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Batterypack for speakersystem!
#1
Music 
Hi! My name is Nicolai from Denmark. First thread from me wuhu!

Pre-story

I've build 12v speakersystems using heavy truck-batteries. Sometimes multiple batteries. You can see my greatest creation here (Scroll down to see final product). This speaker weights like 0,7 tonnes.

Situation

Now I'm going to uni, which is far away from home. I'll be living in a VERY small apartment, but I'm not willing to let go of LOUD speakersystems haha. Thus I'm building a system running on light 18650 batteries. My SURE 2x300w amplifier will work up to 52v. Unfortunately the very common 13s pack that is rated 48v goes up to 54,6V. So I'm going for a 12s solution instead. Choice of BMS

So the pack will be 12s3p -> up to 50,4V with 10,5Ah.  Cool

Questions and doubts

1. Hopefully I can get a hold of a spot-welder. If not - I'll use plastic holders instead. A 18650-cell-lover on youtube have tested them and they can do 4a constant per battery. I'll do 12a peak, so 4a per battery (Remember music is dynamic). If I can get a hold of a spot-welder, i'll use plastic spacers. What do you think of this solution?

2. Is there anything in this setup, which is just plane stupid. I am new to designing such battery, so it wouldn't be a surprise if it was

3. Can you find a good priced charger for a 12s setup. I can find one for a 13s setup, and if that will work on the 12s, then I'll just go with them. REMEMBER: This is not the BMS. The BMS will be for a 12s pack.

Ekstra thoughts:

Funny thought: It's surprising how easy it is to add another parallel layer. And how cheap it is. Right now it'll increase my battery capacity by 33%. If I'm crazy enough I'll increase the parallel number by one or two. It's not gonna increase weight by much. And the BMS is already in place Big Grin

NOTE: If you want to read a bit about the designing-proces:
PART 1
PART 2
FINAL - w/o battery and amp box.

Thanks in advance. And sweet forum you've got here!  Big Grin
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#2
Wow that's a nice setup you got there!
I would recommend going with the LiFePO4 cells because they can handle a much higher amp draw, since you'll be using them for sound systems that is what you probably want to go after

Even though those holders can handle 4 amps, it can't sustain it for a prolonged period of time. The tabs that goes to the circuit board will heat up enough to actually start to melt the plastic.
Running the amp off those cells in a 3P configuration will not give you enough continuous amps to be able to power the amp for very long. The cells will begin to overheat and/or will shorten their life drastically. I would recommend going with at least a 6P configuration.
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#3
(09-14-2018, 01:29 PM)Korishan Wrote: Even though those holders can handle 4 amps, it can't sustain it for a prolonged period of time. The tabs that goes to the circuit board will heat up enough to actually start to melt the plastic.
Running the amp off those cells in a 3P configuration will not give you enough continuous amps to be able to power the amp for very long. The cells will begin to overheat and/or will shorten their life drastically. I would recommend going with at least a 6P configuration.

Thanks for taking your time to give feedback on my project. I actually think I'll end up buying a spot-welder anyway, if I can't access one.

Now the batteries I have linked to can handle constant draw of up to 10A. And if my peak draw is 4A and average is actually 0,5-1A, then I'll be more than fine! (This is estimates, but since I've build speakers like this for some time, they're not far off)
[Image: Cello_Song_Soundwave_Print__74740.148933...00.jpg?c=2]
When looking at the picture above. Imagine that black is power-draw. Only when the speaker is cranked to 100% (Which is next to never) will the sub draw perhaps 240w and the tops 150w during peaks. How often are these peaks? Those tiny black lines that stick out from the rest are peaks. And power-draw is logarithmic, so the middle is actually far less power-consuming than the peaks. 

According to my more in-depth speculations, and not just what the amp-specifications says. Peak-draw will be: 400w/44v = 9a. 9a / 3 = 3a peaks pr. battery.
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#4
Ok, kewls. Just as long as you're aware of the ratings Wink

Out of the listed bms you chose, expect 30A to be the more accurate rating. But if 4A is about the max, you should be fine.

The charger and the bms must match on their series. So if the charger is for 13s, the bms needs to be as well. Otherwise you'll have issues.
That charger for the 13s is assuming you charge to 4.2V/cell. If you use 14s, then that'd be 3.9V. This will increase the life span of the cells drastically, by well over 1000 cycles.

