Help

Hi all- I need help with the settings on my MUST 5kva 48v inverter. I upgraded my panels a week ago. Now I have 6x 400w panels with 6 hours of good sun per day. My battery bank 4x 12v 270ah agms reads 50v at the end of the day around 6pm but never goes up over 56v on the sunniest day. Usually stays atound 53.6v until sundown. I think they're meant to go to 58v for at least 2 hours each day?

Is this related to the same system in the thread below?

When you're using power out of the batteries it pulls the voltage down below their normal voltage for the state of charge. Were you running stuff off the inverter when you saw it drop to 50.8? That's very normal for the voltage to drop back down fast if you're actually using it.

I would suggest that you buy a battery monitor that tracks how much power is really in your batteries instead of watching voltages--but there is some setup work you'll have to do to make sure it's done correctly when you install it. And you have to install a shunt into the negative wire before anything connects to the batteries so it can really watch the system as it functions, that's how it watches how much power the battery charger is really providing.

For me, I've been offgrid for a ton of years and I'm still pretty ignorant about where the batteries are without a shunt. Some other battery chemistries have changed this stuff some, I'm assuming that you're talking about your AGM batteries. For example, my LiFePO4's don't sag as much under load as AGM/lead acid etc.

non-cheap options that I'd buy are-
bluetooth interface only:
bluetooth+display+relay function:

They have an optional 6000amp shunt for it !

Bud Martin said:

Is this related to the same system in the thread below?

Battery Bank after charging

Hi all- I upgraded my panels a week ago. Now have 6x 400w panels with 6 hours of good sun per day. My battery bank reads 50v at the end of the day around 6pm and goes to 48.6v by 7am the next morning. I ran my smart battery charger from my 3.3kw generator for 2.5 hours to top up my batteries...

diysolarforum.com

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Indeed it is.

surfergirl said:

Indeed it is.

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I have 4x 12v 270ah batteries to make up 48v

cs1234 said:

They have an optional 6000amp shunt for it !

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I like to think that this shunt is larger than my car in real life.

surfergirl said:

I have 4x 12v 270ah batteries to make up 48v

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It's possible to run a generator for longer than necessary... Some batteries need to be maintained by being topped off regularly though (1x per week usually for AGM), I'm not sure it was really a waste unless you know when they hit that voltage and how long they were sitting at it. Most people like to do bulk charging on generator and then switch to solar for longer absorb charge cycles (because they know their house will be using part of that solar input, it will leave the other part for a partial/slow battery charge at the top 20% SoC).

How old are the AGM batteries? They often have a 3yr design life and don't always last as long as cheap lead acid batteries that require maintenance. The shunt+battery monitor would show how much power your batteries are still providing you if they have started to decline or you have questions about their real state of charge.

@John Frum

Lilikoi_Heavy_Industries said:

It's possible to run a generator for longer than necessary... Some batteries need to be maintained by being topped off regularly though (1x per week usually for AGM), I'm not sure it was really a waste unless you know when they hit that voltage and how long they were sitting at it. Most people like to do bulk charging on generator and then switch to solar for longer absorb charge cycles (because they know their house will be using part of that solar input, it will leave the other part for a partial/slow battery charge at the top 20% SoC).

How old are the AGM batteries? They often have a 3yr design life and don't always last as long as cheap lead acid batteries that require maintenance. The shunt+battery monitor would show how much power your batteries are still providing you if they have started to decline or you have questions about their real state of charge.

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Thanks so much for the great info. Batt
eries are 3.5yrs old. What batteries should I replace them with? Lithium is out of my price bracket....i love shoes

surfergirl said:

Thanks so much for the great info. Batt
eries are 3.5yrs old. What batteries should I replace them with? Lithium is out of my price bracket....i love shoes

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There really aren't any alternatives.. it's either AGM or LifePO4 unless you want want to go with FLA batteries that you have to maintain periodically by adding water to them and such..

surfergirl said:

Thanks so much for the great info. Batt
eries are 3.5yrs old. What batteries should I replace them with? Lithium is out of my price bracket....i love shoes

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EDIT: The voltage info you posted doesn't mean your batteries are dead, it sounded normal if you had loads running on your inverter. If you get a battery monitor, it will be able to tell you if you're still getting 50% usage of your battery bank. Then you can make a more informed decision on battery bank replacement?

You current battery bank is 6.4kwh usable (discharged to 50%)...

The cheapest option is costco 6V GC2s, around $100 per cell, you can make a 48V 200AH bank for $800, and you'd need to add 4 identical battery wires for the 1 string of 8 6V batteries setup, which is 5kwh usable bank size (10kwh overall). Doubling that to $1600, or maybe $1800 with additional battery wires, it would get you a 2 string battery bank, 10kwh usable bank size (20kwh overall). You'll need to add distilled water to these batteries every few months, and depending on how hard you use them, they'll probably last between 1yr and 5yrs. You also need the space to hold 8 or 16 cells for this option.

I assume replacing your AGMs is more expensive than the option above, but how much more expensive? More expensive than the LiFePO4 option below?

5kwh of LiFePO4 is $1500+shipping (linked below), and it's probably going to last longer than the lead acid batteries, many people believe 2 or 3 times as long... These are one of the cheapest products, I use them and am happy with them. I have two battery packs but my 3000W inverters will start on one battery fine if I want to use them for a smaller system.