MX60 Max Array Voltage? [RE-wrenches]

[Ray Walters]

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Hi All, but especially Chris F.;

What is the collective experience with running the MX 60 with a high 
voltage array to a 48 vdc nominal battery bank. The manual shows a Voc max 
of 140 which looks like I could go with a 72 V nom. array. I'm using 140 
watt modules with a Voc of 42.8. Times three puts me at 128.4 Voc at 25C. I 
know I need to add some Voc for cold weather, but my experience is that if 
the sun is shinning on the modules enough to produce power, it will produce 
heat too. I usually have measured about 30 to 40 degreesF higher cell temp 
than ambient. I know air speed humidity etc play a part too. Basically, The 
lowest temp I would anticipate in good sun would be 20F or -7C. Using 
Outback's chart (1% increase inVoc for each 2.5C below 25C) and assuming a 
20F warmer module (cell temp=40F = 5C) then I should add 8% to 128.4Voc 
which would be a Voc max of  138.7F. Boy that's close.

What happens Chris, if the array does exceed 140Voc? Smoke and fire, or 
temporary shut down? Did I mention the array will be over 300 ft away? Now 
I know supposedly Voc is open circuit and that means no current therefore 
no voltage drop, but wouldn't the meter still see some discernable volt 
drop in real world conditions? ( meter has to pull at least a few micro 
amps to measure voltage) Is the controller switching the array off 
temporarily to check Voc every few seconds? Will the Voc measured at the 
controller for this split second really be the same as at the array or 
would it be a volt or 2 less?
Also, in the MX 60 Manual, they show a chart with various array voltages 
labeled 40, 65, and 95 V Nominal. Is that a misprint and should that be 
labeled V at Max Power instead?
We're even considering running two 24 v modules in series with a 12 v of 
similar current rating, but the racking and look would be awkward.

Thanks for all input,

Ray
Taos Power

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