EPever MPPT external enable/disable

kgol

New Member
Hi all,

I need a set of good MPPTs and was looking at the EPever range as they appear good quality and rather affordable (compared to Victron ones). I would really like them to have an input that allows to enable/disable them, as is described in the Nordkyn articles (TLDR: enable/disable chargers to ensure correct charge termination, for safety the BMS still drives a relay that can disconnect the LFP battery).

All Victron MPPTs appear to have this feature. The EPevers, however, do not appear so. Of course, I can put relays between the MPPTs and the PV panels but relays would add cost and introduce losses. So, I was wondering whether I could fool around with the temperature sensor functionality of the EPever. This hack should be a reasonably fail-safe one, in case it fails the charger should be disabled.

There was a related thread (https://diysolarforum.com/threads/externally-controlling-a-non-controllable-charge-controller.20136/), however, that thread did not focus specifically on EPever MPPTs.

According to their manual, EPever MPPTs allow to connect an external temperature sensor (TS300R47K3.81A, an NTC?). Furthermore, the manual mentions that if the temperature sensor is not connected or shorted, the MPPT assumes the temperature to be 25 °C. From the communications sheet it appears that an allowed-charging temperature range can be programmed.



So, I was wondering... can one set the maximum battery temperature to 20 °C or so (or minimum temperature to 30 °C or so) and then enable the charger by putting a specific resistance that corresponds with e.g. 10 °C (or or e.g. 40 °C) over the temperature sense terminals? Putting the resistance would be done with a small signal relay or maybe an optocoupler.

Looking forward to your thoughts
 

DThames

Solar Addict
It is not clear to me if you are looking for a backup charge termination or to be able to control the normal charge termination. The Tracer series allow you to set all aspects of the charge, so you can cause it to terminate at any voltage you desire. The proper BMS will also allow specific settings to stop charging.

If you are looking for some sort of backup in case the charger loses its little mind, then a relay on the solar input would be an option that would be independent of the charger....because if the charger is in some sort of fault condition, I wouldn't depend so any of the charger functions to be working correctly. You would just need a high voltage protection circuit/board that would drive the relay in event of over voltage on the battery. But again, the BMS is there. I guess if you want to be sure to cut power to a faulty charger for reasons other than the battery, then a secondary control would have value.
 

kgol

New Member
It is not clear to me if you are looking for a backup charge termination or to be able to control the normal charge termination. The Tracer series allow you to set all aspects of the charge, so you can cause it to terminate at any voltage you desire. The proper BMS will also allow specific settings to stop charging.
Appreciate your thoughts. The Tracer series indeed allows setting voltages, yet it cannot measure the total battery charge current. For charge termination we would prefer to take both voltage and current into account, as explained in the Nordkyn article mentioned earlier. However, this is perhaps not the most important reason why we want this feature.

If you are looking for some sort of backup in case the charger loses its little mind, then a relay on the solar input would be an option that would be independent of the charger....because if the charger is in some sort of fault condition, I wouldn't depend so any of the charger functions to be working correctly.
Very true! The enable/disable feature would never be depended on for safety (I guess it will improve safety, though). In case things really go haywire, the BMS will disconnect all chargers from the battery (dual bus system). However, we expect doing so will destroy (some of) the chargers as they cannot handle not being connected to a battery. If disconnecting them avoids a battery fire, excellent, but we want to avoid a disconnection event as much as possible.

So a means to disable the chargers if the problem is not due to a charger appears attractive. Assume for example that one cell goes out of balance, then we don't want to disconnect the chargers, we only want to let them stop charging earlier.
 

DThames

Solar Addict
I think I will take exception to the article statement "any voltage from 3.40V/cell up will eventually fully charge and then overcharge a lithium iron phosphate battery" Constant Current, Constant Voltage charging is the common charging method for lithium batteries. The current is limited until the voltage is reached and then the voltage is held constant at the "charge to" voltage. When the battery reaches this voltage, current no longer flows because there is no voltage difference between the charger output and the battery voltage.

With CC/CV charging you will see the volts raise up to the charge voltage, then see that held while the amps drop to zero. If your "Boost" voltage is set to 3.5v per cell, after the "absorption time" the voltage will be allowed to drop back toward the settling voltage or the float voltage, which ever is higher. The voltage during the absorption time should stay constant and not rise above the boost voltage. There does not need to be a termination current setting or device to govern the charging because it is built in by design.

I am in the process of fine tuning two Tracers that are connected to the same battery bank. I have my float set a little below the normal settling voltage. My system is for emergency use and is idle most of the time. So no charging most of the time. But when I turn on the inverter and a load, it quickly drops below float and hits "boost reconnect". The charger then supplies the load and the charging of the batteries. When it drops out of Boost, it is fully charged and if during a sunny day, normally will stay right there, very close to the settling voltage.....or if the battery is not full, it will boost til full and then go back to settle.

