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@pickit2,

I was in no way critisizing you darling.

lets converge on a good solution

Mike

Relay was a quick response. as you could use the excess voltage, for whatever ie: charge a smaller battery. 
I would use a powered Test load, don't everyone have one in their tool box.

@pickit2,  good thought. dont like relays though

i would add a variable current source (load), big mosfet ( probably several in parallel, with equalising reistor in the Source, so the G-S voltages are the same), big heatsink and fan, and control loop to keep the voltage at 540V.

so the current is variable.

and fuses of course

aditionally,Vgs falls as the temperature increases, so you need the resistor to mitigate and equalise  this.

Aquick look, found a mcrochip part APT6011B2VRG, APT6011LVRG MOSFET MOS5 600 V ..., I am sure there are many others.

how about a comparator circuit with a relay to add a load if the voltage is above the say 540V.
you could even add it to the panel groups, so if a group is below the upper limit they still supply the full power.   

I more or less understood something like that...
you must match the array and the possibilities of the inverter before digging and installing...
the easy move would be to change the inverter now to match the array then.
I don't know if your zener mods will work or not, but it's worth a try.

>Splitting the array is not an option because of how it is wired.
then it has not been wired the right way !
good luck !

The current array is wired in series and I don't want to dig another trench to run additional wiring. 

>Splitting the array is not an option because of how it is wired.
then it has not been wired the right way !
good luck !

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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