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Types of batteries and their transient/steady state properties and aberrations. Need
Types of batteries and their transient/steady state properties and aberrations. Need
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Old 28th March 2020, 01:13 AM   #1
manueljenkin is offline manueljenkin  India
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Default Types of batteries and their transient/steady state properties and aberrations. Need

I'm building a "transportable" battery powered dac+amp combo. The energy source will be one or two 14.8v rechargeable batteries (the ones jumbled together in the form of a square)

As far as I'm aware, power supply is one of the most important components of the analog sections. I'd like to know the list of battery types and their load driving capabilities so I can start designing the power supply network.

Online searches lead me to multiple competing opinions. One says batteries are better suited to constant load. Another says batteries are better suited to pulsed load so that the space where it doesn't operate gives buffer for the depletion region to regenerate. This is apart from the linear models where we have internal resistance models etc.

I'm not super well versed in batteries, but I kind of have two approaches I can think of. In case the battery can sustain a load very well along with transient powers, I could be using a LDO + some filtering and that would be it.

If not, I shall be using two batteries and a switching logic + active components to generate somewhat kind of an AC like waveform (one battery doing positive, one doing negative) and then an active power filter+ rectifier to generate stable dc. Since a single battery is not operating continuously, it might be able to get more stable if that aberration exists, and make the non linear issues of the batteries disappear when seen at the power input end. I could also possibly recharge the battery when in use without disturbing fidelity. The rectification circuit is present in my burson fun where it does a switching operation at about 170khz and then rectifies it, hence pushing any ripple noise etc well beyond the 170khz band.
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Old 28th March 2020, 02:20 AM   #2
manueljenkin is offline manueljenkin  India
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I'd also love to know if there exist blogs/websites who measure batteries. I came across a few, and I'll update this post with that once I get back those links.
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Old 28th March 2020, 03:26 AM   #3
sgrossklass is offline sgrossklass  Germany
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What battery chemistry are we talking? LiIon, LiFePO4, lead acid / gel cell?

What sort of output power do you need? Class D or AB amplifier?

Like everything involving chemistry, batteries are more or less slow. You want no shortage of parallel capacitance for load peaks. Look at what the car audio guys are doing - they use massive supercapacitors. Since you probably just want a few dozen watts, you'll probably get along with more modest sizes, but I'd still expect >10000 F.

Burson Fun appears to be a headphone amplifier, Class A no less? Looks like it can be supplied with a PC Molex, too. Apparently the first thing it does with its input voltage is run it into 2x 2 DC/DC converters, probably a step-up job plus an inverter each to obtain a split power supply of +/-18 V or so.

If that's the case, it shouldn't be too picky. I'd say get a 1000-3300 F / 25+ V capacitor, a DC/DC step-down board (maybe a common 2.5 A type), plus some sort of battery management / charger, and you should be set.

DC input is rated 5 A @ 12 V and the thing apparently ships with a 6 A power supply - does it really need that? Maximum power output is 2x2.1 W into 32 ohms, so that's at least 16.8 W of power input (Class A push-pull efficiency = 25% max) and probably closer to 26 W. (The idle current of at least 180 mA would mean 13 W of idle power dissipation in output transistors alone.) That would be about 30 W in terms of linear power supply and maybe twice that in a SMPS to account for a nervous over-current protection.

That said, if it really were that power-hungry it would get quite nice and toasty. The enclosure is not that big.

Do you have any way of of determining what its actual idle power consumption is? We are potentially approaching the magnitude of a QRP rig or portable boombox here. That's going to be quite a chunky battery if you want some decent play time. It would still be "portable" in the literal sense (I mean, the definition of "portable" in the late '70s was "one man can carry it and it'll fit underneath an airplane seat"), but have you seen portable audio devices from the last 2 or 3 decades? Do you really want to be pressing a device that is in no way optimized for power efficiency into a portable application?
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Old 28th March 2020, 04:05 AM   #4
manueljenkin is offline manueljenkin  India
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Thank you very much for the detailed reply. Yes I'm looking at maybe 2-3 watts into 32 ohms or so load for headphone amplification. My headphone is shure srh1540 and hd800 and with high dynamic range music, I'm near maxing out the pot on my burson fun so I do think I'll need to supply 1 watt peaks. I plant to purchase srh1840 which is a lot more demanding and hence the need for 2-3 watts.

I can just repurpose the burson fun using its molex for a beginner trial but my bigger desire is to build an amp of my own, preferrably current feedback, like the ones from my apogee groove but in a more powerful unit. Regarding the burson fun, i haven't been able to measure it's input power requirements, but it's far from getting hot. I doubt it consumes that much power.

What battery chemistry are we talking? It was actually part of my question. I'd love to know more about different battery chemistry and see how it works.

Regarding battery life, I'd be more than happy if it could sustain 2-3 hours on a charge. I rarely listen for more than an hour or more a day and I almost never have sustained listening sessions above 3-4 hours. I want it to be just movable so I could listen in my garden or balcony while working on my laptop. I hate being strapped to a wall outlet.
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Old 28th March 2020, 09:34 AM   #5
trobbins is offline trobbins  Australia
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You haven't identified the equipment being powered, or its power supply requirements.

KISS - keep it super simple - a linear regulator to provide a constant supply voltage to your equipment, with an indicator or auto-cutoff for a suitably low battery voltage. It doesn't matter what the battery is then, except for having enough voltage and energy, and you having a suitable charger to maintain battery health.
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Old 28th March 2020, 06:59 PM   #6
Mark Tillotson is offline Mark Tillotson
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Basic to Advanced Battery Information from Battery University is a useful resource.
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Old 28th March 2020, 07:14 PM   #7
MartyMG is offline MartyMG  United Kingdom
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This is an eye-opener!
YouTube
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Old 28th March 2020, 07:46 PM   #8
cbdb is offline cbdb  Canada
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Wow. So do the Chineses deliberitly lie about there battery specs! And not just a little.
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Old 28th March 2020, 07:57 PM   #9
Mark Tillotson is offline Mark Tillotson
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Yes, the Chinese amp is a very different beast from the SI unit we know and love. Watts too in many cases. My advice is never buy anything important that doesn't have a datasheet, this applies to cells and batteries too. Of course I refer to the fraudsters not the legit. Chinese brands and suppliers, but the counterfeits are everywhere too so its very hard to know unless you buy via specialist importers who source the real stuff and protect you from the cowboys.
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Old 29th March 2020, 12:43 AM   #10
manueljenkin is offline manueljenkin  India
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YouTube

7.24 is kind of what I meant by transient or steady state power handling (depending on what topology we are looking at). For class A I guess it's gotta sustain that amount of current throughout.
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