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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
2,333 posts
 
I salute you, Harold, and your attitude towards what awaits us all. Condolences for Mary.

About that battery supply, it’s not hard to engineer something like that, but it does have to be engineered. A DC motor’s speed depends on the supply voltage, and when a battery discharges, well, it discharges, and the voltage declines. That means the TT’s speed will be far from constant unless it is precisely regulated, and that means more than just an MC7812 regulator chip.

Unless you want to take it on as a DIY project, I’d buy the power supply, pricey as it is. To DIY, a good place to start is "Art of Electronics" by Horowitz and Hill. More I think about it, I’d buy that battery power supply if I were you.

Full disclosure: I built the power supply for my AC motor TT, full quadrature, silent. But it was a project, and it would have taken real time if I hadn’t been retired with the equipment to hand.
lewm
13,012 posts
 
Terry, you make some very good points, which make me wonder what is the voltage rating of the battery in the Clearaudio kit. You can’t add regulation, which is needed to hold V constant, to an unregulated 12V output and still have 12V downstream from the regulator, assuming the motor requires all of 12V. All regulators consume some V. So either they use a battery that puts out >12V or the motor runs on less than 12V.
millercarbon's avatar
millercarbon
12,531 posts
 
Never misunderestimate the ability of the forum to overthink even the simplest things. Full disclosure: I converted AC to DC battery, did none of that, and it was audibly quite a bit better. Just not that hard. Unless you make it so.
terry9
2,333 posts
 
@lewm , just so. An MC7812 requires 19VDC if I remember correctly. And it's hard to know the characteristics of any internal regulation or the motor, and it may not even be obvious about how motor speed relates to platter speed.

Doable, sure. How much of a project? Depends on your luck and how much test equipment you have lying around. If you don't have any test equipment, it'll take some pretty dumb luck not to void the warrantee.

Only way around it I can see is to measure (or otherwise determine) the voltage on the manufacturer's battery pack. Then replicate with a comparable rechargeable pack of your own. And don't forget to protect the pack with a diode and protect the motor with a fuse!
lewm
13,012 posts
 
Drop out due to VR is usually dependent upon many factors including current draw most importantly. I built a PS for my Klyne 6LX which has regulators on board the audio chassis. The PS needed to put out not more than 4-6V above the needed regulated V. I am sure an 18V battery or a 24V one at most would work for the clearaudio. We don’t have enough info even to guess.
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