• Ray
    402
    In this video, I install a remote disconnect switch for my 500-watt solar panel array.



    I wanted a solar disconnect switch so I can manually disconnect the charging current to my new Lion Energy Lithium battery bank before they come to a 100% state of charge. I've read if the lithium bank is only charged to 80-90 percent capacity, it will increase the lifespan of the battery cells. We spend summer months on full hookups. So, usually, the battery bank sits fully charged for weeks on end.

    I thought a remote switch located in the bathroom next to my Trimetric battery system monitor would be a convenient location. From there, I can manage the charging of the lithium battery bank via the solar disconnect switch.

    Rather than invest in a high end wireless remote switch, I'm trying an inexpensive electromagnetic 12V automotive battery disconnect switch from EKYLIN. - https://amzn.to/2ZaZqCl
    It draws about 1/2 amp to keep relay latched so I do put up with some power loss. But the price was only $40.
  • Greg F
    154
    Having an easy disconnect for the solar is a good idea. Your remote solenoid is a clever inexpensive solution. I chuckled when you noted that it was mounted in the restroom which was convenient since you were in there multiple times a day.

    My roof combiner box drops down through a chase where the gauges and controls are located which made it easy to put a circuit breaker in line before the positive cable drops into the basement where the controller is. On a couple mornings last winter where temps fell into the 20's I would turn off the panels before bed and check battery temp in the morning to make sure they weren't below 32 degrees before charging.

    8auu2ntaoyye7gha.jpg

    I started to use my inverter to run my 2 way fridge last year during the day when solar was good. That is one way you could utilize the solar instead of turning it off and also save some propane. Even though the fridge doesn't burn a lot of LP at once it does add up. Might as well use the sun instead. :smile:
  • Ray
    402
    I started to use my inverter to run my 2 way fridge last year during the day when solar was good.Greg F

    Good idea!
  • RVsolar
    166
    yes great idea I started doing that as well.
  • RVsolar
    166
    so when plug in to power you must have your old inverter charger turned off
    As well or do you just have the one under your front bay.
  • Ray
    402
    Yeah, I have the charge converter breaker off. Just let the solar take care of charging the batteries now since I no longer need to worry about float charging them at night like the old lead acids.
  • RVsolar
    166
    same here have good one .
  • Drew
    9
    Ray,

    I hadn't heard that constant 100% capacity was bad for lithiums- originally that was suppose to be an advantage to having them. Good to know and great job with your mod too!
  • Ray
    402
    Thanks, that's what I'm finding when researching lithium. Seems that high temperatures and long periods held at a high state of charge will make them age faster. Supposedly if you can use them in the 20% - 80% range or even a tighter middle range its best for them. Unlike lead-acid they don't need to be recharged fully, it's easy to do. That got me to thinking its probably not good to have them sitting a full charge on float charge the months that we are on full hookups in the summer.
    If boondocking all the time it's not that big of a deal as time spent at full charge won't be as significant

    I found one really interesting in-depth article done by a marine mechanic all about LiFePO4 batteries. https://marinehowto.com/lifepo4-batteries-on-boats/ This one section really stood out.

    JUST SAY NO TO FLOAT CHARGING

    Hardly a day goes by without someone asking if it is okay to float your LiFePO4 batteries. The answer, from me, is still going to be no. Float charging however has different meanings to different segments. In the lead acid world we charge to a high voltage of say 14.7V then drop back to a “float voltage that well exceeds the resting open circuit voltage of say a 13.6V float. This holds the bank at 100% SOC, a desirable feature for lead acid. LFP has no need to be at 100% and the mere act of storing them at 100% has a negative impact on battery life. I break “floating” & LFP down like this;

    Float Charging LFP = Holding the cells at a voltage that results in the battery being maintained at 100% SOC continually

    LFP Storage Voltage = A voltage that results in the battery being held at a “mid range” SOC or below 100% SOC.

