SCReg. and Electric System Protection against Lifepo4 HVCutoff or LTCutoff

[SOLAR SUPPORT]

Does Solar Charge Regulator need protection against Lifepo4's HVCutoff or LTCutoff event?

In order to close the solar charge controllers safely, the solar panel line must first be closed, and if possible, it is important that the panels are not under sunlight, so that no electric arc occurs at the separated ends.

When the connection between the solar charge controller and the battery is interrupted due to HVCutoff or LTCutoff, what happens in the charge controller? Specialy when the charge controller is powered by the energy from the solar panels? Isn't this an inappropriate shutdown for the solar charge controller even though it happened over a short period of time?

If the solar charge controller automatically detects the system voltage information, things seem to get messy. Considering that the system voltage is cut off and returned in a short time, what is the probability of making a mistake about which voltage the charge regulator will operate at? For example, in a 12 Volt system, can the solar charge controller make a mistake and switch to 24 Volt mode?

[goboatingnow]

A properly designed solar controller has absolutely no issue with the battery being abruptly disconnected , a PV panel is not inductive in any way.

PV panels only generate energy on demand and with an appropriate electrical circuit.

On abrupt disconnection the panel will assume Voc ( voltage open circuit ) which the charge controller should be specified to handle.

It’s no different then disconnecting a 9v battery. The current flow just stops.

[goboatingnow]

the solar charge controller automatically detects the system voltage information, things seem to get messy. Considering that the system voltage is cut off and returned in a short time, what is the probability of making a mistake about which voltage the charge regulator will operate at? For example, in a 12 Volt system, can the solar charge controller make a mistake and switch to 24 Volt mode?

Your wildly over thinking this

Voltage sensing charge controllers can of course typically be fed battery sense information a number of ways. My Victron unit uses Bluetooth.

Secondly if the battery is disconnected it doesn’t matter if the controller wrongly assumes 24v , it’s disconnected after all. ( marine solar controllers mostly are designed to charge batteries not as a power source ) once the battery is reconnected it will instantly adjust to the correct battery voltage again.

[noelex 77]

It is not the recommended practice, most solar controllers want the solar input disconnected before disconnecting the battery, but most of the time you will not do any damage to the solar controller by disconnecting the battery first.

However, disconnecting the main battery without disconnecting the solar input can cause some significant issues for some boat electrical systems. Without any battery in the system most solar controllers cannot regulate the voltage accurately. There will be significant high and low voltage spikes as the solar controller tries to maintain a stable voltage without the benefit of the battery acting as a buffer. Equipment, such as sailing instruments, that are still connected will be subject to these voltage spikes, and it can do significant damage.

This depends how you boat is wired. If when the BMS disconnects the battery the solar can still provide power to main switchboard there is a significant risk of damage.

[SOLAR SUPPORT]

Both of my prismatic 2 x 200 Ah Lifepo4 batteries made in China, connected in parallel, cut off the charge with the HVCutoff protection circuit above 14.2 volts.

This behavior of the batteries was tested individually when not connected in parallel. BMS absolutely does not allow the battery voltage to rise above 14.2 volts. Whereas I would expect it to be 14.5 or 14.6 volts.

40A 12V Mppt charge controller has adjustable max charge voltage feature. Charge controller, 14.6 volts max. was set to charging voltage. Normally, I get off the boat without turning off the mppt charge. When I came to the boat last week, the main electrical control panel turned itself off while the service battery switch was on. All devices on the boat were turned off except for the bilge pump float. The Bavaria 301 12 V board is equipped with many electronic precision integrated circuits. The inoperative main electrical panel was removed and repaired.

I think this event is caused by the mppt control unit I mentioned above. When Lifepo4 batteries are full to 14.0-14.1 volts, the breaker relays that I will place on the mppt solar panel input side will be triggered by a voltage sensitive relay and time delay relay combination, which will turn off the solar charge controller before it reaches the Lifepo4 HVCutoff voltage. To achieve this, I decided to mount the front breaker safety relay assembly before the mppt charge regulator's solar panel energy input.

[goboatingnow]

I mentioned that most mppt solar units are setup to charge batteries. They are not primarily designed as dc power sources

Hence you can disconnect the output , no issues , but you should disconnect immediately at the output of the solar controller and ensure no devices remain connected to the solar controller

Other then that , there are really no issues.

Of course if you want to you can easily rig a relay to switch the panel fees off.

[SOLAR SUPPORT]

Originally Posted by goboatingnow

I mentioned that most mppt solar units are setup to charge batteries. They are not primarily designed as dc power sources

Hence you can disconnect the output , no issues , but you should disconnect immediately at the output of the solar controller and ensure no devices remain connected to the solar controller

Other then that , there are really no issues.

Of course if you want to you can easily rig a relay to switch the panel fees off.

While the Lifepo4 battery is connected to the system and is being charged with solar charge controller, disconnecting the mppt regulator output is not the same as isolating the battery from the system with the HVCutoff triggering of the BMS inside the battery itself.

Opening and closing the output of the solar charge controller while the battery is on, does not cause any problems since the devices connected to the system are currently powered by the battery.

In the scenario I mentioned, the Lifepo4 battery is only charged by solar energy. When the battery is fully charged, the HVCutoff protection circuit isolates the battery from the system. Although the reconnection of the battery with the system takes place in a very short time, the solar charge controller and other devices remain in the system and alone in this short time.

In this very short time, only mppt feeds the system. What is the probability of voltage rise in the system due to mppt's automatic voltage regulation task in this short time until the battery feed return to the system? It does not seem possible to observe what happens during the exit and return from the system, which is carried out in a very short time by BMS on the battery side.

[goboatingnow]

Unfortunately HVC cutoff devices are, for economy reasons , positioned at the battery , hence potentially leaving the charge sources, disconnected from the battery, but remaining in circuit attached to the boats dc supply. This is not a good idea. A charging bus , only connecting the charge sources should be deployed , and the HVC cutoff should disconnect only this bus. There is no need to remove the battery from its consumers in a HVC ( in fact it’s a good idea not to ) .

An LVC event does require the battery to be disconnected it’s consumers.

[SOLAR SUPPORT]

The BMS is generally located inside the Lifepo4 battery. Shortly before the battery isolates itself from the external environment, a communication port on the battery must send a signal to the external environment.

This signal should be sent to the relays at the panel input ends of the mppt and also to the rotor excitation breaker relay of the alternator before the battery self-protection Cutoff event. The pre-warning signal will be useful to initiate the charge cut action before the HV, LV, LT, HT, HC cut-off actions of the BMS and hence turn off all charging sources.

I think battery manufacturers should add a communication port that sends such a warning signal. The communication port should be a standard feature that works to meet the safety requirement of the electrical system for battery production.