The operational manual for the above unit states a nominal PV power of 1000 watts (12v). The specifications note- 1a) The solar charger will limit input power if more PV power is connected.
A common formula I have run across in solar design for input/output of a solar charger is 1000w/12volts= 83.3 amps. This means at 1000 watts input the output amperage exceeds the 70 amps this unit is designed for. And I do NOT want to burn out this unit with too much input.
My question: can anyone confirm that this unit ACTUALLY limits input power so that e.g. if I put 1200 watts of panels I do not run the risk of burning out the unit?
A friend actually had this happen to him on a different make of charge controller.
Yes, The unit will happily limit input power AS LONG as you also stay under the MAX input current of 70A.
your example of 12V - I would assume that you intend using this on a 12V system? So the Max output power would be typ 70A @ 14V or 980W. your input to the MPPT can be as high as 150V (for the 150/70). if you had an input voltage of ~ 95V, your Maximum input power could be over 2kW of modules, still giving a max output of 980W - even on a cloudy day. I’ve had 4.8kW of modules at ~120V connected with no problems. However, my battery voltage is 26-27V, so my max output power was 1890W. Now I have 2 of these MPPT’s as demand has increased and I need faster charging.
I own a SmartSolar 250/100 and a 250/70, and regularly overpanel the inputs with more solar than the nominal wattage. I do use a small quiet fan below them to keep them cool.
Both devices adjust the load on the PV input side so that the output current does not exceed 100A (for the 250/100) or 70A (for the 250/70).
However, it is best not to exceed the rated Isc on the PV input side with too many panels in parallel.
The actual maximum PV wattage you can use at any given instant is (battery voltage * 70A / 0.99 efficiency)
This means as the battery voltage increases, you can actually use more PV power (which isn’t obvious).
I do not exceed the short circuit current on either the 250/100 or 250/70.
On the 250/70 with the 35A limit, I get very close at 33.4A max ever seen, with Isc at 34. something,
The 70 can take Max 50A in on the PV side.
The reason for this limitation is the size of the protection FET - and maybe other issues…
The clamping FET limits the max input voltage, if it sees too much current, it won’t turn off again.
( similarly the series switching fet must be able to take the max current during power search sweeps)
Not to muddy the waters, but I’ve read that the reverse-polarity protection circuit has the Isc current limitation by shorting the input with a FET, in case you hook it up backwards. In other words, don’t do that and it will be fine. At one time Victron apparently said this in community, but I cannot provide a link.
I would still prefer to follow the specifications as provided.
Yes, the Voltage clipping fet also implicitly provides revers polarity protection due to the built in diode in the N channel fet.
So same device= same current limit.
I’ve not checked the data sheet for the 250/70, but yes, 50A is safe for the 150/70. The data sheets can be downloaded from Victron, and the max Isc is specified there.
