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A Yamaha digital piano is powered by a mains power-supply. The power-supply states the following input/output values:
INPUT 100-240V~50/60Hz 0.5A
OUTPUT 12V === 1.5A
(Where I have written === there is actually a solid line over a dotted line).
He is keen to go busking with this piano. I am therefore looking to substitute the mains adapter with a 12V battery which I have to hand. I don't want to risk damaging his piano. Should I place some sort of circuit (voltage regulator?) around the battery to protect the piano. Can anyone assist in telling me exactly what the circuit diagram should be?

pic1 pic2

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    \$\begingroup\$ @newbie 7 Ah! It’s an entirely different physical quantity. \$\endgroup\$ – winny Jul 28 at 11:08
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    \$\begingroup\$ @newbie That’s besides the point. You are comparing kilometers and kilometers per hour as they where the same thing. “How far is it?” “120 km left now.” “How fast are we going?” “90 km/h” “Do we need to walk the last 30 km?” \$\endgroup\$ – winny Jul 28 at 11:14
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    \$\begingroup\$ @journeyman Please measure the unloaded output voltage from the adapter with a multimeter and post the result to give a definitive answer for you. \$\endgroup\$ – winny Jul 28 at 11:15
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    \$\begingroup\$ @winny oh lol i didn't get your point the first time! yes it's 7A per hour not 7A thanks for correcting me. \$\endgroup\$ – Hamed Jul 28 at 11:16
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    \$\begingroup\$ @newbie Gah! You are making it worse. IT’S not per hour! Ampere MULTIPLIED by hour = Ah. \$\endgroup\$ – winny Jul 28 at 11:24
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The power supply looks like a regulated 12V switchmode power supply, therefore it should output 12V under varying load conditions. The battery is not regulated, a charged battery can have more than 13V and the voltage drops when discharging the battery. If the piano needs regulated 12V then connecting to a battery is a bad idea. It is also possible that the power supply is unregulated so the piano might work with the battery. If you have the service manual of the piano maybe a safe voltage range can be determined. Perhaps a range reads on piano 12VDC input connector. It is not even clear how much current the piano needs, it may read on the piano or manual. If you do try this, at least put a fuse (2 Amps?) right at the battery terminal to protect people from burning wires and exploding batteries.

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