east and west panel banks

[jestronix]

Hi All,

Im looking at using a MorningStar MPPT 15 amp regulator, only prob is I have about 17amps in full sun. This could produce over 20amps in cold weather and with MPPT im heading towards 25amp spikes.

Ive been thinking about a two separate banks, in the morning i get a solid 14 to 15 amps catching the early sun, around midday the panels are on angles so that they only get a maximum of 14 amps with MPPT, then in the afternoon I catch a good extended afternoon sun.

More sun hours, not breaking the 15 amp barrier, getting MPPT advantage, the morning and afternoon sun is also cooler making for better MPPT.

I have the following panels. Amps are true amps (hot cells)

PANEL AMPS

40WATT 2.1
40WATT 2.1
60WATT 2.75
60WATT 2.75
60WATT 2.75
60WATT 2.75
OLD PANEL 1

Im thinking Ill break it into

east morning

40WATT 2.1
40WATT 2.1
60WATT 2.75

west afternoon

60WATT 2.75
60WATT 2.75
60WATT 2.75
OLD PANEL 1

Ill have to do some testing to find out what angle I need for midday sun to sit under the 15 amps.

Next problem is MPPT wont find true MPPT as half the bank is running at lower power when the other is at full sun. Full sun bank will have lover voltage and out of sun bank higher voltage.

Answer might be to run the panels in series at 24v into the 12v bank, this would mean the regulator would see basically one panel sitting around 32v and would just find the MPPT of that. Id have to ditch the 1amp old panel, and run the panels in groups of 2s for the 36v.

The 40watt panels could do the afternoon shift.

[Mike90250]

Mixing panels is always a pain to get balanced right, and with 2 array directions, even worse.
What is the V & A spec for the "old panel".

An MPPT controller will generally run to it's max amp limit, and throttle itself to safely stay within it's heat and amp spec. I would not worry too much, the next step up is a larger one. Once the batteries get some charge going into them, or the panels heat up, I thing you will fall below the spec, and not waste too much solar.

[jestronix]

Hi Mike,

Trouble is those figures therse are full temp specs as tested in hot sun. Short circut amps though, so a little less when connected. Still Ill be up and over the specs of the controller. Ill have to double check and see if the sunsaver drops the connecting on overload, or just throttles. It only puts a max of 15 amps in on the batteryside, I think I will go with PWM controller for now, half price and wont chop off the amps. Wont be as good on cold winters day though.

[Mike90250]

I dont know of any MPPT styles that don't throttle back to safe area, watts or thermal. PWM generally only thermal limit as they heat up.

Winters are generally when you need the amps, the C-35 or C-40 are good, solid reliable units.