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zimm avatar image

Will the MPPT 75/15 smart solar handle 2, 100 watt 12v panels in parallel?

I ran the math with the max panel voltage of 18.4v and a 25% safety margin and it looks like it should be okay. I wanted to get real world input. My RV forum is saying I should run a 30 amp controller to handle 2, 100 watt panels in parallel. One will be fixed on the roof, and I'll eventually buy a portable to hook up to it.

MPPT - Solar Charge Controller
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Hello. Nice to read all the questions and answers. I also have a question thats related. I have the victron smartsolar 100/30 and wonder if it will be ok tro try running my 3 panels in serial? They are 37.1 v and 8.3 a. At this moment i only have 2 connected in parallel and they yield very little. Is there any risk of damaging the controller with these 3 panels?


Hi Sinkstar, No it won’t is short answer. When getting full PV and each panel is producing 37vdc that is 3x 37 = 111vdc 11vdc over the rating . However I don’t know what happens if this were the case? Would it damage the MPPT? I don’t know. Would be good for pub harvesting though if is doesn’t damage it

Thanks Brad

@Brad-Australia @sinkstar - If the PV input voltage limit is exceeded the charge controller is destroyed. It is a HARD LIMIT.

There is a maximum of 2 x 37V OCV panels in series on the 100V MPPTs.

The voltage rating on an MPPT is a hard limit, running 11v over on your input side will short the controller. Do not do this.

Late to get to this site and comment.

However I run 2 x 250w in parallel for over two years into 12v lead acid batteries. Max output is limited to just under 240W daily max has been 2.2Kwh.

One panel at 250w rarely exploits the MPPT 75|15 if there's any hint of cloud. I'm in the UK and there can be a week of cloud where the daily output is less than 100w On occasion I had had as little at 10w for a whole day

The output voltage is 37.5v and can be a little higher so I rarely the two run in series.

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Leslieanne avatar image
Leslieanne answered ·

Hi there,

Just some comments from my experience. My 75/15 has handled 280W of 12V panels in parallel, OCV 22V, into a 12V LiFePO4 battery for several years with no apparent problems. When I bought the controller there was no listed max PV current in the specs. It happily limits the battery current to 15A in full sun, but derates as expected if things get too warm, as on 40 deg days. But as time has passed Victron has become more conservative in their recommendations. Firstly they added a PV current limit of 15A, but with a note that higher PV current could cause damage to controller but only pif reverse connected, then later they seem to have dropped that bit too....Regardless it still works fine! The only "problem" I have seen with the 12V panels in parallel, is as already noted, slow to start in morning and early to bed at night. It will also turn off briefly if you drive through shade or under an overpass! So recently have upgraded to 2 X 200W 24V panels in parallel..all within spec, plenty of reserve for winter, and although quite a bit of power wasted in summer is not needed anyway!

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Johannes Boonstra (Victron Energy Staff) avatar image
Johannes Boonstra (Victron Energy Staff) answered ·

Hello, The point is mainly that a 75/15 MPPT starts working as soon as the voltage from the PV panel is at least 5Vdc higher then then battery voltage. So then the charging will start only after the sun is pretty powerful if you connect a panel to this (or several in parallel) with a maximal voltage of 18,4Vdc. It is far more efficient therefore to take several (smaller) panels and connect these in serial connection. The total Pv olathe will then early in the morning reach the battery voltage + 5Vdc with only a minimal sunlight (and remain working longer in the afternoon as well of course)

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elf answered ·

Regarding the series|parallel issue. Whereas it is true that the 75|15 will start a little earlier with series due to the higher voltage. My VoC is 37v and I have 2x 250w in parralel. I have noticed for example that as the sun is setting I may have plenty of volts but the current is less than 0.1A and connecting in series would only allow a charge probably for another 30 min of even less than 0.1A

My view is that if the sunlight is so dim then although series will provide a higher voltage, with such little current it doesn't make much of a change.


