max battery charge current ratings?

[new2PV]

Question, I found some ups batteries the max charge rate is c20/5 and they are rated 75 amp hours, max charge current spec is 15 amps.  If I use the classic 150 and run 4 battery's to get 48 volts with  10 x 295 watt panels=2950 watts= 60amps@ 48 volts. Would this not be too much current and overcharge the batteries?, if I am not consuming the power I am getting out of the cells? Would the rest have to go to a dump load?

[TomW]

Question, I found some ups batteries the max charge rate is c20/5 and they are rated 75 amp hours, max charge current spec is 15 amps.  If I use the classic 150 and run 4 battery's to get 48 volts with  10 x 295 watt panels=2950 watts= 60amps@ 48 volts. Would this not be too much current and overcharge the batteries?, if I am not consuming the power I am getting out of the cells? Would the rest have to go to a dump load?

Simply put, if those are 12 volt batteries, 4 in series for 48 volts you will cook them to a crisp pushing 60 amps into them for any length of time by a factor of about 4 or 5.


You will really want a LOT more battery to utilize that amount of panel, In my opinion.

The Classic can handle it fine but it will be a poorly balanced system that will waste most of your incoming power.

Not entirely sure of your goal but you will not get far with UPS batteries. First, they are tiny, second they are not designed for regular cycling. They are built to provide occasional backup power and being on a maintenance charge the rest of the time.


One of those "it might work" situations that I would avoid.

Just my first thoughts before coffee.

Tom

[new2PV]

Thanks Tom, that is why i am asking these questions. I am trying to use the power from Solar during the day for the house go back to grid at night, but still have a bit of emergency power if needed. Just learning about what will work best. How does the diverson load work on the classic? What about using optima yellow top batteries, it says the charge current is unlimited.

[mike90045]

you don't use a diversion load, you program in a MAX Charge Amps value for your batteries of about 10 -15 amps. (if i understand your initial post that 15a is the MAX they will safely be fed)

[new2PV]

Ok, but then my 3000 watt solar array would only be putting out 720 watts, kinda defeats the purpose? Of having 3000 watts.  I need a better option, no comments on the optima's?

[Westbranch]

You should look for batteries that can accept that hi a charge rate rather  than 75Ah tiddlers, eg they are only 3/4 or less of what a car battery can accept

add: see my system specs...

[new2PV]

What exact battery do  you have?  140 x4@48v CD 900 AH What is that?  4 x 140w batteries? in parallel strings  to make 900 AH?   

[Westbranch]

I have 2 banks of 2V cells, of C&D AGMs at 24V with 900Ah capacity

[new2PV]

A what current are you charging those batteries at?

[Westbranch]

I have a 30A charger.  When the full array is in place I expect the Classic to have to limit it to 90A, 10% , if I get enough 'juice' to get it that high...

[new2PV]

Lifeline batteries can accept a C X 5 rating ie a 100ah battery can be charged at 500 amps! However voltages must not exceed spec. So now I dont have to worry about charging current.

[zoneblue]

C5. Well, yes, theoreticaly. But not in the real world. Charge efficiency will be poor, battery life will be dreadful, and there is zero room for error. Any lead acid battery, but especially AGM with their low internal resistance, over charged at that rate, for even a short time will go into thermal runaway faster than you can say jack robertson.

Youll have a very hard time making an economic case for using any kind of battery to save money on a grid connection. Unless you live in Hawaii... or NZ.

C/4  is about your upper practical limit for agm.

[new2PV]

You could be correct, I am just reading the technical manual, Cx5 seems crazy to me.  I could send them an email and see what they suggest for charging rates in my application

[Paulcheung]

Is there a special reason why you want AGM batteries? Because it is expensive and not last as long as the FLA, unless FLA is not an option if I were you I would get either a bank of Trojan L16RE-B 8x6 volts or Rolls S550 8x6 volts make it 48 volt bank. that will work wonders for your application with 3000watts panels. A lot of people in Jamaica do as you wanted to do.

We set the automatic switch to turn off the inverter when battery voltage drop to a set volt and connect to the grid and in the morning when sun come out and the battery voltage rise to the set volt, the inverter turn back on.

[new2PV]

I went to FLA batteries I just wanted to keep the AGMS in the house, but now I put the FLA's outside..