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Nada

Designing a high efficiency system for running on off-grid battery power

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Please share any design tips for a bespoke DIY high efficiency, audiophile tolerable stereo system, built to run off a minimalist solar powered battery array for a future holiday cabin fantasy.  The power system will likely be low powered with just 12V 390Ah storage. Id like a system that has a maximum peak draw of 20A at 12V so 240W at most with about 50W average maximum. It would be fun to build a system that runs on just 20W if possible. There will be no 230VAC grid or generator backup, thus the emphasis on designing a high efficiency system from the ground up. Maybe that should read from the sun up.

 

  • Is it possible to design gear that runs directly off battery 12VDC (max 13.3V on full charge)  without needing an invertor?
  • Will  D-class power amps be important to minimise the peak power load and W-hr drain?
  • What about the speakers. Will horns be mandatory for high efficiency?

 

:anyone:

Edited by Nada
Mark requested more details

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All you need to do is look at amplifiers and related equipment that is manufactured for the motor car section of the audio market. The battery stack will need to be wired or be capable of being switched, to suit  a standard 12 volt arrangement. A high quality  horn loaded speaker  system  will provide  high efficiency but will tend to be directional. This may be what you are after, if it is for use in a hall or out of doors. 

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If you pay the same for 1w or 1kW draw I see no reason for any amplification other than single ended Class A be that triode of FET.

 

But that's just me.

 

I think the speaker efficiency means little in the scheme of things so I don't think horns are mandatory.

 

As for running on DC straight from the battery, that may be possible but any performance advantage would need to be proven first.

 

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Class D amps run about 93% efficient but you need about 48V of DC to opertate them. High efficiency speakers and a 40W class D would give you all the volume you need. Even a 2W amp will be very loud with 100db speakers. A Raspberry Pi music server with USB storage is extremely efficient and runs on 5V at around 0.5A (2.5W). 

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I think for off grid the high efficiency, and single ended power supply needs of some Class D chipsets might make them a good choice.

 

I have been playing with my low cost "picnic blaster" system that uses an inexpensive TPA3116 amp that sounds surprisingly good for the price. I've been driving it from a 12V SLA battery at 24VDC to get maximum power from it, using 12V->24VDC "laptop adaptor" though the adaptor is a bit cheap and nasty.

 

I just noticed the Sure Electronics site has some very interesting looking higher wattage 12VDC voltage converters.. I haven't used them myself but they look worth investigating:

http://store3.sure-electronics.com/audio-oriented-power-supply-units

 

These look great for upgrading my battery powered system to use beefier/better quality Class D amps that run from 36VDC or 48VDC.

 

edit: although "picnic blaster" uses pretty average Pioneer car speakers I am quite sure it would sound fine with my better quality high sensitivity speakers.. but I don't want to take them outside.

 


 

 

 

Edited by zog

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Start at page 1, of Battery Based Audiophile Story 

From there feel free to shoot a few questions.

 

A suggestion

Forget 12v battery driven DC systems unless you are to install a large 12v battery (always done for my RAPS Stereo set ups)

Tip, use any type of amp even A Class, on your massive RAPS. Treat the room, Treat the room, Treat the room, but then you already know about this minor thing.

Cheers

Matt

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Another tip

Use a second Inverter :thumb: just for the stereo. This ensures a perfect in going un distorted waveform

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On 12/7/2016 at 9:56 PM, acg said:

If you pay the same for 1w or 1kW draw I see no reason for any amplification other than single ended Class A be that triode of FET.

 

But that's just me.

 

I think the speaker efficiency means little in the scheme of things so I don't think horns are mandatory.

 

As for running on DC straight from the battery, that may be possible but any performance advantage would need to be proven first.

 

Interestingly the most striking advantage of this (dc direct)  is the total loss of all the hum generated from a typical mains driven set up, weather it be physical chattering of the power transformers or any hum getting into the signal path. Im talking no hum, not with an ear on the amp, or hiss/buzz at the tweeter.

If you can get the mains driven front end to "interface" properly enjoyed is an utterly free of mains noise system. 

Photo is of my daily 5500W RMS driver, powered from a 350A 12v DC Supply (battery) and proof of concept for off grid.

 

IMG_1075.JPG

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44 minutes ago, 125dBmonster said:

If you can get the mains driven front end to "interface" properly enjoyed is an utterly free of mains noise system.

 

What do you mean by "mains driven front end"? I thought this thread is about battery-driven?

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There are also some decent quality class D amplifier modules designed to run off 12v DC power. Here's an example (which I haven't heard myself).

 

In theory, if your power requirements are low enough (i.e. because your amplifier and/or speakers are efficient) or your battery power high enough, a DC source should provide cleaner power than anything running off mains AC power.

