Xantrex Freedom SW 2012 stopping before batteries are fully charged!

[Rwinike]

Hi All,

I’ve searched extensively on this subject and there are a lot of posts with suggestions but no conclusions it seems…

I just built a 280ah battery with cells from aliexpress and a Daly 150amp BMS. My RV has a xantrex 2012 and I’m trying to find the sweet spot on the charge settings so that it stays in Bulk mode for a reasonable amount of time (currently it kicks on for a few minutes and goes right into absorption, likely because the absorption and bulk voltage settings are the same,) and the batteries reach my desired SOC before absorption times out.

Current Settings:

Bulk and Absorption Voltage = 13.8 (purposefully 3.45 to extend battery life)
Absorption Time = 120 minutes
Float turned off

Can someone please help me figure out how to get it to stay in bulk? And/or to charge to desired SOC?

Thank you in advance for your time!!
Robin

 

[snoobler]

Unfortunately, you don't have full grasp of charging phases.

You want to extend life by limiting to 13.8V, but you want to stay in bulk longer. These are mutually exclusive conditions. You can't have both.

Bulk is the constant current charging phase BELOW absorption voltage.

Once absorption voltage is hit (13.8V), the absorption phase begins. It holds absorption voltage and tapers current.

What you want is to stay in absorption longer, not bulk.

You likely need to set absorption time to 4-6 hours.

 

[Rwinike]

Unfortunately, you don't have full grasp of charging phases.

You want to extend life by limiting to 13.8V, but you want to stay in bulk longer. These are mutually exclusive conditions. You can't have both.

Bulk is the constant current charging phase BELOW absorption voltage.

Once absorption voltage is hit (13.8V), the absorption phase begins. It holds absorption voltage and tapers current.

What you want is to stay in absorption longer, not bulk.

You likely need to set absorption time to 4-6 hours.

Thank you for helping me. Would you recommend I cycle the battery down to say 13.2-13.4v before recharge begins? As opposed to a LA that just maintains in float mode all of the time?

 

[snoobler]

How are you using these batteries?

 

[Rwinike]

How are you using these batteries?

They are in my Rv. So ideally I want it to be low maintenance. I camp 70/30, primarily full hookup vs. boondocking. My goal was to save money by building this myself. However, unfortunately, the diy batteries are proving to need more attention than a prefab would need.
Yesterday, with some experimentation I learned that when the batteries are nearing the top of the charge curve, one cell runs away so I can’t put the charge setting any higher than 13.8v.
Thanks again for helping out1

 

[snoobler]

1. Did you top balance the cells prior to use?
2. If so, did you put them in use shortly after completion, or did you let them sit for awhile?
3. If you top balanced (or you didn't), you could use a 10A power supply to hit each cell individually and charge them to 3.5-3.65V manually (pick the same voltage in that range for all cells), and this will restore balance. This can be done carefully on an assembled battery and using a smart BMS to monitor cell progress.
4. Do you have your BMS set to balance only during charge and above 3.4V?

LFP deteriorates when stored at or near 100% SoC particularly in warmer temperatures. At 13.8V, you'll likely be getting to 98%+ SoC.

Since this sounds like it's an infrequently used battery, as such I would discharge down to 13.2V and set absorption/float to 13.2V when you know you're going to be on shore power. Dial it up to 13.8V when you expect to boon.

The better way to do this is with a decent battery monitor. Even the $50 one Will recommends is better than nothing. You could discharge down to 40-70% and keep it in the 40-70% range until you need it. These things ship from the suppliers at 40-50% SoC for a reason... they don't want them degrading by sitting for months fully charged. With the infrequent use, this may improve the longevity better than your reduced charge voltage.

Consider also if you're having trouble with balance at 13.8V, then you likely have one cell going notably higher than your targeted 3.45V/cell and/or the others falling short. That's creating a situation where the one cell may be wearing notably faster than the others.

Lastly, this use model is likely going to suffer from balance issues far more often than most. These cheaper commodity cells do not seem to maintain balance very well in less frequently cycled application due to the difference cells self-discharging at different rates.

 

[Rwinike]

I did top balance them and then let them sit in parallel for 3 days with a 10 amp bench charger. For the middle 80% of the SoC, the cells are within 9mV of each other. (I also have a passive balancer in play for added security) It’s the low and the high end where they deviate. I have a VictronConnect Smart Shunt showing me the details of the pack as we as the Daly Bluetooth app. I agree that one cell, if not two, might be weak. But they pulled full capacity so I ran with it!

