gnubie
Solar Wizard
- Joined
- Sep 20, 2019
- Messages
- 3,847
Not so sure about that, at least from your post?
Charging method lifepo4 280AH EVE (float or not.)
- Thread starter DiyNuke
- Start date
MisterSandals
Participation Medalist
Hmm, i guess i assumed you were calling the float value the "rebulk voltage". My mistake, sorry.
So what is "rebulk voltage" and where is it set? What voltage is yours?
Ampster
Renewable Energy Hobbyist
That is a good idea. Not to difficult to do because the range of voltage that LFPs settle at is somewhere between 3.30 and 3.35 from my experience but YMMV. As @MisterSandals mentions you want to find the spot sufficiently below that so that your don't get micro-cycling.
MisterSandals
Participation Medalist
I have been researching Victron's "rebulk voltage" terminology and actually found more than i expected.
There was a firmware change (i am running 1.46):
>
Solar Charger firmware: v1.42 / v1.43 for all BlueSolar- and SmartSolar models
...
And the re-bulk voltage has been lowered from 13.7V to 13.4V (for all battery types).
>
Epiphany! (with the help of enough info: rebulk 3.35v)
I never actually get to down to my "hold at float" voltage of 3.3v because the rebulk is .05v above that. THIS would explain what I am seeing: entering a rebulk full charge cycle (just a smidgen above my float value).
This is a relief because i really trust gnubie's knowledge and experience. Thanks for prompting me to dig deeper!
I learned something today!
(thats 2 in one day, thanks to smoothJoey via a different thread)
There was a firmware change (i am running 1.46):
>
Solar Charger firmware: v1.42 / v1.43 for all BlueSolar- and SmartSolar models
...
And the re-bulk voltage has been lowered from 13.7V to 13.4V (for all battery types).
>
Epiphany! (with the help of enough info: rebulk 3.35v)
I never actually get to down to my "hold at float" voltage of 3.3v because the rebulk is .05v above that. THIS would explain what I am seeing: entering a rebulk full charge cycle (just a smidgen above my float value).
This is a relief because i really trust gnubie's knowledge and experience. Thanks for prompting me to dig deeper!
I learned something today!
(thats 2 in one day, thanks to smoothJoey via a different thread)
Ampster
Renewable Energy Hobbyist
I have recently put my Skybox on TOU rate timeing and it does well with that. But I have noticed a weird charging event that occurs in the mornings that my be related to the same thing @MisterSandals is referring to.
MisterSandals
Participation Medalist
I came across this concept of starting each day with a bulk cycle that was new to me (yea, its Victron not for your Skybox):
Re-Bulk next day (Blue Solar) - Victron Community
community.victronenergy.com
Ampster
Renewable Energy Hobbyist
I am increasing my pack size so I can charge just from solar and use the grid as little as possible. In that case I will shift from TOU timing to grid zero self consumption that will force charging from the solar.
Okay but for now i am only going to use it for electric propulsion on an boat. And for half an year the boat will be out of the water so the cells are gonna be in standby for 5months. And for that time i guess i shouldnt charge it fully with the victron and just let it sit. Then it would degrade the battery faster than when i leave it at 60/70% soc
But ya helped me out allot guys.
Now i will charge it and just let it be. That way they should last the longest. So no micro cycling and all of that. So i am relying on the gross over capacity. Since its way more than i need.
But ya helped me out allot guys.
Now i will charge it and just let it be. That way they should last the longest. So no micro cycling and all of that. So i am relying on the gross over capacity. Since its way more than i need.
John Frum
Tell me your problems
- Joined
- Nov 30, 2019
- Messages
- 15,233
That is a good find!
Sojourner1
Itinerant
But why leave it there just because you can, makes no sense other than sell more batteries in 10 years.
John Frum
Tell me your problems
- Joined
- Nov 30, 2019
- Messages
- 15,233
Feel free to turn off your charger.
Ampster
Renewable Energy Hobbyist
To me there is a difference between marketing talk and best practices. Marketing says you can abuse them and no worries. Best practices say treat them with respect and they may last longer than the warranty.
Sojourner1
Itinerant
In my setup I don't turn off the charger. I actually float at 13.6 after charging to 14.1 or 14.2 and done this for the past 4 years everyday.
I do think that all battery charger company's do it on purpose
But its obvious why they say ya can abuse them. They will still last way longer than an lead acid so people are happy with it but it isnt how long it could last if its treated with care.
But yeah they would want you to buy it again in a few years instead in 20years
Ampster
Renewable Energy Hobbyist
Do you always have a load on your system? Even inverter overhead would probably offset that float current somewhat.
Sojourner1
Itinerant
Yes there is always a load. Here is an average day. If you add the charging amps from the GBS display column to the inverting amps from the Me-arc column that is what's being produced from solar. I max at 80a from solar.
MisterSandals
Participation Medalist
Thanks for sharing your data. I was initially looking to see your max voltage, expecting to find 14.x volts but see the max for this day was 13.92v and SoC of 99%.
I realize its early april and probably not the best weather or charging conditions, so maybe not surprising never got to the bulk or absorb values (limits?).
But what i found was interesting was the SoC column shows the 98% level
all the way down to 13.31v (yea, i know, voltage not a good indicator of SoC). Just found that large gap of voltage for a single percentage of SoC.
Your system is sophisticated, i would imagine the SoC is determined by a shunt or other coulomb counter?
@MisterSandals The amount of power in a battery cell between 3V and 3.5V is over 90% (even 95%) of the cell. Just 0.5V difference. So 0.5V over 90% of the capacity. That means that 10% difference in state of charge is given by 0.055V. The top ends and bottom ends of the LiFePO4 curve are negligible when it comes to power, even if they represent a large voltage difference.
MisterSandals
Participation Medalist
I agree with all that you said.
But even with your 90-95% range going to 3.5v, it seems at odds with
3.31v up to 3.91v all being labeled as Soc 98%.
I was not trying to make a point, i was just curious what method of calculating/counting was behind the SoC. Its clearly one of the more sophisticated systems around.
I did read somewhere else that the voltage isnt related too much with the state of charge. Regarding keeping it at an voltage for an long time. So even with an low voltage its able to charge to 100% SOC
So that was my first mistake honestly
