How to drive TDA8954 from batteries? (WARNING: Long and boring backstory.)

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I have a rather ambitious project I'm attempting, but my knowledge about electronics doesn't go far beyond "knows how to solder and use a cheap voltmeter."

The Backstory: (skip this section and next to just get to the question)

About two months ago I bought one of those "Breeze Audio" TPA3116-based amplifiers (in blue) from an eBay seller for US $22. Right out of the gate I want to admit that I was expecting it to be garbage, and I only bought it with the intent to drive a cheap horn speaker. When I got it, I tested it out at my friend's house, first with a pair of bookshelf speakers I bought at a thrift store. It sounded good and got plenty loud, so I moved on to a pair of Panasonic RAMSA WS-A80 8" PA speakers I had in the back of my car. I thought for sure I'd hear some sound but be less than impressed, and probably hear a bunch of noise or severely lacking bass or something. To the amazement of both myself and my friend, they sounded good! I never doubted the speakers themselves, but the amp was driving them loudly, clearly, and fully! Totally didn't expect that!

Anyway, this inspired me to look more closely at Class D amplifiers. I thought "if this $22 paperweight can drive PA speakers almost well enough to run a real gig, there have to be some more powerful versions of this."

I looked around and sure enough, there existed a Class D chip that could run in bridged mono mode at 410W, enough to drive one of my 12" RAMSA WS-A200's comfortably. Enter the NXP TDA8954.

But wait, there's more...

The blue paperweight wasn't done. My friend asked me if I wanted to accompany him on a basic Halloween party gig, assuring me repeatedly that the little blue amp was plenty loud enough, so I caved. I want to stress right here that every instinct was telling me that this little thing should never be used for a real DJ gig, and especially not anything more complicated. Nevertheless, it wasn't my gig, and my friend kept assuring me that we would just be playing background music, so I went along with it. We went, set up my WS-A200's on stands, plugged them into the amp, hooked up an old (oh god, ancient) Realistic-branded DJ mixer that he had, hooked in both of our laptops and a mic for announcements, and started playing some jams.

Of course, as it turns out, they wanted more than just background music. They wanted to dance! They wanted us to turn it up... so... we did! And the paperweight held its own! I was absolutely flabbergasted that this thing was driving my 12" speakers and filling a room LOUDLY! The amp never cut out a single time. Towards the end of the night, I walked out in front of the speakers and heard a hint of distortion, so I know we were pushing the little guy just past its limits, but still, I couldn't believe it!

Anyway, all this inspired me to devise a new plan...

The Project: (skip this section to just get to the question)

I wanted to devise a mobile PA solution based on Class D technology. Basically, I want to devise an add-on to my existing PA speakers that somehow clamps on to them and plugs into their quarter inch jacks, which turns them into powered speakers. I want each speaker to be able to stand on its own, and I want them to be able to run on battery to go truly mobile.

But that's not all...

I want them to have Bluetooth. Yes, bluetooth! Certainly not something to be relied on for any serious gigs, but these RAMSA speakers are great and already very portable, and I'd love to be able to lug one out onto the beach or something and play music loud enough to be heard from out in the water. But of course, there's one more thing...

I want them to be pairable. In other words, while one should be able to stand on its own, should I bring a second one out, they should be able to talk to each other wirelessly and form a stereo pair. Now this is indeed possible with a technology known as True Wireless Stereo or TWS for short. It's fairly easy to source modules with this capability from eBay or Chinese sellers.

In addition to Bluetooth, I do want to add a standard compliment of inputs, basically at least one balanced input and some sort of auxiliary in, either in the form of RCA jacks or a mini jack.

The Question: (finally)

I bought a board based on the TDA8954 and just realized it needs dual-polarity power. Now, I know I could just go 12vdc to a 110vac power inverter and then into a transformer (I guess) and out I get +24v 0v and -24v. Something tells me that I'm in over my head on this whole power supply thing. What do I actually need to power this board? I was thinking of driving the whole project from one or two deep cycle 12v batteries, but I don't know how to go from that to +/-24v. Googling for this honestly didn't turn up much I could make sense of. I did read somewhere that if I wire two batteries in series I could get plus, minus, and ground voltage, but I'm kind of confused on whether or not that would even work here. Does it need to be some type of AC power or does that yield the same result as hooking the two batteries together? I'm really confused!

Is this just a terrible idea? Should I look at another chip? I'm trying to get real PA power onto something I can carry. HELP!

(p.s. I will have follow-up questions touching on the multiple inputs and bluetooth, but for now I just want to know how to get the basic amp working.)
 

