Wellsee MPPT

Re: Wellsee MPPT

Gulch wrote: »

I have a spare Sunforce (they may be junk too, for all I know) 30 amp controller... The specs on it say 25Vmax input... these panels seem to occasionally hit 27 V under load a few times a day, usually only for a few moments at a time... and this during winter... I wonder if that would fry the controller?

The dimensions on modern electronics and transistors are extremely small... When you exceed the voltage input of the design, you are probably causing 1,000's of volts or more per inch of electric field (because the dimensions are so small) on those small features. When you over volt the design, you stress and can punch through the insulating materials on the die.

You may pop it now, or you may weaken it for days/weeks/years down the road--It is very hard to tell what caused a failure without decapping the part.

So--I would not recommend exceeding input voltage ranges ever for reliability. Add inductive kickback from wiring--and it is very easy to exceed design voltage limits if you exceed the controller spec.

One thing I don't quite understand about the controllers: Is the amperage rating on a Xantrex C60 CC only for output, or is it for input also? Will the occasional 70 A surge fry it, or not?

According to one Cx0 spec, they say: "85 amps intermittently-electronically protected"

So, it looks like you are probably OK (not a great idea, but within capabilities).

For a PWM controller--basically Current In equals Current Out (on/off switch--nothing more fancy that that).

Remember that heating is based on I^2*R so:

• (70a/60a)^2 = 1.36

So, you have 36% more heating with only 1.17x more current. That is why running more current seems to overheat electrical devices more than one would expect (squaring current worth of power/heating effects).

And in the same vein: I wouldn't mind (much) spending the money to buy a 'real' MPPT charger for the little RV system, but I can't find a moderately priced one that will handle 425 or so watts on 25V+ input and 12V output... I COULD cut down to one panel, and use the Morningstar 15A MPPT controller, but that would be borderline for running my furnace blower on a couple of consecutive cold and cloudy days.

About the best bang for the buck MPPT 30 amps 12/24 volt unit is the Rogue MPPT at this point.

It will handle your 24 volt array--and MPPT controllers because they are power converters can limit their output to rated current--regardless of how much solar array they have connected to their PV intput.

For a 12 volt battery bank, about the maximum "optimum" size of solar array for a 30 amp controller would be:

• 30 amps * 14.5 volts * 1/0.77 system derating = ~565 watts

That will, on perfect days, push the controller to near 100% output capacity for a little bit--but most of the time, the controller will be operating under its 30 amp maximum current limit...

You can put more solar array out there--but then the controller will hit current limit more often and "waste" the extra solar power that may be available...

Note: Numbers are approximate... 540 bad vs 580 good--Not really--close enough (within 20%) is good for horseshoes, hand grenades, and solar PV systems.

-Bill

Re: Wellsee MPPT

Gulch,

I can move your posts to its own thread if you want to continue the discussion along your needs.

-Bill

Re: Wellsee MPPT

Depending on loads and temperatures, deep cycling to ~44 volts is a pretty healthy discharge. Normally, we recommend that people try to keep the minimum voltage to around 46 volts minimum.

So, these are 500 AH @ 48 volt batteries (single series string)?

• 1,500 watt of lights * 1/48 volts * 3 hours * 1/0.85 efficient inverter = 110 AH per night
• 110AH per night / 500 AH capacity = 0.22 = 22% discharge

That sounds about right for amount of discharge per night...

• 90 watt per panel * 24 panels * 0.77 panel+charger deratings * 1/58 volts charging = 28.7 Amps average charging current

Assuming ~5 hours of sun per day:

• 90 watts * 24 panels * 0.52 system derating * 5 hours of sun * 1/58 volts = ~97 AH per day

The numbers sound OK... Assuming you use the lights less if the batteries are not fully charged / during poor weather.

If you could ever justify it... A Battery Monitor would be interesting to have on the system (current shunt, measure Amps*Hour during charging and discharging).

Have you actually verified the Wellsee model you are using is actually a MPPT charge controller? The few we have seen here are not. They are just simple PWM charge controllers (no large inductors for energy storage as typically seen in switching power supplies).

Assuming the panels have Vmp in the range of 17.5 volts each--A PWM controller would be OK for your application (at least not much different than using a MPPT controller with only four "12 volt" panels in series.

A good MPPT charge Controller, you could put 5 (or possibly 6) panels in series. This would reduce the current (and losses) a bit between the array and the controller/battery bank. It would also allow you to charge/equalize your batteries better in hot weather (which I assume you have a lot of). Solar panel Vmp falls with higher temperatures and that could also limit your maximum charging voltage some too (hitting Vmp-array-hot and Vbatt-charging/equalizing).

-Bill

PS: I see you posted a picture... Yes, that is not a MPPT type charge controller--Just a PWM unit (in my humble opinion--I am not an expert).

Re: Wellsee MPPT

Appears to be an unrelated brand/vitamin company.

-Bill

Re: Wellsee MPPT

Sure--You are more than welcome to start a thread about your design.

Good Luck. You will learn a lot and hopefully have a nice controller in the end.

Are you planning on running a micro-controller to do some sort of MPPT function?

-Bill