Portable 48V

[mrkva]

Hey there, anyone has an interesting and clean solution for 'portable' (generated from lets say 9V) phantom power? Just ordered some LM2577 step-up dc-dc converters, but curious what else is out there! Thanks

 

[PRR]

Five 9V batts gives phantom voltage for about 50 hours. Unless you record many hours every day, this really beats messing with converters, IMHO. Note also that jazzing 45V out of a single 9V batt means 5X the current and 1/5th the life. So unless you will never run 50 hours of phantom, the battery cost is similar (with direct-stack a bit more efficient than jazzing-up).

 

[mrkva]

1/5th of a battery life? does phantom really need that much?
http://www.sounddevices.com/notes/general/phantom-powering-basics/
it is usually 2-3mA so with 9V lets say 10-15mA, which still not that bad

 

[sircletus]

1/5th of a battery life? does phantom really need that much?
http://www.sounddevices.com/notes/general/phantom-powering-basics/
it is usually 2-3mA so with 9V lets say 10-15mA, which still not that bad

PRR is saying that to squeeze 45 V from a single 9V source via a DC-DC converter (9v x 5 = 45v), the trade-off is that the DC-DC converter will have to pull 5x the current the 9V would otherwise be supplying (Power Equation, Ohm's Law, no free lunch in physics, etc.), regardless of current drawn by whatever mic you're powering.

 

[mrkva]

Yes, I understand. Just running around with 5 9V batteries does not seem practical nor cheap. Anyway, found this old thread.. inspiring:
http://groupdiy.com/index.php?topic=12807.0

 

[ricardo]

PRR's 5 x 9V PP3s is likely the cheapest, most trouble free and best portable solution.

But what mikes are you using?  Many mikes work well with much less than P48V .. some down to P12V.  This would simplify stuff and is also more efficient.

 

[JohnRoberts]

You can lead a mule to water...but he may be too stubborn to drink.  A passive stack of 9V batteries seems pretty cheap and easy to me. Also as Ricardo noted, you may not even need 45+V so could use a shorter stack.. Some lower voltage phantom supplies use less than the typical 6.81k build out resistors, but these still need to be well matched or tight tolerance parts, whatever value that is. 

There is probably a lot more discussion here about making 48V from 5V (USB) etc. If this is more of a design discovery project, than meeting a practical need effectively.  May even be an app note from a switcher chip maker somewhere out there. .

JR

 

[ricardo]

Some lower voltage phantom supplies use less than the typical 6.81k build out resistors, but these still need to be well matched or tight tolerance parts, whatever value that is.

There's a DIN standard for P12V which specifies 2 x 680R

But 'true' P12V is very rare.  I only know of some Sound Devices preamps that claim this and they use 6k8.  Probably only vintage German broadcast gear does this 'properly'.

But there are a LOT of 'professional' preamps that have wonky P48V.  My MOTU Traveler is P39V though I note it only claims 'Phantom' and has no spec.  All da wonky P48V's have 2 x 6k8
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http://groupdiy.com/index.php?topic=12807.0

mrkva, this is a good thread but the difference between that and your application is the word 'portable.  If you are a true SMPS guru, you would still only get LESS efficiency & idle current than 5 x 9V PP3s.  So you would probably still carry that pack of 5 x PP3s  ;D

In Jurassic times, I designed & made a 12V to +/-15V switcher with 90% efficiency on full load and small idle current .. but it was a LOT of work including a custom wound ferrite transformer.  Today, the knowledge & parts to do this are much more freely available ... but I would still buy a complete unit in a little shielded can with guaranteed efficiency, idle current & noise spec. if I needed this for real.

The R&D to do a good one is not trivial .. for me, more than the effort to design a SOTA mike preamp.

The 5 x 9V PP3s, I can knock up in a morning with guaranteed efficiency bla bla .. from parts available even in Cooktown, rural Oz, at the edge of the known Universe.  If your requirement is part of a complete mike preamp, I would power it from the 5 x 9V stack too.

But if this thread comes up with a simple design with uncritical layout, guaranteed efficiency bla bla, using only parts from Digikey & Mouser, I will be the first to congratulate you.

Note the design by moamps in that thread uses Unobtainium & only hints at efficiency bla bla

 

[zebra50]

5 times 9V works well!  Good alkali PP3s are still about £2 each from Farnell, so no great cost.

But fit an LED to remind yourself to turn it off.

 

[mad.ax]

But fit an LED to remind yourself to turn it off.

Make sure you use some low current/high efficiency LED then, and/or proper drive, otherwise a standard 20mA LED could severely load your battery pack...

Axel

 

[ricardo]

5 times 9V works well!  Good alkali PP3s are still about £2 each from Farnell, so no great cost.

But fit an LED to remind yourself to turn it off.

Probably more important for your supa dupa SMPS 9V to 48V upconverter.

For the simple 5 x PP3 'P48V' supply, just unplug your mikes. 

 

[emrr]

I'm thinking of a proper 1930ish rig with (6) 9V, a meter, and an adjust rheostat.  Now that would be hipster steampunk. 

 

[PRR]

> does phantom really need that much?

Some mikes use less than 1mA.

The old-old spec was 2mA max.

This was not enough for some mike designers. The present spec is that a P48 should deliver 10mA without harm and without affecting other lines on the same supply.

Some mikes today use under 2mA, but a pretty good number really push the 10mA spec. And you often can't tell by looking at the mike, sometimes not by looking at the sales-sheet.