Down Conversion By MPPT

bajasurfer

?Question?
When 35.4V @ 9.90 Amps from 2 panels is down converted by the Outback for the 12V battery bank, what amps will the battery bank see? How about 35.4V @ 19.80 Amps from 4 panels?

Off-grid system
350W PV initially, ultimately 700W PV.
12V Wet Cell battery bank @ 216 A/hrs initially, ultimately replaced with 12V AGM battery bank @ 424 A/hrs.
note: Existing 100% 12V lighting means 24V battery bank not an option.

350W PV
Two panels of following spec:
Max Power (Pmax)* 175 Watts
Tolerance of Pmax +10%/-5%
Open Circuit Voltage (Voc) 44.4 V
Max Power Voltage (Vpm) 35.4 V
Short Circuit Current (Isc) 5.40 A
Max Power Current (Ipm) 4.95 A

SCC
Outback Power FM60 MPPT

Battery bank [Initial]
2 x 12V 108 A/Hr = 216 A/Hr total

Wiring one way
Panel MCs to Bus Bars: 12AWG x 6'
Bus Bars to SCC: 4AWG x 8'

Usage- 3-4 times per month
DoD ~29% [on 216 A/hr batt bank]
DoD ~31% [on 424 A/hr batt bank]
6.0 to 6.5 hrs [per San Diego WBAN #23188 chart]

Have 3500W generator & Vector 30A charger on hand.

Thank you for your time,
Larry A

mike95490

Re: Down Conversion By MPPT

Easiest way is to convert to watts: 300W in = 300W out (- losses)

So if you have 350W in (35.4V @ 9.90 Amps )
you get 340W out , at 16V = 21A

V x A = W

bajasurfer

Re: Down Conversion By MPPT

mike90045 wrote: »

Easiest way is to convert to watts: 300W in = 300W out (- losses)

So if you have 350W in (35.4V @ 9.90 Amps )
you get 340W out , at 16V = 21A

V x A = W

Thanks Mike.

So, to get a real-world # with the Outback, would I then calculate actual Amperage using the efficiency rating of the unit? Or would that remain a ballpark figure?

Thanks, again.

Solar Guppy

Re: Down Conversion By MPPT

Your panel numbers will be derated as well , both for temperature and isonolation and angle error.

If your in a hot climate, you give up 10-20% for voltage and figure about 950 watt-meter-sq ( panels are spec'ed for 1000 watt-meter-sq )

So peak-rated power of the panels * peak sunshine ( 0.95 ) * Sun-Angle ( 0.90 ) * ( temperature ( 0.90 ) * charge controller efficiency ( 0.92 for 12V operation )

Given your stated figures

350W * 0.95 * 0.9 * 0.9 * 0.92 = 248 peak DC watts into the battery

If Battery is ~13V, 248watt / 13V = 19 amps peak @ solar noon