I will try your idea this weekend for shore power at 13.2v absorption and bulk. I will also extend the absorption time to 4 hours.

what is your suggestion for recharge voltage? I read somewhere 12.6?

Then, essentially regular dc usage will drain voltage to 12.6 where the Xantrex will kick in and charge from 12.6 up to 13.2 or whatever voltage it reaches at 4 hours of absorption, whichever comes first…rinse, repeat. Correct?

thank you for you time, I appreciate having the help tremendously.

 

[snoobler]

"passive balancer" - please elaborate. A passive balancer is typically a feature of all BMS that activates resistors on higher voltage cells when they exceed a defined deviation. These can typically be set to run all the time, during charging only, and only above a certain voltage. A DALY smartBMS should be fully configurable.

Note that the cells hitting peak voltage are not necessarily weak cells. They are just at higher SoC than the others. Once you have a top balanced pack, and you do a discharge test, the cells that drop out first are the "weakest" cells. Behavior at/near 100% SoC is not predictive in that regard.

"active balancer" - this is a device that monitors cells and transfers charge from higher voltage cells to lower voltage, and they typically operate all the time.

Any type of balancing, active or passive that is working all the time will work to UNDO a top balance during operation. To maintain a top balance, balancing should only occur during charging and typically above 3.4V.

That said, knowing that you have a smart shunt, you can pick your own voltages.

Start by a long slow charge to 13.8V with 4 hour absorption until the shunt reads 98+ SoC. If it doesn't make it in the 4 hours absorption, start another charge. This way you know the monitor is calibrated to be fairly accurate. You can even reset it to 100% manually to be sure.

Use the monitor as your guide. The % SoC matters WAY more than any voltage reported.

Use the battery as you typically do and observe your voltage to SoC relationship. It's a little spongy, but it's better than any arbitrary values I may give you.

Be leery of setting the re-charge voltage too high. A heavy load on the battery at 50% may pull the voltage down to the re-charge point even though there's really no need to recharge.

When it comes to recharging for "storage", i.e., you'll be on shore for awhile or it's actually in storage, figure out what charge voltage gets you back to the 40-70% SoC range. You may find that you need to adjust your absorption voltage as well.

This isn't a set it and forget it scenario. You'll have two settings - 1) for boondocking operations and 2) for shore power/storage.

Lastly, being deep in the weeds, I'll qualify it with, if you go boondocking every couple weeks, just set to 13.8V and forget it. Find an absorption time that gets you sufficiently charged for your needs. If you're only boondocking every couple months, use the "two settings" scenario.

 

[Rwinike]

 

[snoobler]

That's an active balancer, not passive.

It has likely "undone" your top balance.

 

[Rwinike]

Ok. I’ll redo after this weekend

 

[snoobler]

Ok. I’ll redo after this weekend

Honestly, I wouldn't bother. If you can successfully operated at the 13.8V level with the active balancers installed, it's just not worth the effort.

 

[Rwinike]

Sounds like a plan, this first weekend will answer many questions…

 

[Rwinike]

What’s your thoughts on leaving the lifepo4 connected while driving? I’ve read the low resistance could draw too much from the truck’s alternator

 

[snoobler]

What’s your thoughts on leaving the lifepo4 connected while driving? I’ve read the low resistance could draw too much from the truck’s alternator

That's a concern; however, there are mitigating factors.

1) if you start with a battery that's been charged at 13.8V for 4+ hours, it's darn full. In that case, the alternator will rapidly hit its absorption voltage (14.X -ish) and start tapering current.
2) the wiring between the alternator and the LFP is likely pretty lossy. It further contributes to the voltage drop and causes the alternator to begin tapering current sooner.

Wrapping back around to an LFP that has been charged to 13.8V for 4+ hours, it doesn't need to be charged by the alternator, and likely shouldn't if it's not needed.

Personally, I would hesitate to charge a LFP with the alternator unless I could verify the voltage drop between the alternator and the current from the alternator.

Lastly, that also means they're in parallel with the FLA/AGM starter battery. That can be problematic if the two are of sufficiently different voltage when connected. The current surge at the time of connection may overwhelm the BMS current limits. Have to watch out for DALY in particular because they have different charge/discharge current ratings.