FilterGuy
Solar Engineering Consultant - EG4 and Consumers
Folks,
(Sorry, this got to be a long post)
I recently wrote and posted this resource on over-paneling.
A reviewer pointed out the Victron Max Isc Spec on the Victron controllers and another forum member PM'd me about it. Since then I have been trying to get a clear understanding of all of the implications of the Max Isc spec and have made a *little* progress.
* The controller manual implies that the Isc is only an issue if the PV id hooked up in reverse polarity. (And that was my belief till recently).
* On the victron community site, one forum manager (that is also a Victron employee) had a post that implied the same thing as the manual. However, when pressed on it he indicated that there are certain uncommon events where the PV input is shorted together and therefore the Isc spec is important beyond a PV reverse polarity situation.
* I was able to contact a Victron person Via email.... but he just pointed me back to the Victron Community forum manager so that did not help clarify things.
* A Victron Comunity member posted a link to an obscure MPPT Error code document that gives a little bit of info on the 'short' situation.
I pressed Victron for a more detailed explanation of why the controller 'shorts' the input but they declined. My *guess* is that if the output voltage gets above the input voltage, something in the circuit ends up enabling a series of FETs between Positive and Negative. (I do not think it is an intentional short... but it is a side effect of the design. )
Another couple of interesting points is that 1) using specs from real solar panels I can come up with configurations that are not over-paneled but violate the Isc Spec and 2) Feeding the 'bad' configurations into the Victron online MPPT calculator does not indicate a problem.
Victron has called the Max Isc spec a soft requirement, with an implication that it may not always be a problem to violate it, but since they declined any further elaboration, I have concluded the Max Isc spec must be followed closely... even if not over-paneling.
I have written the attached update to my resource and would appreciate any comments before I update the resource section. The key pages about Victron are the last two pages and I have copied them here:
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(Sorry, this got to be a long post)
I recently wrote and posted this resource on over-paneling.
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
A reviewer pointed out the Victron Max Isc Spec on the Victron controllers and another forum member PM'd me about it. Since then I have been trying to get a clear understanding of all of the implications of the Max Isc spec and have made a *little* progress.
* The controller manual implies that the Isc is only an issue if the PV id hooked up in reverse polarity. (And that was my belief till recently).
* On the victron community site, one forum manager (that is also a Victron employee) had a post that implied the same thing as the manual. However, when pressed on it he indicated that there are certain uncommon events where the PV input is shorted together and therefore the Isc spec is important beyond a PV reverse polarity situation.
* I was able to contact a Victron person Via email.... but he just pointed me back to the Victron Community forum manager so that did not help clarify things.
* A Victron Comunity member posted a link to an obscure MPPT Error code document that gives a little bit of info on the 'short' situation.
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:
Error recovery:
- 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.
If the error persists the charge controller is probably faulty.
- Error 38: First disconnect the solar panels and disconnect the battery. Wait for 3 minutes, then reconnect the battery first and next the panels.
- Error 39: The charger will automatically resume operation once the battery voltage drops below its maximum voltage setting (normally Equalisation or Absorption voltages), for 250V versions or float voltage for the other units. It can also takes a minute to reset the fault.
I pressed Victron for a more detailed explanation of why the controller 'shorts' the input but they declined. My *guess* is that if the output voltage gets above the input voltage, something in the circuit ends up enabling a series of FETs between Positive and Negative. (I do not think it is an intentional short... but it is a side effect of the design. )
Another couple of interesting points is that 1) using specs from real solar panels I can come up with configurations that are not over-paneled but violate the Isc Spec and 2) Feeding the 'bad' configurations into the Victron online MPPT calculator does not indicate a problem.
Victron has called the Max Isc spec a soft requirement, with an implication that it may not always be a problem to violate it, but since they declined any further elaboration, I have concluded the Max Isc spec must be followed closely... even if not over-paneling.
I have written the attached update to my resource and would appreciate any comments before I update the resource section. The key pages about Victron are the last two pages and I have copied them here:
==========================================================================================================
======================================================================================================