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Old 20th January 2007, 03:27 PM   #1
pjpoes is offline pjpoes  United States
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Default Building a dual rail battery power supply?

Can someone point me into the direction of some information for building a battery power supply. I want to power a phono preamp with batteries and need +/- 12-15 volts.

Some questions I have are, how do you get the negative and positive rails? Also do you still need or is it a good idea to still regulate a battery supply. If so, how important is the quality of the regulators. Would a very simple way to impliment this be to simply insert the battery supply after the diode bridge but before the regulators of a device designed to work on AC.

Thanks for any help you can offer, I appreciate it.
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Old 20th January 2007, 04:30 PM   #2
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Default Re: Building a dual rail battery power supply?

Quote:
Originally posted by pjpoes
Some questions I have are, how do you get the negative and positive rails?
You just tie two batteries in series, negative to positive. The point where they're tied together is connected to ground, and the other ends become your + and - rails.

Quote:
Also do you still need or is it a good idea to still regulate a battery supply.
Some will argue that it is, and they can speak for themselves, but personally I prefer just using a bit of capacitance across each battery, rather like the reservoir caps in a typical AC supply. 4,700uF per rail should be fine for a phono preamp.

Quote:
Would a very simple way to impliment this be to simply insert the battery supply after the diode bridge but before the regulators of a device designed to work on AC.
Well, that would work (Jean Hiraga did such a power supply for one of his power amp designs if I'm not mistaken), but I don't see any need for it. Your phono preamp isn't going to be drawing any current to speak of so it's not going to tend to draw down the batteries appreciably while listening.

I'd recommend using a dual battery charger and then just have your power switch switch the batteries between the preamp and the charger.

While it ain't exactly cheap (about $125 I think), Patco makes a nice dual charger (the IntelliTender 300) that has floating outputs so it can be wired up like a split supply (i.e. positive, negative and ground) which means you can just switch the batteries directly over to the charger without having to separate the two batteries.

se
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Old 21st January 2007, 10:56 AM   #3
Gordy is offline Gordy  United Kingdom
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From your original post I perceive that you have little electronics experience, so I suggest that at this stage you do not attempt to connect anything DIY directly to anything with AC floating around inside it.

Two batteries (or two sets of batteries), centre-tapped to ground and with a little capacitace across the terminals (as noted by Steve Eddy) will be fine for a phono stage. The typical current draw will be just a few milliamps, so build your power supply separate from anything AC and have a listen. Remember to include a switch to disconnect both the positive and negative lines when you are not using the circuit; in this way battery life will be more reasonable.

If you are dissatisfied with the results you can always add regulators later.
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Old 21st January 2007, 04:52 PM   #4
Calvin is offline Calvin  Germany
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Hi poes,

Id use sealed lead-acid accumulators since they are relatively cheap, very easy to handle and last 5-10years. Im runnung such a PS for 13 years now and have changed the accus once.
I use 6 series connected 6V-types centretapped for pos and neg voltage. The charger circuit are simple LM317 constant-voltage regulators connected in series. Both regulators are set to ~21V.
I prefer a regulation behind the batteries to have a low and predictable source impedance and to have really equal and constant voltages and a protection for the circuit (most OP-amps dont like more than 18V max as supply and if the voltages are different, You get offsets at the OP-circuits output).
If I activate my amp a relay switches the 230V AC-Supply of the charger off.
You can easily add kind of a watchdog circuit to monitor the battery voltages and switching the AC-Supply on in case of a battery-low-state. look for TLC7705 and likes.

Ive built a 12V-lead-acid-battery supply for a Turntable manufacturer to supply for the motor. It charges the battery for a certain time (user changeable), depending on the batteries status with two different charging levels (hi-low), and monitors the battery voltage and starts charging automatically .

jauu
Calvin
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Old 22nd January 2007, 08:10 PM   #5
pjpoes is offline pjpoes  United States
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Well I wouldn't say I have little electronic experience. I've been building kits since I was 7-8 years old, and messing with electronics for as long as I can remember. I also went to college for 1 year for electrical engineering, where I did learn the basics, but then changed majors to Psychology, as I couldn't deal with the Math. Having said that, I'm far from experienced either. Most of what I have built has been kits or modifying prebuilt items. Currently I am modifying my Meixing Tube amplifier and modifying an X-LP phonopreamp, which is what this question was for. I have built many regulated power supplies using basic 3 leg to-220 regs, and just recently completed my first Jung regulator. However, I haven't ever messed with battery supplies, and decided I wanted to give it a try. Now that I see how simple it is, I definatly plan on it.

As for the AC/DC business. I never intended to run AC and DC through the unit at the same time, or anything like that. I think one of the other posters understood what I meant when I said, insert this battery supply just before the regulators, but after where the old Diode bridge was located. Another option is to simply remove the regulators and tie in at that point, so I would still have the capacitors in place.

I actually want to try doing it with D cell battiers, like Sutherland did, and because I have multiple universal Energizer battery chargers designed for the new quick charge batteries, which I use for my photo gear. These batteries offer lower resistance and higher voltage than previous rechargables, along with lasting longer. I also have 8 of the D batteries I would need, so it would be a cheaper option for now. I have to see what it will cost to buy 8 more, if its the same price as a set of small rechargeable 12 volts batteries, then I will just go that route, as I already have a charger for those too that might work fine.
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