Why Dynamic Power-Path Design Matters More Than Battery Size

By Dr Dominik Ostrowski, MIET — Founder and embedded-systems engineer, Think Radio

Z-RAY started life as a wrist-worn device, and a wrist-worn wireless light has almost no room for compromise on power. There's no space for a big battery, no tolerance for a bulky charging circuit, and no excuse for wasting current on anything that isn't making light. Those constraints never went away when Z-RAY was re-cast from a wristband into a portable venue light — if anything, the scale-up (a larger high-quality battery, a leading-edge charging system, a real RGBW LED with constant-current drivers) is what has let a system designed for something worn on your arm turn into one of the most power-efficient full-size wireless fixtures.

Charging that doesn't ask you to think about it

Z-RAY charges over USB-C Power Delivery. Practically, that means it charges on any phone charger you already own, and fast-charges on any of the common fast-chargers already in most people's bags — nobody needs to go hunting for a proprietary brick the night before a gig. That sounds like a small thing until you've been the person standing in a green room with the wrong charger for a piece of gear that only accepts one specific plug. It's a common letdown in this category, and it was a careful decision to not repeat it.

Where the power actually goes

Z-RAY runs on a single 18650 cell, and the design goal was simple to state and hard to hit: virtually all the power coming in should end up in the LED, not lost to housekeeping elsewhere. In practice that shows up as two very different current draws depending on what the unit is doing. In standby, Z-RAY draws 12 microamps. Actively listening for the next radio packet from STATION-X, it draws 12 milliamps — which is still very, very low indeed compared to the size of the battery and the typical duration of a gig.

"How long does the battery last?" is the question I get asked more than any other, and I've settled on an honest, slightly cheeky answer: you can do a gig. You can go home, forget to put it on charge, and still do a second gig. Probably best not to try for a third — you might get away with it, you might not. That's not a spec sheet number, but it's a truer answer than a lab-conditions runtime figure, because it's the actual question a DJ or a venue tech is asking.

And when the battery does run out, Z-RAY doesn't leave you guessing. It handles a low battery gracefully — a one-second fade to black, not a flicker, not a stutter, not the light doing something erratic mid-song. If it's going to go out, it goes out predictably.

Dynamic power-path design, and why it's not the same as "has a battery and a charger"

Most rechargeable devices treat charging and running as two separate states: you're either using battery power, or you're charging the battery, and doing both at once is either unsupported or handled badly. Z-RAY uses dynamic power-path instead, which changes that entirely. You can plug it into USB at any point — mid-set, between songs, doesn't matter — and it will run continuously on or off the charger, sharing whatever power is coming in via USB. The LED's needs get served first; whatever's left over after that goes to topping up the battery. Plug it into a fast charger, and Z-RAY can run indefinitely at maximum LED output without ever pulling the battery down, because the incoming power is enough to cover the LED and still leave a surplus.

There's a rule of thumb in battery-powered gadget design that a device should charge at roughly twice the rate it discharges, just to keep the ratio of "time spent using it" to "time spent tied to a cable" reasonable. Z-RAY does about four times that — a 4x charge-to-discharge ratio. In practice, that means it doesn't feel like the unit is constantly owed charging time relative to how much you actually get to use it, which matters more than a headline runtime number once you're actually living with the thing on a regular gigging schedule.

The other features that fall out of getting the fundamentals right

None of this exists in isolation from the rest of what Z-RAY does. Hold Last Light — a selectable, predictable behaviour if the connection to STATION-X is lost — only feels trustworthy because the power system underneath it behaves predictably too. A simple 4-channel RGBW mode and a more sophisticated 16-channel mode with flexible synchronised strobes both draw on the same current budget the power system was built to protect. None of it is the kind of thing a buyer walks in asking about by name. It's the kind of thing that, done properly, they simply don't have to think about — which, on a piece of live-event kit, is exactly the point.

The real world

A bigger battery is the easy way to promise a long runtime, and it's also the way you end up with a heavier, bulkier fixture that takes longer to charge and still runs out mid-show if the charging behaviour underneath it isn't actually good. Z-RAY's approach was the harder one: get the standby and active current draw as low as the application allows, make the charging system fast and universally compatible rather than proprietary, and let dynamic power-path mean the battery and the mains supply are never fighting each other for priority. None of that is visible on a spec sheet the way "8-hour battery life" is — but it's the difference between a light that survives a real gigging schedule and one that just survives a bench test.