Victron MPPT over panelling

I've spent quite a bit of time going through hundred of solar panel datasheets to find a good panel match for this SCC that would enable me to fully utilize this small SCC beast.

Two panels are a darn near perfect match for this SCC, depending on what you have to work with space-wise, temperatures, etc.

So without further ado, here's what I've found to be a good match for this SCC.

A more elegant combo is 100/20 with 3x Sunpower Maxeon3 400w panels in parallel for a total of 1200W
Voc 75.6V & Isc 6.58A per panel.

A more flexible combo, 100/20 with 12x Ecoflow Rigid 100W solar panels in 4S3P configuration
Voc 20,3V & Isc 6.3A per panel.

Ecoflow 100W rigid panel
- almost universally available across the globe
- reasonable price, ability to order online with free shipping mostly
- well protected in the box
- each set of two has a sticker on the box with two SN for each panel so you can activate warranty on their official website.
- since it's a part of the whole line of products it's intended for, there's a certain guarantee you'll be able to add more of the same panels going forward with no concerns will it be available in a few years as with some or most of the other panels. So you don't have to buy 12x panels from the get-go, you can do so in steps.

Anyhow, hope it helps shed light on what panel might be worth considering if you're looking to get the most out of Victron 100/20.

sunshine_eggo said:

The PV input current limit is the maximum Isc the array can have and still retain reverse polarity protection. If you don't hook your array up backwards, then there's no hard limit - except on the aforementioned RS 450/200 (they explicitly state it's a hard limit).

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Is there any truth to what previous posts in this thread have said about the MPPT sweep and that it includes a short circuiting of the array? It seems strange to me if it was, because what useful data can the controller get from that? If I'm correct, then there is no real limit to array short circuit current either, as long as you put a fuse in series with the array.

As far as I understand, if the controller senses something dangerously wrong with the array it can go into protective mode and short circuit the array to protect itself and other connected devices. That's where I think the max Isc value comes from. Is that correct?

BjornM said:

That's where I think the max Isc value comes from. Is that correct?

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I think that's correct. Max Isc rating is relevant to how many amps controller will tolerate when PV is connected in reverse polarity. When that happens there is internal diode that short circuits the panels to protect remaining circuitry.

AntronX said:

I think that's correct. Max Isc rating is relevant to how many amps controller will tolerate when PV is connected in reverse polarity. When that happens there is internal diode that shorts circuits the panels to protect remaining circuitry.

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So as long as you don't crimp black to red you can overpanel by quite a bit?

Yes I think so. I run my Victron smart solar 75/15 from 44V 630Ah battery bank connected to PV input via 5A fuse. It never failed.

BjornM said:

Is there any truth to what previous posts in this thread have said about the MPPT sweep and that it includes a short circuiting of the array? It seems strange to me if it was, because what useful data can the controller get from that? If I'm correct, then there is no real limit to array short circuit current either, as long as you put a fuse in series with the array.

As far as I understand, if the controller senses something dangerously wrong with the array it can go into protective mode and short circuit the array to protect itself and other connected devices. That's where I think the max Isc value comes from. Is that correct?

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I need some education here.

I thought "shirt-circuiting the array" means it will momentarily connect the battery directly to the array to see if array voltage will pull down to battery voltage.

Now I feel like an idiot.

So the controller has some circuitry at the PV input that allows direct shorting of the solar pos/neg?

BjornM said:

Is there any truth to what previous posts in this thread have said about the MPPT sweep and that it includes a short circuiting of the array? It seems strange to me if it was, because what useful data can the controller get from that? If I'm correct, then there is no real limit to array short circuit current either, as long as you put a fuse in series with the array.

As far as I understand, if the controller senses something dangerously wrong with the array it can go into protective mode and short circuit the array to protect itself and other connected devices. That's where I think the max Isc value comes from. Is that correct?

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Shorting is not a normal function UNLESS reverse polarity is detected. Hence the limit.

Still can't believe they don't have voltage sense leads...

AntronX said:

I think that's correct. Max Isc rating is relevant to how many amps controller will tolerate when PV is connected in reverse polarity. When that happens there is internal diode that short circuits the panels to protect remaining circuitry.

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Here is what it says in the SmartSolar 250/100 manual (might be different from the model this thread is about).

8.10.5. PV Short relay reset procedure
This procedure outlines the reset process for the internal protection mechanism, known as the PV Short Relay, in the Smart SolarCharger 250/100.The protection consists of a latching relay, which is mounted across the PV Input. When the firmware detects a short between the PV inputs and the battery outputs, by monitoring the battery voltage for an over-voltage, it engages the relay and, as such, shorts the PV Input.

8.11.15. Error 80 to 88 - PV Input shutdown
When these errors show, the PV Input is internally shorted in order to protect the battery from over-charging.

And in the specs for max 70 A short circuit current, it also says "A higher short circuit current may damage the solar charger in case of reverse polarity connection of the PV array", just like you mentioned.

