inverter that will drain a battery all the way?
“… The point of the deep cycle battery (as opposed to a regular car battery) is that it can be fully discharged without damaging it. …” Not really. Some deep cycle batteries (Optima & Lifeline) can be discharged to near 100% of rated capacity repeatedly without permanent loss of capacity, and even stored for up to a month uncharged, but other lead-acid batteries of deep cycle design (like flooded plate batteries) that are fully discharged for any length of time are going to be damaged. So the first thing is to be absolutely sure that the specific battery that he is using is going to be OK with discharge cycles that take it below 50% charge. Even batteries that are designed for this are going to be less efficient in supplying the last 50% of charge, than they will be in giving up the first 50%, simply due to increasing internal resistance developing as battery charge is lost. Inverters will generally drop at least a little bit in
flabdablet nails it. And based on his calculations, a second battery is warranted, if you want 10 hour run time. You also need to examine what that charger is really doing, for deep cycle battery operation, on its various charge settings. I strongly doubt that a 25 amp charge rate for a deep cycle battery is a good idea. Even a 12 amp charge rate on a deep cycle battery isn’t a great idea. But what really eats you is “So, I use the 12v outlet on the generator to charge the battery rather than the “Speed Charge”, because I figure it’s probably more efficient than stepping up to 120v to run the charger and then back down to 12v to feed the battery.” It may be true that a direct DC charge system is “more efficient,” but it is highly unlikely that a random 12 volt DC outlet is the optimal way of charging your deep cycle battery. For best charging of deep cycle batteries, you need a charger capable of understanding their charge profile, and changing the charge rate and voltage appropriately
By the way: the right way to check whether he’s getting full use of his existing battery capacity is to insert an ammeter into the circuit, right between the positive terminal of the battery and the inverter; measure the current drawn; then time how long he can draw that current before the inverter’s alarm goes off. Multiplying the number of amps drawn by the number of hours of runtime will give him a figure in amp-hours that he can compare to the battery’s nameplate rating. To be kind to his batteries, he should be sizing them such that they can run his camp for about ten hours before going flat. If they discharge in less time than that, he won’t be getting the full capacity they’re capable of. Battery amp-hour ratings are quoted for the 10 hour discharge rate. If you discharge a 50Ah battery at 5 amps, you’ll get your full ten hours; discharge it at 50 amps, and you might get half an hour if you’re lucky. Deep cycle batteries actually lose capacity in response to rapid discharge to a
He responds: Thanks, that’s all useful information! So I guess getting the battery below “60%” may not be realistic after all. Here are some more specifics on my current gear and how I’m using it. I’m willing to upgrade, but likely can’t afford the top of the line options: Battery: “EverStart deep cycle trolling, part: 27DC-C”. Amp Hours: 115; Reserve Capacity: 160. Inverter: Tripp-Lite 500 Watt “PowerVerter” Lights: 10 sets of X-Mas lights, each 0.34 amps running at 120v. I use this setup at camping festivals and am currently gearing up for this years Burning Man. I’d like to be able to keep the lights on at my camp over night without having to run the generator or having the inverter emit that awful high pitched whine. The lighting is just standard strings of x-mas lights, about 30′ long each. I am interested in switching to LED’s but haven’t fully researched viable options yet. I have also tried running a stereo off the inverter and while the equipment would turn on and behave like
Ten sets of 120V xmas lights at 0.34 amps each is 10 * 0.34A * 120V = 408W (watts). Divide that by an assumed inverter efficiency of 90% and we get 450W. Supplying 450W at 12V requires a battery discharge current of 450W / 12V = 38A (amps). Your battery capacity is 115 Ah (amp-hours), and 115 Ah / 38A = 3 hours. This is significantly less than ten hours, which means you won’t actually get the rated 115Ah capacity, which means you should actually expect a bit less than three hours. So, it sounds like your setup is functioning exactly as designed, and you don’t need a better inverter. What you need is more efficiency, and using LED lighting strings running directly off the battery will definitely give you that. LEDs are about ten times as efficient as incandescent lamps; so even allowing for a bit of waste in the LED current limiting circuitry, you should easily be able to achieve 20+ hour runtimes of equivalently bright lights off your present battery. Low voltage DC is much easier to d
