I'm curious, why do people use Ah for batteries, given that there's 3 different common server rack battery voltages (12, 24, 48)? Is 12 just assumed for RVing?
You make a good point. They really ought to be sold with Wh prominently displayed. I'm talking about 1200Ah@12V, although in reality there's a good chance that I'll do 600Ah@24V or 300Ah@48V. It's all the same 14.4kWh and will provide the exact same amount of usable power (ignoring some conversion efficiencies).
I'm using Ah because I'm used to talking to people about 12V battery systems, and Ah is the most prominent number when talking about battery capacity (when the voltage is already implied or agreed upon).
You're absolutely right though, and I should have been more clear about it.
Ah makes sense (that 12V is just implied for RVs). I'm used to dealing with 48V, since I'm doing this for a house, and it seems like they specify batteries both ways in that world. I wonder who uses 24V.
I'm also not really sure why one would pick 24V for most applications. 12V makes sense for RVs, boats, etc. because a lot of devices are designed to operate directly off 12V. 48V makes sense for houses and solar installations, if for no other reason than smaller-gauge wires (and is a big reason I'm considering it; 00 gauge wires are enormous and unwieldy). But 24V? You're likely not running much natively off 24V, so you're already going to be doing DC-DC conversion down to 12V. And there's not much cost difference between 24V and 48V inverter systems (and in fact many of them can already handle both voltages).
My first phase DC system, currently in my RV, is a single 12V lead-acid battery, single 100W solar panel, 12VDC->120VAC inverter, a few buck converters for 5V electronics and USB ports, and a bunch of stuff running off 12V (my cell modem/router and my Beelink mini-PC are 12V direct). 12V adapter for Starlink PoE. I'm waffling on getting one or two 280Ah 12V batteries to wire in parallel, or just sticking with my crappy 12V lead-acid battery for the rest of this year and getting multiple 48V LiFePO4 when I do the full solar build-out next year.
You're not supposed to mix-and-match battery brands, manufacturing dates, time in use, etc. because if there's too much of a mismatch, they'll all degrade faster (so I've read). This is what's preventing me from incrementally building up a 12V battery bank by adding another 280Ah every few months. Instead I'm planning to milk what I have as long as possible, pick a voltage, and buy a whole bank of batteries and solar panels all at once.
Yeah, even with 48V, we're still rocking parallel 4/0 copper, it's still a lot of amperage to try to supply 15 kw at 48V. They are heavy. The ones we got from WindyNation were surprisingly flexible, though, which has made them a lot easier to work with.
Amp hours are what the batteries are specified in, right down to cells that are 1.5V, 2V, 3.9V etc.. Yes, once they're in system you want to know kWh capacity of the system as a whole, but it makes sense that people think of what's written on the batteries first.
caymanjim knows his units, but the general public is so ignorant that it's common to hear people confusing a 1200-amp-hour battery with a 1200-(cold-cranking-)amp battery. even people who built a multi-voltage electrical system for their rv. the struggle is real
