Battery powering a Yamaha P45 plastic piano

For a few years, now, I've been running my Yamaha P45 plastic piano off batteries when I took it out on gigs. Likewise, with the desk light I built for it. I have a battery attached to the piano with adhesive velcro, and another attached to the stand with the light. I also have a second velcro patch on the stand, so that both batteries can be fitted there.

Running off the mains has its problems (being tethered to a wall socket, unreliable multi‑way mains power boards, horrible noises when plugging and unplugging audio leads, and the potential to damage equipment when doing so). Battery powering them, and attaching them directly to the equipment, makes it very convenient when you have to move things around, and avoids a lot of the noisy connection problems.

This was very simple to do with this piano, since it runs from 12 volts DC, around 1 amp maximum. Rechargeable batteries come in that voltage, and there's plenty to choose from with enough capacity (likewise with suitable battery chargers). All that I had to do was attach a suitable lead, through a protective fuse, to a battery.

Be aware that some parts of the piano are directly powered from the 12 volt supply input and expect it to be externally regulated (that means two things—voltage stability, and being very close to 12 volts). Likewise with other battery‑powered devices.

The piano needs up to 1 amp (in my tests), and the supplied plug pack is 1.5 amps, so the fuse should be rated for close to that. If the battery and cable is more than capable of supplying 2 amps, then a 2 amp fuse ensures you won't get nuisance blows, and that it will still definitely will blow if the connection is shorted.

But rather than fuses, I used a self‑resetting 20 watt polyswitch. They get hot when too much current passes through, then go high‑resistance (limiting the current), and stay that way until power is disconnected. Then they cool down and reset (it only takes moments). Considering that these DC plugs easily get shorted out, it's far more convenient, and economical, than having to replace fuses (and having to take spare ones with you).

[photo of] — polyswitch protected battery pack

My piano requires positive on the plug tip, and its circuitry is negative ground. But always make sure of what polarity your equipment uses before making your own power cabling. Make sure you get the polarity right, and fuse the supply side. In the above picture you can see that I've put red and black sleeving on the wiring to show the correct polarity for my equipment, and marked the connectors with T for tip and S for sleeve.

You should always use a protective fuse when using high current sources (and batteries are), particularly when the type of DC connector used can be easily shorted out (and these can). And the fuse should be as close to the battery terminal as possible, to protect against any wiring problems.

During my bench tests, a plug and socket both turned out to be badly manufactured and the socket shorted out the plug, and came close to setting the wiring (and other things) on fire. In the few seconds before I managed to disconnect the battery, there was smoking and melting insulation dripping off orange‑glowing wiring, which then started shorting together as well. Also be aware that the insulation over wiring that's thin enough to fit into these DC connectors can be all‑too‑easily sliced into by accident, as well.

On some of these plugs, the insulation between the tip and sleeve is too small, the sleeve can overlap the insulation going right to the end of the barrel, the external diameter of the tip connector can be too wide and not recessed into the insulation, and can short out against other things while being carried, or plugged into some sockets. During my tests I had a socket where the pin that goes into the tip had a wide flange on it inside the socket, and it shorted out the tip to the sleeve of the plug.

When using these types of connectors you always have to check a variety of mechanical aspects of them. The width of the barrel, its length, the internal diameter of the tip connection, and whether the insulator between them is well formed. Quite apart from badly manufactured ones, they come in a variety of sizes and you need a connector that is a good fit. It should plug in and work, reliably, even if bumped. If you have to fiddle with it to make it work, you have mismatched connectors.

As well as check the electrical characteristics of the device and power supply (the voltage and current, the polarity, AC or DC supplies), making sure that you're plugging the right things together. There's a wide variety of incompatible equipment using the same connectors (this is another reason that I dislike them). Label your power supplies for which equipment they're supposed to go with.

I've had to repair equipment where people have used the wrong supply, and the wrong polarity, just randomly trying different ones until they find one that seems to work. Sometime the damage is cumulative, sometimes it's instant, and sometimes it's unrepairable.

