Too much potential?

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Skip Gundlach
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Joined: Thu Aug 06, 2020 11:01 am
My RE system: 2x360W Sunpower

Too much potential?

Post by Skip Gundlach » Thu Aug 06, 2020 12:03 pm

Our Sunpower 360s are ~70V/6.5A max, each. Our setup is paralleled, with blocking diodes on the + legs.

In an absolutely perfect world, our 720w could produce 60A.

Yet, in the time we've had them, the very most, and at that only once, briefly, we've ever seen has been 50A. Otherwise, and that not very often, it's in the low to mid 40s.
What does a controller do if it gets more amps than its output is rated for? Ignore them (put out the max rated)? Burst into flames (or equivalent)? Something else?

It would be an economic advantage to have a 50A controller...




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My RE system: Flexpower Two: (2) FXR3048A, (2) FM80, MATE3s, FlexNetDC
SimpliPhi 48-3.8 (6 @ 48v)
Outback IBR3 battery enclosure
Suniva 330 watt panels (12 - 6 strings of 2 in series)
Hyundai 355 watt panels (6 - 3 strings of 2 in series)
Honda EU7000is gas fuel generator

Re: Too much potential?

Post by raysun » Thu Aug 06, 2020 12:56 pm

What happens when a controller is overload depends on the controller design, and the nature of the overload. The controllers don't ignore a current overload, they have to deal with them. "Dumping" extra current in the form of heat is common. Too much can damage most controllers. Another scenario would be the controller losing control and dumping the current directly to the battery. This can be hard on batteries.

There are controllers purpose-designed to handle rated overloads, perhaps others who use them can comment on them.

Most controllers are rated for the PV Array's STC power to provide a safe(ish) overhead for overload situations. Best be safe with the ratings, than sorry when an OMG moment comes along.

FWIW, I'm assisting a gent in Haiti who has had two 5kW arrays on two 4kW rated controllers for years. Recently, a battery cell shorted, the overload in PV harvest was no longer being restrained by the battery chemistry, and both controllers burned up.

Everything works great, until it doesn't.

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My RE system: 8330 watts in three strings, Flexmax 60 x 3, Radian 8048A, GSLC load center, Mate 3S, Hub 10.3, FN-DC and 900 Amp, 48V Trojan T105-RE battery bank.

Re: Too much potential?

Post by pss » Thu Aug 06, 2020 4:21 pm


Your post says you have 2 Sunpower 360 watt solar panels connected in parallel to something, what that is, you did not say.
To understand your panels, the 2 in parallel means the amperage is added and the voltage remains unchanged. If they were connected in series, the amperage would not be added, but the voltage would be doubled. either way, the power, expressed as watts, would be the same.
Where it depends on how the panels are connected together is when you have a charge controller that has limits on how much voltage AND amperage it can receive and send to batteries without exceeding the specifications of it's internal components, ie. blowing up from heat.

Now, as for your panels being 360, if you obtain the manufacturer's specification sheets, you will find that this "360" occurs under a set of laboratory conditions. If your panels are not in a laboratory, but outdoors in sunshine, you should not and would not get that rated performance. In fact, lower temperatures under 70 degrees can increase the output of a panel. Panels like sunshine and cold weather. Panels don't like clouds or hot sunny weather. The power is reduced with heat. And they like to face straight at the sun, not at angles.

Now, in an absolutely perfect world, your 2 Sunpower panels would produce 70 volts and 13 amps or 140 volts and 6.5 amps.
The specifications for your panels are not ideal for an FM80 or 60 Outback charge controller because the open circuit voltages are limited to 150 volts. If your Voc is 70, 2 panels in series is 140 volts, way too close to the danger zone. So your array for an FM60, 60 amp capable controllers would be 8 panels connected in parallel, bringing 70 volts and 52 amps to the charge controller. The 70 volts would be okay for a 48 volt battery bank, as well as 36 and 24 and 12.

Hope this helps. If you have further questions, please supply more details of your hardware components.

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