2. analog
  3. 169887-136649

Possibly Dumb Question re:Battery as a power supply

I have bought a new Clearaudio Performance DC Wood turntable.  I plan to drive to the dealer in Atlanta and pick it up next Wednesday.  I have seen the wall wart power supply which comes with the TT, and it is not a pretty sight.  Clearaudio sells an upgraded 12V battery and charger supply for "only" $1,200.00.  I don't wish to present myself as a parsimonious individual,  but $1,200.00 seems a bit steep to me.  I am wondering what problems would ensue if I bought a moderately sized (say 25 or 30 lbs.) , sealed, lead acid, 12V rechargeable battery; attached the proper wires to connect to the TT, and used it as a power supply.  When the battery runs down I could just take it to my workshop and use my electronic, automatic battery charger I use to recharge car, truck and tractor batteries to bring it back to full power.  As little current as the TT uses this shouldn't be too frequent a chore.  It is just a possibility, but if it is feasible I might try it.  I would really appreciate any and all comments, criticism or warnings.
kingharold
terry9
2,328 posts
 
Thank you, @imhififan  for new information. This shows that a 12V battery should be fine. Still, I would never recommend connecting an expensive component to an unfused battery. And while doing that, why not protect the battery too? I mean, diodes don't cost much.

But then again, I wouldn't want to be accused of overthinking the OP's investment.

Phoenix, from the MC7812 data sheet:
ELECTRICAL CHARACTERISTICS (Vin = 19 V, IO = 500 mA, TJ = Tlow to 125°C (Note 17), unless otherwise noted)

One last thing: different battery technologies have different noise levels. It's probably not an issue; but if that Clearaudio pack uses NiCds, maybe it's for a reason, and $1200 for NiCds is not excessive.
lohanimal
659 posts
 
@lubachl 
I actually have an Amazon Model One - it's a superb motor unit - I think that is a great buy because the Amazon motor is actually not your usual DC motor - I think the UK importer at the time advised me it was from a nautical clock. It is exceptionally smooth and quiet.
@kingharold - why more people don't rug up a car battery is beyond me - they can easily be tucked away. Lithium Ion is particularly good as the voltage drop is very consistent. Be careful though not to discharge them too much as they become unstable and in fact volatile. I know all of this from Radio Control car racing. Not all lithium ions are created equally and I am more than happy to recommend those used in RC racing that are of a good quality. 
phoenixengr's avatar
phoenixengr
92 posts
 
@terry9-

ELECTRICAL CHARACTERISTICS (Vin = 19 V, IO = 500 mA, TJ = Tlow to 125°C (Note 17), unless otherwise noted)

That is the standard disclaimer at the top of the chart of parameters. It is the operating point used in all of the measurements below it. One of those parameters is DROP OUT VOLTAGE which was listed as 2.0VDC (assuming 500mA load) on the datasheet I found on-line. The disclaimer does not mean the device has to be operated at those parameters, only that the published specifications were measured at that operating point.

Agree with your point about noise not being an issue. I don’t know that I’ve ever seen a measurement for this on a battery, but the internal resistance of a fully charged battery is extremely low so the equivalent noise resistance should be microscopic.

I would think a Sealed Lead Acid battery would be better (and cheaper) than a NiCad. SLAs tend to last longer and don’t suffer from memory effect if they are not fully cycled between charge and discharge as NiCads do. YMMV.

terry9
2,328 posts
 
Phoenix, agree with what you say, but let me add that 19VDC is the voltage at which the part is known to meet spec. With obvious consequences - which, to an engineer such as yourself, pose no issues.

Battery noise was measured by someone in Germany some years back. I think they were looking at powering phono stages. He found that all technologies made a fair bit of noise, except NiCd, which measured at the noise floor of his HP instrumentation.

Anyway, I'm in the process of designing a new phono power supply based on NiCd's for listening and a linear PS for warming, and the unexpected issue is charging. Seems that no-one does it right - i.e. warning at 1.1VDC per cell to avoid memory effect and separate current source for each cell.

Expect to start building in a couple of weeks, will let you know if it makes a perceptible improvement over alkaline with LC filter.
terry9
2,328 posts
 
Previous experience with improving power has shown a worthwhile improvement in sound. This manifests as smoother with no shrill overtones or sibilance (dare I say 'more musical') as well as quieter. 

1. Isolation transformers
2. Brute force DC rails for amps: 200kg inductors and a Farad of capacitance
3. Alkaline battery with LC filter for phono/pre
4. Quadrature AC adjusted to AC motor

My experience. YMMV
More to discover