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I cant power an amplifier

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adiward

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Hello there, i have a problem, im trying to make a portable speaker 2x15w everything is fine expect the battery, i have 4x 18650 2400mAh 3.7v and im running the amplifier at 14v using a dc dc booster (amplifier except 10v to 25v) and it can t run them, do i have to change the booster or the batteries?
 

Does your amplifier give full output down to 10V? If so, why do you need a dc-dc booster? are you connecting the cells in series (I hope so) or parallel?

Li-ion cells should not be discharged below around 3V or they suffer damage. So, even discharged this low they will still be providing 12V. If you are using consumer 18650 cells with protection circuits in, they will (should) cut off not much below that.

Unless your amplifier needs more voltage, using a converter is probably just losing run time by wasting energy.

All of that aside, you should be able to run the amplifier from that battery, although it might not last long at full output.

More details required.
 
Parallel because i can t charge them in series, this is the problem
 

Have you checked the cell manufacturer's recommendations for parallel connection? Some cells are better made (closer tolerances and more stable) than others, and that impacts parallel connection. Should be OK if they are a major brand and from the same batch, I guess.

Really, without detailed information on your 'booster' circuit, we can't say anything about why it isn't working. Do you have a circuit diagram? Have you checked the output voltage from the booster and done any other basic tests?
 

Hi,

Some calculations:
You want 2 x 15W output (I assume RMS)
With a Class D amplifier you may need 2 x 15W / 0.8 = 37.5W RMS input current. (0.8 = 80% efficiency)
Because this is not DC....you should expect about 75W peak amplifier input power.

Step up:
Now if you have 3.7V battery voltage (and this is not guaranteed, especially not with weak batteries, low charge level and load current)
And a step up efficiency of 80% ...expect about 25,3A input current.
With a duty cycle of 80% and CCM with 20% inductor ripple you need at about 35A max switch current.
But the used step up circuit supports only 4A switch current.

--> you need a much bigger step up circuit.


Klaus
 
Where can i find/build a bigger step up circuit?

- - - Updated - - -

adiward said:
Hello there, i have a problem, im trying to make a portable speaker 2x15w everything is fine expect the battery, i have 4x 18650 2400mAh 3.7v and im running the amplifier at 14v using a dc dc booster (amplifier except 10v to 25v) and it can t run them, do i have to change the booster or the batteries?
Click to expand...

i forgot to say that if i power my amp with a 15v 2A power adaptor its working fine
 

It is simple to see what is not working. When the amplifier is playing: measure the voltage of the battery, then measure the output voltage of the booster.
 

Audioguru said:
It is simple to see what is not working. When the amplifier is playing: measure the voltage of the battery, then measure the output voltage of the booster.
Click to expand...

the booster says 14v and when its max volume its dropping
 

adiward said:
the booster says 14V and when its max volume its dropping
Click to expand...
The booster cannot supply enough current for the 30W stereo amplifier so its voltage drops.
The battery cells are probably old and weak since their marked 2400mAh capacity is much less than 3500mAh cells that are available today.
 

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