this post was submitted on 18 Mar 2024
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A car battery shouldn't be discharged at all. They are meant to supply a short burst of power and then be charged back up again.
A deep cycle lead acid battery can be used to run an inverter. They can be discharged to 50% capacity while still providing hundreds of cycles. If they are used for a backup and are not cycled frequently, they can be discharged to around 80%, but they will provide a lot less cycles.
A LiFePO4 battery is definitely the better choice for anything that needs to be cycled frequently though.
Just wire the inverter to your car battery and run the engine. Hard on gas compared to a 3500 watt generator, but you already have the car, inverters a few hundred bucks, and the genny would be at least 2500 dollars
An alternator can't output full power when the engine is idling. You may only get a few hundred watts before the battery starts draining. You can get a generator that will produce much more power than a typical car alternator for under $400.
You're speaking like an alternator is a generator, and doesn't come in various outputs. Your average larger vehicle can charge itself from near-dead at idle or run a 3500 watt inverter, although I have had the odd small car or motorcycle incapable of either.
Sure but in an emergency? They can handle being discharged as long as you don't go too far.
So if I turn the car battery upside down, a 12v DC battery should run a 120v AC appliance?? Brilliant! I have an idea for how we can use this with two fans to create infinite energy!
It will never beat my idea to strap a buttered piece of toast to a cat and make antigravity.
An inverter will not let you run your fridge until the battery is "dead". It's going to have a low voltage cut off, likely somewhere around 11 Volts, specifically to avoid damaging batteries by fully discharging them.
How many hours you'll get from the battery mostly depends on your ambient air temperature and how often you open the fridge. They don't use that much power when they're idle - my fridge averages at about 90 watts (I'm not running off grid, but I do have rooftop solar and our system produces pretty charts showing consumption). A large car battery can sustain 90 watts for a quite long time - well over 2 hours. Probably closer to 10.
Running a fridge off a car battery long term is a bad idea. But in an emergency? Sure I'd totally do that - especially if your "emergency" is genuine such as needing to keep your medication cold. Just don't open the fridge unless you're taking your medication.
Sure. Way better than lead acid. But that doesn't mean lead acid is useless. When I lived off grid, LifePo4 didn't exist and we got close ten years (of daily use) out of our lead acid batteries. They were bigger than car batteries and also deep cycle ones, but in an emergency a car battery would be a fine choice if it's the best one you have.
At 11V you are already damaging most lead acid batteries, especially starter batteries.
If you only do it a few times it will probably take it, but not much more than that.
I'll need a source for that claim buddy
Actually when I lived off grid for 80 years, we used 7 AAA batteries on a rotation and recharged them by rubbing them on our wool sweaters, so those guys are totally right.
Wait, so you are saying you have either lived continuously on a 29ft boat for 5 years, or only have visited land by dinghy or something while its anchored?
Wild. That's got to be a nasty looking hull though.
I've also done the off grid thing and you can get way more than 2 hours on a car battery if the fridge is already cold and you aren't constantly opening the door. Also have ran modem full sized fridges on 1000w inverters. So YMMV.
I run a fridge freezer off a Delta Pro and 600w of solar during the summer. If we get a few days spell of bad weather I have to place it back on mains. Its good to have in an emergency, though it cost me 3 months wages (plus overtime)