Max input voltage/amperage for MPPT charge controller

[WYtreasure]

Sometimes I get stuff wrong, I don't think this is one of those times.

I would like to clarify a conclusion for this topic, because for some reason, gray areas keep being inserted into the answer.

1. Panel voltage must never exceed charge controller input voltage.

Agreed.

2. The amp rating of a charge controller decides the upper limit of how fast batteries can be charged.

No comment.

3. Panel amperage is irrelevant.

Incorrect.

A charge controller will only use the amps available to perform it's function.

Correct.

Excessive amps provided by panels to a charge controller are simply ignored,

Excess is ignored but only up to the magic number. Exceed the magic number and you create magic smoke.

Overview of Over-paneling an MPPT controller

To get to the paper, click on the orange button at the top of the screen. There is a misconception that putting more panels on an MPPT controller than the controller is able to use will damage the controller. However, in almost all cases it is...

diysolarforum.com

There is a link to this Resource in my signature. I've read the paper and understand it to say "there are some controllers which will not accept unlimited amps".
I have spoken to a manufacturer who stated "do not exceed 1.5 times the limit". I have email from another manufacturer who states "do not exceed 1.3 times the limit". They are 2 different products from 2 different manufacturers.

Will I connect twice the recommended panels to either controller I have referenced? Sure, but half will point East & half will point West.

I am a fan of overpaneling. I also believe there are limits which manufacturers are aware of. Ask a manufacturer.

 

[RobertGreen]

I am a fan of overpaneling. I also believe there are limits which manufacturers are aware of. Ask a manufacturer.

I am also a fan of overpaneling, because as cheap as solar panels have become it presents a nice opportunity to give your system a little boost without having to change any of the other equipment. It seems that whether or not -and to what degree- overpaneling is acceptable depends on the particular circuit design and construction used by each manufacturer.

@bud,
The problem remains; if the charge controller shorts the input from the array with the polarity correct during certain situations, it would smoke the controller with a large enough array attached. I don't know why they are built this way. Some people report massive overpaneling on these units without any issues, but after all the discussion about the topic I will take a more conservative approach and keep it within specs for my own system.

 

[WYtreasure]

I am also a fan of overpaneling, because as cheap as solar panels have become it presents a nice opportunity to give your system a little boost without having to change any of the other equipment. It seems that whether or not -and to what degree- overpaneling is acceptable depends on the particular circuit design and construction used by each manufacturer.

@bud,
The problem remains; if the charge controller shorts the input from the array with the polarity correct during certain situations, it would smoke the controller with a large enough array attached. I don't know why they are built this way. Some people report massive overpaneling on these units without any issues, but after all the discussion about the topic I will take a more conservative approach and keep it within specs for my own system.

Yep.

I think you meant to do this: @Bud Martin

 

[Bud Martin]

I am also a fan of overpaneling, because as cheap as solar panels have become it presents a nice opportunity to give your system a little boost without having to change any of the other equipment. It seems that whether or not -and to what degree- overpaneling is acceptable depends on the particular circuit design and construction used by each manufacturer.

@bud,
The problem remains; if the charge controller shorts the input from the array with the polarity correct during certain situations, it would smoke the controller with a large enough array attached. I don't know why they are built this way. Some people report massive overpaneling on these units without any issues, but after all the discussion about the topic I will take a more conservative approach and keep it within specs for my own system.

If the SCC has shorted out input, that means something went wrong with SCC circuit, so why would input of the SCC short out.
I.E. your AC outlet which is the power source (PV panel is also a power source), if the device plug into the outlet shorts out, that is not due to the fault of the outlet but the fault of the device connected to the outlet. The outlet can supply 120VAC up to 15A so if you connected 100W lamp into the socket, the outlet is not going to push 15A into the lamp, the lamp will be pulling 100W from the oullet and no magic smoke or wasted of unuse 1700W of power from the outlet.

 

[Bud Martin]

Yep.

I think you meant to do this: @Bud Martin

?????? do what???/

 

[RobertGreen]

?????? do what???/

He was correcting my incorrect @.

If the SCC has shorted out input, that means something went wrong with SCC circuit, so why would input of the SCC short out.

What I'm telling you is that according to Victron, their units can and will sometimes short the input from the array while being correctly connected. Interpreting the text about "reverse polarity" in those manuals as being exclusive and absolute is missing the wider picture here.

