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Wayne avatar image

6x250w panels

Hi

I live in Australia

I have 6 x250w panels VOC 37.2

I have 2x 75/15 charge controllers

I want 2 panels to capture the sunrise (East)

I want 2 panels to capture the miday sun (North)

I want 2 panels to capture sunset (West)

what is the best way to wire this configuration to the charge controllers.


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2 Answers
JohnC avatar image
JohnC answered ·

Hi Wayne. Sorry, but this is all bad news, Those mppts are unsuited for your panels, well that many panels.

Put 2x in series, and the Voc totalled becomes awfully close to the 75V limit. In cold weather and sun, may well exceed it and can damage the mppt.

Put 2x in parallel, and the Isc of each panel gets doubled, and will likely exceed the 15A max pv Isc of the mppt, again with failure warnings.

So, by the 'rulez' it's one panel per 75/ mppt...

Ideally you'd have 3x of 100/ mppts for the different panel orientations, the A rating dependent on the V of the batts you're charging.

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Thanks John

I new they were to small the shop told me they would be suitable.

I have 6 2v Batteries @ 200ah each wired to become 12v

What is the best mppt to charge these batteries?


My understaning is that it’s not OK to put more voltage into the MPPTs as that is a hard limit, but it’s totalyl ok to put more amps in (in terms of panel capacity), the controller will only ever pull it’s max amp rating from the PV array and thus any extra will just be “wasted potential”...

which is why many people double up their array size (staying within voltage limits) so as to take advantage of the greater capacity in less than optimal conditions (where the extra will never exceed the controllers limits anywy)....


So, if two panels in series would be dangerously close to the voltage limit, yes that should be avoided. BUT if two panels in parallel would be close to, or just over, or even a lot over, the current rating for the MPPT, that’s fine. In Australian conditions, most of the time a doublling up of panel current would be a total waste, but a little over will not cause any issues.



source: https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-charge-controller-MPPT-75-10,-75-15,-100-15,-100-20,-100-20_48V-EN.pdf


My only uncertainty comes from the note about the short circuit current of the array. (highlighted in yellow) Perhaps someoene from Victron staff can clarify?

You may oversize the array, the controller will limit the battery charge current to either its maximum or the maximum user defined limit.

Do not configure the PV array such that, in the even of a fault, the array can deliver more current than that specified by the "Max. PV shirt circuit current" limit.

WKirby avatar image
WKirby answered ·

Hi Wayne

So you have 3x 500W arrays and a 12V battery bank.
Nominally, each 500W array will need an MPPT which can charge at ~42A (500W / 12V = 41.66A).
So, you need a 3x 100/50 MPPTs, one for each array to get the most from the panels.

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