what charge controller do I need for a 250watt panel

[Bucho]

1. 714 watt panels
2. 900 AH batteries @24 volts
3. 30 Amp Charge Controller. definitely an mppt

The battery bank you're talking about here is too many amp-hours for the system you're talking about to support. 900Ah/12h=75A. So you wouldn't be close to being able to fill FLA's. Even if you decide to expand your AGM battery bank your panels and charge controller are undersized.

P.S. Can you conserve any more energy? Perhaps don't use the desktop and stick to the laptop when the grids down.

[fopoku2k2]

Easy peazy.

Your battery needs to be sized for 5 day Autonomy to CYA for 3 cloudy days before going on your generator. You will need a generator. In addition the 5 day autonomy maximizes you battery life and gives you the best bang for your buck. So 5 days x 4000 wh = 20,000 wh or 20 Kwh. Once you know that then all you need to know is battery voltage. 20,000 watt hours / 48 volts = 416 Amp Hours.

Have you read these Stickies yet? It would have answered all your questions.

Off Grid Battery Design

I just went through your "solar off-grid battery design" thread and I am proud to say you are a through solar legend. I managed to get a lot of information about how to properly size my system. I am surprised you don't have your own YouTube page.

Based on my analysis with your help I am looking at a system with the f.f.
1. 714 watt panels
2. 900 AH batteries @24 volts
3. 30 Amp Charge Controller. definitely an mppt

Based on my countries utility rate I am getting a "rate increase" of about 300% within the first 5 years.
I know the utility rate in my country is definitely going to go up since we have no plans of going nuclear and gas / hydro is getting expensive everyday as well as a rise in corruption and unstable power distribution

[Sunking]

can you help break it down to me esp how you got the 20 Kwh battery, 48 volts @ 400 AH.

Easy peazy.

Your battery needs to be sized for 5 day Autonomy to CYA for 3 cloudy days before going on your generator. You will need a generator. In addition the 5 day autonomy maximizes you battery life and gives you the best bang for your buck. So 5 days x 4000 wh = 20,000 wh or 20 Kwh. Once you know that then all you need to know is battery voltage. 20,000 watt hours / 48 volts = 416 Amp Hours.

Have you read these Stickies yet? It would have answered all your questions.

Off Grid Battery Design
How Many Batteries and Why
Inverter Size vs Battery
Are You Killing your Batteries
Batteries for Dummies
Meet Mr Peukert
Troubleshoot your Batteries
Battery Types
Trojan Battery Guide

[fopoku2k2]

Well it means you need a 20 Kwh battery which is 48 volts @ 400 AH. That requires a panel wattage as low as 1600 watts up to 2500 watts depending on location. Depending on panel wattage will require a MPPT charge controller sized a small as 35 amps up to 50 amps.

Note if you keep the panel wattage below 2000 watts you could go in with 24 volt battery @ 800 AH, but would be more expensive than 48 volt battery. Forget about 12 volts.

can you help break it down to me esp how you got the 20 Kwh battery, 48 volts @ 400 AH. plus i am planning on installing a total panel wattage of 1500 by the end of the year and eventually double that next year. as you already know i currently have 24 volt @ 200 AH batteries installed. as you have advised i would be upgrading to 400 AH next month

[Sunking]

my daily energy need is about 4,000 WH (including a 30% loss).

Well it means you need a 20 Kwh battery which is 48 volts @ 400 AH. That requires a panel wattage as low as 1600 watts up to 2500 watts depending on location. Depending on panel wattage will require a MPPT charge controller sized a small as 35 amps up to 50 amps.

Note if you keep the panel wattage below 2000 watts you could go in with 24 volt battery @ 800 AH, but would be more expensive than 48 volt battery. Forget about 12 volts.

[Sunking]

right on the money. how do you figure these things out so easily? . . . .
So are these Telecom AGM Batteries any good compared to FLA's??

Did not catch that. Because I use to work in Telecom and was the guy who found suckers to buy worthless batteries turning a liability into an asset.

When Telecom buys batteries, they buy large quantities. Your average small cell tower is around 4000 pounds worth. When you have more than 500 pounds of electrolyte in a building or container requires EPA permits and local inspections by the FD and OSHA. The Telecom then has full responsibility of those batteries until disposed of along with all th ered tape paperwork that comes with it.

So after 5 to 10 years the batteries are pretty much shot and boat anchors. To get rid of them requires you to hire someone to go out and remove them and properly dispose them. That cost big bucks, much more then the salvage weight of the batteries. So there are companies out there that buy surplus salvaged batteries. The telecom sales them dirt cheap to the salvage operator and he goes, removes them, and takes the liability off the Telecom.

Then the salvage operator finds people to sale the batteries too for disposal. Tag your it.

The Telecom batteries are designed to be discharged and recharged very quickly unlike Deep Cycle batteries. They have a cycle life of roughly 150 to 300 cycles and a Calendar life of about 10 years. Whichever comes first. The batteries are rarely if ever discharged. They set there in service waiting to be used if the power goes out. After 10 years or whatever the service warranty life the tired batteries get replaced.

