Newbie questions on LifePo integration to existing system

[Skip]

My application is an off-grid home in Montana.
2500 watts solar panels; Conext SW 4024 inverter; Classic 150 solar charge controller.
Batteries are four AGM 12v 180 Ah - two series pair in parallel for 24v, 360 Ah.
The AGM's are near end of life and I'm strongly considering LifePo. I want to be sure of what I'm learning from reading multiple posts and threads here.

My battery storage area is unheated, but does not typically drop below 40 deg F. and stays cool in summer, not exceeding 80 deg F. Is this an acceptable range for healthy charge/discharge for LifePo?

Also, I'm seeing that Ah ratings are based on a 80% to 100% depth of discharge. So, at best, all I can get from my AGM's is 180 Ah, while a 200 Ah LifePo bank would give me 200 Ah.?
If so, this has serious cost implications. LifePo not nearly as expensive as I first thought since I was trying to match Ah ratings LA to LifePo.

Last question is on capacity of battery bank as "pass through" while on full solar charging.
Even with my dying AGM's, if I have full sun on the solar panels, I can put heavy loads on the system and the voltage reading does not decline, as if I'm getting the power from the panels, not the batteries. The batteries just need to be there to pass the power through to the inverter. Am I seeing that correctly? If I were to start out with only 100 Ah of LifePo, would I see the same performance in the system? I don't want to swap out the batteries and then find that the system is throttled when the well pump kicks in.

What I'm looking at now are a pair of 200 Ah 12v smart batteries with internal heaters.

Any cautions about the Chins-US brand?

BTW, I'm retired on limited income. Budget is a restraining factor.
Thanks

 

[jberger]

Skip,
Based on your usage and needs, I'd say you are on the right track.
You mention that the storage area doesnt' drop below 40 so I don't think you need to spend the extra for internal heaters unless you plan to turn everything off and let the area freeze. It would only be a problem if you were trying to charge them below freezing.

Getting a pack with low temperature protection would make sure you didn't try and charge when it's too cold. Normally, a battery is low temp protection is a lot cheaper than batteries with internal heaters. So you can buy more battery for the same $$$.
Foam board is a heck of a lot cheaper than internal heaters.

Right now your AGM's are not limited when it comes to your well pump, they will put out as much power as they can. With LFP it's different, the BMS of the battery is designed to limit the output of the LFP so you might have an issue with the inrush current when starting your pump. You would need to figure out how much starting current your pump requires to know for certain.

For regular heavy loading like Microwaves, etc. the LFP should actually hold up better than your AGM's. It's just when you exceed the BMS rating on the LFP that you can have issues. The BMS is there to protect the batteries, so if it sees a very high draw over a short period of time, it thinks it is a short and turns off the output to protect the battery.

Since your system is 24V, that's the battery voltage you should look for instead of trying to combine multiple 12v to get to 24v. That way you can add additional batteries with ease as you can afford it. Unlike AGM you can add additional packs later on without the limitations of adding into a lead acid system.

 

[Skip]

Skip,
Based on your usage and needs, I'd say you are on the right track.
You mention that the storage area doesnt' drop below 40 so I don't think you need to spend the extra for internal heaters unless you plan to turn everything off and let the area freeze. It would only be a problem if you were trying to charge them below freezing.

Getting a pack with low temperature protection would make sure you didn't try and charge when it's too cold. Normally, a battery is low temp protection is a lot cheaper than batteries with internal heaters. So you can buy more battery for the same $$$.
Foam board is a heck of a lot cheaper than internal heaters.

Right now your AGM's are not limited when it comes to your well pump, they will put out as much power as they can. With LFP it's different, the BMS of the battery is designed to limit the output of the LFP so you might have an issue with the inrush current when starting your pump. You would need to figure out how much starting current your pump requires to know for certain.

For regular heavy loading like Microwaves, etc. the LFP should actually hold up better than your AGM's. It's just when you exceed the BMS rating on the LFP that you can have issues. The BMS is there to protect the batteries, so if it sees a very high draw over a short period of time, it thinks it is a short and turns off the output to protect the battery.

Since your system is 24V, that's the battery voltage you should look for instead of trying to combine multiple 12v to get to 24v. That way you can add additional batteries with ease as you can afford it. Unlike AGM you can add additional packs later on without the limitations of adding into a lead acid system.

Thanks.
This is good information.
In the Chins, the only battery they seem to offer right now in 24 volt is a 100Ah (the 14v, 200Ah is out of stock), so I need two of those in parallel to get 200Ah.
For the pump, it is a shallow well 1/2 HP 240 v pump (in a cistern - head is only about 8 feet) controlled by a relay. Inrush amps should be about 12 - about 2900 watts. Running amps is about 6, or around 1400 watts. Is this within the acceptable range for LifePo? I think it may be: Looking at the Chins site, the peak discharge amps for a single 24 volt battery is 300 amps. From battery stuff.com, converting 240v, 12 AC amps to DC amps gives 132 amps at 24 volts.

Normally, there is no issue with keeping the battery storage area above freezing. Since the lifepo batteries are smaller and lighter, I could mount them on the wall above the inverter/charge controller which both actually generate a fair amount of heat, or just setup a propane tank heater when outside temps become brutally low. But then again, rigid foam and a small incandescent bulb should do the trick.