PRR

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He specifically says he wants batteries, "mobile".

Two channels of 400 Watts is nominal 800+W of power or 33 AMPERES from two 12V batteries.

Speech/music rarely hits full power, and Class D uses much less power at part-power than class B. Let's though assume LOUD music and about 10 Amps average demand. Two large car batteries will run a couple or three hours, a few dozen times, before being damaged by the heavy discharge. Deep Discharge golf-cart batteries are a better buy for this application.

EDIT-- I just realized the spec is +/-24V, not +/-12V. This reduces the current demand but batts are 2V naturally, 6V and 12V are readily available, but 24V is double the number of 12V cat batts or a trip to the heavy truck shop for the 24V jobs.

For what this will cost in batteries, and the suspected loudness of a 800W PA system, it would be worth looking into small generators. I have a 3,200W beast quiet enough to run outside my bedroom all night. They make 1,000W jobs and some of those are spectacularly quiet. And 120V wiring can be run long distance, the batteries need to be very-close to the amp and the amp pretty close to the speakers to reduce line loss.
 
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PRR

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EDIT: this shows +/-12V. For +/-24 you need two 24V or four 12V batts. The 5V regulator for small-stuff will take 24V but needs more heatsinking.
 

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I have a rather ambitious project I'm attempting, but my knowledge about electronics doesn't go far beyond "knows how to solder and use a cheap voltmeter."
nice
I'm trying to get real PA power onto something I can carry. HELP!
How much can you bench press?:D
You could buy smallish 12V SLA batteries or LiPo hobby packs and wire them all up in series and tap "ground" into the central point.
Get the SLA battery data sheet (size wise, 12V 7Ah are cheap and every where) and go to 'battery university dot com' and learn about lead acid batteries.. then 1st realize the name plate 'amp hours' don't multiply in series. After you graduate from Batt. University' and off grid solar, you'll know you must derate the amp hours on this old tech/chemistry to at least half maybe more depending on high discharge curves and charge cycle lifetimes... LiPo battery packs are more compact but the cells need specialized chargers and management /protection circuit boards and software. You can buy this stuff off the shelf for up to four to six cells..Note each cell is 3.2-4.0 Vdc ... but wait, you need up to 16-18 cells in series.. so plan ahead according to the 3S-4S packs that are most economical. Actually there a lot of knowledge that goes into laptop battery power tool tech, sadly they haven't standardized stuff for mobile party rigs.

OR go to a DJ rental shop and ask for the 'all in one package plan' they've done all this stuff before. I'm sure it will involve' inverter generators. BTW i'll bet all your party time will be spent guarding said equipment.
 
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Thanks everyone for the suggestions.

I guess I got carried away describing all the things I wanted to do that I didn't touch on some important information.

The speakers I'm using are only rated at 250W, but I read somewhere that you should get an amp that can drive like one and a half times what your speakers are rated, hence a 400-ish watt amp. Something about it being easier for the amp to drive that way. Better to have slight overkill than underpower, right?

I was looking into cheap deep-cycle batteries (cheap-cycle?) for the rig. You know, the kind used in things like power chairs or those cars they make for kids. I was thinking of using a cheap 12v-24v up-converter originally, but that was before the whole dual-polarity wrinkle caught me off-guard.

Anyway, I know the amp chip can run on 12v, so would it be worth it, just for testing, to take, suppose, two of the cheap-cycle(tm) batteries wired in series as suggested, provide the amp with +/- 12v by wiring them in series, and just see what happens?

The amp board only shipped today from China, so I've probably got at least a couple weeks before I even see it.
 

ICG

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Joined 2007
He specifically says he wants batteries, "mobile".

Two channels of 400 Watts is nominal 800+W of power or 33 AMPERES from two 12V batteries.

[...]

EDIT-- I just realized the spec is +/-24V, not +/-12V. This reduces the current demand but batts are 2V naturally, 6V and 12V are readily available, but 24V is double the number of 12V cat batts or a trip to the heavy truck shop for the 24V jobs.

For what this will cost in batteries, and the suspected loudness of a 800W PA system, it would be worth looking into small generators. I have a 3,200W beast quiet enough to run outside my bedroom all night. They make 1,000W jobs and some of those are spectacularly quiet. And 120V wiring can be run long distance, the batteries need to be very-close to the amp and the amp pretty close to the speakers to reduce line loss.

No, your calculation is way off because the 420W are already bridged (or 2x210W), which means, no doubling that power. And additionally, the TDA8954 only reaches that output at +/-41V. At +/-24V it will be likely only a fourth of that.
 

