Protect your Charge controller from battery disconnect while connected to the PV

[fabieville]

Is there a way to protect your charge controller when there's a battery disconnect while being connected to the PV panels?

I am currently using a  lifepo4 battery and i am thinking that suppose one day my BMS cuts off the output because of a overload or because it suddenly develops a fault of its own so essentially the charge controller connection to the battery would be cut while the PV is still connected to the charge controller. I string my panels in high voltage string of around 100v coming from the panels going to the CC.

Is there a way to protect my charge controller from seeing the high voltage input coming from the panels when there is no battery connect to it?

[DamonHD]

I think that my controller will survive with seeing full input voltage and no battery connection or load.

Indeed, the manual tells me to wire up the PV before the battery or load.

So my controller doesn't need protecting.

Why do you believe that yours does?

Rgds

Damon

[fabieville]

Because  essentially is the battery operates my mppt cc. Without the battery been connected the mppt circuits inside that operates from the battery voltage will see the high voltage and get damage.

[DamonHD]

For what it's worth my controller is also MPPT.

It may be that some are entirely happy to tolerate being disconnected from the battery, and some are not.

Rgds

Damon

[Mary B]

Morningstar MPPT wants battery connected  before solar panels or it will give an error code.

[fabieville]

so can anyone please tell me a method i can implement which would immediately cuts off the pv panels incase the battery gets disconnect from the controller? maybe using some relays i assume. My controller is a Renogy Rover mppt 100amp Li-ion and i am not sure if it would survive if this issue occurs.

[noneyabussiness]

maybe try some rated TVS diodes on the input, big enough to trip your pv breaker ( or even put a fast blow dc fuse that will blow just above normal current load)...

eg. say 10 amp is " normal " from pv, so a 15amp fast blow fuse with a ( or more) TVS diode on the input thats rated to the open circuit voltage of panels... battery drops out, voltage from panels spikes, TVS diodes take the surge and trip the fuse..

[joestue]

Thats not going to work. Solar panels are constant current, and tvs diodes only clamp the voltage to the level they trigger at.


But if you use a tvs as a zener diode in series with the coil of a magnetic latching relay, then the voltage surge on the output will turn off the relay. It may be expensive to do it this way, magnetic latching relays can be hard to find in high currents.


A tvs diode triggered scr would short out the solar panels.

[Solar Mike]

The problem you have is common to all MPPT controllers, if the controller is under a reasonable load charging the battery AND the battery is suddenly disconnected by Fuse blowing or breaker tripping or BMS disconnecting the load, then the current flowing in the buck converter choke suddenly has no where to go, so the output voltage will rise very quickly, faster than what the CPU PWM control feed back loop can handle.

The rate of this voltage increase is determined by the size of the output and input electro's, it may over voltage and destroy some components.

You could place a large TVS diode on either side of the buck inductor with a rating of higher voltage than normally present, this would help prevent blowing up the rest of the components.

On my DIY PV controllers I normally use a voltage sense and fast comparator that turns off the PWM drive to the buck inverter bypassing the CPU.

Cheers
Mike

[joestue]

If you use a synchronous forced continuous mode buck converter, the only voltage rise would be caused by the solar panel v rising, which is minimal.


Cpu driving the pwm directly?  Which controllers are doing that?

[SparWeb]

When the battery BMS disconnects, it may be possible that the + battery line is not just disconnected, but also grounded.  If so, then it can sink a current from another circuit (like a backup battery) to trigger a relay.  That way the relay is not drawing a phantom current draw most of the time, while the NC contacts pass the PV current.  But as soon as the BMS cuts out, the relay coil gets its signal, opens the contacts, and disconnects the PV array.

You would have to check how the BMS disconnects because "floating open circuit" wouldn't help.

[OperaHouse]

I always have a large capacitor on the output of the charge controller.

[Bossrox]

I have the same concern but I set my chargers so that they'll never trigger the bms to shut down from over voltage & never drain them low enough for a bms shutdown but your bms could shut down for under voltage so what I'd do is put a single pole contactor inbetween 1 of the the solar panel input wires & charger with the trigger coil tied to the chargers battery input. As you might guess, if the bms cuts the battery, it'll also kill the panel input. Just be sure you use a proper sized contactor for current it'll handle.

[XeonPony]

Is there a way to protect your charge controller when there's a battery disconnect while being connected to the PV panels?

I am currently using a  lifepo4 battery and i am thinking that suppose one day my BMS cuts off the output because of a overload or because it suddenly develops a fault of its own so essentially the charge controller connection to the battery would be cut while the PV is still connected to the charge controller. I string my panels in high voltage string of around 100v coming from the panels going to the CC.

Is there a way to protect my charge controller from seeing the high voltage input coming from the panels when there is no battery connect to it?

I have actually had this happen all ready, It was due to them getting too cold, so the BMS shut off charging, but the HV setting on the Solar controller kicked in and it shut off the array

I use the MppT 60 from Morning star.

Every thing seems to have survived fine.

I run my panels at apx 74V

But controller still was still loaded by inverter and rest of power system

                                                                             House AC loads                   12V loads
Solar > Mppt control > common buss > Inverter ^  /  BMS / DC-DC converter^

[Bossrox]

I've got Growatt chargers & if there's a battery disconnect, they'll alarm & immediately disconnect the panels. All the chargers I've tried say connect the battery before the panels. That seems to be the way most chargers are designed.