# Q16 Pro: the test protocol for a constant voltage kit > Q16 Pro: the bench protocol for a constant voltage kit, calculating watts from volts and arbitrating between two retail listings that disagree. A device set in volts rather than in watts slips out of the usual comparison. There is no way to line it up beside a 25 W pod or a 220 W box without doing a calculation first. The **Q16 Pro** from Justfog works exactly that way, and that is what makes it the best possible support for laying out a clean protocol: here the wattage is written nowhere, it has to be derived. ## Testing a Q16 Pro with no wattage on the display The method comes down to three operations, in that order, and none of them calls for rare equipment. Measure the cold resistance on an ohmmeter, to establish the true value of the coil fitted rather than the value printed on it. Record the voltage genuinely delivered at each of the steps the device offers. Then calculate the corresponding wattage through Ohm's law, the power being the square of the voltage divided by the resistance. The result is a three column table: step, voltage, calculated wattage, valid for one resistance value and one only. Changing coil means running the whole series again from the top. ## What the listings declare, and why that is not enough The starting point of any protocol is to record the declarations before confronting them. On this kit they are plentiful, precise, and occasionally incompatible with one another. British and European listings agree on the core: a 900 mAh built in battery, a 1.9 ml pyrex tank, a 1.6 ohm bottom coil, a 510 connection and drip tip, a 16 mm diameter body, anodised aluminium construction and micro-USB charging. The adjustment runs through four constant voltage steps, from 3.5 V to 4.4 V, signalled by the number of lit indicators rather than by a screen. Retail listings add a maximum charging current in the region of half an amp, along with a protection list covering short circuit, overcharge, low voltage, overheating and overvoltage. Those two items bear directly on how a charging reading is conducted. The contradictions are a data point in their own right. The overall length of the kit is given as 125 mm on one listing and 130.4 mm on another, for what is presented as the same product. On a single retail page, the 1.6 ohm coil is quoted for 6 to 12 W in one paragraph and 8 to 12 W in another. A bench does not settle those gaps by deduction. It measures, publishes its own value, and flags the divergence in print. That is the only gesture that stops a spec sheet error circulating from shop to shop for years on end. ## Going from volts to watts on the Q16 Pro This is where the protocol becomes useful to the reader, because the calculation can be redone with no instrument at all once the resistance is known. With the four declared steps, 3.5, 3.8, 4.1 and 4.4 V, and the 1.6 ohm coil supplied, the device covers a narrow band running from a little over 7 W to a little over 12 W. Published reviewer notes give two concordant markers, around 7 W at the lowest step and around 11 W a little below the top of the range. That band is the real subject of the **Q16 Pro**. It explains why the alternative 1.2 ohm coil, quoted for a higher band, changes the behaviour of the device without the user having touched the setting at all. At constant voltage, it is the resistance that drives the wattage, and nothing on the body of the device says so. ## The charging protocol on a half amp device A declared charging current is not a drawn current. The difference is measurable, and on a device limited to that region it has practical consequences for how long a session has to wait. The reading is taken with a USB tester between the source and the device. You note the peak current reached, its stability, the moment it starts to fall away and the residual current at the end. On a 900 mAh battery, a theoretical charge time can be calculated from the declared current and then compared against the observed duration: the gap between the two is the interesting part. Whether the source is a computer port, a mains adapter or a power bank changes the result. A protocol therefore fixes one reference source and states it, otherwise two readings of the same device do not compare. The same discipline governs our method for testing a [battery charger](/uk/battery-charger/), where the source is the first thing written down. ## Checking the working domain of the liquid Some devices impose a constraint on formulation, and ignoring it is enough to ruin a coil life reading before it has started. The documentation for this kit states that the coil is not suited to liquids above 50 percent vegetable glycerine, a thicker ratio leading to rapid gunking. A bench respects that limit, mentions it, and fixes a reference ratio inside the permitted domain rather than reaching for whatever bottle is nearest. The protocol adds a priming instruction: after fitting a new coil, a rest period before the first puff, put at five to ten minutes by the maker. That delay is part of the measurement, because it governs how the wicking soaks through. ## What an indicator light allows, and what it forbids On a device with no screen, the state of charge is read by colour, and that granularity limits what can honestly be written in a report. The indicator moves from white to blue and then to red at steps announced around 65 percent and 30 percent of remaining charge. That gives three zones, not a gauge, and it rules out any claim of the form "42 percent left". The only runtime that can be measured cleanly remains the count of puffs taken through to cut-off. That is a limitation of the hardware, not a weakness of the method. A protocol that states what it cannot measure is worth more than a report that invents a precision nobody has. ## Where this kit sits under British rules The 1.9 ml tank on this kit falls under the 2 ml cap that applies to refillable tanks sold in the United Kingdom, which is one reason the model has stayed on British shelves through several regulatory rounds. Nicotine containing e-liquid sold here is capped at 20 mg/ml and supplied in bottles of 10 ml, and a coil life reading has to state which strength and which base ratio were used. Vaping products are not for sale to under-18s in the United Kingdom. ## Frequently asked questions ### Is an ordinary multimeter ohmmeter good enough? It gives an order of magnitude but includes the resistance of its own leads, which weighs heavily on low values. You measure the leads shorted together first, then subtract that from the reading. ### Why calculate the wattage rather than trust the step chosen? Because the step names a voltage, not a power. Two users on the same step with two different coils are not vaping at the same rate, and their impressions do not compare. ### Does the voltage sag as the battery empties? On a device advertised as constant voltage, the electronics aim to hold the step for as long as the reserve allows. Verifying that is part of the protocol: you record the voltage at the start and at the end of a session, and publish both. ### Should a kit be tested with the supplied coil or another one? With the supplied coil first, because that is the configuration the buyer receives. A second series with another compatible value completes the table, provided the two are announced separately. ### How do you handle two listings that contradict each other? You cite both, measure the disputed quantity yourself, and publish the measurement with the gap flagged. Quietly picking the more flattering value amounts to publishing an opinion dressed as a fact. ## Related reading - [Vaptio Cosmo 2: what we measure on a small pod](/uk/vaptio-cosmo-2-review/) - [Doric 60 Pro: the measurements that separate pods](/uk/doric-60-pro-review/) ## What this protocol adds to a spec sheet Applied to the **Q16 Pro**, the method replaces four anonymous steps with a table of calculated wattages, a declared capacity with a weighed one, a stated charging current with a recorded one, and two contradictory listings with a single measurement somebody is prepared to stand behind. None of it requires a laboratory, only an ohmmeter, a USB tester, a set of scales and the discipline to write everything down. The same grid applies at the other end of the spectrum, on the dual cell boxes where it is the sheer quantity of on screen information that blurs the reading rather than the absence of it. Editorial content for adult readers only. Vaping products usually contain nicotine, a substance that causes addiction. Not for sale to under-18s in the United Kingdom. This article is not a buying recommendation.