Solar Controllers--Don't be a Sucker! :(
Just got to say it again, how it is we are sitting here for five months off grid on solar with no problems at all (third season on solar like this), using the non-programmable, non-MPPT, solar control...
Forum Discussion
** Caveat: All of the numbers I am using below are either typical numbers I see during use or averages... there are far too many variables (time of day, temperature, battery SOC, panel angle, etc) to provide absolute data. **
My rooftop A/C is a 7200 BTU Polar Cub. The starting current is ~9A and the running current is ~6A (both at 115Vac)
When running solely from my 2000W sine wave inverter, this equates to ~75A starting (just a few seconds) and ~55A running. With mid-day sunlight, he solar panels can generate ~23A when demand is high (low SOC or high current draws) and the duty cycle of the A/C is ~66%. This means (best case) that to running A/C for three hours on a sunny afternoon will leave me at about about 70Ah away from full or 75% SOC. My Odyssey AGM's perform very well under load and I seldom see the voltage sag below 12.0V. Remember that a 33A draw on my 3-battery bank is only 11A per battery
Fair enough, I confess that I my 12V electrical system probably cost more than yours. However I did have a pre-determined budget when I designed the system, and I stayed within it. I do understand that you can do a heck of a lot of charging with low cost PWM controllers.
My solar controllers were $550+ (had to buy those temp' sensors & serial adaptor, ya' know). They give me the diversion load output that runs my H2O heater (saves $ on LPG), the ability to wire my solar panels in series which means I can charge for more minutes every day, the configurability to program a bulk charge up to 14.70V, absorption charge at 14.70V or 3 hours or until the charge current falls to 300mA (whichever comes first) and then float at 13.60V OR simply float at 13.60V with the flip of a toggle switch... all temp compensated at ±24mV/ºC of course.
By the way, I have a substantial investment in batteries... so some of the money I spent on the charge controllers is insurance against damaging the batteries by over/under charging.
There is no right and wrong here. At the end of the day is all comes down to how you plan to use your RV and your budget. Personally I spend several weeks every year in the northern Nevada desert, where it can be very hot and very cold (in the same 24hr period), there are no gas stations, and no place to replenish my LPG. Running a generator for long periods of time is out of the question. The one thing there is an abundance of is sunlight. So I depend on my solar & batteries for all of my electrical needs and I'm willing to spend a few extra bucks to make sure I can do that.
-Mark
BFL13 wrote:
BTW, how do you run the air conditioner (how big is it)--how much starting draw (voltage drop on that on the 300AH bank?-how much running draw?)
My rooftop A/C is a 7200 BTU Polar Cub. The starting current is ~9A and the running current is ~6A (both at 115Vac)
When running solely from my 2000W sine wave inverter, this equates to ~75A starting (just a few seconds) and ~55A running. With mid-day sunlight, he solar panels can generate ~23A when demand is high (low SOC or high current draws) and the duty cycle of the A/C is ~66%. This means (best case) that to running A/C for three hours on a sunny afternoon will leave me at about about 70Ah away from full or 75% SOC. My Odyssey AGM's perform very well under load and I seldom see the voltage sag below 12.0V. Remember that a 33A draw on my 3-battery bank is only 11A per battery
Several threads/posts about how you can't run the air conditioner off-grid except with the big gen or a smaller gen with inverter assist just for the start and recycle part. So you are doing it with no gen at all. How?Um, well... either those threads are wrong or the authors have different setups than I do. BTW, when I do run the generator (a Honda EU2000i) I let the inverter start the compressor and then transfer the load to the genny.
The rant is about:- what can you do that I can't for $500 vs $78 ?
Fair enough, I confess that I my 12V electrical system probably cost more than yours. However I did have a pre-determined budget when I designed the system, and I stayed within it. I do understand that you can do a heck of a lot of charging with low cost PWM controllers.
My solar controllers were $550+ (had to buy those temp' sensors & serial adaptor, ya' know). They give me the diversion load output that runs my H2O heater (saves $ on LPG), the ability to wire my solar panels in series which means I can charge for more minutes every day, the configurability to program a bulk charge up to 14.70V, absorption charge at 14.70V or 3 hours or until the charge current falls to 300mA (whichever comes first) and then float at 13.60V OR simply float at 13.60V with the flip of a toggle switch... all temp compensated at ±24mV/ºC of course.
By the way, I have a substantial investment in batteries... so some of the money I spent on the charge controllers is insurance against damaging the batteries by over/under charging.
There is no right and wrong here. At the end of the day is all comes down to how you plan to use your RV and your budget. Personally I spend several weeks every year in the northern Nevada desert, where it can be very hot and very cold (in the same 24hr period), there are no gas stations, and no place to replenish my LPG. Running a generator for long periods of time is out of the question. The one thing there is an abundance of is sunlight. So I depend on my solar & batteries for all of my electrical needs and I'm willing to spend a few extra bucks to make sure I can do that.
-Mark
