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Why not split the solar array in half ? take care of the max power input in your inverter but it would have less losses than shunts.

Splitting the array is not an option because of how it is wired.  The other limitation is the charger/inverter only has 2 mppt tracking inputs and both are in use.  

The power loss in a shunt that clamps voltage to 550V in this array would be minimal since the voltage could only exceed this in very vary circumstances.  The main likely scenario is during a sudden sunny episode after a storm in cold weather.  In that situation, the mppt tracker would likely have reduced the load and allowed the voltage to rise to a relatively high level with low solar generation.  A sudden large increase in sun could cause the array voltage to exceed 550V and approaching the 640V open circuit voltage before the mppt tracker increases loading.  This is about the only circumstance in which the shunt would dissipate energy.  I'm uncertain exactly how much energy the shunt would have to dissipate in that situation to clamp the voltage to under 550V, but I'm guessing it should be well under 20% of the array wattage rating so 1 kw at worst.  

So, I'm considering a couple strings of 50 watt zeners in parallel.  I would use at least 2 strings for redundancy.  Another possibility to reduce dissipation in the zeners is to include a light bulb/heating element in the string.  One concern is voltage accuracy of the zeners since typical high power zeners only have 5% tolerance.  

Posted on: May 14, 2025, 03:04:49 15:04 - Automerged
It is curious that some particular zener models of similar wattage are much less expensive than others.  For example, this 1N3336B Zener, 68 V, 50 W, DO-5 is $5 from a distribution.  

https://www.newark.com/solid-state/1n3336b/zener-diode-50w-68v-do-5/dp/10P4952

The zener's in series don't have to all be the same voltage.  I imagine having one that is the rated voltage for a DC fan to cool the heatsink they would be mounted on.  Another problem is I don't have a power supply that operates up to 600V to test this.  Any idea to produce a relatively high wattage 600-700V power supply may be with a variable transformer feeding a step up transformer and bridge rectifier/capacitor.    Since the 600V is well below the breakdown voltage of typical small transformers, it should be possible to use an ordinary 120VAC to 24VAC step-down transformer in reverse.    To get 650VDC, I would need 460VAC so a ratio of about 4 operating from 120VAC utility voltage.  

Why not split the solar array in half ? take care of the max power input in your inverter but it would have less losses than shunts.

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I have a solar array with an open circuit voltage of 640V and a maximum power point voltage of 510V and a charge controller that can tolerate up to 550V input.  So, I'm trying to figure out the best way to limit the voltage to 550V.  In practice, the array would only exceed 550V during unusual conditions (such as very cold and high intensity sun such as immediately after a storm). 

The array has a maximum output current of 10 A (about 5 kw).  The simplest solution seems to be a shunt regulator.  The simplest form may be a string of series connected high power (50 watt) zener diodes with the combined breakdown voltage a bit under 550V.  The shunt regulator would never need to dissipate the full output power of the array since even a modest load (10-20%?) should drop the voltage below the 550V threshold.  I have minimal experience with high voltage electronics.  Anyone have any ideas or experience with this?   

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Note	I am an electronics engineer And I love programming and building hardware I am skilled in building and programming electronic devices I can answer specialized questions in the field of programming PIC, AVR microcontrollers, and hardware design. The purpose of becoming a member is to share experience and benefit from the experiences of friends. Electronics is my job and I enjoy it

I had a look around, but failed to find anything.

Without the full detail, these are chips I'd avoid.

looking for following uC

SC8F072AD614SP
SC8P062AD614SP
SC8P1711E      
SC8P1762E      

CMS80F2313
CMS80F2316
CMS80F2317         
CMS80F7316
CMS80F7318
CMS80F7616
CMS80F7618

PMS134
PFS122B
PGS134
PFS154

This will be right:

Code:

.text
...
.section coeff,psv
COEFF_A: .hword  0x4000,0x8F5B,0x4BB5,0xEE34
COEFF_B: .hword  0x2511,0x6F33,0x6F33,0x2511
.end

I apologize in advance if my question is inappropriate here.
I'm trying to write code in xc16 assembler. I don't understand how to place constants in program memory. In theory, you just need to place data in the program area (after the .text directive). But if I do this:

Code:

.text
...
COEFF_A: .hword  0x4000,0x8F5B,0x4BB5,0xEE34
COEFF_B: .hword  0x2511,0x6F33,0x6F33,0x2511
.end

Then the compiler perceives the labels COEFF_A and COEFF_B as invalid assembler instructions.
If I do this:

Code:

.text
...
.data
COEFF_A: .hword  0x4000,0x8F5B,0x4BB5,0xEE34
COEFF_B: .hword  0x2511,0x6F33,0x6F33,0x2511
.end

The compiler places constants in the data area.  
Tell me what I'm doing wrong?

Posted on: May 07, 2025, 09:59:15 09:59 - Automerged
If I do this:

Code:

.text
...
.section .const
COEFF_A: .hword  0x4000,0x8F5B,0x4BB5,0xEE34
COEFF_B: .hword  0x2511,0x6F33,0x6F33,0x2511
.end

The data seems to appear in the program memory area. But in my opinion, this is not quite the correct syntax.