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[2020-05-07 05:07:19] <guru3> The limiting factor for how much your battery can handle isn't so much the capacity in amp-hours, but it's discharge current.
[2020-05-07 05:08:26] <guru3> If your batteries are 33Ah in capacity and have a 1C discharge current, they will supply at most 33A of current, which at 12V gives you 396W for one hour.
[2020-05-07 05:09:05] <guru3> 12 batteries would then give you your 4000W for one hour.
[2020-05-07 05:09:58] <guru3> But discharge current depends on the battery chemistry. Lithium-Polymer (LiPo) batteries tend to have insanely high discharge currents, around 30C. That, and their light weight, are why they're so popular with drones, RC cars, etc.
[2020-05-07 05:11:27] <guru3> So the upshot is you may need more batteries unless "33AH at 10 hours" was a typo, and you meant 33A at 10 hours, for a 330Ah battery capacity.
[2020-05-07 05:11:56] <guru3> But if you're not drawing peak current from each battery, then of course they will last longer.
[2020-05-07 05:12:32] <guru3> Another factor to consider is that the more current you draw from a battery, the more internal resistance (which is why most battery chemistries don't discharge faster than 1C), and so they heat up more reducing the life of the battery.
[2020-05-07 05:13:06] <guru3> Discharging from 10 batteries at 0.2C is much better than discharging from 5 batteries at 1C, because you're spreading out that internal resistance and heat generation.
[2020-05-07 05:13:40] <guru3> The point I was getting to mentioning the heat generation is that your batteries may need cooling when charging or discharging rapidly.
[2020-05-07 05:14:24] <guru3> You should also be aware of the risks of over-charging batteries. LiPos tend to explode I believe, NiMh outgasses hydrogren (which is explosive!) and I think Lead Acid batteries outgas something equally nasty.
[2020-05-07 05:15:30] <guru3> With regards to charging the batteries, seperating them from the circuit while charging is pretty much mandatory, and you'll need to manage the levels of the batteries to some extent otherwise you're increasing the chances of blowing up your diodes as they overheat from holding back the power.
[2020-05-07 05:16:22] <guru3> Lead Acid and NiMh batteries can be "dumb" charged at a constant current until their voltages raise, but any Lithium derived battery will need to have a charging circuit to control current to the battery.
[2020-05-07 05:17:32] <guru3> Going along with all this high power stuff, make sure your wire gauges are all big enough for more than the peak current. The gauge will need to be bigger as length of the wire run increases. (Hurray another type of internal resistance!)
[2020-05-07 05:19:00] <guru3> And in a scenario like this I'd guess that all of the electrical switching will need to be relay based, which will add in delays.
[2020-05-07 05:19:15] <guru3> I'd be super wary of high current through anything solid state.
[2020-05-07 18:27:59] <Lucifer_arma> I'm on it. As for cooling, the battery bay is an open-air bay, but there's no fan. It was designed to take two 8D batteries, and being built in 1987, those were flooded lead acid batteries.
[2020-05-07 18:28:55] <Lucifer_arma> I'm putting AGM lead acid batteries in there, which have lower discharge capacity (current), but longer total discharge time. The 33Ah @ 10 hours is basically the same as any other Ah statement on batteries, just that the @ 10 hours is added because industry standard is @ 20 hours
[2020-05-07 18:29:29] <Lucifer_arma> so for a battery that simply says something like 10Ah, or 1000mAh, that's @ 20 hours if it's not otherwise stated
[2020-05-07 18:30:13] <Lucifer_arma> the rule of thumb, near as I can tell, is that it means "can draw [these] amps for [this long]" and then it's 100% discharged.
[2020-05-07 18:31:05] <Lucifer_arma> Lead Acid batteries outgas hydrogen when charging. At least, the flooded cell batteries used in cars do, but I think it's safe to assume AGM batteries outgas hydrogen as well
[2020-05-07 18:31:43] <Lucifer_arma> For overdischarge protection, I've got this:
[2020-05-07 18:32:16] <Lucifer_arma> https://www.amazon.com/gp/product/B07N4HJCD5/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&psc=1
[2020-05-07 18:33:08] <Lucifer_arma> the load I'll be connecting it to is a 20amp standard automotive relay, normally off. That relay, in turn, is what'll allow the flow from the battery into the power system
[2020-05-07 18:34:03] <Lucifer_arma> These are the diodes:
[2020-05-07 18:34:05] <Lucifer_arma> https://www.amazon.com/gp/product/B07NS63XJH/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
[2020-05-07 18:35:10] <Lucifer_arma> For now, without a charging controller, I'll probably just hook up a few diodes per battery in parallel and let the system flood charge, like it was designed to do
[2020-05-07 18:35:18] <Lucifer_arma> you know, being from 1987 and all
[2020-05-07 18:36:22] <Lucifer_arma> the car battery I'll be adding to the system is already designed that way, and I won't be putting the overdischarge protection stuff on it because it's designed for this kind of use cycle, sorta
[2020-05-07 18:38:15] <Lucifer_arma> the battery bay connects to the power system with giant cables, like 0/2 gauge or something like that, so my wires won't be going longer than one or two feet
[2020-05-07 18:39:02] <Lucifer_arma> I think I settled at 16 gauge, or something. I looked for 15amp capacity and rounded up to 20amp. If I need more, I'll either buy bigger gauge wires or wire more of these in parallel
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