Metspitzer said:
Is there any chance of damage to a car's electrical system leaving a
USB charger hooked up?
I plan on getting one of these:
http://www.newegg.com/Product/Product.aspx?Item=N82E16882021230
Any reason not to leave it in the cigarette lighter port? Would it
hurt to forget and leave a phone charging for several days?
If a charger has a transformer, it will always draw some current when
plugged into a live source. The ones typical you use in your home to
plug into a wall outlet or power strip are always drawing some power
whether or not they have a load (i.e., whether the charger is plugged
into a device or not). However, from what I've seen of a few USB car
chargers, there is no transformer. There may be a coil for use as an
inductor in the circuit but it is not a step-down transformer (no
secondary winding, not enough windings at all to make it a
transformer). The input side (from the battery) typically goes across
a capacitor (which could short or blow open) through a diode and into
an IC that regulates the output voltage and limits the current output.
A zener diode is used for protection to ensure the IC on failure
doesn't result in 12V for output; however, the heat produced in the
zener for clamping down errant high voltage means it would burn up
since there is no heatsink used inside this type of USB charger.
When plugged in and with no load, the cigar receptacled USB charger
should draw any power from your battery. There may be some leakage
current in the IC or across the cap but it is infinitesimal compared
to, say, the current draw of your car radio to maintain the time and
its memory. Only if the cap fails (shorts and then blows open), bad
wiring which causes a short, or other failure that produces
catastrophic failure would there be a current draw without load. The
charger should remain cool with no load.
Don't exceed the rated current draw of the charger. I see nothing in
the circuitry to "blow" in case of over amperage other than a zener
that will overheat and blow or burning out the IC both of which means
the charger is dead thereafter (when it blows, it's dead). There is
no fuse so there isn't one for you to replace. In fact, there is no
fuse or link to blow to protect the plugged in devices, either. It
looks like they're relying on a zener diode to clamp down the voltage
to 5.6V but there's nothing to dissipate the heat produced in that
small component so it'll overheat and burn out leaving no further
output over-amperage protection (since it is across the output lines
instead of inline with it). The safety to the plugged in devices
appears solely the responsibility of the IC. If it fails, your
devices would receive no power, too little power, or experience over
voltage. So I don't recommend leaving devices plugged into these type
of chargers. Leaving them unattended while charging also means the
charger could fail and it burns up and/or your device gets over
volted. The circuitry in these chargers is minimal without almost no,
if any, overvoltage protection.
Presumably you want to know about battery drain while the charger is
plugged into the cigarette lighter receptacle and with nothing plugged
into the charger. Obviously if you leave something plugged into the
charger that draws current then there will be a drain on your car
battery. If you leave your MP3 player continuously playing music when
you shutoff and leave the car then that power for the still-playing
MP3 player has to come from somewhere.
I noticed the unit is Rosewill branded. Hopefully the plastic used
for the housing isn't flammable should the unit short and burn out or
the user accidentally impinges an excessive current draw by a plugged
in device (and the IC fails to limit the current). Rosewill doesn't
manufacture anything. They spec out to the Chinese. If quality and,
in this case, flammability are not in their spec (something Rosewill
doesn't seem to specify) then you get their product that meets their
spec but nothing beyond. I don't know that beyond the contractor's
(Rosewill's) specs that the Chinese have to comply with US
regulations, like flammability. I saw nothing in the specs at Newegg
or at Rosewill stating the flammability rating of this device.
Remember that you will be leaving it plugged in unattended inside your
car. Sometimes Chinese craftmanship is good, sometimes bad. Depends
on the plant of manufacture and how detailed were the specs they were
given regarding manufacture. What happens if wires inside the unit
for the 12V contacts happen to short? If there is still enough
resistance in a contact short, the fuse might not blow, especially
since the cigarette lighter is designed to handle several amperes of
current. The wires heat up and probably burn apart but meanwhile
there is a lot of heat. That itself isn't a big problem since the
cigarette lighter receptacle is obviously made to contain the element
that heats up but what happens to that plastic shell for the charger?
Since I rarely see a flammability rating for Chinese stuff, the only
way to tell is to buy 2 and see what happens to 1 when you try to
ignite it. There is no fuse or fusible link inside these USB chargers
to prevent them from overheating during catastrophic failure. You
will find no way to open to replace a fuse. The tip contact end isn't
connected to a fuse inside. If the IC fails to limit the current or
it fails to limit the voltage and the non-heatsinked zener blows
trying to clamp down the voltage, your plugged devices will fry after
being overvolted or the charger's shell catches fire and might cause
worse damage. The circuitry inside these chargers is very minimal.
They don't have [room for] catastrophic failure protection.
For a working cigar receptacled USB charger, it should be cool when
nothing is plugged into the charger. It's when you draw power through
it and when it has to drop voltage from 12V to 5V that it will produce
heat. It may feel warm to the touch when you are drawing power from
it for plugged in devices. Alas, since the electronics are in the end
of the charger that goes into the cigar receptacle, you probably won't
feel any heat at the end that only encases the USB ports.
Because these chargers have no reasonable overvoltage or current
limiting protection and no fusing, I would test leaving the charger
plugged into the receptacle. Sit in the car, plug it in (with no
devices attached to it), wait 10-20 minutes, and feel if it is warm.
It shouldn't be warm. Then I'd feel okay leaving it plugged in. Of
course, it takes little effort to pull on it just enough to disconnect
the tip connector from the cigar receptacle's contact plate; however,
it's not the effort but remembering to do so when you leave the car.
I wouldn't leave the car unattended while using one of these to charge
devices. I'd be charging them while driving and when the devices
should NOT be used. You shouldn't be prattling on cell phones or
watching MP3 players while driving so use that time to charge the
devices. When you get to your destination, pull out the charger (not
necessarily all the way out but enough to disconnect).
You may get reports from others saying they have never had a problem
with a cigar receptacled USB charger. You're not them so do you
really want to rely on individual reports on usage regarding the
safety of your car? Just go read the reviews of powered USB hub at
Newegg to notice how many users report hot (overheating) USB ports or
devices that got fried by powered USB hubs. It happens. That it
doesn't happen to a few respondents here doesn't obviate that it does
happen.
To be safe, plug it in when you are using it to charge devices.
Charge while you are there in the vehicle and not using those devices.
Unplug when you leave the vehicle. This applies to all cigar
receptacled USB chargers, not just this one.
The above is my personal opinion based on the circuitry that I've seen
employed inside these cigar receptacled USB chargers. For better
statistics, just call your own car insurance agent to find out if
their company has any incidences of damage or fire caused by these
devices. It's just a phone call but make sure the rep actually
investigates the statistics rather than reporting their own personal
experience. If you Google around, you'll find reports by users
claiming the USB charger overheated (or the devices plugged into it)
and cause a fire.
Also check if your cigar receptacle actually has power when you turn
off the car. You might think you will be charging the plugged in
devices while you're away but the receptacle is dead and you return to
the devices in the same state or worse regarding power charge. If
your car is designed to disconnect the cigar receptacle when the car
is turned off then there is no problem in leaving the USB charger
always plugged in. Of course, that also means the charger isn't
charging anything while you are away but that's the safest setup
anyway.
Also remember that this charger is NOT providing the same 0.5A current
of USB ports in computers. It has "charging" ports to decrease
charging time. These charging ports can provide 2-3 amps of current.
If something goes wrong in the charger (or in the device), these
charging ports have more than enough current to fry your devices. In
particular, I see little or no overvolt or overamp protection in these
plug-in cigar receptacled USB chargers.
When charging with these unprotected over-amperaged chargers, you
should be there. If you're not there, don't charge there.
