I think I understand how Victron MPPTs work but I find some terminology confusing or at least ambiguous.
Taking the SmartSolar 150/100 as an example, my understanding was that that charger operates on a 48v battery bank. The incoming PV voltage can’t be more than 150 PV string voltage (both the Victron online manual and datasheet call this “Max. PV open circuit voltage” hence the name. All this makes sense).
My confusion starts on the following point: the PV short circuit current (known as ISC by PV panel makers) can’t be more than 100a, hence the 100 in the name. But confusingly or ambiguously, the Victron online manual calls this “Max. battery current” (I don’t know if the hard copy is different) but the online datasheet calls this, more accurately, “Rated charge current.” I assume this is a “Max. battery charge current” as my batteries can discharge much more than 100a but I’m not sure that my understanding is correct. See the online manual here: 9. Technical specifications and the datasheet here: https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-charge-controller-MPPT-150-70-up-to-150-100-VE.Can-EN.pdf
My questions:
Wouldn’t it be more accurate to call the 100 as “Battery charge current” or better still, “Rated charge current” as the datasheet does?
Is the 100a used by the MPPT a short circuit current figure, as used by the PV panel makers (ISC), a battery charge current limit, which can be different from a short circuit current figure or both? I ask this because the 150/100 MPPT is rated for 70a short circuit current (I assume this is the rated MPPT’s short circuit current, not the PV’s, in which case, the terminology “Max. PV short circuit current” that the online manual uses is ambiguous. It’s my understanding that the PV panel string can produce a short circuit current of 100a but the MPPT will only safely absorb 70a). Does this mean that the MPPT will charge the batteries with up to 100a but if the PV shorts, the MPPT will not be protected if the incoming PV current is more than 70a?
Related to the above, apart from protection from reverse current, are there other risks of exceeding the MPPT’s (not the PV’s) rated short circuit current?
If my interpretation of points 2 and 3 is correct, can we conclude that you exceed the MPPT’s short circuit current (70a in this case) even if you keep within the MPPT’s charge current limit (100a in this case) at your own risk?
If the above reading is correct, and an MPPT’s short circuit current rating is important, why does the online MPPT size calculator recommend a 150/85 (rated at 70a short circuit current) for a 71.20a string?
Feel free to refer me to relevant resources as I’m keen to learn (yes, I signed up to Victron Professional).
The format is “Max Input Voltage / Max Output Current”. So a 150/100 can accept up to 150v from the PV, and will output up to 100A to the battery. As you’ve noted, an xx/100 MPPT cannot be connected to a 100A PV array, as it’s not rated for that.
Neither the published input voltage nor input current limits should ever be exceeded.
Output current will of course be higher than input current because the controller works by taking high voltage at low current from the input, and flipping it to high current at low voltage to the output.
The way @Justin has explained it makes a lot of sense. But I’m still puzzled by 3 things:
Where do I find the published input current limit? The RS 450/100 and RS 450/200 seems to have it (“Max. PV operational input current”?) but the online datasheets/manuals for the smaller MPPTs e.g. 150/100 don’t seem to have an equivalent. Do I simply calculate it? How?
On the limits, I have seen at least 3 different versions. Which (or which combination) of the versions below applies in addition to the PV voltage (VOC) limit?
a) PV panel short-circuit current as published on the panel label.
b) MPPT short-circuit current as published in the MPPT datasheet.
c) MPPT’s battery charge current as published in the MPPT’s datasheet.
If the MPPT’s short circuit limit is important, why does the online calculator recommend a 150/85 MPPT with a short-circuit rating of 70 amps when my PV string has a short-circuit current of 71.2 amps?
Sorry for being such a pest. I’m trying to clear my head.
Please post the array specifications that you put into the calculator? An array with a short circuit current of 71.2A would be… very unusual in the typical use-cases that I see relatively small solar controllers like the 150/85 used in.
MPPT input current limits can be found published in the datasheets (as well as the manuals as far as I’ve seen), like:
The first number is the max voltage it can handle from the panels (hard limit). The second number is the maximum amps it can push towards the battery (regardless of battery V) and also a hard limit.
I think these numbers are the most useful to put in a product name. Making the product name longer by saying 150/70/100 or so would make it confusing to me. In my experience if you start designing from the string voltage, it’s hard to exceed the Isc unless you do some crazy over panelling and paralleling.
Thanks @Justin and @Skipper for the quick responses. Both help my understanding of this point. And thanks to @M_Lange for showing interest in helping.
@Justin you are spot on: all the manuals and datasheets I have seen have that parameter. In my mind, that was the wrong parameter to look at. I think I was confused by the RS 450/100 and RS 450/200 datasheet which has both a “max. PV operational current” (16 A per tracker for both units) and a “max PV short circuit current” (20 A per tracker for both units) and the recommendations of the online calculator. Was I looking at the wrong figure all along?
@Justin and @M_Lange , here is a screenshot of my calculator inputs. I suspect I’m doing something wrong, but I don’t what. Enabling or Disabling “allow oversizing above 130%” has no impact, as I would expect in this context. For information, I derive 71.2 A from the panel label of 14.24 A, arranged as 2 series panels in 5 parallel strings. BTW, this is not an isolated case as I get similar unexpected results with other models. This is an apparent problem for me, as I lean heavily on the online calculator.
@Fideri
It is a fairly simple volts × amps conversion.
100A at 48v is 4800 watts.
If the panel voltage is at 150v then on the pv side it is pulling 32A (150V x 32A = 4800W = 100A x 48V) minus losses.
The short circut rating is important as the mppts short their inputs (mppt error 38/39 in some protection scenarios) the isc is always on panels and 2 strings is 2x isc. Easy to manually calculate. Note ISC is not the same as operating amps.
