lithium battery with any controller could be a wrong idea??

[Marc G]

hi, i’m new and this is my fist post!
happy to be here with people which hope to build (or try to understand) solar system..

because all controllers need the battery connection first and some manufacturers have upgraded to lithium,
my question is simple:
because lithium have BMS with cut-off protection, how any controller can charge it in a low voltage cut-off situation??
(less any damages to the controller when the sun come back to the solar panels).. and for all other which have user
setting capability (ideal for li-ion for example) can’t to deal with the cut-off situation..
imagine this situation where during the night, for some reason, a cell in low voltage activate the cut-off BMS.. so the controller is shutdown.. the morning come with the sun and the voltage is now applied to controller less the battery (most of manufacturers have a warning damage about this situation).. i agree that the battery (or BMS) have to be verified but how manufacturers can be lithium updated (if it’s true) and able to charge a battery disconnected (or have no damage during the cut-off situation when the sun is there)?
i try to figure it and for now that look very hazardous.. maybe i misunderstand something..
if someone can to explain it shortly, i will be very happy!!
thanks and regards,
Marc

 

[snoobler]

Welcome to the forum.

Some BMS only cut off one or the other, not both. Overkillsolar will cut off discharge if voltage to low, but allow charge. If voltage is too high, it will cut off charge, but permit discharge. This is a "separate port" BMS.

NOTE: Charging with solar may be disabled due to the fact that the battery powers the MPPT. The battery will need to be charged separately or "jump" started with another attached battery.

See this post to alter BMS settings to allow charging:

lithium battery with any controller could be a wrong idea??

hi, i’m new and this is my fist post! happy to be here with people which hope to build (or try to understand) solar system.. because all controllers need the battery connection first and some manufacturers have upgraded to lithium, my question is simple: because lithium have BMS with cut-off...

diysolarforum.com

Common port BMS cut off both. In those cases, the battery is completely isolated until the voltage has settled back into the acceptable range, which they will always do provided they are not damaged. In that case, the BMS resumes normal function after several minutes.

In most cases, while many charge controllers caution against panels connected with no batteries, many have tested this theory (on purpose and on accident), and it rarely cause problems.

Best to get a "separate port" BMS that only cuts off the undesirable operation and permits the desired operation.

 

[MisterSandals]

Trying to destory my SCC's: I can't do it!

So I took every EPEver/Victron/PWM/Renogy solar charge controller, and tried to fry it by connecting it only to solar panels, and not to a battery... guess which one survived? EVERY SINGLE ONE! I couldn't destroy any of them, and I left them connected to a high voltage array (80 volts) for 4+...

diysolarforum.com

 

[Hedges]

We think charge controllers generally need battery connected first when first commissioned, to learn battery voltage. It MAY be that they don't care about order of PV vs. battery after that. Obviously fuses and breakers could result in a battery disconnect. There are probably some bad charge controllers which will burn themselves up.

Some charge controllers have a maximum PV Voc rating which varies depending on battery voltage, e.g. "24V battery + 72V = 96V" or something like that. It would seem if that had battery disconnected and was trying to feed a load of zero volts, anything over 72 Voc might damage it.

If you do have a BMS that disconnects due to low voltage, likely you need a way to bypass BMS and get some charge in. Maybe once disconnected from load it will come back up on its own. Some BMS have separate ports for charge and discharge - this lets them prevent charging below 0C but still allow discharge.

Same issue for my Sunny Island even with lead-acid batteries. Once it goes into battery protect at 80% DoD, it won't close relays to connect AC input (grid or generator). Instructions for emergency charge from an AC source are offered. I think I would connect either a battery charger or string of PV panels directly to the battery.

I've read of over-discharged electric power tool batteries needing to be "bumped" up with repeated mating to the charger before they come back to life.

What you want is for your inverter to have a cut-off mechanism which activates before BMS does, so BMS is only emergency shutdown.

 

[MisterSandals]

so BMS is only emergency shutdown.

This!

Folks tend to think of a BMS for daily battery charge management. But the reality is that if your BMS cuts out, you probably have some work to do on your overall system before bringing it back online.

 

[Jim Burrow]

I'm using two 12v lead-acid batteries in series for 24v. These two batteries are junk as I found them in a recycle bin out at my local airport. I have the MTTP LV2420-MSD controller/inverter (all-in-one) and the battery needs to be connected before it will fire up.

However, I ran a test with no utility power or solar and let the batteries run all the way down until the controller/inverter shut itself off. So at this point, everything is dead.

I then turned on the utility power and the controller/inverter came alive and started to supply power to the load and started charging my batteries.