Ok, re-read your post. 52V being the max, this makes things a little more difficult. I believe you can use a buck converter that would allow you to use 57V pack (14s) and still have 4A available to you.
There was a pretty powerful buck converter I saw on here the other day. Don't recall who posted it, tho.
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Dollar Shave Club. Best Razor I've ever used
Certified 18650 Cell Reclamation Technician
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#5
(09-14-2018, 08:52 PM)Korishan Wrote: Ok, kewls.  Just as long as you're aware of the ratings  Wink

Out of the listed bms you chose, expect 30A to be the more accurate rating. But if 4A is about the max, you should be fine.

The charger and the bms must match on their series. So if the charger is for 13s, the bms needs to be as well. Otherwise you'll have issues.
That charger for the 13s is assuming you charge to 4.2V/cell. If you use 14s, then that'd be 3.9V. This will increase the life span of the cells drastically, by well over 1000 cycles.

Ok, re-read your post. 52V being the max, this makes things a little more difficult. I believe you can use a buck converter that would allow you to use 57V pack (14s) and still have 4A available to you.
There was a pretty powerful buck converter I saw on here the other day. Don't recall who posted it, tho.

So you’re suggesting using a higher voltage and then a step-down, to make sure I don’t exceed the max-voltage of my amp?

What charging voltage is needed per cell? Does it exceed 4,2V per cell? That would make me unable to play and charge at the same time Sad
In 50 years when oil runs out. This forum will explode
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#6
You use a charger that can go to about 58V, this will make each 14s 4.14V max. If you use a standard lead acid charger for 48V, it can top out at around 56.4V (14.1V per "12V" battery)

So, you'd have:
Charger -> Battery -> Buck Converter -> Amp

Or, another way to look at it is:
Code:
.       / -  Charger
.Battery
.       \ -  Buck Converter -> Amp

You'll be able to charge the battery while using the buck converter. As long as the charger outputs more amps than what the Amp/Buck are consuming, that is.
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Dollar Shave Club. Best Razor I've ever used
Certified 18650 Cell Reclamation Technician
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#7
(09-14-2018, 11:42 PM)Korishan Wrote: You use a charger that can go to about 58V, this will make each 14s 4.14V max.  If you use a standard lead acid charger for 48V, it can top out at around 56.4V (14.1V per "12V" battery)

So, you'd have:
Charger -> Battery -> Buck Converter -> Amp

Or, another way to look at it is:
Code:
.       / -  Charger
.Battery
.       \ -  Buck Converter -> Amp

You'll be able to charge the battery while using the buck converter. As long as the charger outputs more amps than what the Amp/Buck are consuming, that is.

Now - Would this be necessary if I get a 12s3p battery? I actually found a charger for a 12s setup. It’s only 2a, but that’s just fine for me

And the amp will still do lots of watt for the speakers with a voltage of 44V. More than enough. And I don’t want any of unnecessary processes that lower efficiency.
In 50 years when oil runs out. This forum will explode
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#8
Yeah, as long as everything fits good, then go with it. The higher series will just get you longer jamming time Wink
But so will higher parallel count too
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Dollar Shave Club. Best Razor I've ever used
Certified 18650 Cell Reclamation Technician
Reply
#9
(09-15-2018, 03:22 PM)Korishan Wrote: Yeah, as long as everything fits good,  then go with it. The higher series will just get you longer jamming time Wink
But so will higher parallel count too
Thanks for your interest in the project!

I think 12s3p will give me a VERY good battery for the time that the speaker will be "in the field". The battery will give me atleast 10hrs play-time when max'ed out.

To compare.
A soundboks has a 99kWh battery. Uses 3x 72w amp. Totals about 215w. They claim a 8hrs play-time at full volume. Though that is probably more like 6hrs. (Because real-life parties plays more bass-music than during their testing-methods). So...

99Wh battery / 215 amp effect = 6hrs.

The correlation between battery life, play hrs and amp effect is:

Battery Wh / (Amp effect * 0.077).

In my example: 600 / (600 * 0.077) = 13hrs playtime.

The example above is very estimating since several parametres will have an impact on the outcome. Most dominant: Music genre and actual amp-output.

Maybe I'll come up with a way of having interchangable battery-modules. This way I can do some battery-harvesting like I've seen you do on this forum. The BMS is not that expensive after all. Then I'll build perhaps 3x 12s3p batteries.
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#10
Grymer, it sounds like you can use the Headway 38120 cells instead.

Google it, like you have this community here that mainly specialises in powerwalls, there's also a community that's into audio.
Mostly for car audio but since you want to work with battery it's the same.

The Headways are even Lifepo4 cells as Korishan suggested.

Nice project anyway.
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