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Class D Switching Power Amplifiers and Power D/A conversion

Does my system design look right?
Does my system design look right?
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Old 30th November 2017, 01:39 PM   #1
jackstraw is offline jackstraw  United States
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Join Date: Jun 2016
Default Does my system design look right?

Hi guys. I used to make these little novelty beer keg amps using the old LM386 chip:

Click the image to open in full size.

I'm wanting to make a new and improved 12v version that uses a class D amp, is bluetooth capable, and uses lithium-ion technology. I'm also planning to put a 12v output port where the beer spout used to be, as seen in the picture. Even with my past experience, i would consider myself a newbie to this stuff. Would you guys mind looking over my plan to see if my logic is correct and that i'm not missing something important?

Click the image to open in full size.

The components i'm using:
Notes & Questions:
  • The charging board doesn't have a place to connect any LED charging status indicators. I'm planning to use THIS cigarette lighter insert to monitor battery voltage, and provide a phone charging port for emergency use. I plan to remove it when not needed to extend battery life.
  • Per the seller of the BMS, I should be able to charge and use the amp at the same time by connecting everything to the charge/discharge (P+ & P-) location on the BMS. Any current not used by the load will go to charging the batteries.
  • I'm combining the left and right channels coming out of the bluetooth module to go from stereo to mono. Do i need to put 1k resistors on the left and right channels before i combine them? In the past i never did that and it worked fine, but i seem to remember someone telling me that it should be done.
  • The input/output places on the boards in my drawing may not be technically in the same spots on the actual board. I just did that to make the drawing easier and less confusing to look at.
  • Did i wire that pot correctly? I got the 10k-50k values from someone here on this forum, so i'm hoping that is correct. Also, should i be using a logarithmic pot, or does it really matter?

Thanks for your time and advice!

Last edited by jackstraw; 30th November 2017 at 01:46 PM.
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Old 30th November 2017, 01:48 PM   #2
Sma1033 is offline Sma1033
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Join Date: Nov 2009
maybe you should check if your BT module can work under full battery operation voltage.

3 cell Lion bats pack. voltage can vary from 9.6V to 12.6V.
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Old 30th November 2017, 01:58 PM   #3
jackstraw is offline jackstraw  United States
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Join Date: Jun 2016
Quote:
Originally Posted by Sma1033 View Post
maybe you should check if your BT module can work under full battery operation voltage.

3 cell Lion bats pack. voltage can vary from 9.6V to 12.6V.
Good point, thanks for that! The listing shows a typical voltage of 12v, but doesn't have a value in the min/max columns. I've emailed the seller to see if he/she knows. The voltage could be as high as 13v when plugged in for charging. If it needs to be exactly 12v, then i'll need to figure out how to make an efficient 12v regulator, or where to buy one.

EDIT: I got my hands on the info sheet. It's all in Chinese but i was able to use an image translator to get the information. The translation is a bit dodgy, but it looks like it can take a wide range, from 6v-42v.

Last edited by jackstraw; 30th November 2017 at 02:04 PM.
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Old 30th November 2017, 02:04 PM   #4
Sma1033 is offline Sma1033
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Join Date: Nov 2009
I believe your 3S 25A Rated Li-ION BMS. module is overrated for your usage.

you are going to use 6x 18650 lion battery in 3s2p config. ?
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Old 30th November 2017, 02:08 PM   #5
jackstraw is offline jackstraw  United States
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Join Date: Jun 2016
Yes, that's my plan. Maybe 3S to start, and then increase to 3S2P if i don't like the battery life. I did realize that 25A was way more than i should need, but didn't think that was a problem. Is there a down-side to using a BMS rated so much higher than what i actually need?
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Old 30th November 2017, 02:14 PM   #6
Sma1033 is offline Sma1033
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Join Date: Nov 2009
Quote:
Originally Posted by jackstraw View Post
Yes, that's my plan. Maybe 3S to start, and then increase to 3S2P if i don't like the battery life. I did realize that 25A was way more than i should need, but didn't think that was a problem. Is there a down-side to using a BMS rated so much higher than what i actually need?
Using overrated BMS module may cause over current shutdown protection not able to work. I'm not sure if you think it's fine for your design.
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Old 30th November 2017, 02:35 PM   #7
jackstraw is offline jackstraw  United States
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Join Date: Jun 2016
Quote:
Originally Posted by Sma1033 View Post
Using overrated BMS module may cause over current shutdown protection not able to work. I'm not sure if you think it's fine for your design.
I'm not sure at all... i'm a totally new to li-ion batteries. I've been doing a lot of research online, but i have zero experience. I'll try to research this potential problem now and see what i come up with. Thanks for the heads-up!
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Old 5th December 2017, 09:56 PM   #8
FauxFrench is offline FauxFrench  France
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Join Date: Dec 2017
Your potentiometer connection is no good, but you should know by now.
TPA3118 volume control

I'm pretty sure that you show a well known TPA3118 board but the terminals (input/output/power) are not as you show.
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Old 5th December 2017, 10:27 PM   #9
jackstraw is offline jackstraw  United States
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Join Date: Jun 2016
FauxFench, thanks. Yes, i mentioned that in my original post.. i labeled them in the image the way i did just to make it look less confusing. Actual wiring will use the correct terminals. Thanks for the pot confirmation in my other thread. I appreciate it!
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