Think I destroyed my batterys

[SolarRat]

Your cells are only dropping 50mv under load (0.05v)...don't sweat it. Sounds perfectly normal to me. But why are you only charging to 26.4? Bump that up to 28v or so and give'r a capacity test to ease your mind.

 

[John Frum]

Further to what @SolarRat says. lifepo4 charge voltage

 

[Greenan_Energy]

Your cells are only dropping 50mv under load (0.05v)...don't sweat it. Sounds perfectly normal to me. But why are you only charging to 26.4? Bump that up to 28v or so and give'r a capacity test to ease your mind.

Appriciate it man. I'll give it a try next time your m down

 

[SolarRat]

Further to what @SolarRat says. lifepo4 charge voltage

Yes, and if you go by those tests, charging to 3.3v per cell (26.4v) doesn't give you much capacity. So I'd expect a lot of voltage sag. The blue line on the left is the discharge curve of a cell only charged to 3.3v. You can see that bumping the charge to at least 3.4vpc makes a huge difference.

 

[Greenan_Energy]

Yes, and if you go by those tests, charging to 3.3v per cell (26.4v) doesn't give you much capacity. So I'd expect a lot of voltage sag. The blue line on the left is the discharge curve of a cell only charged to 3.3v. You can see that bumping the charge to at least 3.4vpc makes a huge difference.

Ah solar rat you legend. I finally get it man, that's cleared up a lot. Looking at the graph I still had questions as I wasn't exactly sure what was going on. Great explanation. Thank you

 

[JoeHam]

I *may* have an answer to how your Victron setting got changed. If you provide the model number someone can confirm or deny this theory.

Many SCC have an “auto sense” whereby they switch to settings appropriate for the connected battery. If your battery voltage got low enough while you were gone the Victron may have switched to 12v settings.

 

[Greenan_Energy]

So judging from the data on the Mppt the lowest it got was 25.5V. The mppt is the Victron 75/10 without Bluetooth. I've it connected to a dongle

 

[nosys70]

i doub a 24V battery can go low enough (around 15V ?) to do this.

 

[nosys70]

it is also possible (we discussed that in another thread) that the measured voltage at victron charger is not what you get at the battery terminal, so, you are under charging.
charge battery to 28.4V, then disconnect battery , wait 1 hour and check battery is still in the 28V range.
if not, you have to set your victron charger to 29V
Do you have a correct size wiring ?

 

[Greenan_Energy]

it is also possible (we discussed that in another thread) that the measured voltage at victron charger is not what you get at the battery terminal, so, you are under charging.
charge battery to 28.4V, then disconnect battery , wait 1 hour and check battery is still in the 28V range.
if not, you have to set your victron charger to 29V
Do you have a correct size wiring ?

Yeah all I've checked the terminal with a multi meter and you are correct but the Mppt is only off by 0.02V. The cable size are correct

 

[Steve_S]

I read though the comments here and I see you have a few issues all coming together to cause confusion. KISS being tossed in here.
First, the charging profile info:
@ 3.65V (100% full) x 8 Cells for '24V pack' = 29.2 Volts.
Low Volt disconnect should be no lower than 22.0V (2.75V per cell)
@ .2C Rate charging (200AH X 0.2) = 40A @ .5C rate = 100A

(generic, applicable to SCC & Inverter/Charger settings)
Set your BULK @ 28.8 (3.6v per cell)
Absorb, float, not needed. if unable to disable, set to 26-28V.
Equalize OFF or 28.0V for as short a time possible.
Low Cutoff 22.0V Hi Cutoff 29.2V
NO TEMPERATURE Compensation !
* Absorb Cutoff is needed: @ 0.01C (200AH X 0.01C = 2A)

Next deration !
Ensure that the SCC, Inverter and everything are on. Have no load demand, so no demand on the inverter & no DC stuff pulling. IF you have a 24V->12V buck converter, do have that on.
Take your DVOM (Digital Volt Ohm Meter) and take a reading on the battery pack terminals, and note it.
Next take the same reading on the SCC (batt side) and note the voltage.
Next, again take a reading on the BATT terminals of your inverter and note it.

These will vary because of the wire used, this is called deration. You have to correct for this. The "true" voltage at the battery terminals is what you need to focus on. If the SCC says it sees 25.5V but at the batt terminals it is 26V then you are losing .5V to the wire, so the values of your setting in the SCC have to compensate for that, because with LFP a 1/2 Volt can man a LOT. This does not apply the same way as it does with Lead Acid Batteries.

Now if you look at your inverter input post voltage, it may be even lower, say 25.3V while the batt is actually 26V. So if you set the LVD cutoff in the inverter to 22V but do not correct, it will cut off at what IT thinks is 22V but in reality it will be 22.7V. IF this is also a charger and you use it to charge and set the Charge Full cutoff @ 29.2 (100% @ 3.65 cell) it will cut off at what IT thinks is 29.2 BUT it will in reality be 29.9 and you've damaged the batteries IF the BMS did not cut it off. We should never rely on the BMS to do that, that is a fail safe mechanism (backup safety). Therefore you have to adjust the voltage settings on your equipment relative to what is actually being read at the battery bank.
** IF you have one battery this is simple, just the voltage off the one battery pack. IF you have more than one pack in parallel, then you take the voltage at the main bus line where all the packs come together. Although it is wise to check the voltage between the packs and the main bus block to be sur that everything is within the same spec voltage.

Excellent Doc from Victron on wiring up your battery bank. See pages 9-12 especially for learning how to setup a properly balanced parallel bank.

https://www.victronenergy.com/upload/documents/Wiring-Unlimited-EN.pdf

The SCC - Changing Voltage: I have never heard of that happening at random. An SCC when powered up, reads the battery and immediately adjusts to that voltage. Most will do 12,24,48 automatically, Victron included. When an SCC goes dead OFF (no power @ battery or Solar) when it get's repowered, it will auto-sense the battery bank voltage and set itself to that. They should maintain the charging profile configuration in non-volatile ram. There is obviously something else going on here, defective or incorrect wiring ? The battery would not do this, it can't go that low to seem like a 12V battery 8 cells @ 2.0V = 16V the BMS would have turned it off by 2.4V per cell (pending on it's programming). To diagnose this, photo's and a logical diagram of your setup would be helpful. It is possible you got a dud SCC, it happens, even with Victron.

Hope that helps...
Steve

PS: This is a good read, written by Rob Beckers, an EEng and the owner of SolaCity and someone I also consider a friend, he knows his stuff !

How to Find Happiness With LiFePO4 (Lithium-Ion) Batteries – Solacity

By: Rob Beckers You have just sold your first-born into slavery, remortgaged the house, and bought yourself a lithium-ion battery! Now you want to know how to take care of your precious new purchase: How to best charge lithium-iron batteries, how to discharge them, and how to get the maximum...

www.solacity.com

 

[Greenan_Energy]

Your cells are only dropping 50mv under load (0.05v)...don't sweat it. Sounds perfectly normal to me. But why are you only charging to 26.4? Bump that up to 28v or so and give'r a capacity test to ease your mind.

Thanks man. What float voltage would you recommend at thay charge limit