Do SCCs have a minimum amperage input requirement

[daveemac]

I understand: VOC input operates within a range, with minimum and maximum values which are strict for operation and safety respectively

And Amperage input has a maximum value (which can be exceeded, although energy will be wasted)...but does it have a minimum value the same way VOC does? That is, is there a minimum amperage input below which the SCC won't work, the same way it won't work if there's insufficient voltage?

I'm 99% sure there isn't one, but I saw a blog somewhere that suggested that there is

For instance, I'm considering a system that could potentially be 150 VOC w/5amps

THANKS

 

[sunshine_eggo]

I've never seen one, and I would be shocked if there was one.

 

[Mattb4]

What you want from solar panels is watts. Amperage comes into play because W=VA.

At the moment my 1200w array is creating 18w (33v at .54a). This is presently due to the fact Winter sleet, fog, freezing rain is reducing how much sun makes it to the panels. I however have seen even less wattage in full sun. The reason? No loads.

So to answer your question the only minimum amperage you need is that required to give you any wattage demanded by loads.

 

[HighDesertOffgrid]

Post #6 from this thread seems to indicate some charge controllers may act as if there is a minimum current draw.

 

[RCinFLA]

General answer to your question is Yes, there is a minimum PV current requirement.

It depends on SCC. There can be a minimum amount of required PV power to run the circuitry of the SCC. This is required overhead power to run the MPPT DC to DC converter. Many PV to battery SCC's power their circuitry from PV power. Most AIO inverters power the overhead power for SCC and other circuits required for charging battery primarily from battery or AC input power.

PV terminal voltage will rise to Voc when the illumination generated current exceeds the shunt leakage resistance current of panel. The panel voltage rise triggers the SCC to wake up and make a startup attempt.

It is much easier to design a SCC that is powered from battery supply. When powered from PV, the SCC only gets indication that Voc has risen but does not have any indication of how much output power the given illumination level may support.

If SCC is powered from PV and PV illumination cannot support the SCC overhead power, the SCC startup attempt will cause the panel voltage to collapse and startup attempt to fail. After some amount of time delay, the SCC makes another attempt until there is enough illumination to support SCC overhead power consumption and keep the SCC running.

The SCC output load is not relevant, although many rely on detected battery voltage to select default charging parameters based on attached battery voltage.

Overhead power for SCC can range from a couple of watts for a small PV to battery SCC, to 50-80 watts for a HF AIO inverter SCC battery charger.

When SCC derives its overhead power from battery there is the possibility of a depleted battery that must be dealt with by a secondary trickle charging path.

It is not uncommon in the morning, on an AIO inverter, to see PV active but still have drain from battery until the PV illumination level gets strong enough to make more PV power than the AIO inverter overhead power consumption.

On an RV installation, using HF AIO inverter with only two or three panels, you may find you don't get battery charging until 10-11 am in the morning where sun illumination level gets strong enough to produce enough power on limited panels to exceed inverter overhead power requirements.

 

[Camp20144]

SCC “overhead” - Is this correct?
The Victron SmartSolar 150/60 SCC says “Self-consumption” = 35mA @ 12V. (Blue line in figure) Therefore, to calculate the SCC’s “overhead” we take W=(Amps)(Volts) = (35mA)(1000)(12V) = 0.42Watts. Is that correct? The Victron 150/60 SCC has an “overhead” power requirement of 0.42 Watts? Victron says the SCC will “start” when voltage in equals battery voltage(bV) + 5 volts. So when bV+5volts the SCC will need 0.42 Watts to operate and any power above 0.42 Watts goes to battery?
So, is this “Self-consumption” “overhead” a “minimum” input “requirement” for the SCC to “operate”?
Thank you

 

[RCinFLA]

The Victron spec refers to power taken from battery, likely also during the night. The charge controller DC to DC converter takes more overhead power than 0.42 watts but that is while running and is taken from PV supplied power.

 

[12VoltInstalls]

For instance, I'm considering a system that could potentially be 150 VOC w/5amps

For some panels- like my 100W panels- 5A is somewhat normal for either a single panel or a series string of them.

The commodity charge controllers handle this fine; I’ve seen as low as .61A in some of that lovely weather mentioned in an above post.

In my case, the 100W panels are 4S2P for a potential nominal ~10A at a nominal 88VOC as each string contributes a nominal ~5A to the solar input of their SCC. At the moment it’s snowing and I’m seeing 77.46V from the panels at 0.55A, and the charge controller is putting ~2.5A to 12VDC loads and 0.9A to charging the batteries.

You will be fine with what you are asking.