I have a smart solar 150/45. When I leave the cabin, I disconnect all loads. The controller will bulk normally, absorb for just a minute, and transition to float. Batteries typically do not go below 26.2 when I’m gone. Settings are adaptive, Tail Current 2 amps, BMV Tail is 2 percent, max duration:2:30. Is that normal.
The behavior is normal for charges following:
1) Very shallow discharges where tail current is hit very quickly - regardless if fixed or adaptive is selected..
2) Shallow discharges where the adaptive algorithm varies the absorption time based on the depth of discharge.
https://www.victronenergy.com/upload/documents/Adaptive_charging_how_it_works.pdf
There could also be a configuration issue.
Sounds good.
Think of absorption as filling the hard to fill parts after bulk charging has finished. If there's no discharge, it was full to start with. So no absorption needed. Every day the charger turns on from sun. Goes immediately to bulk, battery is almost full (overnight self discharge is all) switches down to absorption. Battery says I'm full (tail current), switches down to float. If it stays in absorption unnecessarily, service life of the battery is shortened.
I am trying really hard to understand "best" settings for my LifePO4 battery bank. I have 3 batteries, 630Ah (48v). I want to run my batteries 17% - 90% SOC to length their life cycle.
I am looking at setting my bulk charge voltage to 56v and absorption to 54v for 2 hrs and 0 tail current.
I can't figure out 2 things:
1) What should be my "float" setting?
2) What the heck exactly is "tail current"? I think I want it set to 0 to allow cell balancing. But I don't actually understand what tail current is.
I live in very sunny AZ so I want my MPPTs to keep running even after my batteries hit my target of 90%SOC so the MPPts can power my AC, etc. in the afternoon. But I am at a loss to really understand how I can accomplish my goals of not over/under charging my batteries while maintaining my MPPTs production and not drawing my batteries down when full sun is present.
Any thoughts, ideas, suggestions?
You can't target % SoC based on Voltage. LFP doesn't work that way.
56V will get you to very near 100%. Holding it for 2 hours with no tail current will absolutely, positively get you to 100% and beyond.
If your goal is to maximize cycle life in exchange for slower charge times, charge to 3.45V/cell with 2 hour fixed absorption and about 10A tail current. This should get you to about 95-98% SoC in a "low stress" fashion and help maximize cycle life while maximizing usable capacity at the expense of increased charge time.
1) Float at 3.375V/cell
2) Tail current is another charge termination criterion. Once absorption is hit, it is held, and the current tapers. If the current tapers to "tail current," then the MPPT drops to float.
Float is what will force the MPPT to hold the battery at 3.375V/cell and power loads with PV. If load causes battery voltage to drop, MPPT increases current to hold voltage. That current essentially is then fed directly to the load. When load is removed, voltage increases above float, so MPPT cuts current as needed to maintain float.
Recommend you get a smartshunt or BMV-712 and put it in a VE.Smart network with your MPPT. If you have a GX device with smartshunt or BMV, enable DVCC and enable SVS, SCS and if you have a temperature sensor, STS instead of the VE.Smart network.
First Off...THANK YOU ! !
So "tail current" is the AC power amp draw on the system? Kinda like an "at rest" normal household amp draw? Or is it the DC amp draw on the battery in "at rest" normal household amp draw?
So the question is...is the tail current an AC or DC amp figure? I am thinking it is the AC loads that cause a DC amp draw. Now that makes sense if I am right.
Let me see if I get this, in absorption...my AC loads add up to 11a draw (tail current) and stays there (and my tail current setting is 10a) then my system will never drop to float. yes?
But, in absorption...my AC loads add up to 10a (tail current) or less (and my tail current setting is 10a) then my system will drop to float. yes?
And in float, if the AC loads cause the battery to noticeably discharge (DC voltage drop) then the float causes the MPPT to increase charging current (amps) to keep the battery at a steady SOC by powering the AC loads directly from the MPPT (if there is enough sun to do so)?
And reverses that process when the AC load drops and the MPPT float charging returns the battery to 100% SOC?
Please say I am right!! If I am right then I think it finally makes sense :)
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I added a BMV-712 (w/shunt) last year, never got it working right. It will be removed from the upgraded system.
I have a GX Color Control that will stay with the upgraded system and be attached to my new Lynx Shunt.
I love Victron equipment!!!!! But dang, there is so much to learn about it...beyond all the normal solar stuff.
No. Tail current is the charge current at when the absorption cycle stops, i.e., once absorption voltage is held to the point that the current drops to the tail current, that signals the charger to switch to float mode.
There's essentially no way for the MPPT to know what the AC current is, and it wouldn't have any meaning for it whatsoever.
Your description of float behavior with loads is accurate. Float is a target voltage for the MPPT or other charger to maintain. If anything (loads) causes the voltage to drop below float, current is added to maintain float.
Not sure why you couldn't get the BMV to work right. The biggest mistake folks make is if they don't follow the guidance. Many will set charged to 0.2V below FLOAT, which is fine for reliable AC chargers, but bad with solar. With Solar charging, this runs a common risk of false synchronizations where it jumps to 100% when it's at a lower state of charge. Simply enter your capacity, set charged voltage to 0.2V below your absorption voltage and set tail current of 6%.
I have no experience with the Lynx Shunt.
