Car stereo USB question

[stretch0069]

I just bought a JVC KD-AVX77. Nice little stereo for the pickup.

I was reading through the manual and it has a warning:
"Do not start the car engine if a USB device is connected."

I thought maybe having a USB device connected would initiate firmware update or some crap.


So I emailed JVC Customer Support and this is the answer I got:

"I understand that you are inquiring about the USB port of your JVC Mobile stereo. The main reason why the manual is suggesting to disconnect all USB devices while starting your vehicle's engine is to protect the unit (as well as your USB device) from any possible electronic feedback that may occur during the engine cranking process. This feedback will cause any electronic devices to glitch or malfunction over time."

I don't pretend to know everything....but I can't imagine how a simple thumbdrive would be affected. MAYBE a powered USB device like an iPod, but even then.......


Anyone have any ideas??? I have a cheap 1GB thumbdrive that I wouldn't care if it got toasted, but I am a bit concerned about the head unit.

[shovenose]

Re: Car stereo USB question

liability...if you lose your data or your ipod dies you cant sue them

[yyonline]

Re: Car stereo USB question

I'm not an expert on car audio stuff. That said, here goes...

When you start your car, your alternator starts spinning. This causes a brief surge as your power goes from battery power of ~12.5V to alternator power of ~13.5-14V. The head unit is designed to deal with this, since it's for automotive use.

Any USB device you have plugged into your USB port may not be designed to handle such a surge. USB power is 5V, but there still may be a brief surge as the circuitry in the head unit compensates for the change in power.

So, the warning is there for the sake of the connected USB device, not the head unit itself. Is it very likely you'll fry your USB device? I would guess no, but the waning is in the manual just to cover their butt should it happen.

Edit: Now that I think of it, there's going to be a voltage drop as your starter is energized, and then a voltage surge as the alternator kicks in.

[stretch0069]

Re: Car stereo USB question

yeah...see...if the thumbdrive dies, its no biggie. Taking what I know about cars and stereos and 'puters......i just can't see the thumbdrive, or any USB device, getting messed up.

....hmmm...maybe i'll borrow the digital o'scope and watch the 5v line.....

[seanc]

Re: Car stereo USB question

When I had my Seat Ibiza, starting it up would cause my iPhone to reboot when it was connected to the car charger.
Usually only did it after I'd filled the tank up with fuel :/

[stretch0069]

Re: Car stereo USB question

When I had my Seat Ibiza, starting it up would cause my iPhone to reboot when it was connected to the car charger.
Usually only did it after I'd filled the tank up with fuel :/

don't ya just love those "undocumented features"???? sometimes i think there is a bit of "seat-of-your-pants" engineering with electronics.

[dood]

Re: Car stereo USB question

I have a Pioneer receiver with a USB port. I've used it with USB thumb drives, as well as a 1.8" laptop drive hooked up to a USB converter. With the thumb drive, it's been plugged in for about 6 months with no problems. The hard drive doesn't seem to be effected by starting, either.

The point about the increase in voltage when the alternator starts spinning should make no difference. The USB port is a 5v regulated output. If the HU is sending any power to it at all, it should be 5v or nothing.

One interesting thing about my HU is that it is a USB spec, and claims to be able to charge iPods and the like from the port while playing. However, if I hook up a 2.5" drive to my IDE->USB converter, it will not spin it up, even though that's the only way the converter works with 2.5" drives. The only way I got a HD to spin up on the converter is to have a 1.8" drive that's in a 2.5" shell with a standard 2.5" ATA connector. I guess it's not capable of as high of a power output as standard desktop USB ports are.

[alexanna]

Re: Car stereo USB question

Automobiles interrupt the voltage supply to everything except anything that’s needed for the car to start.
Hell I’m so old I wouldn’t know what a USB dose with a stereo ,But if that’s where it’s getting power from it couldn’t be good.
Al.


I should have said interrupted power to accessories

[kc8adu]

Re: Car stereo USB question

may get corrupted if it does not get dismounted properly.like pulling one from the pc while it is still being accessed.

[stretch0069]

Re: Car stereo USB question

I'm in the same mindset as dood. I haven't put the o'scope on it to confirm, but I'll try Wednesday. I'm guessing there won't be any issue.

I does say not to remove when its reading the thumbdrive......but to me, the worst that would happen is the data on the thumbdrive would get horked. No biggie for that.

[Agent24]

Re: Car stereo USB question

If the headunit can't keep a reliable 5v supply to the USB port when engine is starting doesn't that mean it's a piece of junk?

[kc8adu]

Re: Car stereo USB question

most unnecesary loads are shut off during starting.this includes radio's.cranking while the radio is reading is like pulling it out of your pc while it is reading/writing.
might corrupt it but thats all.

[Agent24]

Re: Car stereo USB question

Yeah, that makes sense. But this doesn't:

disconnect all USB devices while starting your vehicle's engine is to protect the unit (as well as your USB device) from any possible electronic feedback that may occur during the engine cranking process. This feedback will cause any electronic devices to glitch or malfunction over time.

Whatever this "Feedback" is - surely the headunit will be designed to prevent against it? I mean, the thing is designed for use in a car where this "Feedback" will potentially occur. If it can't handle the environment it's designed for, then it's not a very good design, in my opinion.

They suggest to disconnect your USB drive, well what about the headunit itself? Do you need to disconnect that as well in case of "Feedback"? or does the simple act of removing the USB drive prevent any problems happening to the headunit, as the quote suggests? Sounds pretty weird to me...

[alexanna]

Re: Car stereo USB question

Wonder if the head unit is smart enough to protect itself [shut itself on power interruption]
Where the USB is not?
Al.

[Agent24]

Re: Car stereo USB question

The headunit is supplied with around 12volts from the car - USB devices run on only 5volts.

So there will be a regulator or whatever in the headunit to supply the 5 volts to the USB drive, all that will be powered from the headunit, if the headunit's power is cut off, then the USB supply would be off as well.

[beggarmaster2000]

Re: Car stereo USB question

hey, guys here is a neat trick for usb audio users!
use a usb card reader and memory card instead of a thumbdrive. and noise from your alternator/ac/engine will be eliminated!
enjoy music without the hiss

[kc8adu]

Re: Car stereo USB question

nonsense!only difference is the reader and flash are seperate.

hey, guys here is a neat trick for usb audio users!
use a usb card reader and memory card instead of a thumbdrive. and noise from your alternator/ac/engine will be eliminated!
enjoy music without the hiss

[370forlife]

Re: Car stereo USB question

Even so I don't get any noise with my radio with a flash drive plugged in.

[Agent24]

Re: Car stereo USB question

I think that guy is some kind of spammer probably... well he kinda sounds like one anyway.

Then again if he's the same guy as http://forum.lowyat.net/user/beggarmaster2000 then maybe not..