Hope that is some help.
 

mikefitz

Solar Addict
I need a set of good MPPTs
Why do you need a set?
EPever MPPTs allow to connect an external temperature sensor (TS300R47K3.81A, an NTC?)
Is most likely a 10k NTC. If the Epever is set to the lithium default setting , below 5C inhibits charging. There is some confusion with the temperature sensor operation in lithium mode. As I understand, in the default lithium mode it will protect below 5C, but not with the user settings mode.
If you need to disable charging easily use a Victron product or have a fet or relay switch in the solar feed.

Developing a suitable control system will be an interesting challenge.

I think I will take exception to the article statement "any voltage from 3.40V/cell up will eventually fully charge and then overcharge a lithium iron phosphate battery"
This statement is correct.
A voltage of 3.4 volts will charge the cell to almost full capacity, it will take time for the last 40% or so but it will charge. Try it and see.
then see that held while the amps drop to zero
Depending on the target voltage, available charging current, and battery Ah capacity, the battery will be fully charged well before the current drops to zero. Holding the voltage constant whilst the current drops to zero may damage the cell. Most specification data states that at 3.65v the cell is fully charged when the current falls to 0.05C, 5 amps per 100Ah.
If the target voltage is lower, then the current at 'full' would be less, for example at 3.50 volts, the cell would be considered full at 2.3 amps per 100Ah.

Below is the chart showing cell state of charge with charge voltage (from Eric Bretscher).
state of charge.jpg
Mike
 

DThames

Solar Addict
Why do you need a set?

Is most likely a 10k NTC. If the Epever is set to the lithium default setting , below 5C inhibits charging. There is some confusion with the temperature sensor operation in lithium mode. As I understand, in the default lithium mode it will protect below 5C, but not with the user settings mode.
If you need to disable charging easily use a Victron product or have a fet or relay switch in the solar feed.

Developing a suitable control system will be an interesting challenge.


This statement is correct.
A voltage of 3.4 volts will charge the cell to almost full capacity, it will take time for the last 40% or so but it will charge. Try it and see.

Depending on the target voltage, available charging current, and battery Ah capacity, the battery will be fully charged well before the current drops to zero. Holding the voltage constant whilst the current drops to zero may damage the cell. Most specification data states that at 3.65v the cell is fully charged when the current falls to 0.05C, 5 amps per 100Ah.
If the target voltage is lower, then the current at 'full' would be less, for example at 3.50 volts, the cell would be considered full at 2.3 amps per 100Ah.

Below is the chart showing cell state of charge with charge voltage (from Eric Bretscher).
View attachment 47754
Mike
I said,
"I think I will take exception to the article statement "any voltage from 3.40V/cell up will eventually fully charge and then overcharge a lithium iron phosphate battery" Constant Current, Constant Voltage charging is the common charging method for lithium batteries. The current is limited until the voltage is reached and then the voltage is held constant at the "charge to" voltage. When the battery reaches this voltage, current no longer flows because there is no voltage difference between the charger output and the battery voltage. "

The part "....and then overcharge.." is what I take exception to. This is not a description of normal CC/CV charging. I tried to clear that up by explaining CC/CV. CC/CV will not overcharge as described in the article. This thread is about a minimum current threshold setting/control, so the comment was related the statement that indicated you must have some current sense to stop charging.
 

DThames

Solar Addict
Why do you need a set?

Is most likely a 10k NTC. If the Epever is set to the lithium default setting , below 5C inhibits charging. There is some confusion with the temperature sensor operation in lithium mode. As I understand, in the default lithium mode it will protect below 5C, but not with the user settings mode.
If you need to disable charging easily use a Victron product or have a fet or relay switch in the solar feed.

Developing a suitable control system will be an interesting challenge.


This statement is correct.
A voltage of 3.4 volts will charge the cell to almost full capacity, it will take time for the last 40% or so but it will charge. Try it and see.

Depending on the target voltage, available charging current, and battery Ah capacity, the battery will be fully charged well before the current drops to zero. Holding the voltage constant whilst the current drops to zero may damage the cell. Most specification data states that at 3.65v the cell is fully charged when the current falls to 0.05C, 5 amps per 100Ah.
If the target voltage is lower, then the current at 'full' would be less, for example at 3.50 volts, the cell would be considered full at 2.3 amps per 100Ah.

Below is the chart showing cell state of charge with charge voltage (from Eric Bretscher).
View attachment 47754
Mike

I think you are confusing charging theory and profile with charger behavior. You need to understand charging theory and profile to design a charger. But a properly designed charger manages proper charging. If a charger is in Constant Voltage mode of the profile, the voltage of the charger is <desired volts per cell> x <cells in series> (3.5v x 4 = 14.0 for example). When the battery reaches that voltage (internally) the current will be zero because there is no voltage difference between the charger output and the battery internal voltage.

If however you have a power source that is not voltage limited that is a different matter. This is not a condition with a proper charger, but something you would see if connected directly to a power source/ power supply without a charger.
 
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