When we are on the road in our vehicles, we usually have a large number of electronic devices with us. However, navigation systems, smartphones, tablets, DVD players and laptops usually only have a short battery life and constantly require energy. Few vehicles have special USB charging sockets, so the only option is to use the cigarette lighter. To use the 12-volt vehicle voltage for charging USB devices, you need an automotive USB charger, also called a 12-volt charger or car charger. There are many different versions, with one, two or even four 5-volt USB outputs and some with an additional 12-volt socket. Which charger is the right one and what are the advantages of so-called fast chargers?? Our comparative test explains what to look out for when buying a car USB charger or. What advantages and disadvantages certain concepts and products have.
Warning
The 12-volt voltage via the adapter is usually only fused with three amperes. Connecting loads that exceed three amps (36 watts) can blow the internal fuse, which may need to be replaced on some chargers.
A 12-volt laptop power supply or a cool box can easily exceed the output power and can therefore not be used on intermediate plugs! In addition, the intermediate plug can heat up significantly due to the double contact resistances!
Cramped conditions: the garmin charger with 12-volt socket only just finds room in an audi A4 ..
More space: the particularly small chargers from proidee and revolt are especially compact ..
Ensure good contact!
to achieve the performance measured in the test, a good connection between the car charger and the 12-volt socket in the car is necessary. For this purpose, the contacts on both sides should be free of corrosion and grease. Bad contacts, even if plugged in too easily, can lead to massive power losses and enormous heat development! In this context, the design and the depth of the connector play an important role. Chargers with short designs in particular tend not to be able to be sunk deep enough into the socket on some vehicles. if in doubt, only measure the depth before buying!
The dimensions can be taken from the table, the value for "plug" here refers to the maximum required depth of the socket.
A 12-volt voltage is required?
Before you start thinking about the number of usb-outputs and their power, you should think about whether you also need a 12-volt-connector. A 12-volt socket is required. The car USB charger occupies the cigarette lighter socket, which is usually only available in the vehicle, and therefore it is no longer available for other devices that also require a 12-volt plug (navis, coolers, car notebook chargers, …). some car usb chargers therefore have a 12-volt socket, which loops the vehicle voltage through and thus enables parallel operation of 12-volt consumers.
Disadvantage of the intermediate plug solution: the adapters are significantly larger due to the 12-volt socket and can lead to problematic space conditions in the vehicle, depending on the location of the cigarette lighter.
What output power is required at the USB port??
The output power at the USB port is decisive for which devices can be charged at all and how fast they can be charged. Most small devices such as MP3 players, navigation systems and cell phones make do with the USB standard of 2.5 watts (500 ma), which all car chargers can supply without any problems. However, smartphones and especially tablets sometimes require much higher power of 5 or 10 watts to be charged at all or within a reasonable time. Larger tablets charge with up to 12 watts. If more than one usb port is available, the output power of some car chargers is split up. For example, the revolt car distributor with its 4 x USB outputs offers an output power of 8.9 watts, which is divided among the four outputs. So if you connect a total of four consumers, each consumer does not even have the 2.5 watts required by the USB standard at its disposal. Accordingly, a smartphone may not charge at all or charge very slowly.
an output power of more than 12 watt per usb-port usually does not result in much faster charging times, because even most tablets only use a charging port of 2.4 ampere and do not use higher currents and therefore power. If a device is charged via micro-USB or mini-USB, it will draw more power according to the "battery charging specification" (z.B. Android smartphones) maximum 1500 ma and therefore 7.5 watt. a possible output power above this 7.5 watt is not used or. Requires.
Notice: also the charging cable has an influence on the charging performance. It often makes a difference whether data or pure charging cables are used. If a data cable is used, the charger must signal to the connected device what power it can provide, so that the device also recognizes it as an adapter. It is impossible in the context of such a test all combinations of div. test smartphones and cables to check which combinations achieve the maximum charging power. To check for yourself if the charging power can be increased with a data or charging cable, the following are required. USB power meter useful. these small devices plug between the power supply and the device and display voltage and power consumption. (caution in some cases, power meters affect detection as power resistance increases).
manufacturers advertise "up to four times faster" – is this true??
Tomtom advertises its high speed multi-charger with the claim "up to 4 times the speed", but what is meant by this?. First of all, the question is: faster than what?? We use the standard USB 2.0-port with max. 500 ma at 5 volt as a basis and thus reach 2.5 watt. the tomtom high speed mulit-charger provides a maximum of 12 watts at the fast-charge output, which is 4.8 times more power than a standard usb port. advertising statement correct? Not quite, because first of all it is like already described for the output power, that most devices – especially not tomtom-navis – can take a power of 12 watt. the tomtom GO 1000 has a power consumption of approx. 2.4 watts and is therefore charged at the same rate with all chargers! If, on the other hand, you take a new apple tablet, it may well have a power consumption of 12 watts and will therefore indeed charge much faster. Promise kept? Not quite: lithium-ion based batteries can only be used up to approx. 80 percent of its capacity is charged at full power. The last 20 percent are charged technically with increasingly lower current, which goes to zero shortly before the end of charging. This last phase of the charging process cannot be accelerated any further, no matter at what power it can be charged to begin with. Depending on the battery, it is not unusual for the last 20 percent to take more than 50 percent of the time. In summary: even a tablet that can take the maximum output of the fast charger in the first charging phase will not be 4 times as fast as a standard USB-2, at least when charging to 100 percent.0-connection.
What does the temperature in the table tell you??
The car adapter converts the voltage from 12 to 5 volts. A voltage conversion is not loss-free and therefore there is a power loss, which is given off as heat. The use of high-quality electronic components lowers power losses and reduces waste heat. We measured the maximum temperature at the case under full load operation. The housing heats up unevenly, of course, which makes temperature measurement difficult and inaccurate. Therefore, the temperature should only serve as a rough guide to the efficiency of the adapter. Of course, devices with higher power also have a higher power loss. Small car chargers also have a small surface area to radiate heat from components and therefore reach higher temperatures. That’s why manufacturers use metal on the housing of small car chargers to keep temperatures under control. The temperatures were measured at an ambient temperature of only 20 °C and are likely to be significantly higher in some cases inside the car.