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What's the easiest way to regulate a 12 V battery to a regulated 12 V power source?

Preferably, I'd like a ready-made product so that I could avoid having to show my lack of skill with the soldering iron. :-) More complex answers are fine, too, as long as they are insightful.

I'm thinking of powering a 12 V / 600 mA stage piano/synth by replacing its AC/DC converter with a small car battery for portable use. Because the device is not designed for in-car use, I understand that regulation is the safest bet. (Of course, I could buy an inverter, but I'd like to "do it right" and get rid of the DC/AC AC/DC conversion.)

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  • \$\begingroup\$ there are major differences here if the input already has some regulation on it. I would be that it does not. \$\endgroup\$ – Kortuk May 5 '11 at 11:32
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    \$\begingroup\$ Here is a recent 12V supply question that may provide some useful background: electronics.stackexchange.com/questions/13421/… \$\endgroup\$ – Andy May 5 '11 at 15:46
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    \$\begingroup\$ Are you willing to open up the synth and see if it has an internal regulator on the power supply connector? \$\endgroup\$ – endolith May 5 '11 at 19:00
  • \$\begingroup\$ Thanks for all the answers. I understand that unless I can get proof that the device is happy with 10-14V, there is a risk involved when plugging it directly to a car battery. However, regulation via some sort of boost-buck converter is a more complex solution that also wastes some power. I guess opening up the synth and trying to find the possible internal regulator is the way the proceed, although I'm not sure if I can find it. \$\endgroup\$ – ahnurmi May 9 '11 at 11:22
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What a regulator actually does is to smooth out variations in voltage to make a source look more like a battery. In a case like this, you don't have to worry about the source voltage changing much, so the main advantage of regulation is moot.

Often equipment that's designed for low-voltage DC will actually accept a range of voltages. Sometimes it isn't, and really does expect a regulated supply. The problem here is, what's the range that the synth will find acceptable? Admittedly, applying regulation solves that problem by nailing the voltage down to something that's supposed to work, but the thing is, voltage regulation gets complicated when the source and the output voltages are closer than about 2 volts, because regulators need some headroom to work with. Automotive batteries nominally sit around 13.8V; worryingly high if your device wants a regulated 12V input, annoyingly low if you want to regulate it to 12V.

If you can measure the voltage from your present AC/DC converter, while it's connected to the synth, with the synth turned on, and that voltage is with say, half a volt of the battery's open-circuit voltage, you would probably be able to directly connect the battery, without a regulator.

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  • \$\begingroup\$ I would suggest adding some information about a buck-boost regulator. I do not have time right now, but if you cannot get to it I can try to look up information later. \$\endgroup\$ – Kortuk May 5 '11 at 11:32
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If you do this with a single battery, you will probably be fine. But if you decide to move it to a car, you must be very careful of load dumps. If you are using your synth in your car and you turn the headlamps off while the alternator is running, the energy in the alternator doesn't go away instantly. Instead, it appears as a high voltage spike - in some cases as high as 60V! I'd highly recommend a TVS and at least an LC filter to get rid of the noise which other systems in the car produce.

Also, don't forget an "idiot diode", to stop you reversing the polarity. Many manufacturers omit input polarity protection diodes.

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  • \$\begingroup\$ It would be interesting to see the OP move his "stage piano/synth" into a car. Headlamps on or not. \$\endgroup\$ – Kripacharya Jul 23 at 18:09
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Many musical keyboards don't particularly care about exactly what voltage they get, because they have internal regulation. Unfortunately, devices rarely specify the exact range of voltages they'll tolerate, in some measure because few wall bricks specify the exact range of voltages they might put out. A keyboard which nominally accepts 9-12 volts may be perfectly happy with anything from 6 to 15, especially if the voltage only goes up to 15 at times when the synth's current draw happens to be minimal, but if the manufacturer labeled the unit as accepting 6-15, someone might expect it to work with a so-called 15-volt wall brick that actually puts out 18.

Many devices with a 12-volt nominal input would be perfectly happy if driven directly by a car battery that was not connected a charger (or worse, something like a starter motor--starting a car can cause its +12 rail to swing up and down by dozens of volts).

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How about this from PowerStream? It's 12 V to 12 V for a UPS when used with an external battery. 3A, ready-made, rugged.

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Just use the battery as is. As long as you charge it properly. Maybe what you need is some kind of voltmeter on the battery to check if it's running down, instead of regulating it.

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I've done it often in the past (and precisely with some synthesizer) without any problem. A fully charged 12V car battery measures about 13V, and with that voltage I've never damaged anything.

I've also used 6V Lead batteries to replace 6V supply of my old Atari Lynx

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I once fried a 12v router with an attached USB air-card while using it on a RV. The router input was marked as 12VDC and the power supply was 120VAC and marked as 12V output as well. So I decided to run the router off my 12V RV house battery when there was no AC to plug in the normal adapter. In my defense, I knew from experience that a cheap 12V adapter might vary from 10v to 16v and that there was some leeway, at least enough I would imagine from the 11.5V to 14.2V range I observed from my RV dash voltmeter. What I hadn't observed was a scope pattern trace that might have shown me voltage that momentarily exceeded the window the device could tollerate, especially with a flakey alternator regulator of which in my old RV, everything is a little flakey. No worries though, I only planned to use it while the vehicle was parked.

I used it this way a long time, normally only using it when I was parked but I forgot and left it plugged in once and when I got to my destination, the thing would never work again (all the lights were on and it was frozen). I had to buy a new router so this time I purchased a 12V regulated supply to go on my new router and air-card which has eliminated the problem.
12V Rebulated adapter for router Of course this unit is only 1A (1000ma) output so I would imagine you would need something a lot more powerful if you are running an amp and speakers.

Still the issue I would imagine as is my experience is that running in a car would be your main concern with the alternator over voltage spikes as explained above. As the voltage gets too low, you start hearing so much distortion that you usually shut it down when it drops too low because it simply sounds so bad from distortion.

Anyway you said you don't like to solder but I found some cheap 12-20V in to 12V output oltage regulator ICs on ebay recently. I'll try to find one and give you the part number after the holidays.

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