So I assume the Isc current limitation is for both the reverse polarity protection and the short relay.

BjornM said:

So I assume the Isc current limitation is for both the reverse polarity protection and the short relay.

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OK makes sense. I did not know about battery overcharge protection shorting relay. That's smart.

Checkthisout said:

I thought "shirt-circuiting the array" means it will momentarily connect the battery directly to the array to see if array voltage will pull down to battery voltage.

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It is the opposite of that. It connects the two input leads from the solar array together (short circuits them), so that no current can flow from the array to the battery.

sunshine_eggo said:

Still can't believe they don't have voltage sense leads...

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I have accepted it now, when I get such a fine current cutoff function that I didn't have before!

BjornM said:

It is the opposite of that. It connects the two input leads from the solar array together (short circuits them), so that no current can flow from the array to the battery.

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I assumed that if it was part of the MPPT sweep that it was checking to see if direct connection was most efficient under the given light level.?

Maybe overpaneling in terms of watts is fine, SCC regulates temperature. Quite gradual effect.
Maybe overpaneling in terms of Isc amps is a problem. Regulation of current is milliseconds of FET switch on time.

An SCC could reasonably accept PV input up to the output current it can deliver to battery.
Wattage could be higher according to higher voltage, or limited by heating of transistors and inductor.

"Should" not the legalese "Shall" regarding Isc limit.

As mentioned, reverse-polarity protection diode has a current limit. That would only apply if you connected array backwards. If you connect one string, make sure it works, then add the rest, you would be protected there.

Some SCC are a buck converter, where shorted FET would apply PV panels directly to battery (like PWM.) That would boil a lead-acid battery to death, over-voltage a BMS and do worse to lithium. Some SCC are HF transformer isolated, so if not switching, no voltage applied.

FET (or relay) to short out array would be one way to protect battery with non-isolated SCC. Remote tripping a breaker would be another.

In normal operation, buck converter connects higher voltage source (PV) through inductor to lower voltage (battery). A boost converter would momentarily short array PV+ through inductor to PV-, then release so voltage flies higher.

Assuming buck, if PWM goes wide enough, could reach Isc of array flowing. Over-paneled in terms of ISC, could kill FETs. We would rather the controller stopped before then, but if not, Isc limit would protect. It does sweep from Voc down to lower voltage, to find peak power point. That could be where it is at risk.

Hedges said:

Assuming buck, if PWM goes wide enough, could reach Isc of array flowing. Over-paneled in terms of ISC, could kill FETs. We would rather the controller stopped before then, but if not, Isc limit would protect. It does sweep from Voc down to lower voltage, to find peak power point. That could be where it is at risk.

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For a regular buck converter, the input sweep can't get to a voltage below the controller's output voltage though, i.e. the battery voltage. So it can never technically short circuit the array in this mode. But for a 200 V array taken down to say 15 V to match a 12 V battery the array current would probably be pretty close to the short circuit current anyway.

sunshine_eggo said:

Shorting is not a normal function UNLESS reverse polarity is detected. Hence the limit.

Still can't believe they don't have voltage sense leads...

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I guess this is what I was referring to. But it was explained to me as part of every sweep. Supposedly as a test of the max current available.
I don't remember who told me this. (A member here)
But I must have found them to be knowledgeable. As I added the information to my memory banks. lol

timselectric said:

I guess this is what I was referring to. But it was explained to me as part of every sweep. Supposedly as a test of the max current available.
I don't remember who told me this. (A member here)
But I must have found them to be knowledgeable. As I added the information to my memory banks. lol

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I have never personally observed 0V while directly monitoring the MPPT on it's trends tab that updates about every two seconds. It could certainly happen inside that 2 second gap, but I can't see that an MPPT sweep could ever be productive below battery voltage, so I could see a short or near short to battery but not across the PV terminals. Victron rules also indicate that MPPT operation can only continue if PV voltage is +1-2V above battery.

sunshine_eggo said:

I have never personally observed 0V while directly monitoring the MPPT on it's trends tab that updates about every two seconds. It could certainly happen inside that 2 second gap, but I can't see that an MPPT sweep could ever be productive below battery voltage, so I could see a short or near short to battery but not across the PV terminals. Victron rules also indicate that MPPT operation can only continue if PV voltage is +1-2V above battery.

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That definitely makes more sense.
Thanks

timselectric said:

Connecting more PV than a SCC can use.

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So if a victron unit can handle more than twice the PV than it can output, it isn’t really limited? And in fact is over panel friendly.

Again assuming you stick to the published specs of VOC and ISC.

Subscribed for later.

In case it is useful, the bogart SC 2030 self limits to 30 amps, so you can over panel if you want to.

For better or worse, it is a pwm type, so it will turn on earlier in with a lower panel voltage, but is not as good when the panel voltage is high.

It is limited to 12 / 24 volt systems. Might be able to run 36 volt.