Lifepo4 for engine off car stereo questions.

whipsley

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Nov 5, 2023
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Minnesota, mn, usa
Okay, this is proobably a very simple question to answer.

I want to run my pounding stereo system for hours with the engine off, but im somewhat unsure of how to wire it.

Alternator is 160 amp (might upgrade to a larger 250amp)

The stereo is made of two amps. 1300watt and 600 watt (might add another 600 watts later))

My plan is to install a 50amp dc-dc charger and a 100ah lifepo4 battery (will be addings another battery later)

Now here is my confusion.

can i connect the power input on the amps to both the battery AND the alternator? (See attached diagram) i want to be able to fully charge the lifepo4 with the full 50 amps while playing music.

In the past, ive done something similar, but i basically just ran the stereo off of a secondary battery, it seemed to work awesome. This time im thinking of doing it a bit different since the system power draw is a bit higher! And im probably going to be needing to power a 250 watt laptop sometime down the line, and maybe some fun blinking lights to get the rave vibe going on.

Also. I dont need the car stereo head unit to be turned on because i have a bluetooth connection on the amp.


Anyway, thanks!
 

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I could tell you but then I would be a hypocrite as I am that old guy that will yell at you to turn that fkn stereo down when you drive in my neighborhood and wake up everyone and disturb the animals and babies.

Hey I was young once and played my music loud (have the tinnitus to prove it) but with age you realize how that loud music damages your hearing and disturbs everyone around you.
 
Higher volumes are for when im speaking in some random desert hot spring in the middle of nowhere.

I have a pretty slick amp that has remote adjustable gain profiles, so the max volume is limited. I dont like my ears ringing. I also dont listen to rock music with its ear bleeding highs.

But like i said, the main need for high volume and length of play with the engine off is for the deserts :) nothing i like better than laying under the stars in the desert soaking in hot water and tossing back drinks for 6 hours at a time :)
 
Im proobably overthinking it, and i dont actually think the stereo will drain much from the charging system enough to slow the charging of the battery.

I think i should just order the dc-dc charger and battery tonight after work.
 
Damn.

I bought a 50 amp dc/dc charger and a 100ah battery with a recommended charge of 20 amps.

Do i have to buy a second battery? Or 3?
 
Have you ever wound everything up to full tilt bogie and put an amp meter on the power leads? Until the load is known everything else is a guess.
 
You don't want to charge the battery at greater than recommended current. Or while battery is below 32F.

You've got about 1200Wh gross. You want to enjoy it while wasted (wasting away?) for 6 hours. That's about 200W average.
As wme said, find out what your current draw is to design the system. Your capacity needs may solve your charge current problem.

20A charge sounds low for a 100 Ah battery (0.2C), but is perfectly fine if you've got 5 hours. You may not have 5 hours of driving, and your alternator may not appreciate being called upon to deliver an extra 600W continuously (amps is one thing, continuous operation may or may not deliver as much. I'm sure your alternator doesn't contain the 2/0 cable we normally use for such current, probably has to run close to 200C with skinny wires). An AC powered charger while at home might be good. Other batteries probably accept 0.5C for a 2 hour charge.

Do you do this in the daytime or the night time? This is DIYSolarforum, after all, not DIYthumpin'baseforum, and we're going to suggest PV panels on your car roof.

1699408446911.png
 
Have you ever wound everything up to full tilt bogie and put an amp meter on the power leads? Until the load is known everything else is a guess.
I have not ever tested its actual power draw, but its highly doubtful that the amps will ever be pushing out the full wattage (lol, i just did the math, the door/dash speakers only accept 500 watts from the 1300 watt amp, max, and the sub is 600 watts max. I went over kill on the 1300watt amp) i doubt the continuous draw at high volume is even half that as i can play it for an hour+ from my agm starter battery.
You don't want to charge the battery at greater than recommended current. Or while battery is below 32F.

Minnesota is starting to get cold, thats for sure, and i need to figure out a heating system as i didnt want to spend a grand on a self heating battery. As for charging, I'm not sure what to do. I have two incompatible devices. Do i buy a new charger or a new battery?
You've got about 1200Wh gross. You want to enjoy it while wasted (wasting away?) for 6 hours. That's about 200W average.
As wme said, find out what your current draw is to design the system. Your capacity needs may solve your charge current problem.

20A charge sounds low for a 100 Ah battery (0.2C), but is perfectly fine if you've got 5 hours. You may not have 5 hours of driving, and your alternator may not appreciate being called upon to deliver an extra 600W continuously (amps is one thing, continuous operation may or may not deliver as much. I'm sure your alternator doesn't contain the 2/0 cable we normally use for such current, probably has to run close to 200C with skinny wires). An AC powered charger while at home might be good. Other batteries probably accept 0.5C for a 2 hour charge.

From the battery to my amplifiers is 0 gauge OFC. Im probably should work on doing the "Big 3" wire upgrade (alternator/battery/ground)

I just noticed the renology 100ah blue tooth battery takes a 50amp charge, open box, its damn near the same price as the power queen battery i just bought. Can i run them in the same circut?

Will reviewed a big 200ah power queen and seemed to say they were decent. The power queen 100ah mini battery was the perfect fit for where i wanted to install it, so i bought it.


And now i just noticed power queen has 50ah batteries that take a 25amp charge. 118/each



The mini i already bought and either two 50ah or a single 100ah from renology all will tetris fit in my available space. More capacity isnt a bad thing. Its never a bad thing to wake up to music still playing :)

Anyway, this shit snowballed into quite an expensive project. :) especially if i need to buy a high output alternator in the next month or two


Anyway, can i charge all of these batteries with the same charger singe the combined max cahrging current will exceed the max charging current of the charger? Does it matter if they are mismatched?
Do you do this in the daytime or the night time? This is DIYSolarforum, after all, not DIYthumpin'baseforum, and we're going to suggest PV panels on your car roof.

day and night. I generally snowbird and fly to the desert south west for the winter

Funny thing about that pic. One of my future purchases will be a solar panel for the hood. And after i build a roof rack, there will be a small 100 watt pa el up there. I was planning on waiting on that because its winter in minnesota, and i dont know if the sun shines up here in the winter. Although, with 200ah of capacity, 200 watts of solar might just be of little use other than a starter battery maintainer with the renology dc-dc/mppt charger.
 

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Well, being reduced to a SWAG it looks like you are looking at 150-200 amps at 12 v from the battery. Look at the BMS ratings
 
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