This can be triggered by an assortment of different conditions, not all of which have been laid out in detail by the manufacturer.

Have a look at https://www.victronenergy.com/live/mppt-error-codes if you like....

Here's a quote from the relevant section:
-----------------------------------------------------------------------------------
"Err 38, Err 39 - PV Input shutdown
To protect the battery from over-charging the panel input is shorted.
Possible reasons for this error to occur:

• The Battery voltage (12/24/48V) is set, or auto-detected, incorrectly. Use VictronConnect to disable auto-detect and set the Battery Voltage to a fixed voltage.
• There is another device connected to the battery, which is configured to a higher voltage. For example a MultiPlus, configured to equalise at 17 Volts, while in the MPPT this is not configured.
• The battery is disconnected using a manual switch. Ideally the charger should be switched off before disconnecting the battery, this avoids a voltage overshoot on the charger output. If necessary the voltage trip-level for the PV Short protection can be increased by raising the Equalization voltage set-point (note: equalization does not have to be enabled in this case).
• The battery is disconnected using a Lithium charge relay connected to the “allow-to-charge” output of a BMS. Consider wiring this signal to the Remote terminal of the charger instead. This shuts down the charger gracefully without creating a voltage overshoot."

------------------------------------------------------------------------------------

edit: When you read between the lines of this error note, it makes it sound as though a BMS triggering it's protection and disconnecting the battery or the main fuse blowing and doing the same could possibly trigger this condition. To fail safely and gracefully when that happens, the charge controller probably shouldn't be overpaneled beyond its specifications

 

[Bud Martin]

So they use crowbar protection on the input so the current will be the Isc of the panels, I wonder what kind of device they are using, may be using high DC voltage relay as disconnect is too expensive for the BOM.

 

[RobertGreen]

So they use crowbar protection on the input so the current will be the Isc of the panels, I wonder what kind of device they are using, may be using high DC voltage relay as disconnect is too expensive for the BOM.

I wish I knew! The first thing I did when pondering this question was begin to try to disassemble the unit so I could take a peek, but they are filled with glue and apparently it's quite difficult to open the case in a non-destructive fashion.

 

[ChadK]

No,

I think statement 3 is incorrect.

its not incorrect. A true MPPT controller takes whatever amps it desires, at specified voltages, and performs it's function, just like any other electrical device. A pwm controller is different, because it is basically a pass-thru device and relies on a batteries demand for current, which can exceed the capacity of the pwm engineering.

 

[ChadK]

... with panels that are capable of delivering such current ...

 

[ChadK]

... with panels that are capable of delivering such current ...

So, I hope this ends this never answered question. Please stop making it a gray area. It's not gray, it's a black+white answer.

 

[RobertGreen]

So, I hope this ends this never answered question. Please stop making it a gray area. It's not gray, it's a black+white answer.

edit: I do not intend to convey a rude tone with this post-- I really, truly don't. I'm simply trying to stick to the facts here, and I apologize if I have offended anyone here.

You are simply incorrect. While it is possible to design and construct an MPPT charger that is immune to this issue, some widely available commercial mppt charge controllers can/will fail when overpaneled to a high enough level. Some of them will not (depending on how they are designed, constructed, and operated)

That's what makes this a gray area.

People constructing diy systems come to this forum for technical and helpful information about their real world applications. Hopefully the resources and guides shared on this site can prevent someone from needlessly frying their gear and voiding their warranties.

 

[WYtreasure]

To continue with the fact there is a "GRAY AREA".

This is an excerpt (page 1) to which I referred in post 21 and has been linked in my signature for months.


Hopefully it will be read now by those who do not believe.

 

[TheAlmightyOgreLord]

I am also a fan of overpaneling, because as cheap as solar panels have become it presents a nice opportunity to give your system a little boost without having to change any of the other equipment. It seems that whether or not -and to what degree- overpaneling is acceptable depends on the particular circuit design and construction used by each manufacturer.

@bud,
The problem remains; if the charge controller shorts the input from the array with the polarity correct during certain situations, it would smoke the controller with a large enough array attached. I don't know why they are built this way. Some people report massive overpaneling on these units without any issues, but after all the discussion about the topic I will take a more conservative approach and keep it within specs for my own system.

So could you make a SCC that can't be over paneled, work by installing an automatic reset circuit breaker on the PV side? That would also protect from surge currents like lightning strikes...