DIY bluetooth speaker

[SentinelAeon]

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.

Version 1:

Version 2:

 

[Nigel Goodwin]

You can probably buy specific chargers for 5 cells, the protection boards are just that - they aren't charger boards.

Here's one charger example:

https://www.banggood.com/21V-3A-AC-...-p-1398068.html?rmmds=search&cur_warehouse=CN

 

[SentinelAeon]

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]

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.

 

[SentinelAeon]

Would this do the job ? I would like the price as low as possible.
**broken link removed**

 

[SentinelAeon]

This is the BMS i am using
**broken link removed**

 

[audioguru]

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.

 

[SentinelAeon]

Can i ask why my second picture would not work ? 5 chargers, charging each cell individualy ?

 

[Nigel Goodwin]

Would this do the job ? I would like the price as low as possible.
**broken link removed**

That should be fine - pick the 21V version!

 

[Nigel Goodwin]

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.

 

[SentinelAeon]

Thank you, i found an even cheaper one:

**broken link removed**

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]

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?

 

[SentinelAeon]

If you look at the picture they forgot to write 1 additional red wire to the last battery. At least it looks that way

 

[SentinelAeon]

I found this on ebay, this seems to be the correct way to wire for 5S:

 

[SentinelAeon]

If anyone has any better cheap idea for a 5S BMS, please let me know

 

[SentinelAeon]

Well this wiring of this BMS is strange. The way it is wired, it cant control the 5th battery :S

 

[SentinelAeon]

How about this one. It doesnt have the balancing option, but at least it does have the correct connections. And i like the way they say overcharge is between 4.14 and 4.24V. Obviously this is not optimal but at least maybe they are telling the truth and it will not go beyond 4.24V.

https://www.aliexpress.com/item/21V...-Module-PCM-18650-Li-POLYMER/32844842468.html

 

[SentinelAeon]

Nvm, this one has the same problem, not properly protection the last battery. Some link to a proper bms would be great

 

[SentinelAeon]

I found this one. At least on paper it seems to work fine:

https://www.ebay.com/itm/BMS-3S-4S-...var=472230498831&_trksid=p2057872.m2749.l2649

 

[Nigel Goodwin]

Well this wiring of this BMS is strange. The way it is wired, it cant control the 5th battery :S

It's the same as your original one, perfectly fine - just that the original wiring diagram missed out two of the wires. Why do you think it can't control, the last battery?.