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12v subsystem and DC charging specs

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esteed

OD 10/25, MYP, MSM/Black, no tow, no FSD, DD 12/21
Oct 27, 2021
37
19
Cottage Grove, MN
I’ve searched around and can’t seem to find anything specific to what I’m trying to do. I’m looking for information on the DC charger that keeps the 12 V battery charged up, or more specifically access to the DC charging itself.

i’m looking into using my own lithium battery pack for an ad on subwoofer and amplifier. I have a 4S2P headway lithium pack containing eight 38120 3.2v cells with busbars that I’d be using for my battery. Ideally, so that I don’t tank the primary 12 V battery, I would somehow tap into the DC charging capability to charge my lithium battery separately and have that be the source of power for the sub amp. I’m not planning on going crazy, I would probably target between 1000 to 1500 W for the amp. I’ll be using a battery management system to monitor and control charge.

I know there are third-party add-ons that have options for one or two 8 inch subwoofers that go in the storage holes in the back of the model Y along with an aftermarket amplifier to power them. This would just be a little bit larger scale, I plan on using the extra storage below the floor as an enclosure for the speaker, probably a 12 inch.

For anyone that has done a project like this on the scale, what have you run into as far as performance, affects on battery life, etc?
 
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I do this in my car, but I don't bother tapping the car's electrical system. I simply pull the quick-disconnect (Anderson plugs) on the amp's battery pack and charge them inside the house. I monitor with a simple cigar-lighter voltage meter, and shut off power when I reach 13.2v on my pack (4s26p of Tesla NMC cells).

Since your profile says Minnesota, I would expect you to do the same, since Lithium batteries can't be charged when they drop below 40*F.

My amplifier performs 100% top notch, since the supply voltage never dips. The amp also hasn't complained when my NMC pack is charged up to 80%, 16.1v

I don't know about your Model Y, but my old Model S will only spare an extra 600w of 12v safely, or 1000w dangerously. There's a report of an owner using a 1200w amp and frying his DC-DC converter. He was under warranty but Tesla told him this abuse wasn't covered, and he'd have to pay for the DC-DC converter replacement.

If you do tap into your 12v, you won't notice a difference in your range. Your consumption is around 75% propulsion, 24% HVAC, and less than 1% for all 12v loads combined.
Also, you need to know your model Y has a 15.5v lithium battery, so that's what your low-voltage wires run at all the time. The 12v lead acid battery is long gone.