Victron mppt sizing

[mikash]

I have spent many many thousand's of pounds upgrading the house solar. When a controller bounces of limit due to overpaneling, a way round that is to set the controller 1-2 amps lower than its rating, to keep it going. Sometimes works, sometimes overshoots the controller and resets again. If irradiation is constant, it works, if you have a cloud pass, as it disappears and sun pops up, it can overwhelm the controller.
Fit a larger controller and job done.

So it would be the rapid ramp-up that'd overwhelm the controller? Interesting.

 

[Raul]

So it would be the rapid ramp-up that'd overwhelm the controller? Interesting.

Not always, it depends on battery and loads as well.
Theoretically the controller can modulate anything from 100vdc incoming and 20A dc incoming. As example for the 100/20. But, if panel configuration exceeds amps IN limit, this is when the controller goes in protection and reset. Of course we stay away from the 100vdc incoming by a margin of 10-15% to allow for the cold temperature voltage spike.

 

[1967bowesj]

I find the Victron MPPT sizing site to give some unexpected recommendations.

Generally I approach the decision in two steps:
1. Add up the voltages (if in series) as this is critical, give yourself 5-10% leeway (you will need to know your panel voltages - most Victron up to 185w are around 20v)
2. Calculate the maximum wattage and divide that by 13 (13.2 is also usually fine)

So two 185w panels would be roughly 20x2 =40v
185x2 =370w, 370/13 =28.462A
So a 100/30 would be the correct one

Thanks RogerIvy that was calculating before I went on the blue site and got their recommendations of the 20amp one.
I’ll be getting the 30 amp to be on the safe side.
I can do without any clipping as spare amps when batteries are full get diverted to the power bank, oh goss that’s started it lol

 

[Guigsy]

My brother had a temporary setup with a 75/15 attached to a 400w domestic panel. It didn't reset. It just capped at roughly 15A output.

 

[RogerIvy]

My brother had a temporary setup with a 75/15 attached to a 400w domestic panel. It didn't reset. It just capped at roughly 15A output.

Interesting. Totally different behavior to what we experienced.

I’d still rather over size the controller so I harvest all yield possible

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[fishplug]

For the price difference between the 20 and the 30 it's not a difficult choice in my opinion.

I went with the 50 with the view to possibly add extra panels at some point and while it is a step up in price I've been really impressed by how much yield I've been getting even over the winter months.

It's most likely overkill, but I tend to over spec everything.

 

[Raul]

My brother had a temporary setup with a 75/15 attached to a 400w domestic panel. It didn't reset. It just capped at roughly 15A output.

I'm sure will work in that scenario, as the single panel amps does not exceed the controller amps IN. The controller can modulate the power as long as the amps IN are not exceeded. See my post #32.
Your post just confirmed my findings.

 

[mikash]

I'm sure will work in that scenario, as the single panel amps does not exceed the controller amps IN. The controller can modulate the power as long as the amps IN are not exceeded. See my post #32.
Your post just confirmed my findings.

Ah so the issue causing the controller dropping out is not really overpaneling, but exceeding the spec for max SC current on the panel side?

 

[Raul]

Ah so the issue causing the controller dropping out is not really overpaneling, but exceeding the spec for max SC current on the panel side?

And it will be logged in the controller history as error.
Exceeding the ISC IN, is because of poor choice of panel configuration, or overpaneling. You can overpanel as long as you don't exceed those two parameters: ISC IN, and VOC IN.
Many controllers, the smaller ones have the same ISC as the output value.
On larger controllers, 150-100, 250-100, the output may be 100A but the ISC IN is allot smaller.

 

[1967bowesj]

Little update, thanks to all for the input especially Gordo on post#9, mppt arrived safe and sound today, was only posted yesterday so that was a brucie bonus from Royal Mail lol.
Fitted and all back up and running, even fitted cable ferrol Ends so no more split wire ends.

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