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Portable speaker Answered

Hi,
I need some help building a portable speaker with a td3116 2x50, 1x100 amp.
II want details on how to build a 24v rechargable battery for my project...

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VassilisT
VassilisT

3 years ago

Actually I don't have any electronics education...that's why I need help lm searching a lot and I need suggestion...I have tested the amp with 12v and its not enough...in forums they suggest 19-21v...so I'm trying to reach that...

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3 years ago

Why do you need 24V for a portable speaker? You would be better off using a lower voltage and a lower impedance driver (speaker cone) 4 ohms is more common for 12V systems.

If you really do need 24V, look into the RC LiPo batteries. Don't bother with the C rating, it's not necessary for your application. Get one that is 6S (six cells) And get a balance charger to go with it.

Be VERY careful not to short out those batteries, they can deliver hundreds of amps, and sometimes over a kilowatt! They can also explode and go up in flames if abused and mishandled.

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Second easiest option if weight is not a concern, go lead acid. Lead acid batteries have conveniently the same charging method as lithium, but you don't have to be nearly as careful with them. Lead Acids are tolerant to abuse.

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The "best" option would be many small lithium ion 18650 cells or something simalar. You can buy those really kickass panasonic 18650 3400mAH cells for $6 a cell on amazon in quantity. I think I payed like $34 for 6 cells. (which is what you need) They offer outstanding capacity, and small / lightweight form factor. But if you buy the raw cells, you will need to spot weld them together in series to make a pack, and get a balance charger to charge them. Same as LiPo's, these cells can be very mean when mishandled. But they are safer than the LiPo's due to increased internal ESR which limits output current when shorted, and typically have electrical and mechanical safety mechnisms to prevent catistropic failure.

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VassilisT
VassilisT

Answer 3 years ago

I have an amp that works with 18-24v that's why I need such a battery...I want to use cells like https://m.aliexpress.com/s/item/32319126080.html with built in PCM. Do I also need a balance charger?

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Answer 3 years ago

Did you actually test the amplifier's performance over the nominal input voltage range and verify that it will not not work under 18V? If you are feeling brave, you could test the amp with slightly higher input voltage as well. If you want to be really though you would also do these tests under different operating temperatures. That's much harder though.

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Because secondary lithium cells produce a voltage between 3 and 4.2V, 6 cells in series will produce a voltage range between 18V and 25.2V. You will be able to use the full capacity of the cells if your amplifier can tolerate that maximum voltage. If you choose 5 cells in series, you get a voltage range from 21V down to 15V. You may not be able to use every last drop of energy in the cells, so the effective (usable) capacity will be slightly reduced.

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Yes I already said yes. You DO need a charger capable of balancing the cells. Or better yet, a battery management IC that keeps them balanced while charging and discharging. This is especially true when you buy the batteries separately, and they are not carefully matched in factory. As the case with some cheap chinese craptacular cells you are buying.

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VassilisT
VassilisT

Answer 3 years ago

I would like to use li polymer cells, 3,7v 5000...I want a 22,2v battery with 10000mha, can you help me with the circuit?

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Answer 3 years ago

The pack you are trying to build is borderline ridiculous for a basic speaker. Unless you are trying to build a 100W battery powered stage amp or something for some very special purpose.

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22.2V / 3.7v = 6 cells in series. If you use 3400mAH 18650 cells, then you need at least 6 batteries of at least 3 paralleled cells. Take those 6, 3P batteries and connect them in series. You need 18 cells in total. This pack will cost about $108.

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Then you need to get a balance charger to ensure that the cells stay balanced. Lithium secondary cells do not balance themselves like NiCd or lead acid because they do not tolerate overcharging at all. So an additional $30 will go into that, as a bare minumum. About $50 to $100 for a good one.

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rickharris
rickharris

3 years ago

Radio control type battery AND charger.

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Downunder35m
Downunder35m

3 years ago

I would really just buy a battery, builing one is not easy for obtaining the right chemicals and equippment required.
Can't be too hard to use two 12V batteries can it?

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iceng
iceng

Answer 3 years ago

:)