 

It's also possible to find higher voltage high current Li-Poly batteries that at least in theory could power a higher voltage amp (again, I haven't actually tried these myself, but I plan to). There are some interesting looking examples available at this site.

 

Cheers,

Andreas

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On 12/8/2016 at 11:10 PM, Newman said:

 

What do you mean by "mains driven front end"? I thought this thread is about battery-driven?

conventional TT and Valve pre

There is a bit of faffing about involved, but worth the effort :)

Edited by Guest

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Guest scumbag

Nada,

Some operating parameters would be good here. e.g. what is the accepable draw that you  would want the equipment to make over time in watt/hours? What is the viable peak draw that you can accomodate? also, i would assume you're solar system is set up to deliver 230 volts ac? there are tonnes if options - as we've seen -but knowing the type of and limitations of the power delivery that your solar system can give you will help to sort out the best solution 

Edited by scumbag

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8 hours ago, scumbag said:

..... Some operating parameters would be good here. .......

 

bespoke DIY high efficiency, audiophile tolerable stereo system

built to run off a minimalist solar powered battery array for a future holiday cabin fantasy

low powered with just 12V 390Ah storage.

Id like a system that has a maximum peak draw of 20A at 12V so 240W at most with about 50W average maximum so the battery can pump out music  over a run of a few cloudy rainy days

It would be fun to build a system that runs on even less juice if possible.

There will be no 230VAC grid or generator backup, thus the emphasis on designing a high efficiency system from the ground up. Maybe that should read from the sun up.

Edited by Nada

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On 12/10/2016 at 7:01 PM, Nada said:

 

bespoke DIY high efficiency, audiophile tolerable stereo system

built to run off a minimalist solar powered battery array for a future holiday cabin fantasy

low powered with just 12V 390Ah storage.

Id like a system that has a maximum peak draw of 20A at 12V so 240W at most with about 50W average maximum so the battery can pump out music  over a run of a few cloudy rainy days

It would be fun to build a system that runs on even less juice if possible.

There will be no 230VAC grid or generator backup, thus the emphasis on designing a high efficiency system from the ground up. Maybe that should read from the sun up.

 

I think I already have almost all components for a system like that, just need the solar panels :). @andreasmaaan mentioned T1 from Hifimediy which is TK2050 based amp running on 12V. I have it at home and especially considering the price it is very good. You would need highly efficient speakers though as it doesn't have enough juice to push hard anything lower than 90dB. If you have digital volume control then bypassing its pot can be beneficial too. The great thing about this amp is that it costs peanuts and you could easily have an active system with 4 or 6 of them. 

As for the DAC I would again use Hifimediy and get their USB powered ES9018. It's such a good chip that even despite very limited PSU you will get pretty good results. If you want better, there are Lipo battery based modules that can feed most of DAC boards. The only problem is charging as the smart chargers come as 230V SMPS but you could replace it with Arduino module that has some simple logic protecting Lipo baterries from overcharging. Of course you can use a very decent power regulator instead but feeding DAC from the same battery as the rest of the system may not be the best.

Then there is a server. Mini computers running on 12V are more and more popular so you should not struggle to find something appropriate. 

 

This would be a very decent system but obviously not the top one. If you wanted to go hard you can always think of building an active system with multiple amps, software based crossover and multichannel DAC/crossover like the awesome Analog Precision UPXO for examaple. This could blow away most of 230V systems but to get some serious party running you would need to consider an inverter and an amp that can shake a thing or two.

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Opps, off topic.

For somethig frugal on power, like suggested

 

A Rasberry PI, HiFi Berry DAC+, External drive

A quality D class 12v 25w x 4 bridgable

Could throw a miniDSP 2 x 4 (12v) into the mix as well and have an active 2 way horn of choice. 

Hmmmm, 

Edited by Guest

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Nada, more ideas

could your supply be stretched to 12 and 24v supply :rolleyes: (and the miniDSP).

with WiFi you can operate the PI from a phone. Unknown is if the miniDSP will talk to the PI,

24v Mimic pre for the TT if you can find a battery powered one :D . Lycan 24v  Buffer (class A)

 

IMG_1091.JPG

Edited by Guest

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Hi Nada,

IIRC the maximum power available from a power amp in bridged mode using only the 12V rail is approx 18W.

When I was mucking with car audio years ago there were power amp modules specifically designed for this - ie maximum power from the available voltage with internal bridging.

The modules were stereo 2 x 18W rms (with internal bridging).

I used multiple of these modules in a tri-amped car stereo setup:

  • 1 for tweeters
  • 1 for midrange
  • 2 for the bass

It provided ample volume in the car...back in the day

 

In the quest for power all car based amps these days will use an inverter to raise the rail voltage.