Given the 500w I have and the 75|15 the best I get is around 240W at 16v @ 15A per hour on a good day. However I have had as little as 10W for a whole day on 18th Dec 18 from the 500w.

There was plenty of voltage so series would not have helped.


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swordoski answered ·

Hey Guys.


What do you think now ?! .

I have them in series now.





1.jpg (387.1 KiB)
2.jpg (239.5 KiB)
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Hi Swordoski, is there any load on the batteries that is not through the load output on the MPPT?


Looks ok otherwise

Hi @Brad-Australia


All load output is through the MPPT.

But i think to install 12v fridge (6ow) Is it enough or do i need to add more panels ?!

where are you based? fridge efficiency varies a lot depending on cooling method (fridge type), insulation level, ambient temperature, contents, cooling temperature setting.


for a rough idea, I recently got a 23L Waeco 12/24v compressor fridge which is using on average 200w - 400w depending on above factors (or more if I put it on freeze temps which I rarely do)...


so if you’re making on average 120w daily and consuming over half of that already, I’d say you‘ll need more PV...

however maybe your stats are just what you’re using, and not the limit of what your system can produce? in good conditions you should be able to generate 600w quite comfortably with that setup, based on your graphs...


again also depends on where in the world you are based..

To me, your numbers look way low for 200 watts of panels. I am running 240 watts of inefficient flexible panels. and today in mostly full sun I got 1,400 watts. Peak power was 184 watts.

  • You should be seeing peak power of over 150 watts aimed at full sun.

Now, a big variable is sunlight strength and if panels are aimed. I manually point mine at morning sun then afternoon sun. I might lay em flat midday if I notice. Makes a difference.

Also, are you 100% sure you have ZERO shading?


this controller has a maximum power rating of 145w at 12v, anything more will be ”wasted” if conditions are good enough...

Hi adev - I saw you give that number out before. I think your math may be off some. 15 amps @ 12v is 180 watts, right? Or am I missing something? Also, I have the same 75/15 controller, and as mentioned, I'm getting peak power readings as high as 184 watts, confirming to me that "this controller" will show (and presumably deliver) up to that much power at least.

So, a peak of 133 watts will not reflect any limits with a 75/15 CC.

@ swordoski : In retrospect, I should add that your low panel output may NOT indicate problems as I said before and simply be what one gets with weak sun in northern lattitudes.

OR, as adev commented: "maybe your stats are just what you’re using, and not the limit of what your system can produce?" Good point!

To test this, I'd run something (lights, whatever) that draws a good load on your batteries during the day and see if that brings up your daily power "harvest". Then you will be more assured that you can run a fridge. I think that your current setup should handle it, but yes, will need to be able to "harvest" well over 500 wh daily to do that. It should.

And if your systems doesn't deliver more charging power when needed, then a third panel would be the cheapest way to raise your charging wattage up for most of your charging day.


cheers,

Steve

My mppt 75/15 has peaked 230w from 2×125 Watts wired in series. But am only 15km south of the equator

Interesting data point - good to know. A number like 230 watts does make me wonder if the reported peak in history is what the 75/15 sees AND what it passes on as charge? Again, by my calculations, @ 12v it should be cutting off any further charge beyond 180 watts.

On the other hand, at 14 volts charging voltage, 15 amps might allow a charging power up to 210 watts, perhaps this is how it works.

Also interesting to hear what you are getting from your 120 watt glass panels. As I said, mine are flexible and known to under perform much more than glass. in comparison to nominal ratings

I've used mine in Southwestern USA summers at 7000 feet and am fairly certain that I' could not find much stronger sunlight.

elf avatar image
elf answered ·

Late to get to this site and comment.

However I run 2 x 250w in parallel for over two years into 12v lead acid batteries. Max output is limited to just under 240W daily max has been 2.2Kwh.

One panel at 250w rarely exploits the MPPT 75|15 if there's any hint of cloud. I'm in the UK and there can be a week of cloud where the daily output is less than 100w On occasion I had had as little at 10w for a whole day

The output voltage is 37.5v and can be a little higher so I rarely the two run in series.

