@destraht You might consider having two inverters on your system; a small pure sine system for your laptop, routers etc; and a large 2000-4000 one to run things like the fridge and tool battery chargers. A bank of parallel deep cycle batteries can handle the motor start current of a fridge just fine, but if you plan to heavily use something like a table saw, plan with marine type batteries.
Also decide upfront if you want to build a 12v system which offers the most variety and price competitiveness. More serious systems are set up as 24 or 48v which halves/quarters the gauge of wire you'll need, and I'm pretty sure the inverters are more energy efficient as well. You can always start with a basic 12v system and upgrade.
Lithium batteries are more expensive and tempremental, and on a stationary system I'm not convinced they're the bigger better deal compared to traditional flooded lead acid. You'll need a purpose built charge controller for lithium too.
You'll want your battery bank in a temperature controlled but ventilated space. Room temperature to say 95f is ideal. Many batteries have a vent nipple so they can be externally ventilated through a tiny tube. Even with this you don't want a hermetically sealed battery space. They generate hydrogen and oxygen during charging especially during overcharge events. I've had to help hold a crying grownup's eyes open to flush the sulfuric acid off his corneas after a battery explosion. It's rare especially with proper precautions but serious when it happens. Nothing compared to a lithium fire though! Elevate them even just on a piece of pallet; never sit them on a cold concrete floor. Temperature extremes greatly affect performance and longevity.Read More
I've read that lead-acid is not good at powering something for many hours at like 50-100W because they're designed for higher loads for just minutes to a half hour.
This is true of standard car batteries, because the design of the plates is optimized for a short large current draw to crank the engine, then to get recharged once the alternator is spinning and recharging the battery while providing all the power to run vehicle systems.
You want deep cycle batteries for an off grid system. These are built with thicker plates that handle longer, deeper discharge cycles between charging.
Marine batteries are a compromise between the two, meant to be capable of cranking an engine while also providing lots of capacity for discharge between engine-on periods, such as fishing or overnighting.
It's down to the plates inside, which repeatedly convert sponge lead to lead sulfate and back. When a standard car battery gets deeply discharged frequently, the plates become "sulfated" to a state where they lose the capacity to accept a charge molecule by molecule. As sulfation progresses, the plates become brittle and eventually pieces flake off and bridge/short the stacked plates, resulting in a "dead cell" thus ending the battery's usefulness.
AGM and Gel Cell batteries are much less forgiving of voltage excursions than traditional flooded lead acid. Avoid these for a stationary home system, there is no advantage for the higher price. Many off gridders seek out used forklift batteries that can be had for scrap prices. They are huge and can work for years for a modest home backup system's needs, long after they've gotten annoyingly weak to continue using in the forkliift.
Lead-acid batteries are rather unforgiving of voltage getting too low during discharge or too high during charging. Luckily, Chinese solar charge controllers are cheap as sand; you can choose a variety of starter versions suitable for a 2-3 panel system for under $20. The one I'm running now even has 2 USB ports that are handy for phone charging.
The so called "Solar Generators" that are popular today make a convenient form factor especially if you want to use it on the go. For a home backup system, a guy like you can do much better choosing and assembling components. Better battery capacity and better output numbers.
The inverter is one of the more costly components of the system. Most generate a "modified sine wave" that is fine for appliances and lights but finer electronics don't appreciate. True Sine inverters cost a lot more for a given capacity. You want to watch quiescent current as well. Cheap inverters have an annoying fan running constantly; better ones like the Vector one I'm running use soft start fans that only run when actually needed. This factor will greatly influence the runtime from a given battery bank.
(to be continued)Read More
@destraht Battery capacity is more imp in backup applications.
This product is advertized with 36Ah at 12V (the standard is to wire batteries in parallel, if its in series then use 48V, i don't know what '4x12V' on the website means).
Assuming 80% DoD, 95% inverter efficiency and 75W avg requirement for your laptop:
Hours = ((36Ah x 12V x 80%) / 75W) x 95% ~ 4hrs 20mins
Do a similar calc for your house. You'll need more batt capacity to power your house. If you're not sure contact the seller.
I don't know if lead acid batteries are bad at constant long discharge. @MentORPHEUS can help here.
@MentORPHEUS It's not an emergency, but I've been wanting to get a serious battery backup system for my house. I've just barely started researching it. There is a link below that you can translate with the built-in feature in Chrome.
I've read that lead-acid is not good at powering something for many hours at like 50-100W because they're designed for higher loads for just minutes to a half hour. Basically I want something that I could run my laptop off of for 5-20 hours, and to maybe even run my fridge for a a short time. Maybe that's fantasy, or not even a big deal. It also could be used to power a 4G cellular modem and router.
Even without anything extra, time is money and so being able to just continue working normally for a day without needing to rush out to a cafe to work could be profitable if done several times. The central power station is reliable here, but my location is not. They seem to test the lines a lot during the day so that we are guaranteed to have power at night when people might need it to survive. They're Russians, which means that they have that serious Siberian culture around survival, even if the weather is quite tame here by comparison (and also much more tame to the harsher parts of the US such as bad parts of North Dakota, Montana, etc).
I'm asking you because you have a lot more experience being off-grid. I can easily waste my money on some big heavy box that doesn't provide me with any real notable luxury, but I'd rather not do so if it's not a good fit.
There are also serious lithium-ion batteries specially made to charge laptops, but they tend to be smaller capacity (due to retarded airplane restrictions around total energy capacity), and they're very expensive. I can't really find them anyways.
My quick research points to it not being so simple as just adding up the total energy. I guess also that you have a lot of experience with lead-acid batteries due to being a mechanic.Read More