Inverter technology has got better and better, and they're very efficient these days...

...but IF you can avoid requiring an inverter for your power amps, then you'll consume less power.

 

Tweeter and midrange won't be the issue (assuming "reasonable" SPL requirements), but I'd recommend a small tapped horn for bass, something like the 38Hz Volvotreter

http://wp.volvotreter.de/projects/th-2/the-tangband-38hz-horn/

Also look at the double folded version - very compact.

For high efficiency low down, you'll need to leverage Hoffman's iron rule and have a big box - in your dream "future holiday cabin fantasy" - mount them under the floor if required, and accept it still may need a power amp with an inbuilt inverter for decent SPL.

 

Having several friends that quite successfully live "off grid" all the time - consider going 24V rather than 12V...

...as @125dBmonster says, it provides more options.

 

Not at all "apples with apples", but my large T20 tapped horn sub in my room needs remarkably low volume settings to keep up with my stereo TD18 mid bass direct radiators - Hoffman's iron rule working in reality.

 

cheers

Mike

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Thanks chaps for all the useful advice for designing a super efficient low power off grid stereo that have got me dreaming.  My fantasies so far must be full of naive errors and will need your corrections please:

 

Source: nuclear fusion fueled radiation to Solar panels. Seems to be going fine for a few billion years so far so seems reliable enough as long as Trump doesnt make too many clouds.

 

Batteries: four 6v gel lead acid batteries.

Why? I imagine it allows them to be charged with 12v  PV's but wired for 6v, 12v, 18V or 24v on occasions eg running a stereo loud outdoors on a calm starry night. The best room is no room right? As well paralleling will lower the output resistance and current draw for cleaner power while preventing deep discharge thus lengthening the battery life.

Why lead acid? They can provide very low noise DC (noise in nanovolts according to one research paper) with the ability for high current bursts -so no need for capacitors banks/inverters/trannies.

 

File server:

SD-card based WAV/FLAV player

  advantages:

  • can run direct off SLA 12v-12.8v
  • no fan
  • I2S out
  • low power eg <2W
  •   likely to sound good with no SMPS/no fan/no CPU/no HD/no USB noise.....

 

DAC

nil - the best DAC is no DAC right?

 

Amplifiers

PWM Class D with direct I2S input. Clever way of avoiding digital-analogue-digital inter-conversions.

about 80% efficiency

Use active drive ie one amp  per driver-horn

Crossover via PWM module internally programmed.

can run on wide voltage ranges so battery Voltage sag with discharge should be inconsequential

 

eg STA333BW  looks good in mono mode (stereo mode in Fig.20) for maybe

  • 30W per 16ohm driver in PWM  parallel-mode at 18.9v supply with <0.1% THD. 
  • 12W per 16ohm driver in PWM  parallel-mode at 12.6v supply with <0.1% THD. 
  •   2W per 16ohm driver in PWM  parallel-mode at   6.3v supply with <0.1% THD

 

STA333BW THD versus output power.JPG

 

SPEAKERS

five way 100dB/w horns in stereo

bass horns designed into the roof cavity ie the shacks roof pitch behind the stereos front wall designed to make a pair of bass horns that emerge from high on the front wall.

 

POWER USAGE ESTIMATE

24watts at normal loudness levels:

 

Server 2W

Amps: 10amps x 1w idle = 10W

a. normal listening 80dB at 4m  => 10 x 1W x 120% = 12W  total 24W ie 2amp load on 12V battery

b. loud outdoor listening  10 x 12W x120%   = 144W  total 160 watts ie 80amp load at 12v so best for sunny days with the solar panels pumping

 

It would be fun to run it on a little battery at normal volume just for kicks. A little 24AH 12V gel battery is only 170mm long and could run it for two hours still leaving 80% capacity.

 

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Wow, if your fantasies materialise you will have one hell of a system.

My thoughts/questions are as follows:
- it seems you want to build top notch speakers and compromise on other elements. Speakers are by far the most important part but the rest of your system needs to match and your chosen amps have THD reaching 10% at 10W (very moderate power when outdoor) which is way beyond acceptable level. Can you elaborate more about what speakers you want to use outdoor?
- With multiamping, how do you want the volume control to work? Can PWM amps be synched and locked at different volume level for each amp?
- what's your crossover and can you time align and eq the drivers? This will defo be needed if you want to use part of your roof cavity for the bass
- file server works well but it may not be convenient to use. I'd sacrifice on I2S output and go for a miniPC. You can then store music on SD, SSD or even stream over wifi. Many media players allow to control the music from a mobile or tablet which is very convenient if you already want fully file based system
- No DAC may simplify the setup but it put limits on the choice of amps. If you can synchronise PWM amps then it could be a good enough selling point but otherwise I'm yet to hear a PWM amp which sounds better than a decent class D. Multichannel DACs can also act as amazing crossovers with almost unlimited DSP capabilities but the price is obviously higher.

