DIY bluetooth speaker

[audioguru]

The BMS is very cheap, is Chinese and is no-name-brand. Its spec's are dangerous because it appears that they do not know anything about a BMS.
In addition to its very high 15A charging current, I forgot to say that its 15A, 25A or 30A of discharge current is way too high, its 4.33V of over-charging voltage is too high and its 2.47V of over-discharge voltage is too low.

Since the power supply has a max or typical current of 1A then it might blow up or catch on fire before the battery blows up.

 

[SentinelAeon]

Well i will have to carefuly test this to make sure it doesnt draw more amps than it is safe.
I have another question. This amplifier as we saw works best at 25V. My batteries will suply between 21 and 25V (6S). Would it be possible to use a step up to always suply 25V ? Would it make sense to do this ? Is it possible ?

 

[Nigel Goodwin]

Well i will have to carefuly test this to make sure it doesnt draw more amps than it is safe.
I have another question. This amplifier as we saw works best at 25V. My batteries will suply between 21 and 25V (6S). Would it be possible to use a step up to always suply 25V ? Would it make sense to do this ? Is it possible ?

It's certainly possible, but why you think you would need to do it?.

 

[SentinelAeon]

Well looking at the graph, it is clear that you get the most out of bluetooth speaker at 25V, and basicly that is all that i care about, speaker being as loud as possible. And there is some loudness difference between 25V and 21V

 

[Nigel Goodwin]

Well looking at the graph, it is clear that you get the most out of bluetooth speaker at 25V, and basicly that is all that i care about, speaker being as loud as possible. And there is some loudness difference between 25V and 21V

Yes but not much - and if you're wanting as 'loud as possible' perhaps you shouldn't be looking at BlueTooth speakers

 

[SentinelAeon]

Well i need something to take out and use batteries, need it to be compact, etc.

Btw i did some testing of my old nicd drill. I charge its batteries, short them out and get 4A. This is insanely weak, i dont know how this drill even works, and it does, pretty well for its age. Anyway i think i should have no problems using 4s3p or even 4s2p chargin it, since shorting laptop battery cells gives me 5A. Which means 2 paralel gives me 10A which means it will work much better then existing drill battery.

Btw, u said that BMS overcharge is at about 15-20 amps. Well that is a big problem since it will burn out liion charger if connected. Is there some safe way to test it before i use it ? Maybe use some resistor before connecting and checking how much amps this BMS takes when charging ?

 

[audioguru]

A burnt battery or burnt power supply is why I said to use a lithium balanced battery charger, not that cheap BMS that has many things wrong with it.

A graph on the datasheet of the TDA7492 amplifier shows that with a fully charged 6 series cells battery (25.2V), the output power into an 8 ohm speaker with fairly low distortion is 26W. When the battery voltage drops to half charge (22.2V) then the power is 21W. You will not hear that very small change in power. Half the power sounds only a little less loud.

You do not short a battery to measure its current, instead you load it. If the output of both channels are producing 26W into 8 ohms then the RMS current from each channel is 1.77A so the battery current will be 3.9A for that loud moment. A used laptop battery might not be able to do it. The power will depend on the health of the battery.

Did you see what you get when you buy cheap Chinese 18650 battery cells from ebay? Look at this video:

 

[SentinelAeon]

Good thing i didnt order 18650 from ebay, instead i got them out of old laptop batteries. 3.9A sounds ok, since i will use at least 2 in parallel so thats 2A per cell, i might even go for 3 parallel if i feel like i need more capacity.

 

[SentinelAeon]

Btw i did infact order some batteries from ebay, its 1200mAh 1.2V AAA nimh batteries. And well, i ordered 8 of them, from 2 different supliers and so far all of them are giving me about 200mAh capacity. It is good enough for what i need them (tv remote and remote keyboard) but i am just curious, is it possible that my batteries have a smaller battery in them ? I just wanna pry open 1 of them

 

[Nigel Goodwin]

It's a BAD idea using rechargeable batteries in remote controls, as they start off pretty flat anyway as they are only 1.2V instead of 1.5V - so need charging up much more often that alkalines would need replacing.

 

[SentinelAeon]

Hmm, why is it a bad idea ? Remote seems to be working and rechargable batteries are so cheap, u save some money on replacing them.

I have 2 more questions:

1) i have a litokala 500 charger. I wanna implement thermal protection to protect batteries from overheating. It can charge 4 batteries at once. I was thinking of connecting grounds of this charger to a thermal fuse. Will connecting all 4 ground pins together hinder the charging or can i do it ?

2) I was testing some batteries to figure out how much amps they can pump out. NiCd from drill pump out 4A when shorted, liion from laptops pump out 5A when shorted (i know, not the way to test it, but its quick). But i have a question i cannot explain. When i put 2 nicd batteries in series, i get 2.4V, which is ok, but the current i was expecting is 4A. Instead, it gave me over 6A. In series, voltage is summed and amps should be the same ? What am i missing here ? IT also explains why drill works at all. 4A is not enough for it to work as well as it does. So whats up with this magic, 1 battery 4A, 2 batteries in series over 6A ?

