Originally Posted by ASIcons
I am going to park my Globetrotter and my Sovereign
at my farm (in VA) and hopefully use a solar system. I really need help with this so if one of you kind, technically proficient people would look at the system below and let me know if it is a practical alternative I would be most grateful. I will need to run the AC off it, it being 100 + regularly here lately. Thank you SO much!
The Goal Zero Yeti 1250 solar generator kit silently cranks out big backup power—suitable for big appliances, such as a refrigerator or freezer, and for home health-care equipment.
Kit includes 2 Boulder 30 solar panels to charge the Yeti 1250 in 20 - 24 hrs. using clean, free solar energy—or plug it in and charge it from the wall in 16 - 20 hrs.
Multiple ports including DC, USB and AC make it easy to power up a wide range of devices; activate the ports with a single master switch
Uses no gas and makes no noise or fumes, so you can use the Yeti 1250 solar generator indoors or out—wherever a source of power is needed
Included cart makes it easy to move the Goal Zero Yeti 1250 solar generator close to appliances, minimizing the need for long extension cords
Inputs include two 8mm charge ports (16 - 20 volts at 10A max/200 watts each and 1 power pole charging port (16 - 48 volts at 20A max/250 watts)
Outputs include 3 standard North American AC outlets, female 12 volt port, two 6mm 12 volt ports, 12 volt power-pole port and 3 USB ports
The Goal Zero Yeti 1250 solar generator kit includes protective fabric carrying cases for the solar panels
Sorry to shoot down your aspirations, but your Yeti 1250 is simply a small AGM battery bank coupled to a small (1250 watt) pure sine wave inverter in one very expensive
package. This is coupled to 60 watts of solar for charging? If it will take 24 hours to charge from a 60% depth of discharge, you are probably looking at batteries with a capacity of about 200 amp/hours (which, BTW, they conveniently omit from the specifications).
I calculate this by using their 60 watt solar array (5 amps max.) during 4 peak charging hours (10-2:00) and the residual for the rest of daylight hours yielding 40 amps to the batteries, 24 hours (3 days) gives you 120 amps of charging.....probably a 200 amp/hour battery pack.
That won't even come close to touching a roof A/C's 120VAC requirements, especially with only a 1250 watt inverter. Then there is a little thing called the Peukert effect:
Peukert's law, presented by the German scientist W. Peukert in 1897, expresses the capacity of a lead–acid battery in terms of the rate at which it is discharged. As the rate increases, the battery's available capacity decreases.
Manufacturers rate the capacity of a battery with reference to a discharge time. For example, a battery might be rated at 100 A·h when discharged at a rate that will fully discharge the battery in 20 hours. In this example, the discharge current would be 5 amperes. If the battery is discharged in a shorter time, with a higher current, the delivered capacity is less. Peukert's law describes an exponential relationship between the discharge current (normalized to some base rated current) and delivered capacity (nomalized to the rated capacity), over some specified range of discharge currents. If the exponent constant was one, the delivered capacity would be independent of the current. For a lead–acid battery however, the value of k is typically between 1.1 and 1.3. It generally ranges from 1.05 - 1.15 for VRSLAB AGM batteries, 1.1-1.25 for gel, and 1.2-1.6 for flooded batteries. The Peukert constant varies according to the age of the battery, generally increasing with age. Application at low discharge rates must take into account the battery self-discharge current. At very high currents, practical batteries will give even less capacity than predicted from a fixed exponent. The equation does not allow for the effect of temperature on battery capacity.
Simply put, the capacity of any battery bank decreases exponentially with the increase in the draw from that battery bank. You would need a minimum
of an 800-900 amp/hour battery bank coupled with at least
a 2800 watt sine wave inverter. To keep this charged properly with solar, you would also need 800-1000 watts in your solar array. I have placed 800 watts on a newer 27' Airstream in the past, but that was about the limit. A 30-34' trailer could get 1000+ watts using the proper panels (AM Solar GS-100 to be precise).
Still, from all of this, you will still only be able to run a roof A/C for less than 2 hours after doing the Peukert calculations. PM me for the actual calcs. if you like, but basically you reduce a 900 amp/hour battery bank (6 Lifeline GPL-6CT AMG golf cart batteries) to 50% depth of discharge maximum draw. This give you a usable battery capacity of 450 amp/hours.
At a 16 amp draw (for the compressor and fan of a 15K BTU roof A/C), you would expect that you could run that A/C (not even counting inverter loss) for 450 amp/hours divided by 16 amps =28 hours. But because Peukert shows an exponential drop in battery capacity based on the higher amp draw, you actually will reduce the capacity of this 900 amp/hour battery bank to a mere 30 amp/hours, giving you less than a 2 hour run of your A/C.
PS: I've tried it and it works out pretty closely to the formula!!!
Guess old Peukert know his stuff!!!!!!!