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DIY bluetooth speaker

I got news, i succesfuly connected batteries and BMS and nothing exploded so far :D BMS seems to be working because until i connected all those control wires, it only gave me 2V on output pins. Once i connected all wires it gave me a clean 20V. I charged batteries manual to different voltage, 3 of them were around 4.15V, 2 of them were 3.9V. This way to test if BMS will work. But it seems it didnt have to. Charger refuses to charge, it starts and stops. I am guessing that it detects 20V and stops. Or maybe BMS detects 1 of batteries is 4.15V and stops, i dont know. I am discharging all batteries to under 4V now and will test again. I dont mind if it stops charging at 4.1V, i know i lose some capacity but i will include plenty of batteries, 5s2p or even 5s3p if i need to. Whats important to me is that nothing explodes and that speakers are loud :)
 

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audioguru

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Maybe the cheap Chinese BMS is not designed to do what you think it should do, or maybe it is defective.
Are the connections described clearly in the installations manual?
 
Nope i am pretty sure its the charger. I simply think it charges until 20V are reached (i read in some other chargers description that it charges to 90-95% and then charges very slowly). I know that i lose some capacity but on the other hand, its less likely that something will blow since batteries are very close together as far as capacity goes and it never goes to high. Now i just have to figure out a way to charge all batteries to the same capacity.
 

audioguru

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I looked in about 100 replies and could not find your "charger" in this thread. It seems that everything used is Cheap and Chinese.
 
Ofcourse everything is cheap and chinese, that is the first rule of my project, cheap. Otherwise i would just buy JBL extreme for a million dollars. The point is to do it as cheap as possible and as loud as possible, i am pretty sure i said that many times :)

This is the charger, though i am not sure whether i belive it to be charger or a simple 21V DC. It does stop charging as we proved though so i guess it has some kind of brain:

 

audioguru

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The JBL speaker sells tor $200 because they do not make a lot of them and they like to get lots of profit. Some people like them because they sound good.
Your cheapo speaker will probably sound awful, but some frequencies will be loud. It probably will not last long.

The 1A power supply that is wrongly called a lithium battery charger is used to charge an 18650 cells lithium battery that has a protection circuit that balances the charging. Nobody knows if the power supply turns off when it detects its rated voltage when the lithium battery is only 60% fully charged, or when the charging current drops when it is fully charged. Four 3000mAh cells paralleled will be fully charged in 12 hours.
Maybe your cheap BMS did not balance the charging properly.
 
Well i connected it together to test it and i am amazed. I only tested 1 channel with 2 4 ohm speakers in series and this thing is looud. Only running at 20V mind you, didnt connect step up, and this speakers are some cheap thing. This thing will be awesome. I am getting some other speakers today, 8 ohm i think and i will decide whether to run 2 8 ohm speakers or 4 4 ohm speakers. Currently i am leaning towards 4 speakers because well, i just love how they look.
 

audioguru

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4 speakers need an enclosure twice the volume of an enclosure for 2 speakers, if the speakers are the same size and you want the same kind of sound.
If the enclosure is too small then the bass will be less and upper bass sounds will be boomy like a bongo drum. Speakers in series also sound boomy because the high impedance at resonance blocks the resonance damping from the extremely low impedance of an amplifier's output.

Good sounding little speakers use a "passive radiator" to replace a port hole.

Is the amplifier IC a TDA7492? Then at low distortion its produces 17 Watts into 8 ohms per channel with a 20V supply. Full blast it produces 68 Whats total. Sure that is loud (at a few frequencies).
 
I am speaking about TDA7492 yes. Audioguru, in your words i can sense that you do not support what i am doing, cheap parts from ebay and so on. But still i am grateful for your help with it, you obviously know a lot more than me about this. Hang in there with me :)

Here is a video of me testing. Suplying 20V, using only 1 channel, using 2 4 ohm speakers in series, mind you cheap speakers i got for 5 euros for a pair second handed, the guy said they are 30W but god knows how much they are. Here is the video of me testing it.