 

[Nigel Goodwin]

Hmm, why is it a bad idea ? Remote seems to be working and rechargable batteries are so cheap, u save some money on replacing them.

Because they need recharging VERY frequently, and are essentially flat when you put them in. The correct alkaline batteries should last a few years before needing replacement.

 

[unclejed613]

Well looking at the graph, it is clear that you get the most out of bluetooth speaker at 25V, and basicly that is all that i care about, speaker being as loud as possible. And there is some loudness difference between 25V and 21V

that's because it's a class D amplifier. i once repaired a Panasonic "all in 1" home theater that used an adjustable power supply as the "volume control". i thought it was a clunky way of controlling volume. maybe they did it as a proof of concept, or "because we can"...

 

[SentinelAeon]

I am wondering how this speaker will compare to lets say JBL extreme with extreme price. I think JBL extreme is 4x10W when connected to external power and undefined less when running on batteries. If i run this amp of mine on 25V and connect 2x25W, will JBL extreme still be much louder or will they be close ? Also, since all the items are ordered i guess its time i start thinking about speaker enclosure, to maximise volume and bass. Any ideas ?

 

[SentinelAeon]

Oh, another thing, i just got my stepup thingy from ebay:

https://www.ebay.com/itm/Automatic-...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

So i am wondering. What if i put this between my batteries and amp, to always suply steady 25V even as batteries go from 25V to 21V ? Its supposed to hande 3A, 4A if i improve cooling. That is plenty for me since i will use about 2A (20-25V power suply, 2x25W amp). There is some low, it says its about 88% efficient, but that isnt a problem for me, i got plenty of batteries and i can easily make the speaker play for many many hours.

 

[Nigel Goodwin]

I am wondering how this speaker will compare to lets say JBL extreme with extreme price. I think JBL extreme is 4x10W when connected to external power and undefined less when running on batteries. If i run this amp of mine on 25V and connect 2x25W, will JBL extreme still be much louder or will they be close ? Also, since all the items are ordered i guess its time i start thinking about speaker enclosure, to maximise volume and bass. Any ideas ?

It depends entirely on the speakers and cabinets, and how efficient they are at converting electrical power into audio power.

However, as has already been pointed out in this thread you need TEN times the power to be twice as loud, if using the exact same speaker.

Assuming you can equal the speakers of the JBL, then the 40W to 50W (both fairly imaginary) will be too close to hear any difference.

Just build it, enjoy it, and don't worry about specs or comparisons.

 

[audioguru]

The JBL Xtreme2 is a tiny little portable speaker rated at 20 Whats per channel. Bose make a similar one I heard in a demo at Costco at about the same extreme price. It might produce 10 Watts of low distortion output plus another 10 Watts of distortion since distortion is not mentioned in the power rating. A tiny speaker like that usually makes lots of heat power and not produce much sound power.

You will need new name-brand batteries to produce 2.1A at 25V so the amplifier output can be 25W per channel. The voltage boosting thing will not increase the volume when the battery voltage drops, it will simply make the voltage drop faster.

Please post a link to the detailed spec's for the raw speakers you will use.

 

[SentinelAeon]

Sadly i can share nothing about the speakers since i got them very cheap, they are supposed to be 20W 4Ohm, but i cant even verify that since there is nothing written on them. They seem very light though, barely weight anything, which kind of doesnt give me a very good feeling about their quality. For comparison, i just got tiny 6W speakers from ebay and i think they weight as much as those 20W speakers even though diameter of 20W speaker is 3 times than those small speakers.

Remember, price is the most important factor here, i am trying to verify if i can get something similar to JBL to play, sound quality really isnt important, i just need something to listen when we go out somewhere. I ordered cheap items for this speaker to see how close to JBL i can come. I have to be honest here that part of me wishes this would work just to show how much overpriced JBL is (because im pretty sure they use cheap chinese things just like me and get huge margin on those speakers). If indeed things work, i will surely invest in better speakers/amp/bms. But right now its about how cheap i can make something loud for drunk ppl to listen to

 

[audioguru]

Cheap lightweight speakers with no spec's are garbage and will soon burn out with the power you will give them. I have been talking about using common good quality name-brand 8 ohm speakers but your 4 ohm speakers will use much more power and the amplifier will get much hotter. The datasheet for the TDA7492 shows that the maximum power supply is 22V with 4 ohm speakers and then the power will be almost 40W per channel and a fairly large heatsink is needed. Of course the higher power uses much more current then your cheap little batteries and power boosting thing are useless.

 

[SentinelAeon]

I mentioned a few times that my amp is 2x25W, not 2x50W !