LiFePo4 charging

[craig333]

So if I read this correctly, I should plan on a 100ah LifeP04 being more a 90ah battery in order to keep it happy. Not really a big deal as I already assume my agm's are half their capacity (still in the 50% crowd). Still should be plenty of power for a week of no charging (at my assumed usage rate of 10-15% per day).

 

[rando]

You may need to tune these voltages a little for your particular battery, but your are correct, the whole point is not to leave the battery fully charged, at least while you are not actively using the camper. If you set the float at 13.2, it will bleed the battery down to 13.2, then the solar panel will pick up the load. Based on the power stream data, much above 13.2 any you will end up charging your battery back up to 100%.

Honestly, this is probably all pedantry, and you will get plenty of life if you leave the voltages at the standard lead acid settings. Most of us will likely have sold our campers before we hit even a reduced cycle life.

 

[rando]

So if I read this correctly, I should plan on a 100ah LifeP04 being more a 90ah battery in order to keep it happy. Not really a big deal as I already assume my agm's are half their capacity (still in the 50% crowd). Still should be plenty of power for a week of no charging (at my assumed usage rate of 10-15% per day).

Pulling out 100Ah now and then is no big deal. It is still 600 cycles at 100% DOD. Even if you are doing that every single week, it will still last over 10 years.

 

[buckland]

yup .. It will no doubt "see me out" ... Fun though learning the new stuff on how it works. The weight savings alone allow for a case of beer!

 

[ClimberRob]

Any ideas about "floating" a battery come from FLA/AGM/GEL batteries, which lose voltage at rest. Lithium batteries don't need a "float" stage. If you want to power your electronics off of solar or your AC charger, etc., that's fine, but you would ideally just charge your LiFePo4 battery fully, then shut off the charge current (which is handled by the BMS on most batteries).

Drawing your battery down 100 AH really isn't a big deal. How many times have you done that on your laptop or phone?

 

[Stokeme]

Just wanted to follow up with a quick discussion I had yesterday with the lead tech, formally w/StarkPower, now w/TorquePower. It basically mirrors Rando’s post #51 & adds some support to a preferred, lesssr SOC (not critical) when in use & also not in use. As a perceived drop in replacement for LA the “retail” V parameters are stated for 99-100% SOC. It would be a little less stressful, when in active use, & non use more so, to keep full SOC a little, or more, below this %.

When in use he recommended absorption V be set@13.8-14.0. Cell balancing with passive equalization should take about 30 minutes after reaching the highest V setting. So, he recommended setting absorption time to 45-60 minutes. Float V set to 13.5. He estimated for my Batteries this would result in ~95% full SOC. Settings were based on my average usage of 8%(low)-15%(high)/day of my 150Ah capacity. My controller had been set to 14.4 & 13.8 respectively. Time 6hr. This was the auto set for LFP4 with my 100/30 Smart Victron. When not in use, he recommended absorption V be @13.6-13.8, float @13.2-13.5. Monitor how the battery responds to the V setting.

An added note: re min/max temp thresholds. I am not that concerned about the high of ~150F, it seems to me extreme. For low temp of ~20F, I live in the NorCal SF Bay Area. Frigid Storage for me is not a concern. I will be out having adventures in 20F weather, but my Camper will never likely be under 40F. I have not purchased the Victron temp charge control monitor yet. I was told that the battery will generate a slight bit of heat as it discharges in very cold temp, which is safe, (cannot be safely charged) which helps a little bit with the internal temp. I would be curious if anyone has experienced low temp threshold issues with their Battery.

Lastly he conveyed that SOC was less critical to long Battery life overall as compared to the number of times the Battery is drained below 80%. This would limit my Battery to ~2,000 cycles, as opposed to ~3,000-4,000 cycles if kept above this drainage parameter.

 

[buckland]

Next up are two questions... I have two panels: on the roof 160W Solar Boulevard. I have a Renogy flex 100W as a portable (wall plug). They are currently wired in parallel to the terminal bar and then together into the Victron 100-20 controller. They are almost the same voltage rating.

Sometimes I want to use both on a cloudy day but generally the 160 does it all on a sunny day. If the camper is parked in the shade I would like to be able to put the flex portable in the sun.

* So... my first question is: what is a good switch that would allow me (like a stereo speaker A B A&B switch) where I could switch between one, the other , both OR not at all.... to avoid the float cycle. This last bit has me perplexed as I have the camper on but nothing really consuming electricity and the panel is sending juice to the battery (LiFePo4) and it is on float as it is full. (see photos).
* Second question is why is it on float?

 

[rando]

1. I am not sure what purpose an A/B switch on the solar panels will serve (except extra complexity). Just put both panels in parallel, the one with the most sun will provide most of the power and you may get a little extra from the other panel or maybe nothing if it is completely shaded. There is no need to disconnect the shaded panel. If you need to switch solar charging off, you can do this through the Victron App, no need for extra hardware.

2. What are the battery parameters you have programmed into the controller? It looks like the charger thought the battery was fully charged, then switched to float. However you will notice that the charger is not actually putting anything into the battery (0W) so I am guessing that the battery voltage is still above your float voltage setting.

In general if you want to avoid constantly floating your battery, then set the float voltage in the charge controller to something in the 13.2 - 13.3V range. This will be enough to support loads, so the battery doesn't run down too far, but won't really charge the battery. With my similar set up set to a float voltage of 13.25V I see about 5W from the solar panel in float, which is about equal to my 'parasitic' loads.

 

[buckland]

Thanks for the reply. The switch was for the controller should I get another panel that did not match close enough voltage wise. The Victron manual says never hook two different panels up together to controller. I have the absorption at 13.8 and the float at 13.3.
I just noticed the "charger enabled" button. I turned it off and got a message that one should only do that for maintenance, so I turned it back on. (?)
As I store the camper in the barn during the winter (6 months!) I believe I need to drain the battery down to 11.2 volts? and let it sit w/o charging? so I wanted to disconnect the controller as the barn has windows and it could actually still charge as nothing is turned on.

 

[rando]

As long as the panels are the same approximate voltage (ie both 12V or 24V nominal) panels, there is no issue hooking them up in parallel. It would be unwise to put a 12V panel in parallel with a 24V panel, but I doubt you were thinking of doing that. I am not sure why they label the charge off switch as being for maintenance, but it seems to shut off the charger and can't see a problem in leaving it in that mode.

Definitely don't want to drain the battery down to 11.2V - that would be dead flat. I think I am making too big of a deal about the storage SOC, it would do minimal harm to store fully charged, particularly if you are storing it at lower temperatures.

However, ff you do want to do something - charge it all the way up, run a known load for a few hours to get it down to ~50 -70% SOC and then disconnect for the winter.

 

[buckland]

Thanks ...I have learned a lot and appreciate your help. I think this has been a great addition to our camper. Looking for a new winter project that absorbs the think through in the dark months like this one did.... maybe a 'raspberry' computer to run home security camera.......... my camper is all set (after 8 years of mods)...
Rob