Replacing AGM Batteries with LFP batteries

EdKirkpatrick

I just replaced my 4 110 Ah AGM batteries with 4 HLX2400Wh 200Ah batteries.

EdKirkpatrick

My settings for the new batteries were: Batt type=custom, Batt capcity=200
Ah, Charge cycle=2 stage no float, Absorb time 2 minutes, HBCO=57.6V, LBCO=49V, Recharge volts=51V, equalize disabled, Bulk Voltage=56.4, Absorb voltage=56.4. When I connected the LFP batteries they were fully charged. When the solar panels are connected, the charge controller cycles between charge and discharge every several seconds and this has been happening tll the SOC for the batteries goes down to about 30% at which time the batteries go on standby. During bright sunlight the CC will charge till the batteries hit about 40% SOC then begin to cycle between charge and discharge. I don't think this is normal and I must be missing something in the Xantrex settings. Would appreciate any help.

Horsefly

You've given only sketchy info, so it's a little hard to make suggestions.  You said you replaced 4 AGMs with 4 LFP batteries. I tried to Google HLX2400LFP and got no results.  It seems obvious that you have a 48V system, although you didn't say. I'm not sure what charge controllers you are using. So, a little hard to figure out what you haven't told us, but here's some thoughts....

1. Although LFP don't require a float like LA does, it's better to not disable float so that you can use the solar power during the day for loads. Otherwise you are just running down your battery during the day until it hits recharge. Just use a lower float voltage, like around 3.35V per cell, or 53.6V for your 48V system.
2. I think a 2 minute absorb time is really messing with you. For LFP batteries the current will drop down quickly once it hits the target charge voltage, but not that quickly. Without knowing about your solar charge controller, I would hope it has a "tail current" or "end amps" setting, or at least a default. My Schneider MPPT150-60 has a default end-amps of 0.02C, which is mostly fine. Since I can't tell your configuration with 4 200Ah batteries, I don't know what specific end-amps you should have. In my system, I have max absorption time set to 60 minutes, and it usually hits end-amps and goes into float way before that.
   
3. 56.4V for bulk and absorption is fine. In fact, my settings match that (28.2V for my 24V system).

EdKirkpatrick

You are correct, I have a 48V system. The four AGM batteries I have were working fine, however they are getting old so I thought I would replace them with the Kilovault HLX+ series batteries which are labeled 2400 HLX+. These four batteries are rated at 200Ahs each.

I have a Xantrex XW6048 inverter/charger and two Xantrex XW-MPPT-150 charge controllers. The operating instructions for the KiloVault batteries advised to set inverter and chargers to no-float or as you have advised, 53.6V. the instructions also advised to set the Absorb Time to 2 minutes or less, which I did think was awfully low. The thing that is bugging me is that the chargers keep cycling from charge to discharge every few seconds. I can set the chargers to 3 stage and set the float to 53.6V to see if that will stop the cycling?

EdKirkpatrick

My system is on-grid, however out of the last 10 months I have only paid for the connection charge. Using the larger capacity batteries, I was hoping to get to a point where I am only paying for the connection charge and using solar with batteries, I would continue the connection to the grid mostly as an additional power source.

Horsefly

Ok, so the batteries are 12V batteries, so it sounds like you have one 48V bank built from 4 of these 12V batteries in series. I don't know much about the Kilovault batteries, but I'll assume that you've verified it is OK to wire them 4 in series (some manufacturers don't recommend it).

Setting the max absorption time to 2 minutes should actually kind of work, but the batteries will never get to 100% SoC, which is actually OK. It's only my opinion (matching many others that I have seen) that it is better to let the current drop down to something like 1-2% of the rating of the battery.

I don't have much of an idea why your charge controllers are cycling. Have you tried to run with only one charge controller? 

EdKirkpatrick

I have done a lot of research on the LFP batteries and the KiloVault batteries may be wired in series to provide up to 48V.  Although the batteries are capable of being fully discharged, KiloVault recommends that their batteries go no lower than 20% SOC (80% DoD), in order to maintain a higher number of recharge cycles. I had tried disconnecting one of the XWMPPT60-150 charge controllers to see if that would solve the problem of the controllers cycling back and forth between charge and discharge every few seconds. That did not work. I didn't think that would be the problem since I was using the "cascade" feature that XW system provides to sync all the components linked via the Xanbus.

Last night I set the chargers to 3 stage and set the float to 53.6V and set the absorption time to 20 minutes to see if that will stop the cycling. I may also  try disabling the "cascade" feature.  Thank you for providing additional information.  I tried contacting KiloVault, and Xantrex, however they have not gotten back to me as of yet.

EdKirkpatrick

I finally got it right!!  With my 6kW Xantrex inverter, two Xantrex Charge Controllers connected to two strings of solar panels (2Kw each string), I think I have finally figured out the right mix of settings for the four 12V Kilovault 2400 HLX+ batteries connected in series to provide 48 volts. My Settings are: Battery Type - Custom, Battery voltage - 48V, Battery Capacity - 200Ah, Maximum Charge rate - 100%, Charge cycle - 3 stage, Recharge voltage - 51V, Absorb Time - 20 minutes, Equalize Support - Disabled, Bulk Voltage - 56.4V, Absorb Voltage - 56.4V, Grid Supply Support - 53.7V, AC charge - Disabled, Cascading - Disabled, LBCO - 48V, HBCO - 58V, Float voltage - 53.6V. 

I found that the Grid Supply Support must be higher than the Float voltage for the system to work correctly. My batteries are not cycling on and off every few seconds and they are completely charging with full or partial sunlight.

I plan to tweak the Grid Supply Support voltage, the Float voltage and the Absorb Time, to see if I can get the maximum electricity use out of my new batteries.