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I missed your post before. But you also are able to see (and use) well over 200 watts with the 75/15.

Again, a good argument that three 100 watt panels are still a reasonable input for the 75/15. On paper, it's a bit over but in use, it's still quite good.

Some suggest multiplying your panel rating by .9 to match a controller. I am now thinking that if glass panels. going with rating x .8 is still fine. So 300 watts x .8 = 240 watts.

Again, it's good to emphasize that while we can quite reasonably run the Victron CC with extra wattage somewhat beyond it's published VA limit, voltage is another issue and should never EVER exceed the spec of the CC.

swordoski avatar image
swordoski answered ·

I have put them in series now but don´t you think the yield is low ?!


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The idea of the MPPT is to efficiently convert power (volts x amps) to your 12v setup, so it 2V x 1A is the same power as 1V x 2A so series or parallel should be the same power.

Caveats a) in series you will get twice the voltage so charging will start earlier and end later and cope with eclipses maybe :) b) You awill get an error and disconnect if the series voltage goes over 75V (mine is 2 x 37.5v

In parallel, just that if the voltage is a bit low you get no charge and a disconnect if the current goes over 15A (mine can reach 30A)

ripper avatar image
ripper answered ·

I had 4x 265W in parallel first on 12V, then on 24V batteries. Made sure to attach wires at night. Really got that little thing hauling at 440 W for hours on a good day. Most of the year one is not even close and a bigger regulator makes no difference. Only changed when I needed a DCDC converter and it overloaded the Load exit. Now have a 100/20 on 8x 270W 4 in parallel and 4 in series. Gives me enough electricity even on a bad day.

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Eirik answered ·

In Southeastern Norway (58-60 degr N) in summer (June/July) I produce with my 2x100w panels horizontally placed, subject to occasional shading, appr. 700-950 Wh per day on a sunny day. @Swordowski, your daily yield seems far too low, although you have peaked at 82W, unless these are overcast days. I would check the installation, but not sure what could be wrong if the above is representative. Your Bulk time is probably influenced by the size of bank (large) and the yield of panels (limited), but you need to look at the settings, etc.

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@Brad-Australia @Eirik

I always have a feeling something is strange.... I did this installation in July 18.
No load was on from this screenshoot.
The battery bank is 500ah hopefully they have survived this winter!!


But i´m thinking my next steps is to do as @Eirik suggested earlier in this post.
Or what can i do ?! Is there som more setting in the MPPT ?



@Brad-Australia @Eirik

I know i have one new 50w somewhere.

So i could do a test with 100w+100w+50w in series and see what happends......

Yes do this and see what happens, Please post a screen shot after a few days.

You will halve the PV current if you do this. The 50W panel will only let half as much though as a 100W panel. You could connect 2 X 100W and one 50W all in parallel, provided their VOCs were close. You would then, however, exceed Victron's recs for max PV current, but I did that for years with no problems....they did not list a max PV current when I bought mine!!

I´m confused

Can i have mix different watt in series or ?

Here are specs from the panels both 50w+100w


@Leslieanne @Brad-Australia

100w.jpg (72.8 KiB)

Sorry for any confusion. My reply above was not strictly correct. The halving of current only applies to the maximum current. Looking at the specs for your 100w panel, I guess the 50w would have a max working current of about 2.8A. If in series with a 100W panel, then 2.8A would be the maximum current that could pass. So in ideal conditions (which rarely happen!!!) you might only get say (3 x 18V) x 2.8A = about 150 watts from 2 x 100w and a 50w in series. In poor conditions, say when only 2.5 amps are flowing, that series combination would outperform just 2 x 100w panels in series. Hopefully that makes sense!

Cheers, Leslie

Think I have confused myself....please ignore from "In poor conditions" in my last comment!! Current will be halved in any conditions.

