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Old 17-03-2018, 13:12   #1
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Sizing Victron MPPT Controller

Iím hoping all the solar gurus can help me out. I have 6 panels in parallel going to a Morningstar PWM 30A controller. The panels total 480 Watts.

Iím trying to max my production and I understand upgrading to MPPT should see fairly substantial gains in my charging. My existing panels are around 10 years old so I doubt they are actually capable of putting out the full 480 Watts anyway.

Long story short Iím debating between the Victron MPPT 100/30 or the 150/35. The larger is a substantial price increase ($100) but technically is correctly sized for my panels.

The 100/30 states it works with up to 440 Watts in my 12 volt system, and my existing controller is 30 amps and works properly. Reality is that the best Iíve ever seen out of the panels is 23-25 amps in the Puget Sound region in early summer.

My question is whether or not the larger one is worth the extra cost? With my older panels is it unlikely I will even see their full output anyway?

To further complicate it I am adding a separate 300 watt array with its own Victron 100/20 controller this summer, which is why I want another Victron controler.
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Old 17-03-2018, 13:40   #2
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Re: Sizing Victron MPPT Controller

Have you tried the mppt sizing calculators?

https://www.google.com.au/search?q=m...obile&ie=UTF-8
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Old 17-03-2018, 14:14   #3
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Re: Sizing Victron MPPT Controller

Since they are already wired in parallel another option is to get two smaller Victron controllers and separate it into two banks. This might give you better overall performance if you have any shading issues or the panels are not all oriented on the same plane.
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Old 17-03-2018, 14:25   #4
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Re: Sizing Victron MPPT Controller

Output voltage should be around 14V, meaning your ideal 480W gives 34A. To achieve that, you'll need all panels pointing perfectly on the Sun, not shaded at all and be cooler than 20įC. What do you gain? A little more power when you have plenty of power anyway.

However, you can indeed use 3x 75/15 controllers for a little more than a 100/30.
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Old 17-03-2018, 14:59   #5
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Re: Sizing Victron MPPT Controller

No the 30A one will be fine. Get the dongle functionality, and ideally a temp sensor wire to the bank for voltage compensation.
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Old 17-03-2018, 15:01   #6
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Re: Sizing Victron MPPT Controller

And yes, one 75/15 per panel will give greater total output when one is shaded.

These days under $100, and one dongle lets you fine tune all of them.

Only internal temp sense though, mount right at the bank.
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Old 17-03-2018, 15:05   #7
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Re: Sizing Victron MPPT Controller

Thanks for the replies.

I think there might be a bit of confusion. I am looking to replace my Morningstar PWM unit with one that will play nicer with my second new bank. I already have a Victron 100/20 unit for the new 300 watt bank whose panels are not yet mounted.

Out of curiosity I hooked up the 100/20 to my existing panels to see if it makes much difference. I figured with the weak sun this time of year I had no risk of overloading the smaller unit for testing purposes.

Note I am in Juneau Alaska with weak sun and it is lightly cloudy today (part sun). The panels havenít been cleaned other than rain in 6 months. This testing is done at 12:30pm.

The Morningstar was reading 7-9 amps (averaging 8.4A) actual output. The Victron is reading 8-12 amps (averaging 10A) in the same conditions.

Looks like the MPPT isnít just hype, they are indeed more efficient.

I understand the Victron simply limits output to its rated level if there is too much power available. It sounds like the chances of ever seeing that 34A output is low, and it wonít hurt anything if the panels put out a bit too much, am I right?
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Old 17-03-2018, 15:26   #8
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Re: Sizing Victron MPPT Controller

Right. You'll see the max input power (above which you may damage the SC) is much higher that the max output, and Victron builds in a high fudge factor there.

But not so on Volts, stay below 90% of that max rating with the total VoC.

The point about a 1:1 ratio is worth at least considering.
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Old 17-03-2018, 15:32   #9
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Re: Sizing Victron MPPT Controller

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Right. You'll see the max input power (above which you may damage the SC) is much higher that the max output, and Victron builds in a high fudge factor there.

But not so on Volts, stay below 90% of that max rating with the total VoC.

The point about a 1:1 ratio is worth at least considering.

Understood on everything, except what you mean by the last line. By 1:1 ratio are you referring to breaking up my 6 panels to more than one controller to help with shading decreases? Could you please clarify?
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Old 17-03-2018, 16:22   #10
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Re: Sizing Victron MPPT Controller

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No the 30A one will be fine. Get the dongle functionality, and ideally a temp sensor wire to the bank for voltage compensation.
The most recent versions of these controllers (SmartSolar vs. BlueSolar) have bluetooth built right in for less than the cost of the dongle as I recall.
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Old 17-03-2018, 16:40   #11
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Re: Sizing Victron MPPT Controller

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The most recent versions of these controllers (SmartSolar vs. BlueSolar) have bluetooth built right in for less than the cost of the dongle as I recall.


They do and thatís what I have. The app on the phone is a great way to monitor it.
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Old 17-03-2018, 17:47   #12
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Re: Sizing Victron MPPT Controller

Most MPPT controllers will limit their maximium current to protect themselves, although I am not a great fan of relying on this mechanism in the long term. MPPT controllers are not the most reliable electronics, even when kept within their specifications.

The Victron MPPT have some restrictions on this protection mechanism. For the 100/30 they warn that damage may occur if the PV short circuit current is over 35A. You don't mention the specific solar panels that you are using, but with "12v" panels at 480w they may be close to the limit, so it is worth checking. I would certainly be happier with the 150/35 or the 100/50. The latter will have more headroom and room for expansion. It may also be cheaper despite the higher current rating, as the provision for a higher input voltage needs expensive components.

Better still, as others have recommended, would be to use a single controller for each panel, or as you have six panels, one controller for two panels. Without knowing the details of your panels it is hard to recommend the correct controllers, but the idea is to replace one 150/35 with say three 75/15. This will provide slightly more output, as the MPPT will be more accurate, and it adds some redundancy. The main drawback is more complicated wiring. The cost is often similar to a single larger controller, but this is dependent on the specifics.

The only other thing to consider is that the Victron units have a high start up voltage. Thus they are probably not a good choice for those 12v panels with lowish Voc, especially if you are in hot conditions. It is not clear if the practical effect of this limitation is significant. Some more detailed user reports would help. Certainly I am happier recommending the Victon units for high voltage panels, or at least 12v panels that have a Voc on the high, rather than the low side. Once again, details of your panels would help.
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Old 17-03-2018, 18:17   #13
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Re: Sizing Victron MPPT Controller

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The most recent versions of these controllers (SmartSolar vs. BlueSolar) have bluetooth built right in for less than the cost of the dongle as I recall.
That's correct but AFAIK even 2 "old" controllers + 1 dongle will be more economic than 2 "new" models.
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Old 17-03-2018, 19:49   #14
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Re: Sizing Victron MPPT Controller

Any chance you will head south?

My 15 year old panels have put out more power than they were rated for down here in the Caribbean (350W out of a 320W bank).

Personally I would size you controller %10-%15 over the maximum your panels can produce.
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Old 17-03-2018, 21:11   #15
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Re: Sizing Victron MPPT Controller

Quote:
Originally Posted by noelex 77 View Post
The Victron MPPT have some restrictions on this protection mechanism. For the 100/30 they warn that damage may occur if the PV short circuit current is over 35A.
This is what the manual has to say about the 35A limit:
A higher short circuit current may damage the controller in case of reverse polarity connection of the PV array.
So it is probably not be that big of an issue if everything is wired correctly (I have never tried it myself).
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