ICG

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Joined 2007
The speakers I'm using are only rated at 250W, but I read somewhere that you should get an amp that can drive like one and a half times what your speakers are rated, hence a 400-ish watt amp. Something about it being easier for the amp to drive that way. Better to have slight overkill than underpower, right?

Yes, that's right, better to have more power than driving into clipping. But you are saying speakers, which would imply you want to use the amplifier in stereo (2 channel) mode. That would mean you won't get that power figure, the TDA8954 can only deliver 2x210W and that is at +/-41V and - this is also very important - at 4 Ohm. If you have a typical PA speaker, it will be likely 8 Ohm, which halves the power figure.

Assuming the 8 Ohm speakers, that gives following options:
  • Buy a 2nd amp and use both in bridged mode, which gives you the power you're aiming at with a voltage of ca. +/-36V. 3 12V batteries for each voltage rail are needed, that will be bulky, heavy, expensive, depending on what batteries you'll buy.
  • Buy or build 4 Ohm speakers, they will draw more power from the amp. You need to use around 40V on each rail, which might require to build your own special batteries from single cells. The loading electronics, protection (overload, deep discharge) and capacity will be likely a challenge. I'd say that's a lot of effort for the power, remember you need two of each (because of the two rail voltages).
  • Buy or build a different amplifier which only needs one rail voltage, which is much easier and cheaper to realize. Generally such a system is not recommended to be built with an amp that needs symmetrical voltages.

Anyway, I know the amp chip can run on 12v, so would it be worth it, just for testing, to take, suppose, two of the cheap-cycle(tm) batteries wired in series as suggested, provide the amp with +/- 12v by wiring them in series, and just see what happens?

The datasheet (PDF) says it starts working at 12,5V, in reality it might start at a bit different voltage. The usual car batteries provide more than 12V fully charged but you cannot use the full capacity of it. And it will be a whole lot less power, probably around 20-30W/4 Ohm, half of that on 8 Ohm. If you have the batteries laying around, go for it. If you have to buy them, I'd scratch that though.

Maybe you could describe your speakers and the use you have in mind? That would help a lot to search for a better solution. I mean, open air or a room, do you have to carry it or drive with a bike, car etc? How loud does it have to be? How many listeners will be there? Background music? Party-level? Disco?
 

ICG

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Joined 2007
That DC-DC converter is really tempting.

They got 4 different versions:

Model Name Mains Outputs the output voltage on the car
Type A 2 groups ± 66V (12V input) ± 77V (14V input)
B type 2 group ± 42V (12V input) ± 49V (14V input)
C type 2 group ± 30V (12V input) ± 35V (14V input)
D type 2 group ± 21V (12V input) ± 25V (14V input)

Type B is too much, the converter is not regulated, it would exceed the maximum voltage of the TDA8954 (+/-42.5 V), type C would provide usable voltages. Unregulated usually means higher ripple. I don't know how much ripple and noise it brings or how the amp reacts on it.

At +/-35V of the type C one the TDA8954 got 2x150W/4 Ohm or 75 on 8 Ohm, which seems a bit low. Adding a second amp and bridging both would bring the output up to 300W/8 ohm but that's way more than one of the converters can handle, a second 12V Boost Converter is then needed too.

It's getting quite expensive, 50 bucks + customs (I assume, don't know about that in the US or additional taxes) and two amps, that's getting close to 200 bucks and there's no enclosure, wires, plugs and connectors in it and neither are the battery(s).
 
Yup. And you just might find a class D car amplifier on sale that costs less than this build. But what fun is that? :)


As far as ripple I wouldn't worry about it. It will be in the 10's - 100's of kHz and easy to filter with a small LC or RC filter.


There's also this kind: +-48V Audiophile Digital Power Amplifier Board 350Wx2 IRS2092 HIFI 2Ch Class D AMP | eBay

Using that, and the boost module would cost $125CAD not including the large deep cycle SLA...




And an actual car amp. The 3000W rating is horses*it since 12VX70A=840W but it gives you an idea...



Boss Armor AR3000D 3000 Watt Mono Car Audio Class D Power Amplifier Amp + Remote | eBay
 
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PRR

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Joined 2003
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No, your calculation is way off....

I have no idea which of my calculations is "way off"; or how bridging matters.

He thinks he wants two channels at 400 Watts. Ignoring efficiency, this is 800 Watts demand at maximum output. For two-12V and two-24V options (assuming that voltage suits the amp, whatever the amp is), this must be at-least:

800W/(12V+12V) = 800W/24V = 33 Amperes
800W/(24V+24V) = 800W/48V = 17 Amperes

These will be VERY heavy drains on any battery I would call "mobile".