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Brad-Australia answered ·

Hi Swordoski,

Is there any load on those batteries?

How many ahr is the Battery bank?

Long time in Bulk!!!

Get another panel and series them see what it does, Max Pv was under 21vdc so you could go 3 panels.


You're only making 240Wh a day. Im in Perth Western Australia Latitude 31.83s, from a 250w 37vdc panel i make over 1kw a day, Panel flat on roof of vehicle.

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swordoski answered ·
i found som screenshoot from summer.

What do you think of this ?!

@Brad-Australia @Eirik




4.jpg (404.8 KiB)
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swordoski answered ·

Good input from you guys @Brad-Australia @WKirby
@Eirik i´m close to 60 degr too :)

Can i add a third panel to this setup in series 3x100w with the 75/15 ?!
I´m thinking about add one more MPPT with a new panel 200w (to catch the morning sun) and have multiple controller to my batterybank.
What do you think of that ?!

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No, provided that you have 12V batteries, 3 x 100 W panels on the MMPT 75/15 would be too much: Max theoretical output from the panels would be 300W (although admittedly, that is rarely reached), and given a batteri voltage at around 13.3V, the output current would be 22.55 A, thus 50% above maximum output fro the MPPT.

A 200W panel with a separate MPPT controller, i.e. the 75/15 would be fine.

What you could do is to buy 1x100 W panel, 1x200 W panel and 1x MPPT 100/20 (or maybe a 100/30 to be safe) controller. You hook the latter MPPT controller to the 3x100 W panels, and you use your current 75/15 on the 200W panel.



I would monitor the battery state for a period of use to see if your yielding enough Pv, are you running loads out of the Load output? What are the loads? If more Pv is required then I would add another 100w in series and try it. The history will show min and max battery voltage and Pv yield data.

200 watts of panel on a 75/15 is what I'm running also. I see maybe 10 amps in full sun high altitude, aimed well. 300 watts of panel will very rarely, if ever, break 15 amps in the best of solar situations. And if does, not a problem.

I just saw an AM solar discussion of choosing MPPT with slightly higher amp panels than controller is rated and they say that it's ok, that you will not damage anything with higher amps as the MPPT will limit current and though you could lose some efficiency at very top of your curve at noon, you still get more efficiency in the rest of the day.

https://www.youtube.com/watch?v=Di499j08IeY


I'd try it out first to see. Panels I've seen don't give rated watts even at full sun. So will probably top out at 250 for three 100 watt panels. and be lower most of the time.

Over voltage is another question and that will damage the MPPT I understand. Still, three panels at under 25 max vdc seems to slide in under 75 if you do connect in series, which is recommended for getting a longer charge period.

short circuit current limit is also something to be careful of.

three banks connected in series of two 100w panels connected in parallel would make total of around 66v at max 12.3a short circtuit (Isc(A)) which would be within the safe working limits of the controller.

It does mean that in optimal conditions the power would be limited to 145w as per the controllers specs, but that maximum power would be retained better in much less than optimal conditions (so almost constantly in all but the worst conditions... more or less.).

Brad-Australia avatar image
Brad-Australia answered ·

Hi Zimm


I agree with Johannes Boonstra (Victron Energy Staff) and WKIRBY, I'd wire them series so the Output reaches the trigger point earlier and runs longer. The max vdc of your "12v panel will be around 22-25vdc so two (44-55vdc) is well under the max for the 75/15. The wattage and subsequent amps is largely irrelevant as the MPPT will limit it to 15a output.


Please let us know how you go

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the wattage and amps is only irrelevant if the total excedes the power limit of the controller AND conditions are optimal so that those limits are met or exceeded. In all other cases, the wattage and amps are very relevant and the more the better (within the voltage and short circuit current limits)...

