daveb's recent post in the following thread is touching upon some thoughts I have been having recently about how big and what type of house batteries I should buy as I get closer to redesigning my system.
Read any post by Sunking and SunEagle here:
http://www.solarpaneltalk.com/forumdisp ... amping-etc
Both posters are brutally honest about the inadequacies of solar for recharging a house battery in an rv setup. Basically the idea is that the truck alternator has much more recharging capacity than solar when compared to an rv's limited real estate for panel installation. See quote from thread below.
"Those are a UPS batteries. However they are not made to be cycled. If cycled you get 100 cycles and they are pretty much done. You do not want them, they are chit.
A 12 volt 9 AH battery if discharged at a very slow 20 hour rate of 5 watts have 50 watt hours usable. Discharged at the 10 hour rate of 10 watts only 30 watt hours usable. However any USB charger you buy today is a Serial device meaning if it uses 2 amps or 10 watts @ 5 volts, it draws 24 watts or more from the battery. Or about 2 hours till dead on a 12 volt 9 AH battery. That is one or two cell phones. Good luck with your plan.
Your whole idea is badly flawed based on bad information and assumptions. If your truck has a two heavy duty batteries and electrical system like you claim, you do not need anything. If anything just a simple 20 to 100 watt panel connected directly the truck battery so you fell better by spending money. Or run the truck engine for 10 minutes which will do more will do more than a 100 watt panel in a week. Your truck battery and alternator has more than what you need to do what you want by a magnitude of 10.
But if money is burning a hole in your pocket at least do it right. A 100 Watt Panel panel, 10 amp Controller, and an Optima Blue Top D31M, or Odyssey 31-800. Should not cost you a penny more than $500. That ought to cool your pockets off.
If it were me just use the truck."
http://www.solarpaneltalk.com/showthrea ... -do-I-need
Granted he was talking about small uninterruptable power supply batteries in the quote above, but the concept applies. Solar vs running the truck to recharge our house batteries.
Peeling the onion even further. There is a discussion in the offgrid subforum of solarpaneltalk.com that smart controllers are going from bulk to absorb to float mode too quickly and undercharging and thus killing batteries prematurely and not because the battery is at a state of charge that it only needs to be topped off, but because the solar array doesn't have enough voltage output as the sun moves so that it can only power the controller to do float when the battery really needs bulk. In other words, just because your solar charge controller is in float mode, doesn't mean that your battery is fully or nearly fully charged. So some of the newer advice is to program the MPPT controller that bulk=absorb=float so that it never leaves the bulk mode. These same posts say that amps-out / amps-in State of Charge counters like my BMV are worthless and misleading. That has been my experience, because the additional variables are way too much for the counter to monitor. In my case, when I reset it and I had to reset mine frequently, it was never reset on a fully charged battery - try as I might to recharge the battery fully at home with a 10 amp battery charger. I just bought this battery charger:
http://www.napaonline.com/Catalog/Catal ... 0006389653
I like it because it is a smart charger with desulfation but a big amp charger too. Unlike the BatteryMinders which cannot charge or desulfate until the battery has been brought up to at least 10 or so amps by a bulk charger. But I may try to take it back and get the next size up.
Peeling the onion even further, there was a discussion of whether it is better to have a faster recharging type of deep cycle battery paired with a bulk output solar controller to maximize the few hours of usable sunlight available. Concept is that if you only have ___ hours of usable sunlight a day, you better not expect that a slow recharging type of deep cycle battery will be recharged by a solar controller. (I received my beta test "Kid" (PWA) controller from MIdnite but I haven't installed it yet.) But apparently faster recharging types of deep cycle batteries don't have as many cycles before failure as slower types of charging deep cycle batteries.
But what daveb is talking about is becoming to be the key for me in house battery discharge and recharging design. I don't know what to design into my system yet, but these design concepts are floating to the top in my mind:
1. Battery AHr size/capacity should be based on expected usage/loads WITH expected mean(s), speed, volt output, and frequency of recharge in mind. (I.e., running the engine at idle or fast idle every morning to recharge or nearly recharge the battery. In my case, normally only a weekend, two nights of furnace, constant power to the Engel refrigerator/freezer. Depending on how fast the battery recharges from the alternator, a smaller AHr house battery may be all that's needed, thereby reducing weight and initial purchase expense and expense from burning vehicle fuel to haul around a heavier larger AHr house battery;
2. Battery recharge profile paired with alternator output (or in my case battery charger output - this applies to you inverter/charger guys in spades - in my case the 5kW AC producing Auragen on the second alternator position on the diesel). A fast recharging 14.8v accepting Odessy battery like those mentioned by
daveb has a use for the military and likely for us;
3. Balance quick recharging from alternator with the amount of cycles one gets from a quick recharging battery type. Apparently there is a trade off to be aware of.
4. Hook up after the weekend at home (or whenever possible) to shore power with a smart charger of sufficient amperage output which does true Bulk, Absorb, Float, Desulfation with an output profile paired to the battery's recharge profile to recharge but not destroy the house battery.
My first solar/house battery design was flawed from the beginning. Too much money and not enough thought expended.
Now, I believe that
daveb has pointed us to the starting point. The speed and max volts recharge profile of the batteries sized to our expected loads with the expected mean(s), speed, volt output, and frequency of recharge in mind.