(09-02-2022, 04:49 AM)admin-rich Wrote: 400a/h is enough to run an air conditioner? For how long?
Great question Rich! As one might expect, there are a bunch of variables, including battery types and count, various equipment used, size of RV, and humidity, but generally speaking when it’s hot, the sun is also shining (assuming few clouds), and this is done concurrent with solar…For just a baseline, when I had only two 6v golf cart batteries, I could run the 11kbtu air conditioner for between 1 to 1.5hrs before reaching say 55-50% SOC (state of charge), this is with the fan on low-speed and with the compressor cycling (beyond the initial cooldown)…So the problem with wet-cells is that the usable capacity is only to about the 50% SOC point, because to go any lower risks damaging both the battery AND the air conditioner due to excessive voltage sag…
Lithium’s (LiFePo4) are a different animal, in fact I bench tested one of my 200a/h batteries using a 500w halogen shop light and Victron BMV-12 coulomb counter SOC meter, and it showed the actual capacity at 215a/hr, (7% above advertised!), and while voltage sag was negligible all the way down to ‘zero%’ SOC, at which time I even brewed a cup of coffee at whopping 126a (dc) using the Keurig!!…So the usable capacity of lithium might suggest 100%, but LiFePo4’s don’t like being at a full state of charge for an extended period past a full re-charge - a full re-charge is necessary only occasionally, mainly to perform just a periodic cell-rebalancing cycle which generally takes about another say 15-30 min of additional time past a full charge (depending on the number of batteries)…A far better ‘every day’ charge routine might be to not exceed 90-95’ish % SOC, this in the interest of extending battery longevity…JMO
Now back to your question!…My Coleman Mach 1 P.S. uses about 90-95amps during hotter weather, yet beyond the initial cooldown (say after about 45 min…), the compressor duty cycle drops to about 65-60%, so this would equate to about 62-57amps (dc) per hour, though concurrent with solar harvest…
Due to the vagaries of weather, I like to plan on a conservative harvest rate of about 50% (can also vary depending on type charge controller; i.e. PWM vs MPPT), and for just a thumbnail sketch, a 100w panel is typically rated at just over 5amps IMP (max power), but this in the most ideal of laboratory conditions…So for planning I prefer to assume a ‘real world’ number (considering variable harvest) of about half that, thus, one might plan for four 100w panels to yield an average harvest of say 2.5a per panel, or 10amps recovered per hour, though likely somewhat more during peak harvest hours…
So for this attempt at a ‘fair example’ taking say ‘just two’ 100a/hr LiFePo4 batteries at a starting SOC of say 90% (180a/hrs) and planning for an ending SOC of 20% (a 40a/hr reserve) equals 140 ‘available a/hrs’, four 100w panels (at 50% efficiency), and a duty cycle of say 65%, thus one might expect:
95a (dc) air conditioner at 65% duty cycle = 62amps - minus,
Solar harvest @ 10amps = 52amps (more during peak harvest hours)
140 available a/hrs / 52 = 2.7hrs
This may not sound like a whole lot (a purposely somewhat conservative calculation here…), but trust that the ability to occasionally run the air conditioner during roadside ‘sandwich stops’ or late afternoon arrival has been a real boon for us (especially having 400a/hr batteries and 660w solar!) where in my case I’ve run the air for nearly 6 hrs without a hitch - but now having added (per previous post) three more portable 120w panels for longer term camping (results pending)…
FWIW, During my first initial driveway test which included the three new panels (@ 12:30 in the afternoon), my Victron showed a combined total harvest of 46amps from a combined total 1,020w worth of panels (a mix of 760w MPPT, 260w PWM), but in previous test (minus the new panels) with 660w at the same time of day, typically about 29’ish to a high of about 33amps…
Also realize that one’s total harvest period (discounting driving) will typically extend well before the heat generally kicks in, e.g. before air conditioner ops begin…
Hope this helps
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Upon re-read, I might also add that while LiFePo4’s are very capable of a deep depth of discharge (DOD) possible even near to 100%, some consideration should be made (based on one’s actual experience…) as to what the next days harvest is likely to yield…For instance (using the aforementioned example…), if one’s ‘informed expectation’ of the next day’s pre-noon to say’ 1:00 pm harvest were to yield (say, in light of ‘peak sun’ conditions):
Hypothetical 400w harvest (estimate only),
0900-1000 = 06a
1000-1100 = 09a
1100-1200 = 17a
1200-1300 = 17a
(overall, an assumed 60% harvest efficiency seems realistic…)
So by 1:00pm, about a 50a/hr recovery, added to the already 40a/hr morning’s two batteries reserve = 90a/hrs (unlike previous day of 180a/hrs) before potential resumption of air conditioner…This is where more panels and another battery can make a difference, OR a travel day in-between will do, Just saying