Eirik avatar image
Eirik answered ·

I have the same setup as the OP: 2x100 w panels and an MPPT 75/15. The MPPT is handling the panels without any problems as the current rarely exceeds 11A (I am located at 60 degr N). The panels are located under the boom on a sailing boat, and from time to time there will be shade on one (or both) of the panels, from the boom, the sails or the mast. Because of this shading, I have wired the panels in parallel, as output suffers considerably whence in a serial setup, one panel is shaded. This is based on consensus for such situations with shading of one panel. For that purpose, I have yet to try a serial setup, but would welcome input if e.g. the particularities of Victron MPPTs should be contrary to consensus.

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Not even Victron MPPT's can circumvent the laws of physics. The consensus of series wired panels still stands. If you suffer from shading then parallel would likely be the better option for you.
If you don't suffer from shading then series would probably work better since the controller would be kicked out of bed earlier and will party on later into the evening due to the higher Voltage.
It's all about maximum yield for the duration of the day considering your location, trees, booms, masts or whatever else may cast shadows upon your array.
You can try a series connection for free and see if you get a better daily yield or not.

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swordoski answered ·

ok.Thanks

So parallell is not an opition ?! @JohnC

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It's an option, just not the best one. In the washup, you may be satisfied either way, and I hope you are. Advice is free here, and mine's at the lower end of that. If you've special needs, like even "I can't be bothered to rewire it", ok by me too.

Your choice, I just hope to get the technicalities across so you can make it..


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swordoski answered ·

The Voc on my panels is 22.2

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So string them in series for best results. Even 3x of em for a 75/, matched of course. If they can't handle that, they were landfill when they left the factory. You'll save on wire too.

Regardless, do the math. A 75/15 with 3 X100w set up will shut down at 180 w. It can only output 15a. 12v X 15a is 180w. I have 3 X 100w setup now as a test and it’s a waste of an extra panel.

With respect, try testing closer to dawn, dusk and under serious cloud too. It depends on your application, but if daily-cycling and in winter with short days and low angled sun, extra panels are a godsend. The sooner in the day my panels 'clip', the better my day.. :)

I have been using 2 x 250w (500) for some years now, charging Rolls batteries at 15v (recommended voltage). That's 225w.

There is no such thing as waste, just unused resource and in the UK, here, there is lots of cloud so the extra panel produces on those many days for those unpredictable and many hours.

JohnC avatar image
JohnC answered ·

Hi (all). For a 75/ mppt, look at the Voc of your panels. Best to string them as high as you can, but within the limit of 75V. Leave a margin to allow for the panel's Voc increase in low temps. Critical, exceed that V and your cc is toast.

Vmp is where your pv spends much of it's day, and the greater the differential between the series'd Vmp and Vbat, the more productive your day. It does make a difference in poor light, dawn, dusk..

Adding a panel must either be 'an addition to a string' (within the rules), or an additional identical string.

There can be quirky situations that might arise, but usually by then a /15 cc is underspecced.


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swordoski answered ·

Yeah ?!
Would be great to know which way to go here ?!
As i thinking about add one more MPPT and more panels to my setup.

@Johannes Boonstra (Victron Energy Staff)

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swordoski answered ·

OMG!


This is my setup.!

I have 2x100w and i have the Smartsolar 75/15 to a batterybank of 500ah.

And this is "not advise as the charging should be minimal" ?!

What is the suggested then as i think of add more pv and antoher MPPT in parallell ?!

@Johannes Boonstra (Victron Energy Staff)


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That is how I am setup aswell. X2 100w panels in parallel to a 75/15 smart controller. I still cannot understand how putting them in series will make them charge earlier than two panels in parallel. Since the battery starts charging when the panel voltage is 5 V higher than the battery voltage. So as I understand it if my battery voltage is at 12.5 V it’ll start charging at around 17 V from the panels

Just for clarification - is it advisable for me to change my setup from having x2 100w panels connected in parallel to series setup. Thanks in advance

Johannes Boonstra (Victron Energy Staff) avatar image
Johannes Boonstra (Victron Energy Staff) answered ·

So yes, you can theoretically connect 2 x 100Watt but this is not to be advised as the charging will be minimal.


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