I just got a 1000W inverter to turn 12VDC into 120VAC (they must exist for 240V lands). I can run power-tools from my car/truck. Assuming I do not saw/drill steady, the 80 Amp peaks are covered by the 50AH battery so the car's 40A alternator about keeps-up. I suspect this thing will comfortably power a 2*200W audio amplifier (plain wall-plug, not car-sound or bare-board). The 3dB "short" should not ruin the gig. Larger inverters are available, but unless duty cycle is low (in speech/music it may be), might be too much for many car's electrical systems.
 

ICG

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Joined 2007
I have no idea which of my calculations is "way off"; or how bridging matters.

He thinks he wants two channels at 400 Watts. Ignoring efficiency, this is 800 Watts demand at maximum output. For two-12V and two-24V options (assuming that voltage suits the amp, whatever the amp is), this must be at-least:

800W/(12V+12V) = 800W/24V = 33 Amperes
800W/(24V+24V) = 800W/48V = 17 Amperes

These will be VERY heavy drains on any battery I would call "mobile".

Well, firstly, he only got ONE amplifier. So, no 800W, only 400. But it's not even close to that either because..

..Secondly, you don't seem to understand that the rail supply voltage determines how much power the amplifier can put through. You cannot simply divide/multiply the maximum power ratings to get the actual power output. That is because Ohm's law, it still applies. On lower than maximum rail voltages you get - surprise - lower power output. Look at the available voltages: 12V, 24V, 36V and 48V, via multiple batteries or the (unregulated) DC converter. Only two of these voltages are effectively usable and therefore the amp will have much lower power already. Look at the datasheet, it will tell you how much output you can expect at which voltages. (or look at my former post)

Thirdly, the output of the amplifier is also dependent on the impedance. Maximum output specs are only reached at the specified impedance. He got higher impedance, so there will not be much power left at the output. How much? Read my post up there again.

So there we determined your calculation is off by at least factor 4 to >20. And yes, that is what I'd call 'way off'.

I just got a 1000W inverter to turn 12VDC into 120VAC (they must exist for 240V lands). I can run power-tools [...] I suspect this thing will comfortably power a 2*200W audio amplifier (plain wall-plug, not car-sound or bare-board). The 3dB "short" should not ruin the gig. Larger inverters are available, but unless duty cycle is low (in speech/music it may be), might be too much for many car's electrical systems.

That does not help. Because the amp runs neither with 220 nor 112V AC, it runs with symmetrical (+/-) rail voltages. So you have to add another power supply to work with the 110 or 220/240V AC and provides the needed rail voltages. Cheap non-regulated inverters work fine with crude power tools which draw a mostly steady current, the huge voltage variation with of their output with current fluctuations makes it very difficult for a lot of amplifiers to cope with.

It would be an option though to use such an inverter and use a cheap PA amplifier (i.e. an used iNuke 3000). That might be a solution for the situation but it's not a solution for the TDA8954 amplifier though - which means, he can't use anything he got so far.
 
Cheap non-regulated inverters don't like reactive loading. They rarely work with anything that isn't powered by a SMPS. If he's running a power tool I suspect it's at least stepped sine, if not pure sine.

In any case trying to get 800W from 12V is going to be a challenge. Even if it was 100% efficient, that would pull 67A from a 12V source.

That means the average 12V car battery would be dead within an hour.


As mentioned a gas generator would be a better solution, as would be using standard AC powered amplifiers.
 
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ICG

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In any case trying to get 800W from 12V is going to be a challenge. Even if it was 100% efficient, that would pull 67A from a 12V source.

I already wrote it twice, it isn't 800W! At 36V with 8 Ohm speakers it's 200W peak with both channels driven and losses, which means around 50W rms.

That means the average 12V car battery would be dead within an hour.

Even if it was 800W, that would be peak only. And that means, it would last at least 4 times longer with music of 6dB crest factor, IF it's all the time full power.

As mentioned a gas generator would be a better solution, as would be using standard AC powered amplifiers.

Yes, I agree on that. Especally the run time is not an issue anymore with a generator. The question is if a generator is acceptable in weight, dimensions and noise. Without some feedback of the thread starter it's only guessing. If a generator is okay I presume a PA amplifier would also be okay and in that case I'd just get a used PA amp. That, ofcourse, is not a solution for this amp. On the other hand, it would be most likely cheaper and better power-wise and in terms of safety and relyability.
 
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