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How to drive TDA8954 from batteries?  (WARNING: Long and boring backstory.)
How to drive TDA8954 from batteries?  (WARNING: Long and boring backstory.)
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Old 11th November 2017, 11:55 PM   #1
daveError is offline daveError  United States
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Default How to drive TDA8954 from batteries? (WARNING: Long and boring backstory.)

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.)
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Old 12th November 2017, 01:54 AM   #2
rayma is offline rayma  United States
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Originally Posted by daveError View Post
What do I actually need to power this board?
How about a couple of these, you don't really want batteries. Amazon.com: ALITOVE AC 100-240V to DC 24V 5A Power Supply Adapter Converter Charger with 5.5x2.1mm DC Output Jack for 5050 3528 LED Strip Module Light: Home Audio & Theater

Last edited by rayma; 12th November 2017 at 02:02 AM.
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Old 13th November 2017, 03:57 AM   #3
PRR is offline PRR  United States
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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.

Last edited by PRR; 13th November 2017 at 04:12 AM.
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Old 13th November 2017, 04:09 AM   #4
PRR is offline PRR  United States
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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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Last edited by PRR; 13th November 2017 at 04:13 AM.
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Old 13th November 2017, 04:17 AM   #5
PRR is offline PRR  United States
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Have you digested this very similar project?
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Old 13th November 2017, 04:30 AM   #6
Tiido is offline Tiido  Estonia
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It should be noted that the TDA8954 can only produce the 400ish W output with +/-41V power rails.
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Old 13th November 2017, 01:50 PM   #7
infinia is offline infinia  United States
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Quote:
Originally Posted by daveError View Post
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
Quote:
I'm trying to get real PA power onto something I can carry. HELP!
How much can you bench press?
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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Last edited by infinia; 13th November 2017 at 02:18 PM.
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Old 13th November 2017, 03:14 PM   #8
daveError is offline daveError  United States
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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.
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Old 16th November 2017, 05:30 AM   #9
basreflex is offline basreflex  Spain
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the other option is to look into ebike battery packs. you can pedal towards the gig, lift 2 battery packs to connect them in series. the speakers can go in the 2wheel cart behind your bike. go green!
there are 36V ebike packs around.
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Old 16th November 2017, 05:06 PM   #10
ICG is offline ICG  Germany
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Quote:
Originally Posted by PRR View Post
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.
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