MPPT -- which need calibration?

Grinnin

I have been off-grid, mostly solar* for 12 years. Time for the real house, new system, and new solar.

My charge controller is the Blue Sky Solar Boost 50 MPPT (SB-50).

Setting up the MPPT requires tuning the MPPT power voltage. This requires full sun, discharged batteries, cool outside temperatures, and stable loads (preferably no load).
The procedure is to open the SB-50 and turn a trimmer pot clockwise and counterclockwise while watching the charging current and watching the MPPT incicator LED to make sure it stays on. Try to leave the trimmer pot wherever the current is highest

While the SB-50 has worked fine, I cannot imagine that the power point found during my configuration is also the maximum for other weather.

I have seen other systems that seem to automatically "sweep" to find the maximum power point. Outback, I believe, does this.

So my question: Which charge controllers require calibration, like the Blue Sky SB-50, and which automatically find the MPP dynamically.

Thanks.

* I have run a generator for 8 hours in 12 years. I also have a very small wind generator that was on a test tower.

BB.

Re: MPPT -- which need calibration?

As far as I know, the mainstream Midnite, Outback, MorningStar, Rogue, etc. do not need any trimming to optimize MPPT. They will "sweep" and determine the optimum Pmp=Vmp*Imp every few minutes (plus or minus).

The Midnite, I believe has one (or several) different MPPT algorithms that can be used if the owner wants to experiment.

For use of MPPT controllers on Wind Turbines, some controllers can have the MPPT voltage manually set--Or (for at least the Midnite), you can load an IV curve to match a wind turbine's output curves.

-Bill

Grinnin

Re: MPPT -- which need calibration?

Thanks for the news. I suspect you're right. I hope others will chime in with their experience.

You mentioned MPPT for the wind turbine. I wound the coils for 12V and have seen 3.5 amps rushing into the batteries without any overload. :roll: The PVs are wired for 24V. There is really no chance that this wind turbine will overcharge the batteries. Conversely the output is so small that investing in electronics to optimize it would be money misspent. I just rectify the 3-phase AC and let it blast away at my batteries. But it was a fun project and helps just a little during the lowest sun. (My nightly use can vary from 120Wh to 400Wh. There should be sun tomorrow so I'm headed toward 180Wh tonight -- 30Ah at 12V.)

There are probably other practices here that don't look rational, but I learn lots, have fun, and keep in reasonable health.

westbranch

Re: MPPT -- which need calibration?

Are you planning an expansion? From what you have stated your system though dated appears well balanced... I think the BS line is the only old technology MPPT equipment still out there. I know there is a similar adjustment on the 2000e model.. I use/semi-retired mine on to the guest house system...

Grinnin

Re: MPPT -- which need calibration?

westbranch wrote: »

Are you planning an expansion? From what you have stated your system though dated appears well balanced...

. . . I know there is a similar adjustment on the 2000e model.. I use/semi-retired mine on to the guest house system...

I built this building in '01 as an insulated garage with a temporary wall where the large doors go. One thing and another and I never built the house. While the building has water and septic, it has zero closets, a dimensional-lumber kitchen counter, and many other, um, oddities.

My PV system cost about $5,000 in '01. The PV panels were $499 each -- essentially $2,000 before shipping. The system is fine and does most of what I want. There are a couple of things I gave up when I moved here that I'd like power for: table saw and electric welder (oxy-acetylene is fine, but trickier in some assemblies). The price of PV and battery then just made them impractical.

With a new building, the old system just doesn't make sense. The price of PV is down so far that I can more easily get through this darker part of the winter if I just buy lots of PV. Which allows a battery bank large enough to deliver the amps for an inverter large enough to deliver a solid 3kW.

My Blue Sky SB-50 will be semi-retired to the garage.

EDIT: Panel prices now -- that same $2,000 would buy 8x 245W SolarWorld panels from N. Az Wind & Sun -- 4kW instead of 400W. Example is based on easy math instead of value.