diy solar

diy solar

Protect charge controller

Cuemaker

New Member
Joined
Oct 28, 2021
Messages
95
Location
Winchester, Ohio
I have an Aims 100amp charge controller.
4kw solar panels.
Lithium 280ah battery bank with a Daly 16s-48v-250a BMS
A few days ago, I was charging the battery bank with the Aims 6kw-48v inverter/charger, it over charged the batteries & the BMS shut the battery bank off & the whole system shut down.
I was really lucky, it was about 4am so the solar panels were not producing.
Manual states to turn off CC disconnect solar panels 1st, negative then positive, then disconnect battery, negative then positive.
My question: how do I protect the CC if the battery bank shuts off during the day?
 
I have an Aims 100amp charge controller.
4kw solar panels.
Lithium 280ah battery bank with a Daly 16s-48v-250a BMS
A few days ago, I was charging the battery bank with the Aims 6kw-48v inverter/charger, it over charged the batteries & the BMS shut the battery bank off & the whole system shut down.
I was really lucky, it was about 4am so the solar panels were not producing.
Manual states to turn off CC disconnect solar panels 1st, negative then positive, then disconnect battery, negative then positive.
My question: how do I protect the CC if the battery bank shuts off during the day?

You don't. While those instructions exist in almost all manuals, this issue has been "field tested" on many different makes and models, and it's not an issue.

Your BMS is not functioning correctly, or something else is wrong. In an over-charge situation, the BMS should just prevent charging - not shut the system down.

With a properly functioning BMS, the scenario you describe (overcharge) is not a concern. While the BMS may have cut the charge, it did not cut the discharge, so the MPPT would still be powered by the battery - the battery would just not accept charge. Battery would still be connected at both the positive and negative.
 
You don't. While those instructions exist in almost all manuals, this issue has been "field tested" on many different makes and models, and it's not an issue.

Your BMS is not functioning correctly, or something else is wrong. In an over-charge situation, the BMS should just prevent charging - not shut the system down.

With a properly functioning BMS, the scenario you describe (overcharge) is not a concern. While the BMS may have cut the charge, it did not cut the discharge, so the MPPT would still be powered by the battery - the battery would just not accept charge. Battery would still be connected at both the positive and negative.
Thanks for the info, really appreciated!
I set the overcharge parameters wrong on the BMS.
But something shut the whole system down & it happened when one cell hit the 2nd alarm stage.
I have EVE280ah-3.2v cells X 16 = 51.2v
Daly BMS computer program has a 2-stage high cell volt setting, now it is set at 3.65v & 3.75v.
Before I had it set lower but forget exactly what, it gave warning at 1st stage & when it hit 2nd stage everything shut down.
Can't figure out what else it could be, maybe like you said, BMS not working properly.
 
Thanks for the info, really appreciated!
I set the overcharge parameters wrong on the BMS.
But something shut the whole system down & it happened when one cell hit the 2nd alarm stage.
I have EVE280ah-3.2v cells X 16 = 51.2v
Daly BMS computer program has a 2-stage high cell volt setting, now it is set at 3.65v & 3.75v.
Before I had it set lower but forget exactly what, it gave warning at 1st stage & when it hit 2nd stage everything shut down.
Can't figure out what else it could be, maybe like you said, BMS not working properly.

Normal operation for these BMS is to cut off charge if a high voltage limit is exceeded, NOT shut the whole thing down. I would double check all your settings to confirm nothing is amiss. I'm not familiar with the specifics of the DALY BMS.
 
You don't. While those instructions exist in almost all manuals, this issue has been "field tested" on many different makes and models, and it's not an issue.

Your BMS is not functioning correctly, or something else is wrong. In an over-charge situation, the BMS should just prevent charging - not shut the system down.

With a properly functioning BMS, the scenario you describe (overcharge) is not a concern. While the BMS may have cut the charge, it did not cut the discharge, so the MPPT would still be powered by the battery - the battery would just not accept charge. Battery would still be connected at both the positive and negative.
Looked unsuccessfully for a similiar thread for this scenario: when the battery hits low voltage cut-off, is the MPPT at risk for damage due to presence of PV voltage and an open battery circuit?
 
Last edited:
Looked unsuccessfully for a similiar thread for this scenario: when the battery hits low voltage cut-off, is the MPPT at risk for damage due to presence of PV voltage and an open battery circuit?

A charge cut-off is no different from the perspective you present... MPPT charging and then suddenly, the battery blocks all charge. MPPTs often spike in voltage due to the short lag in cutting off current. Sending X Volts, Y Amps and Z power... suddenly, nowhere to go.

In discharge protection mode, the battery does NOT block charge. It just prevents discharge. The MPPT is likely to see the voltage drop below what it can use and simply shut off. With a Victron MPPT, once battery voltage has been programmed, they can be powered purely by PV w/o issue (even if battery is completely removed). They are particularly useful in recovering LFP batteries in discharge protection mode.

While they can power a steady state system without a battery, the MPPT algorithm is typically too slow to keep up with rapid load changes.

Lastly, Victron MPPT are very useful in reducing the need for a pre-charge resistor. In the event of a low voltage disconnect, the MPPT will charge the inverter capacitors and reduce the chances of the BMS triggering short circuit protection.
 
A charge cut-off is no different from the perspective you present... MPPT charging and then suddenly, the battery blocks all charge. MPPTs often spike in voltage due to the short lag in cutting off current. Sending X Volts, Y Amps and Z power... suddenly, nowhere to go.

In discharge protection mode, the battery does NOT block charge. It just prevents discharge. The MPPT is likely to see the voltage drop below what it can use and simply shut off. With a Victron MPPT, once battery voltage has been programmed, they can be powered purely by PV w/o issue (even if battery is completely removed). They are particularly useful in recovering LFP batteries in discharge protection mode.

While they can power a steady state system without a battery, the MPPT algorithm is typically too slow to keep up with rapid load changes.

Lastly, Victron MPPT are very useful in reducing the need for a pre-charge resistor. In the event of a low voltage disconnect, the MPPT will charge the inverter capacitors and reduce the chances of the BMS triggering short circuit protection.
If I'm reading this right, how does a BMS prevent battery discharge but retain voltage at the terminals? Wouldn't that still allow discharge?
 
Think if it as a highway with separate lanes for each direction. When the discharge mosfet is open, travel can only be in one direction - charging. When the charge mosfet is open,travel can be in only one direction - discharging.

Voltage measurement requires at least a tiny flow of discharge current. If current can't flow, no voltage measurement, but that doesn't mean if you apply a voltage to the terminals that current won't flow in.
 
Back
Top