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.
Thanks @MichelleKonzack I was assuming, rather wrongly, that 0.06 is not brilliant but OK. After your comment, I dug into this a little more:
Victron panels have 0.040 temp coef. They are not an option for me because they are not available locally. Even my reliable authorized Victron agent stocks another brand.
Jinko, which I have used in the past, has 0.046. I could use these but they are very expensive locally. I can’t find a reliable Chinese supplier.
Yangtze, which I have used in the past, has 0.046. The single problem I have with this is that they have a rather large footprint - about 2500x2000mm compared to 2500x1000mm I plan to use.
I plan to use Shinefar Solar from China. As you noted, these have a rather high 0.060. They come highly recommended as a “tier 1” brand (whatever that’s worth) and the price is pocket friendly. I figured that in my particular context where temp doesn’t change much (normally 17-25 degrees Celsius but can dip to 15) the temp coef value is not important. But I can still change.
Do you you know a reliable supplier of PV in China specifically?
You have hit the nail on the head @MichelleKonzack . I plan to use two 250/100s in the configurations you propose, despite the calculator recommendations.
One 250/100 will have four parallel strings of 3 panels in series each. This will keep the strings within the VOC and ISC limits. However, the over-paneling will be 137%. Not efficient but not harmful. Agreeable all round, I believe.
A second 250/100 will have 3x3 PV. This will also stay within VOC and ISC limits. Over-paneling will only be 103%. Perfect.
Special thanks to a one Chasen who posted the original question and a one Filterguy who asked some crucial questions. I do not intend to summarize the thread but only to note 2 points:
Opinion is divided on the value of the short circuit parameter. One group says it’s should simply be ignored, another group says it’s vital, and yet another group says it’s only relevant in a case of reverse polarity. Others lie somewhere on that spectrum. Victron documents (I don’t know if they have since changed) are not definitive on this point, or even misleading or contradictory. It’s possibly a fool’s errand to expect an authoritative answer. Personally, I have decided to respect the short circuit rating as much as possible.
In that thread, @guystewart suggests that exceeding the short circuit limit is not covered by warranty and offers to have the online calculator looked at again to make sure it’s consistent with other Victron documents. Seven years down the road, nothing has changed. As of yesterday 24 Jan 2026, the online calculator still recommends MPPTs which exceed the short circuit limit. In my view, a Victron tool should never recommend a situation that’s not backed by warranty without an explicit warning. If a change tracking system exists within Victron, it needs to be reviewed.
The MPPT RS as long as you do not reverse polarity the input (with consideration for the MC4 limits) you can go abive the ISC
On the older ones like the smart solar and blue solar you do not wver exceed (or come close to if poss) as they work differently in their protections (error 38/39 shorting the inout to stop charging) if you exceed the isc it will fail.
As with any other product you need to know the model and capabilities. So referring to data sheets and tech specs is important.
All MPPTs list the max ISC on the input it should be treated the same as the max VOC and treated as a hard limit in all operating circumstances.
What is important when using the calculator is making sure input detais are correct, forgetting the - in from of anco efficient can totally change the outcome.
For this set up 2x 14.2A is 28.4A is well below the ISC of the mppt recommended.
@lxonline thank you for further inputs. I certainly wasn’t aware of the nuances of the different models. I will now take that into consideration going forward.
Yes, 14.24a doesn’t violate the short circuit current limit. But that’s only 1 string. I have 5 strings. That’s 71.20a which clearly violates the ISC limit, but the calculator is happy to recommend a 150/85. No one can yet point out a flaw in my calculations. You are welcome to play around with my specs on the calculator posted above.
What I have found is that the online calculator, without saying so, just ignores (or uses it in a mysterious way) the ISC limit. This is not an isolated case, as noted before. This appears to be a serious flaw of the online calculator.
