Can I over panel by 300%?

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ddxv asked Jun 14, '24

Can I over panel by 300%?

I'm looking at the 450/100 for a single line from far away panels (120m). On the other end I have 3 strings combined.

The combined total coming in would be (and I want to add more for winter):

277 V / 400 VOC
40+ amps

As this is coming in on 1 wire to the MPPT, it would only be using a single tracker. Checking the 450/100 spec sheet I see it shows

"Max PV operational input current: 18a"

I see two main opinions about this:

1. Excess power is 'lost' with no harm to MPPT. Similar to plugging in a small light in a socket, it only pulls what it needs.

2. The danger is the MOSFET switching on and off quickly during some weather change which could cause damaged components if it pulls too much amperage.

Are these both correct? How likely is it to happen?

MPPT Controllers amps

1718325070013.png (39.1 KiB)

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John Mitchell commented · Jun 15 at 03:26 PM

No. Plus it's more complicated. The max is 7200W per MPPT. This is calculated from 450VOC = 360V when driving the MPPT x 20A. Exceeding that will void your warranty. At 7200W you're already overprovisioning by 1.4kW. So if you were to do that on both MPPTs that would be 8.6kW or roughly 130%.

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ddxv John Mitchell commented · Jun 17 at 01:52 PM

From the other thread here, it seems like each tracker can go up to 30amps:

In the manual it says:
"MPPT PV inputs are protected against reverse polarity, to a maximum short circuit current of 20 A for each tracker.

Connecting PV arrays with a higher short circuit current is possible, up to an absolute maximum of 30A, as long as connected
with correct polarity. This outside of specification potential allows for system designers to connect larger arrays, and can be useful
to understand in case a certain panel configuration results in a short circuit current just slightly above the maximum of the reverse
polarity protection circuit."

That sounds like it is saying an absolute maximum of 30A per tracker.

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Answer 1 · 2024-06-14T04:25:28Z

Alexandra answered · Jun 14 at 04:25 AM

@ddxv

The absolute max amps in is 30A with temp compensation. It can't take more.

There is not much voltage drop over 120m. I have some running arrays about that far each on an individual tracker. No appreciable power loss.

Keep within spec or warranty is void. Use the other strings for tracking. Fuse each string as well.

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ddxv commented · Jun 15 at 01:07 PM

Where did you get 30A? I see each trackers max amps is 20 in the screenshot? Do you mean it's safe to send 30A per tracker or 30 total?

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nickdb ♦♦ ddxv commented · Jun 15 at 05:43 PM

The panel limitation beyond Voltage, is 20A Isc. It is unlikely you could oversubscribe by such a ridiculous amount without exceeding that. Specs are clear, the calculator is accurate. Use that and avoid trying to bend physics.

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Alexandra ♦ nickdb ♦♦ commented · Jun 15 at 05:51 PM

@ddxv

In the install manual.

The catch is if you reverse polarity the string there is no protection and you wont get a warranty replacement.

It is not really worth going over 30% more in practice anyway.

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ddxv Alexandra ♦ commented · Jun 16 at 04:48 AM

Thank you Alexandra. I found the 30 amps in the manual as you suggested:

"MPPT PV inputs are protected against reverse polarity, to a maximum short circuit current of 20 A for each tracker.

Connecting PV arrays with a higher short circuit current is possible, up to an absolute maximum of 30A, as long as connected
with correct polarity. This outside of specification potential allows for system designers to connect larger arrays, and can be useful
to understand in case a certain panel configuration results in a short circuit current just slightly above the maximum of the reverse
polarity protection circuit."

That sounds like it is saying an absolute maximum of 30A per tracker.

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