So in theory, in the middle of the night, my batteries are drained and everything shuts off, as soon as the solar and or utilities come online, everything starts working and batteries get recharged.

Anyway, that is my experience when testing for totally drained batteries at night.

 

[Jim Burrow]

I'm using two 12v lead-acid batteries in series for 24v. These two batteries are junk as I found them in a recycle bin out at my local airport. I have the MTTP LV2420-MSD controller/inverter (all-in-one) and the battery needs to be connected before it will fire up.

However, I ran a test with no utility power or solar and let the batteries run all the way down until the controller/inverter shut itself off. So at this point, everything is dead.

I then turned on the utility power and the controller/inverter came alive and started to supply power to the load and started charging my batteries.

So in theory, in the middle of the night, my batteries are drained and everything shuts off, as soon as the solar and or utilities come online, everything starts working and batteries get recharged.

Anyway, that is my experience when testing for totally drained batteries at night.

Note: I do not have any BMS connect to my batteries or anywhere and I don't thing they would be internal to my controler/inverter.

 

[Mex Rider]

Welcome to the forum.

Some BMS only cut off one or the other, not both. Overkillsolar will cut off discharge if voltage to low, but allow charge. If voltage is too high, it will cut off charge, but permit discharge. This is a "separate port" BMS.

Common port BMS cut off both. In those cases, the battery is completely isolated until the voltage has settled back into the acceptable range, which they will always do provided they are not damaged. In that case, the BMS resumes normal function after several minutes.

In most cases, while many charge controllers caution against panels connected with no batteries, many have tested this theory (on purpose and on accident), and it rarely cause problems.

Best to get a "separate port" BMS that only cuts off the undesirable operation and permits the desired operation.

Welcome to the forum.

Some BMS only cut off one or the other, not both. Overkillsolar will cut off discharge if voltage to low, but allow charge. If voltage is too high, it will cut off charge, but permit discharge. This is a "separate port" BMS.

Common port BMS cut off both. In those cases, the battery is completely isolated until the voltage has settled back into the acceptable range, which they will always do provided they are not damaged. In that case, the BMS resumes normal function after several minutes.

In most cases, while many charge controllers caution against panels connected with no batteries, many have tested this theory (on purpose and on accident), and it rarely cause problems.

Best to get a "separate port" BMS that only cuts off the undesirable operation and permits the desired operation.

 

[Mex Rider]

Hi @snoobler , first let me preface with I'm old and have a poor/faulty memory. I do have an Overkill BMS and when it did a LVD it then would not accept a charge. With Steve's good support I went in to the BMS settings and lowered ( temporarily) the LVD setting which then allowed the battery to charge and after charging, restored the LVD to it's previous higher setting.

 

[snoobler]

Hi @snoobler , first let me preface with I'm old and have a poor/faulty memory. I do have an Overkill BMS and when it did a LVD it then would not accept a charge. With Steve's good support I went in to the BMS settings and lowered ( temporarily) the LVD setting which then allowed the battery to charge and after charging, restored the LVD to it's previous higher setting.

Edited my post. Thanks.

 

[Marc G]

if your controller is setted < 14v or 14.2v for longer lifetime, on a LFP battery, the DALY bms will never balance the cells!! ..with Bluetooth, if the voltage can be changed for balancing is different but less to able to change it, it’s a bad new!!

 

[HRTKD]

Hi @snoobler , first let me preface with I'm old and have a poor/faulty memory. I do have an Overkill BMS and when it did a LVD it then would not accept a charge. With Steve's good support I went in to the BMS settings and lowered ( temporarily) the LVD setting which then allowed the battery to charge and after charging, restored the LVD to it's previous higher setting.

I knew this, but it hadn't really sunk in. Thanks for the information.

My first thought was that I could connect to shore power to get the batteries charged from the converter. I'm fairly sure that would work. However, I'm rarely in a position to connect to shore power.

In the absence of shore power, I could fire up the on-board generator to get power to the converter. That will work right now because the battery to start the generator isn't the LiFePO4 house batteries. I retained a smaller lead acid battery on the tongue to start the generator. I've been looking into eliminating the lead acid battery and going with just the LiFePO4 batteries.

While a complete drain of the LiFePO4 batteries would be a rather exceptional situation, it could happen. Now I'm reconsidering my plan to eliminate the lead acid battery.

 

[Mex Rider]

Redundancy is always good, unless the FLA is bad and needs to be replaced, why eliminate?

 

[HRTKD]

Redundancy is always good, unless the FLA is bad and needs to be replaced, why eliminate?

Weight reduction. One less maintenance item. Freed up space on the tongue gives me room to put in a toolbox.