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DIY bluetooth speaker

I am building a homemade bluetooth speaker. It consists of 2x25W bluetooth amplifier (voltage 10-25V input), some 2x20W speakers and batteries from old laptop batteries. I decided to use 5 batteries in series to give me 21V. I ordered BMS board for those 5 batteries. All that is left now is to find a way to charge the speaker. I am looking for the cheapest option, i made 2 images, 2 versions of how i plan to do this. First option is to just hook everything to 21V DC power suply and pray that BMS makes sure charging is ok. Second option is to just buy 5 cheap chargers for 70 cents a piece on ebay and charge each battery individualy, and connect all 5 chargers to 1 power suply.

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Version 2:
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Thank you for your reply. I dont get it how this charger is any different than normal 21V power suply. It doesnt look at individual cells and cannot know if any of them went over 4.2, can it ? The reason i am asking is that i have plenty of power suplies at home and want to make sure that this charger really is different than them.
 

audioguru

Well-Known Member
Most Helpful Member
You provided no information about the BMS. The BMS might be a simple protection circuit but can it also be a charger?
In your photos there is no protection for the 5th cell. The two end wires for the battery are not connected and the power supply and amplifier wires might be wrong.
A lithium charger made to balance-charge 5 cells to a total of 21V probably needs a power supply voltage higher than 21V.
You cannot charge the cells in series with separate chargers powered by a single power supply.
 

audioguru

Well-Known Member
Most Helpful Member
It looks like the Banggood power supply is not balanced and hopes that the BMS prevents the battery from blowing up.
My LiPO batteries are safely charged with a balanced charger (with separate wires to each cell) but has no protection board. My load limits the current and disconnects when the discharging voltage becomes low.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
It looks like the Banggood power supply is not balanced and hopes that the BMS prevents the battery from blowing up.
My LiPO batteries are safely charged with a balanced charger (with separate wires to each cell) but has no protection board. My load limits the current and disconnects when the discharging voltage becomes low.
Chargers don't need to be balanced, that's what the protection/balance board is for - it's a pretty clumsy charger if it needs 6 or 8 wires connecting to the battery pack?.

Yours seems somewhat inferior, with no protection for the battery and excessive discharging and ruining the batteries easy to do.
 
Thank you, i found an even cheaper one:

https://www.ebay.com/itm/9V-12V-12-6V-16-8V-21V-25-2V-1A-Lithium-Li-ion-Charger-Adapter-for-18650-Battery/202614664125?_trkparms=aid=555018&algo=PL.SIM&ao=1&asc=57476&meid=666a35b730614d73bb9c2ba2cf4582ff&pid=100005&rk=6&rkt=12&sd=113351299434&itm=202614664125&_trksid=p2047675.c100005.m1851

Ok so to sum it up. I dont have a balanced charger now, so BMS will have to make sure cells dont go over 4.2V. I will test charge it a few times and carefuly check if it really stops at 4.2V.

But now i am wondering why the first picture i posted wouldnt work, 5 individual chargers ?
 

audioguru

Well-Known Member
Most Helpful Member
Why do you think that a 4S protection board will work with your 5S battery?

Your extremely cheap 5S protection circuit seems to have its very high numbers of 15A and 56A mixed up. An 18650 cell will not be protected with a 56A charging or discharging current. Does it have instructions showing what B- and P- connect to?
 

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