Recommendation for Tough MPPT CC ?

Re: Recommendation for Tough MPPT CC ?

HI Neil & boB,

Thanks for the replies.

boB, Nothing smoked, or even smelled bad, but, would note that hours after sunset -- total darkness, the PV input would be about 100 VDC. Would switch the input (PV) breaker to the MX to the off position, and the voltage would rise a bit above that. The MX-60 got a bit warm, the fan ran, and power was totalized as if the MX was really making power. Think that it WAS making power from the batteries via leakage (in my uninformed opinion) -- but of course it was a net negetive. First noticed this 'cause, as a Ham (also) noted the little birdie @ 3759 Khz at night. This has always come from the MX. Went to look, and there it was. That night happened to be a full moon. Commented to someone that was making power from moonlight. But the second night switched off the PV breaker and noted reality.

That MX went back to OB, and asked what was wrong with it. FETs was the answer. I do not know the real topology of the MX's buck converter, just thought that basically, the FETs were connected twix the PV input and the Battery output with an inductor/diode(s) and some filter caps etc.

My max Voc was recorded as 136 VDC as I recall ... close to the limit. Our climate is mild, so very few days per year is it above 130 VDC, and then for fairly short periods.

Our peak ambient temps are about 95 degrees F in the power room, this occurrs on many summer afternoons. And at the peak Ta, we are in Float (for hours) at about 122 VDC Vin.

Had wondered if this long duration elevated Vin and Ta could take a toll on the FETs, more than the unusual morning or two at 130-ish Voc.

Realize that your Midnite Classic may be offered (later) in an HV configuration, but think that I am on the way to hurting a second set of FETs. Now, when the PV in breaker is switched to off, see about 45 VDC Vin, as reported by the MX. Have no spare MPPT CC here, and am thinking about finding an even tuffer spare. Some/all of this may be illogical, perhaps too much guessing from too little data.

Edit: AND Crewaer, thanks for the thoughts ... Well we had an unusually COLD winter this past season. The lows were in the 24 Degrees F ... locals said thet this is the coldest noted in the past 12 years, but colder will happen.

Interesting thoughts re the summer Voc, but will add that will always have stacked inverters to run as absolute minimum loads, which prob takes a bit off the ultimate Voc value, short of a fault condition. Have noted that even on summer afternoons can supply hundreds of watts at 120 VDC Vin, however. So any clipper that I make needs to be good for about 500 Watts or so. Perhaps I need to make better use of the XS power. Had wondered about dumping the PV DC into a medium sized electirc water heater, but might need to add a heat exchanger to keep that load constant.

thanks, all ... (end edit)

Anyway 73 for now es TU, Vic K6IC

Re: Recommendation for Tough MPPT CC ?

Thaks Neil and Jim,

First, boB, as I recall, the MX did go to sleep as the sun faded, but awoke later and making the phantom power (perhaps that function needs a patent !)

Yep, While I was writing and posting my War and Peace reply to the first two posts, Jim's post was there.

Edited my orig post to try to respond to Jim ... perhaps not a good idea.

The closest town to me is Tracy, CA ... abt 8-10 airline miles.

Thanks Crewzer for the info on the cap precharge function ... guess that had not switched off the PV at night before and noted the result .. good info.

Neil, no did not look at the current and its direction, as it was funny to see, but the MX was obviously in need of repair, so back it went.

For me the birdies are small, and happne during the day when the MX is active doing PV work. Am never on the lower bands then. With each octive increase in frequency, the artifacts diminish quite a lot. And they were quite small to begin with -- have lotta shielding and ferrite in the system. Were it for my extension cord or two, probably these thingies would be another 10 Db or more lower. These big switching MPPT boxes sure work well. To me the MX-60 is amazingly well designed. More info than I need presented in an exceedingly intuitive fashion. Have never seen a piece of gear which had such an intuitive interface. And find the Aux functionality to be quite flexible. Great product ! I just should have gone with 71 Vmp, wanted to reduce the IR drops in the PV runs. 71 Vmp is high enuf to allow Solar EQ even on hot summer days.

Neil, the BCB stuff is tuff, but a multi section toroidal filter will do the job, unless you have multiple 10 Kw or larger stations close to you. The main reason for this off-grid site is to get away from the awful Power Line interference and ALL of the unsuppressed switching gizmos in people's homes. Now, the Treck Lighting switching power supplies are by far the largest source of interference. The off-grid site has S-zero background noise save for Lightning static and noises that I make. Thanks again for all the info. Vic
Thanks a