powering a 50 w amplifier by battery???

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ottotunz

Member
2016-01-30 2:14 pm
Hi everyone, first of all I would like to apologize for my poor english...
I was wandering if it's possible to power a tda7492p amplifier by battery. if it's possible, which kind of battery should I use in order to keep it working for 10 hours? thanks in advance for any answer
 
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Mooly

Administrator
Paid Member
2007-09-15 8:14 am
No problem. I see you've edited the first post :)

To deliver 50 watts (rms) into an 8 ohm speaker means that you need a DC supply of around 60 volts in total. That can be a single 60 volt supply or a split 30-0-30 dual supply.

You need a voltage that high so that the amplifier can put 20 volts rms (AC voltage) across the speaker. That figure corresponds to 50 watts rms.

To do that with batteries isn't really practical.

There are probably better options available. If your speakers are lower impedance (4 ohm) then you can get more power for a lower voltage.

Other options are Class D amplifiers (probably the best bet for battery use), or you could look at bridged 'chip amplifiers' a little like the TDA7294 but even here you would at least two 12 volt batteries. You would be probably be looking at VRLA types (valve regulated lead acid... like you get in alarm systems)

10 hours use on music shouldn't be such an issue.
 

ottotunz

Member
2016-01-30 2:14 pm
sorry if I ask you this question, but I'm new in the diy audio field... can you please suggest me an amplifier as powerful and cheap as the tda7492 but can work using a battery? I would have liked to use it with two 4ohm speakers. Another thing... how many amps should the battery be to make it work for 10 hours?
I do apologize again for my poor english
 
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Mooly

Administrator
Paid Member
2007-09-15 8:14 am
The first thing I would do is try and decide just how much power you really do need. It might be much much lower than you imagine.

You can get a very good idea by trying this. All you need is a digital meter that can measure AC voltage, and to download the test files in the second post. Its fun to do and you might be surprised.

http://www.diyaudio.com/forums/mult...much-voltage-power-do-your-speakers-need.html

Something like the TDA1558 might appeal to you. It would run off a single 12 volt battery (having multiple batteries to charge is inconvenient and messy). If you look at figure 4 in the data sheet then that shows a bridged amplifier.

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The battery capacity would probably be something like a 12 volt 7AH as a minimum capacity for typical music use.

There are many many chip amps available, but I'm afraid I'm not very well up on what is available in that line. It might be worth you asking for recommendations by posting a thread in the 'Chip amps' forum.

Your English is fine by the way :)
 

KatieandDad

Member
2011-11-17 3:49 pm
UK
However you do it you will need a huge battery. Getting more than 12 or 24V is normally achieved with an SMPS but then the current required increases proportionally.

Just assuming a few details here.

If you want 50W x 2 = 100W.

Let's assume that the amplifier is 70% efficient, this will require a supply of 140W.

If the SMPS is 80% efficient this will require 180W.

If this is supplied from a 12V battery this will draw 15A.

So for 10 hours of operation you would need at least 150 A/Hr battery.
 
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ottotunz

Member
2016-01-30 2:14 pm
I see... but I'm looking for a pre-made amplifier ahahah
I wasn't able to find one based on the tda1558... there is the tda1558Q, but it seems that no one sells it.
Can you suggest me any cheap pre-made amplifier?
sorry if I'm asking you al lot of questions, but i need to build a boombox and I don't have a lot of time to do it ahahah
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
Battery drain depends hugely on what you play through the amplifier. There is a massive difference between a 50 watt amplifier delivering 50 watts rms into an 8 ohm load, and an amplifier playing 'loud' music.

Something like this drives 2 ohms (so your two 4 ohm speakers in parallel) and runs off 12 volts.

http://cpc.farnell.com/unbranded/sk038/20w-mono-amplifier-kit/dp/HKSK038
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
It looks to use the TDA2005 chip,

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It will draw around 100ma or less with no signal, so that means a standby time of at least 70 hours on a 7AH battery. How much current it draws when playing depends on the music. It really does.

A 12 volt 7AH battery has 84 watts of energy available to deliver to the load. Its up to the music how that is used. Continuous sine wave output would flatten the battery in perhaps 2.5 hours.

You need to study the data sheet and see if its going to meet your requirements. Is as good as going to get without you using higher voltage batteries.

And try the test I linked to earlier.
 

ottotunz

Member
2016-01-30 2:14 pm
i'm from italy and I need more or less(possibly more) 30 W RMS of power. At the moment i have two 4 ohm 40w speakers...
hope these information would be useful...
P.S. while looking for an amplifier I have found one based on the tda7377 amp chip... do you think it could be useful to my project?
 
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Mooly

Administrator
Paid Member
2007-09-15 8:14 am
30 watts rms into 4 ohms is a tough project to do from batteries. That means you need to deliver 11 volts rms to each speaker and so that means an amplifier running on a 30 volts dc supply as a minimum. The speaker is pulling not far off 3 amps rms at that output level.

If that is what you really want then battery power for a 10 hour endurance isn't practical.

A bridged amplifier (like all these chips such as the TDA7377) almost halves the supply voltage needed compared to a 'normal' amp but they still won't do 30 wrms into 4 ohms. The TDA7377 power outputs are not true rms values but are measured to EIAJ standard. Its an easier test and makes the amp seem more powerful than it really is.
 
However you do it you will need a huge battery. Getting more than 12 or 24V is normally achieved with an SMPS but then the current required increases proportionally.

Just assuming a few details here.

If you want 50W x 2 = 100W.

Let's assume that the amplifier is 70% efficient, this will require a supply of 140W.

If the SMPS is 80% efficient this will require 180W.

If this is supplied from a 12V battery this will draw 15A.

So for 10 hours of operation you would need at least 150 A/Hr battery.

But that is for continuous full power during that time. Average power is probably 10% of that so that cuts your battery requirement by 1/10 right there and then.

Jan
 
i'm from italy and I need more or less(possibly more) 30 W RMS of power. At the moment i have two 4 ohm 40w speakers...
hope these information would be useful...
P.S. while looking for an amplifier I have found one based on the tda7377 amp chip... do you think it could be useful to my project?

Why do you need battery power? Are you moving out into the desert? :)

It is no use to change amps all the time. If you need 30+ watts of power from batteries that defines the battery required. A different amp with the same power will still need the same battery. Unless you go to class D.

Jan
 
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