Although it was tempting to fit the battery somewhere inside the piano, that would bring about its own problems. There probably is enough space, somewhere, but it means removing a lot of screws to disassemble the piano (since there is no battery hatch). Batteries inside equipment get forgotten about, and can cause damage if they fail. And there's the issue of how to connect them to a charger.

For this project I decided to use old‑school gel cell lead acid batteries, rather than the new‑age lithium ion batteries, because I feel that they're far safer. And yes, this page does detail some hazards with using them (because they can supply a lot of current). However, with these types of batteries what is most likely to happen under un‑fused fault conditions is that the battery will melt the wiring off and disconnect itself within a few seconds. And with a protective fuse, it'll just pop and that's the end of the problem within a fraction of a second. Lithium ion batteries are well known for requiring special chargers to try to protect them (general‑purpose chargers are often lacking in safety regards), spontaneous explosive combustion (when being charged, being used, or even when disconnected and completely isolated), belching out thick poisonous smoke, and burning people's houses down. Spent ones also need specialist disposal, which most people seem to be unaware of.

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Because of the near‑disasters with wiring as described above, and an incident where I can only presume a barrel plug got wedged against a positive battery terminal while being transported (shorting out the unprotected negative wire and burning its insulation off in mere seconds), I eventually made a few modifications:

First, I put 20 watt polyswitch protectors on both positive and negative wiring (that's something that I'm not that keen on doing).

Then, later on, I decided to replace the battery wiring with heavier gauge wire with thicker insulation—which won't fit into the barrel plugs, so I replaced them, too (I've never liked that kind of connector, anyway, they're often a very poor fit and unreliable). Changing them for something where both conductors are completely covered up.

And fitted matching power sockets on the piano and lighting accessories (the piano has its original socket, plus the new one, fitted in a spot where it won't get a ¼″ TRS plug accidentally poked into it while trying to find the pedal or headphone socket without looking).

The underside of the piano got plastered with a few labels, since it's often viewed from odd angles while cables are being patched in, and the original raised black writing on black background is damn near impossible to read (so it got a white paint texta dabbed over it). The toggle switch is an added option to keep the speakers enabled when something is plugged into the headphone socket.

These types of plug and sockets were commonly used for microphone connectors on some equipment (more so the 4‑pin versions), and are often used as power connectors on a variety of equipment. They have a screw‑on locking collar which will stop them falling out accidentally, which is handy to prevent that, but also means the connectors can't simply unplug themselves if the cable is yanked. I've seen them described as GX16 aviation connections, sold locally with versions from 2 to 8 pins as two‑way radio microphone connectors. And they come in a small variety of sizes, reflected in their name; the GX12 chassis connector has a 12 mm mounting hole, the GX16 needs a 16 mm hole, the GX20 has a 20 mm hole, and there's some even larger versions (with the larger versions able to carry more conductors than the GX12). Unfortunately, neither these, nor the barrel plugs, are particularly robust against being stepped on or crushed in transport. I'd have to go to something like 4‑pin XLRs to be that robust, but XLRs are too big to fit into this equipment in a convenient spot.

There is no standard pin‑out for using these connectors, for anything. Everyone who uses them has their own way of wiring them up, for whatever it is that they're using them for, so I simply went with positive on pin 1 and negative on pin 2.

They're not a perfect connector, but are a reasonable choice, and will be fine with people who handle equipment sensibly. It is possible to force some of them in the wrong way (considering their traditional use, for microphones, this probably wasn't a major concern). Of course I have the common sense to not force connectors together, to first get them closely into the correct orientation by eye (and I've added some white paint into the plug's alignment notch to make things more obvious), then just giving a slight wiggle to properly line them up. But some people pay no attention to what they're doing, and will aimlessly poke things into place and grind things round and around until it seems to fit, breaking things in the process. If I expected other people would be using my equipment, I might opt for the 4‑pin version, instead, where a plug forced in the wrong way around wouldn't be able to electrically connect the battery. Again, a 4‑pin XLR (an video production industry standard connector for 12 volt DC connections) would be a better choice, except that there isn't room on this piano for one where its connector bay is located.

Battery powering a Yamaha P45 piano

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