to the 1000W inverter?

32 minutes ago, Scorp007 said:

What size 12V battery do you want to use to the 1000W inverter?

I was thinking of getting a 100Ah one. 

14 minutes ago, TheOracle said:

I was thinking of getting a 100Ah one. 

If lead acid you will only be able to use 600Wh before the 15-20% losses. Is it worth the money.  From what will the 100Ah be charged?

7 minutes ago, Scorp007 said:

If lead acid you will only be able to use 600Wh before the 15-20% losses. Is it worth the money.  From what will the 100Ah be charged?

My understanding is that you can use 50% (50Ah).

I'm only going to use it a few times a year. 

I will charged the battery with a charger during the days when I have enough sun. 

 

Edited July 22, 20222 yr by TheOracle

2 minutes ago, TheOracle said:

My understanding is that you can use 50% (50Ah).

I'm only going to use it a few times a year. 

Yes that is correct. 50Ah=50x12=600Wh.

A lot of work to keep it charged during the year for a few days of use.

Do you have a grid connection?

4 minutes ago, Scorp007 said:

Yes that is correct. 50Ah=50x12=600Wh.

A lot of work to keep it charged during the year for a few days of use.

Do you have a grid connection?

No, I'm not connected. 

1 minute ago, TheOracle said:

No, I'm not connected. 

I asked earlier on how will you charge the 100Ah?

Just now, Scorp007 said:

I asked earlier on how will you charge the 100Ah?

I will charged the battery with a charger during the days when I have enough sun. 

I guess my alternative would be to use a generator. How big generator would I need? 

18 minutes ago, TheOracle said:

I guess my alternative would be to use a generator. How big generator would I need? 

It all depends what load you have to put on the generator. Another way could be to check the sun hours for the next 6 days going forward and try and manage your load on the current battery. An APP like this giving the sun hours going forward could help. Knowing Monday is only 5hrs forecast one then use less on Saturday and Sunday.

Edited July 22, 20222 yr by Scorp007

I only need a solution to top up my battery. 

Isn't it better to get another pylontech battery? It will be more expensive but makes the most sense to me. Buying a 12v battery will probably add less than 20% charge to the one you have.

16 minutes ago, phidz said:

Isn't it better to get another pylontech battery? It will be more expensive but makes the most sense to me. Buying a 12v battery will probably add less than 20% charge to the one you have.

Yes, it is an option but as you said it is expensive. I live in Gauteng and we don't get many cloudy days. 

An inverter/generator has also the advantage that I can use it if my main inverter fails for some reason. 

10 minutes ago, TheOracle said:

Yes, it is an option but as you said it is expensive. I live in Gauteng and we don't get many cloudy days. 

An inverter/generator has also the advantage that I can use it if my main inverter fails for some reason. 

When one is off grid then a genny becomes just as important as panels and inverters. Part of standard tool kit.

Looking at the 7 bad days in Dec in Gauteng I am not so sure about not having many cloudy days.

Jan and April also provided their fair share.

2 hours ago, Scorp007 said:

When one is off grid then a genny becomes just as important as panels and inverters. Part of standard tool kit.

Looking at the 7 bad days in Dec in Gauteng I am not so sure about not having many cloudy days.

Jan and April also provided their fair share.

Pretty much tallies with what I have as record too.
Very true about a back up gennie.

 

I have done some reading and it seems the Axperts is very sensitive to fluctuations in voltage and frequency. 

Not sure if a generator is a good fit for the Axpert. 

Are there work arounds to mitigate the problem?

1 hour ago, TheOracle said:

Not sure if a generator is a good fit for the Axpert.

Well, there are generators and generators. With one that is fairly stable it should work. Important is to limit the charging current (11) on inverter settings according to the power capacity of the generator. Divide its rated power by 50V to get its 48V battery charging current capability.  Apply 10 to 20% safety margin.

12V 100Ah is peanuts in comparison with the 3kWh you have. Improve your system with additional battery of the same type and more PV panels. In the long run it's the better investment.

 

 

Edited July 23, 20222 yr by Beat

13 minutes ago, Beat said:

Well, there are generators and generators. With one that is fairly stable it should work. Important is to limit the charging current (11) on inverter settings according to the power capacity of the generator. Divide its rated power by 50V to get its 48V battery charging current capability.  Apply 10 to 20% safety margin.

12V 100Ah is peanuts in comparison with the 3kWh you have. Improve your system with additional battery of the same type and more PV panels. In the long run it's the better investment.

 

 

Thanks for the response, how would one know if a generator is stable or not? 

22 minutes ago, TheOracle said:

how would one know if a generator is stable or not? 

Do not look for the cheapest one. Talk to the seller and expose your problem. Perhaps he would agree to a trial.

4 hours ago, TheOracle said:

Thanks for the response, how would one know if a generator is stable or not? 

FWIW Inverters and generators

https://www.bundupower.co.za/inverter_with_generator.php

If this option of a "back-up" battery is only for a couple of times a year, then another Lithium battery doesn't make financial sense. In that case, it would be a lot cheaper to get a decent size gennie that can then be used for those times of year where it is necessary.

I think the most cost effective solution for me will be to rent a generator for those few times a year. 

Will rent one this week, to make sure it works with the Axpert. 

What will the total cost be to set this up and how much power will it deliver to your inverter (after going through all transformations)? You need a charger for the 12v battery; then you need a charger to charge the 48v pylontech from the 12v battery (would love to know if that is even possible!). Then you need the 12v battery. You mention a 100ah battery - is this normal lead acid? Best case you get 30% out of it unless you want to kill it quick. Thats 400W usable from the 12v battery, but after all the conversions how much will actually be available at the end point (your house)? If the loss between the 12v and the pylontech is 20% and the loss between the pylontech and the Axpert is 20% (I'm guessing here) that leaves 64% of the 400W = 260W. Is that enough for a rainy day?

I'd rather get a good quality pure sine wive inverter. 2kVAs go for around R12000 - heres the first hit doing a search. Just run straight of the genni when the battery is dead for the 2 or 3 days a year when you need it.

For the test I going to use the following settings:

03 (AC input voltage range) - APL

11 (charging current) - 20

16 (Charger source priority) - utility first

Any other settings I must check?