The Eco-w's new VOC limit
The last Eco-w 20a controller came while we we camping. The first thing I noticed was it now comes in a printed box with graphics and the info on it. The second thing I noticed is on the box the VOC l...
Forum Discussion
JiminDenver wrote:
I've sent the message about the change in the VOC limit but didn't think to ask if it applies to the older ones. I'll ask when they reply.
Another difference from the manual to the box is the watt rating has dropped from 300/600 to 275/550.
Using my extremely accurate magic secret formula, where 130w gets you 8.2a at Isc, then the limit for a 20a controller, with no allowance for panel exceeding ratings, is
20/8.2 x 130 = 317w. With MPPT getting you say another 10% in amps, then the 8.2 is now 9a, and
20/9 x 130 = 289w so 275 seems low unless they expect MPPT to do better than 10% "extra" above PWM.
EDIT something is screwy with that thinking but can't put my finger on it just now. Problem is that MPPT amps do not depend on panel Isc, but depend on panel wattage as affected by temperature of the panel.
so moving right along---- :) --
BTW, when using PWM 20a controllers that do not clip their amps and could overheat if above rating, you must allow a 20% margin for when amps are above panel Isc at times, so that means 16amps "expected" and allow another 3.2 =19.2
16/8.2 x 130 = 254w would be the limit for a PWM 20a controller. 275w for an MPPT 20amper that clips its amps (Assuming the Eco-W does that, can't say--never got that high even in cloud effect with my 230w) sort of fits in.
However the MPPT is not like the PWM in that the MPPT's own "efficiency" where it loses some of the panel watts on the way to making amps must come into play. (PWM just passes the panel Isc amps through) So maybe the ECo-W folks found out they had to reduce their idea of panel wattage from real life compared with design?