The BMV was my fault. My version 1 system had no Victron equipment and was 15-year old technology, including the busbar layout and wiring. Then I added the BMV but its wiring needs were not compatible with the then current wiring...meaning I wired it wrong. I was going to rewire it correctly but I decided to just leave it be until the upgrade next month.
OK, I think I might have the tail current thing now. When the charge current in the absorption mode hits the tail current setting it drops into float. That means the absorption charging has done its job and the charge rate/current is dropping off due to lack of need.
OK, thank you for letting me know I finally understand the float mode. I hear folks saying float mode is not needed. But it sounds as if float is a pretty cool way to maintain a battery bank and keep loads powered up when there is enough sun to do so.
Now to the settings based on all of the above...I am looking at :
Well, does that sound about right?
Your help has been amazing!! Feel free to send me an invoice :)
I'll let others comment on the numbers.
Battery capacity in the BMV/smart shunt is only used to tell you SOC. If you reduce it as you're proposing, it will report your 95% full battery as being at 100%.
But up should also consider the BMS cell balance. This only happens when batteries are close to full. Actual point depends on the BMS. If you don't charge to full regularly and let the cells balance, you run the risk of damaging the batteries. It's one of the reasons that Victron charge to full. LFP isn't badly affected by charging to 100% the way Li-ion is.
There is no value in setting an artificial capacity. If you ever find yourself needing to use all your capacity in an emergency, do you really want it to read "0%" and not know how much you actually have left?
Bulk and absorption are opposite sides of the same target voltage. Below "bulk/absorption," the charger is providing maximum current. Once "bulk/absorption" voltage is hit, it is held and the current tapers as the battery can accept it. Some converters have a lower "absorption" voltage, but it's not best practice.
54V absorption will literally do nothing.
Bulk/absorption should be 3.45-3.55V/cell. 2 hours absorption at 3.45 and 30 minutes at 3.55V/cell, i.e.,
55.2V for 2 hours fixed absorption, .02C (.02 * 630Ah) tail current.
56.8V for 30 minutes fixed absorption, .05C (.05 * 630Ah) tail current
54V float
FLOAT is not needed for LFP batteries if you're just going to put them in storage. If you're going to use them in a cyclic power system, a float must be established to force the MPPT to power the loads. Failure to set a float means the battery fully charges, the MPPT cuts off, and then the battery powers the loads until the "re-bulk" voltage is hit. Then the MPPT starts the charging again. This results in unnecessary "micro cycles" to the battery.
FYI...based on all the info:
I didn't take fully into account cell balancing. Thank you for reminding me.
I checked with the battery manufacturer. The BMS handles the capacity and "full" charging so I don't have to worry about it. The cell protection is built into the BMS.
Thank you again to ya'll !!!!!
Looks good. Tail current must be in actual Amps, so 31.5A
If you still had the BMV in the system, you would set charged voltage to 56.6V and tail current 6%.
For cell balancing, the 55.2V and 2 hour absorption allows for more balance time; however, if you can hit 56.8V consistently without balance issues, it's fine.
There are few days where I can't hit 56.8 for several hours each day, but not many. Sunny AZ...but not the desert. I think the longest stretch with clouds and limited charging was maybe 4 days...one time...broke out the genset. So I should be OK. I will watch the cell balancing in the Trophy to make sure I am right. If not, I will take your advice and go to the 55.2v/2hr/2% setting.
Everything I've read so far shows I can drop the BMV and replace it with the Lynx Shut hooked into the Color Control GX. I actually like the Color Control a lot...very visual representation of what is happening with the system and gives me settings access as well.
Thank you again sir!
I feel your pain.
Our spot is up past Show Low on the way to Concho in high desert, but subject to snow and clouds. Generally great sun, but my DIY Lithium NMC battery in an uninsulated shipping container can't be charged below freezing, so unless I get some decent solar heating on the container, I may not charge at all even in decent conditions.
Agree on BMV vs. Lynx Shunt. I have a BMV-702 that's integrated into the system.
Have a CCGX. Expect to upgrade to a Cerbo in the future. CCGX is pretty limited. For me, I'm going to want to eventually connect multiple MPPT via VE.Can meaning I'll need to move my BMS to the VE.BMS port on a Cerbo as the CCGX doesn't have the two options. Only has 2X VE.Direct ports. I may also want the additional temperature sensing options on the Cerbo in the future. Ultimately, I regret the decision to get a CCGX, but I didn't know any better at that time.
99% of the time, I use VRM or remote console on my phone or on the web, so the display and touch pad are essentially useless to me and comparatively limited vs. VRM. I won't be getting a screen for the Cerbo when the time comes.
FWIW : https://ahtrimble.com/2023/01/17/keeping-lithium-batteries-warm/
Also...we are neighbors. I am north of Show Low, south of Taylor.
Bingo!!! It all finally all makes sense.
Thank you guys a whole lot!
For some reason this just couldn't get into my head and make any sense.
Hi everyone
I’m also new to my Victron set up of a 100/50 mppt and a bmv
I have a battery bank of 530ah banner bull lead 12v
Should I keep the default settings in the mppt of 2A
And 4% tail current in the bmv
I am getting early syncs showing at least 4ah consumed still left but 100% so a little confusing
I