I don't feel knowledgeable enough to comment on your battery choice and setup but I'm sure there are folks here who know everything about it.

Let us know how your speakers will look like. I'm really curious and a 5 way horn sounds very intriguing...and challenging :)

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Generally for a battery charging regime to work properly it would be quite simple.

Use a current limiting  MPPT of solid output, say 30A minimum, and for the OP's system suggest a 250w panel or 2. This would form the basis of supply  maintenance..

 

If your front end source streamer is a different voltage, use a dcdc converter, like the 5 buck (pun intended) adjustable 10A in the photo (my 5v Raspberry PI 3 supplier)

 

Would also suggest never underestimate the need for solid capacitance.

Have found that strategically introducing capacitance for supply bus rail stiffening an absolute must, even with larger, say 770Ah 12v, yea true.

 

This is true for both amplification stage and front end, from experience

 

Watching on.

 

I have the same mains power inverter as you so some interesting things could come out of that. 

 

 

 

IMG_1145.JPG

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Note, don't go pulling multi voltages from the same string of batteries,,,,,,,,,trust me this leads to problems (been there)

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Thanks guys for the input and advice.

 

Just to clarify:

 

The fantasy is a long-term option after retirement from a city based job. By the time I can do it models of batteries and Class D car audio gear will have evolved significantly so the design stage Im doing is about broad concepts rather then particulars.

 

The I2S input Class D chip and amp I linked to above seems to have volume control inbuilt plus programmable individual attenuation and equalizers-crossovers so future chips should be even more sophisticated.  So in theory 10 chips can be linked to one volume control allowing one remote to control the lot in sync.

 

The figures I calculated are power at less then 0.1% distortion which I think is insignificant compared to driver-horn THD so hopefully the amps wont be too much of sound bottleneck. In theory digital input Class D with no DAC or preceding analogue stage should be able to sound great.

 

I think the best way to listen outside will be to design the shack so it explodes open with the outer walls folding back for indoor-outdoor living and allowing the horns to just be toed out and with their controlled directivity blasting into the garden.

 

Its a fun fantasy and dreaming at this design stage might allow even more fun making it happen in future.

 

 

Edited by Nada

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Wonder how sophisticated the amp synching is at the moment. Could you paste the link to the actual amplifier you were considering? I can only see the search results in aliexpress.

How would you like to work around the timing issues between the main speakers and the bass in the setup where the wall is open and you tilt the speakers to face outdoors? If the bass if fixed you would need switchable settings to time align the bass. I'm also worried that in such a setup your wall/doors behind the speakers could act as a "rattling device" and some serious acoustic treatment would be required for indoor listening.

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3 hours ago, baMarek said:

Wonder how sophisticated the amp synching is at the moment. ....

 

Amp Syncing? I was thinking of using just one master clock to rule them all.

 

As an example of one DDX unit with I2S direct input there is http://www.st.com/content/ccc/resource/technical/document/datasheet/9b/59/47/c6/2d/59/4c/56/CD00166760.pdf/files/CD00166760.pdf/jcr:content/translations/en.CD00166760.pdf 

 

By the time I retire there will be even better chips so Im not taking this chip seriously but as an example note the external pins on the STA333BW for bit clock and word clock input allowing superb synchronization.

 

 
Quote

 

The serial audio data input interface accepts all possible formats, including the popular I²S
format. The high-quality conversion from PCM audio to FFX PWM switching provides over
100 dB of SNR and of dynamic range.
Also provided in the STA333BW are a full assortment of digital processing features. This includes up to 5 programmable biquads (EQ) per channel ......audio preset volume loudness, preset volume curves and preset EQ settings.
The DRC dynamically equalizes the system to provide a linear frequency speaker response regardless of output power levels..

 

 
plus internal channel mapping to run them in mono config with cross-over and time delay programmable options.
 
I think this kind of programmable DSP-DAC-pre-amp module could dominate future active speakers allowing as it does for a perfectly integrated product.

 

3 hours ago, baMarek said:

.........I'm also worried that in such a setup your wall/doors behind the speakers could act as a "rattling device" and some serious acoustic treatment would be required for indoor listening.

Thanks for the warning. I wonder if cunning design and good build could sort your valid concerns eg   RIBA HOUSE OF THE YEAR 2016

OF

 

 

 

 

:

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On 12/30/2016 at 5:15 PM, Nada said:

 

Amp Syncing? I was thinking of using just one master clock ring to rule them all.

 

 

One_Ring_Render.png

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