[fopoku2k2]

No. The current is determined by panel wattage. If you have 1000 watts of panels on a 12 volt battery using a MPPT controller you had better have a 80 amp Controller. You had also better have a 12 volt 640 AH to 960 AH battery to connect to it.

MPPT Output Current = Panel Wattage / Battery voltage.

You connect a 1000 watt panel to a 20 amp controller on a 12 volt battery and you have a new boat anchor. You connect a 100 watt panel to a 15 amp controller and a 12 volt 500 AH battery and you will soon have a very nice heavy boat anchor. Everything has to be sized to work with each other.

It all starts with how much energy you need in a single day. Then the design starts. Fail to do that and you have very expensive Boat Anchors. If you just go willy nilly and piece stuff together, you will have boat anchors.

@Sunking looks like i need to follow your lead and size my system properly ones and for all. Ok, so my daily energy need is about 4,000 WH (including a 30% loss). find attached my data sheet. Capture.JPG
So Sensei can you please please school your student???

[SunEagle]

right on the money. how do you figure these things out so easily? . . . .
So are these Telecom AGM Batteries any good compared to FLA's??

I didn't see anyone answer that question so I will.

No those Telecom AGM batteries were not designed for a high number of deep cycles as compared to a Deep Cycle FLA battery.

Those Telecom batteries were made to sit there for long periods fully charged and then deliver a lot of power when the grid goes down. You then recharge them back up to full power and wait again. The number of times you can discharge and recharge them is very small compared to good Deep cycle FLA type batteries.

[Sunking]

Oooh ok, but isn't this the reason why charge controllers were invented??

No. The current is determined by panel wattage. If you have 1000 watts of panels on a 12 volt battery using a MPPT controller you had better have a 80 amp Controller. You had also better have a 12 volt 640 AH to 960 AH battery to connect to it.

MPPT Output Current = Panel Wattage / Battery voltage.

You connect a 1000 watt panel to a 20 amp controller on a 12 volt battery and you have a new boat anchor. You connect a 100 watt panel to a 15 amp controller and a 12 volt 500 AH battery and you will soon have a very nice heavy boat anchor. Everything has to be sized to work with each other.

It all starts with how much energy you need in a single day. Then the design starts. Fail to do that and you have very expensive Boat Anchors. If you just go willy nilly and piece stuff together, you will have boat anchors.

[fopoku2k2]

He is referring to Charge Rate in hours of C/8 to C/12 window. Where C is the battery AH capacity, and the number is Hours. Example a 100 AH battery charged at C/8 is 100 Amp Hours / 8 Hours = 12.5 amps. Same battery at C/12 charge rate is 100 AH / 12 H = 8.33 Amps.

C/12 is the minimum charge rate for FLA batteries to prevent them from stratifying (water floating on top of acid in the battery jar). C/8 is the maximum charge rate to prevent over heating and excessive gassing spilling electrolyte.

Oooh ok, but isn't this the reason why charge controllers were invented??

[Sunking]

why only charge them between 1/8 to 1/12 and not to its full capacity??

He is referring to Charge Rate in hours of C/8 to C/12 window. Where C is the battery AH capacity, and the number is Hours. Example a 100 AH battery charged at C/8 is 100 Amp Hours / 8 Hours = 12.5 amps. Same battery at C/12 charge rate is 100 AH / 12 H = 8.33 Amps.

C/12 is the minimum charge rate for FLA batteries to prevent them from stratifying (water floating on top of acid in the battery jar). C/8 is the maximum charge rate to prevent over heating and excessive gassing spilling electrolyte.

[fopoku2k2]

I'd believe 4,800Wh That would be 200ah x 24v.

If your batteries are deep cycle FLA's you should charge them between 1/8 to 1/12 of their capacity so once you get your MPPT you should be in good shape.

why only charge them between 1/8 to 1/12 and not to its full capacity??

Yes, you can charge from multiple sources as long as you stay below 1/8 of your capacity (assuming you have FLA's).

what do you mean by unless i stay below 1/8 of my capacity??

[fopoku2k2]

FLA = Flooded Lead Acid or wet battery. What you have is a Telecom AGM battery made for Emergency Stand By service in a UPS or small cell site. Let me guess you gotta a deal from some guy who has access to a telecom or data center right?

right on the money. how do you figure these things out so easily? . . . .
So are these Telecom AGM Batteries any good compared to FLA's??

[Sunking]

What is an FLA battery? I have a Northstar NSB 100FT Silver battery (specifications sheet attached) [ATTACH=CONFIG]6564[/ATTACH]

FLA = Flooded Lead Acid or wet battery. What you have is a Telecom AGM battery made for Emergency Stand By service in a UPS or small cell site. Let me guess you gotta a deal from some guy who has access to a telecom or data center right?

[fopoku2k2]

Yes, you can charge from multiple sources as long as you stay below 1/8 of your capacity (assuming you have FLA's).

What is an FLA battery? I have a Northstar NSB 100FT Silver battery (specifications sheet attached) Capture.JPG