Also on a side note ... i wanted to convert my nicd cordless drill to lithium with laptop batteries, i wanted to make 4S3P, that would mean about 3-4A from each battery. But i decided against it since i found 4 20A 2500mAh real tested batteries and i will use those and just sell the 12 laptop batteries to cover the charges. See, even i can be pragmatic sometimes :p
 

audioguru

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Speakers without an enclosure are useless. Much of the sound from the rear of the cone comes around and cancels sounds from the front. Also, the enclosure type (sealed or ported) and volume should match the detailed spec's of the speaker.
Speakers in series should play the same but only one of your speakers was moving a lot.
Those speakers are tiny woofers that play upper bass and mid-range sounds. They need an additional tweeter to play high audio frequencies and an additional real woofer to play low frequencies. A crossover network is also needed.

I think you had the volume turned up too high so the amplifier was producing clipping distortion. Maybe the speakers were smashing their voice coils against the magnet structures since they had no enclosure.
 
Oh i have another question. I will be using a stepup to get from 20V to 25V. This stepup has a screw which sets how much voltage it is outputing. How wrong would it be to use that stepup as a volume button ? Since this amp doesnt have a volume button and when someone connects and he has accidently set mobile phone volume at maximum, it would be very akward for the first few seconds, this thing is loud.
 

audioguru

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If you change the power supply voltage for the audio amplifier then the volume will not change. Only the maximum volume where severe clipping distortion will change only if you change the real volume control.
The TDA7492 produces an output of about 18W into 8 ohms where clipping begins with a supply of 20V and produces an output of about 29W where clipping begins with a supply of 25V. The difference of the point where clipping distortion occurs is a very small change in loudness that you might not notice. EDIT: You will notice the smoke since the amplifier will produce more power than it is made for.

You never posted a link to the Chinese amplifier so we can see how big is its heatsink and its maximum voltage and power ratings. The REAL TDA7492 datasheet shows about 40W into 4 ohms per channel when the supply is 22V and the IC has a good heatsink. With a 4 ohm load then the value of the parts in the output filters must be changed. I assume that the Chinese amplifier uses parts values for 8 ohm speakers.
 
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audioguru

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Why is 1 of the speakers moving more then the other ?
Because one of them is defective. It is probably the one that does not move much that has its suspension too tight or is stuck. The one that moves a lot might have its suspension broken.
 
This is the link to the amplifier:


If needed i can add heatsinks but need to know to which parts. Anyway if i have two 4 ohm speakers in series per channel that is 8 ohm per channel. Will it be ok if i run that at 25V as is stated ?
 

audioguru

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I knew something Chinesey is wrong. The TDA7492P is obsolete and is not made anymore.
Digikey says it is obsolete and they do not have any.
ST Micro says it is an obsolete item.

BUT Digikey has many TDA7492 ICs with different ending letters.
The Rev 6 TDA7492 datasheet is the latest and has no ending letters. The datasheet talks about a heatsink ON THE BOTTOM of the IC that the Chinese amplifier does not have. The graph for output power into 8 ohms shows a max supply of only 20V.

Does China make their own copy of an old design of the TDA7492 that becomes defective when powered with 25V and ST Micro changed the design to work good with a 20V supply? Who knows!
 

audioguru

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Digikey.com also has the datasheet but today I went to ST Micro.com and entered TDA7492. The sales page is here:
Today it says the TDA7492P is active but yesterday it said it is an obsolete item.

It says the output is 25W per channel with horrible clipping distortion into 8 ohms when the supply is 25V.

Click on or download the Rev 6 datasheet. The graph on page 13 for 8 ohm speakers stops at a supply of 20V and shows output powers with 10% and at 1% clipping distortions. If you turn down the level to 21W per channel then the datasheet shows 1% clipping distortion. If you turn down the level more then at about 18W per channel you will not hear any distortion.

This new Rev 6 datasheet says it does not need a datasheet but the Rev 5 datasheet said 40W + 40W at THD=10% with Rl= 8 ohms with a 25V supply then a heatsink is required. This new Rev 6 datasheet does not show graphs for 4 ohm speakers anymore that were on the old Rev 5 datasheet.
 
I succesfuly assembled the speaker and am happy with its loudness. Obviously, the very low frequency response isnt that great since the box is way to small for the amount of speakers, but total cost of it is between 10-12€. I would call that a success. Video will follow shortly, if my mobile phones camera decides to work
 

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