    Why do I break it down to “float” and “storage”? Because there is a lot of confusion surrounding this subject and the term float is really a lead acid charging subject. Many folks, who get stuck in a lead acid mind set, want to try and adopt lead acid charging practices to LFP and this can negatively impact cycle life.

    Dockside Use: If you’re in a situation where charge equipment can’t be turned off or set to achieve a “mid-range SOC” and would necessitate floating the LFP bank, you can wire in a cross-over lead acid battery to handle dock-side loads. For dock side or unattended uses you ideally want to be able to discharge the LFP to 50-60% SOC and take it off-line. With the LFP bank in storage mode the small lead acid bank & shore charger can run DC system loads.

    Alternatively a “storage voltage” can be applied that will allow the battery to slowly discharge to a mid-range SOC and then be held there by the charger. This approach essentially allows the charger to supply the house loads while the battery is comfortably sitting at a more comfortable storage voltage. Of course with this approach, if you lose dock power, you are relying on your BMS to protect the LFP bank where as with a lead acid battery taking dock side duty you lose a $100.00 battery as opposed to a 3K to 15K bank.

    STORAGE SOC EXPERIMENT: I recently ended a very expensive experiment regarding storage at 100% SOC. The test duration wound up being 12 1/2 months using four 100Ah CALB cells where they were charged to 100% SOC and then left to sit idle with no connections to a BMS or other parasitic loads. The low temp recorded over the 12 1/2 months was 46°F and the high temp was 87°F and was meant to be a representation of the real wold.

    A min/max capture thermometer was used to record the peaks. The cells, prior to letting them sit at 100% SOC for 12 1/2 months, were regularly testing at 101.2 to 101.3 Ah’s of capacity (previous 6 Ah capacity tests) as a 12V nominal bank. After 12 1/2 months the cells were discharged to a cut off voltage of 2.9V for the lowest cell. After 12 1/2 months of doing nothing but sitting there, at 100% SOC, the cells had lost 11.6% of their previous rigorously confirmed Ah capacity. Now imagine if you additionally stressed the cells by continually float charging them. Ouch!!!!

    “The cells lost 11.6% of their confirmed capacity just sitting at 100% SOC”

    How can these manufacturers suggest that the mere act of storage, at 100% SOC, is bad for the cells, which I have now confirmed is, and then suggest it is okay to float? How can they say “store at 50-60% SOC” yet then give you a “float” voltage? Really?
  • Rush and Lola
    104
    After reading that article, no thank you. As he said, a product that is so expensive, and so easy to ruin,
  • Greg F
    154
    Ray, you are going down the same rabbit holes I did building my system. I must have read and reread all of the Nordkyn Design stuff a dozen times. He would consider my system pretty primitive and possibly even irresponsible. :gasp:

    It is interesting to read the perspective from the marine side. While us land dwellers rely on power for somewhat superfluous reasons DC power on the high seas can be a matter of survival as much as convenience.

    I think it's a good thing to turn off your batteries when they are full and discontinue full voltage trickle charging. This is why I only charge to 13.6ish volts. My 100% SOC is well below the individual cells maximum so I never actually get to potential 100% SOC. Despite that I still don't let the bank idle at small trickle charging. When looking at the charge curve for LiFePO4 you see that it is vertical between 13.6v and 14.4v. There is so little energy to gain pushing cells to the max. With a BMS it is possible, to what end I'm not sure. A lower finishing voltage would further protect the battery. The only upside I see is that keeping voltage as high as possible allows for a faster charging rate towards the end of the batteries capacity.
  • Drew
    9
    Ray, Thanks so much for providing the link and the article-very interesting reading. Although we'll never have lithiums (we're rv park people mostly) it's nice to have the knowledge to pass along to friends who boondock regularly.

    Drew
bold
italic
underline
strike
code
quote
ulist
image
url
mention
reveal
youtube
tweet
Add a Comment