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Subject: Re: Archos Car Adapter

Re: Archos Car Adapter

From: Manuel Dejonghe <limbus_at_gmail.com>
Date: 2005-02-12

Hi,

this now renders me absolutely clueless.

300mA @ 13 V are not even 4 Watts.

May it under certain circumstances be that your testing power supply
of 13V is not pure DC ? Maybe it has a rectifier (so it's not real AC)
but the capacitors are missing or damaged, so you got a fluctuating
input voltage with 50 Hz ?

stumped, Manuel

On Fri, 11 Feb 2005 21:20:28 -0600, Tom Clemmer <t-clemmer@comcast.net> wrote:
> Just finished some more testing. First, it is a player, not a recorder.
> Bought it used off of ebay.
>
> I measured .3A between the Archos and the regulator. I also measured .3A
> between the power supply and regulator. I am putting 13V on the input for
> testing, as my Jetta seems to run around 12.8V.
>
> I breadboarded up my extra L4940 so there would be no soldering on this
> circuit. I did not have a 22uF so I used a 100uF, figured it would not
> matter, just take a few more seconds to come up to 10V.
>
> Everything measured the same and the poor little L4940 just kept getting
> hotter and hotter. Its not instant heat, it takes several minutes to get
> hot enough to burn your fingers. 300mA just does not seem like a lot.
>
> Take care,
>
> Tom
>
> ----- Original Message -----
> From: "Manuel Dejonghe" <limbus@gmail.com>
> To: "Tom Clemmer" <t-clemmer@comcast.net>; "Rockbox development"
> <rockbox@cool.haxx.se>
> Sent: Friday, February 11, 2005 5:26 PM
> Subject: Re: Archos Car Adapter
>
> you're always welcome.
> I dunno why, but I felt somehow that I was explaining more than needed :-)
>
> Well, if you are techie by profession, you've had much more education
> in that area that I have.
>
> Nevertheless I think you must have been measuring something wrong. I
> don't think ANY electronic circuit is able to get too hot to touch it
> with bare hands by draining 70 mA at 12 V (assumed), 0,84 Watts if I'm
> not barking up the completely wrong tree here. That would be something
> like the invention of a new power source.
> If the regulator circuit is REALLY draining solely 70mA to your power
> supply/car, maybe then your circuit is draining somehow power by the
> archos ?
> This will certainly show up as soon as you measure the current flow
> between l4940 and your archos.
>
> There is another thing I just think of, that I could think of could
> apply if you connected by mistake a RecorderV2 to the circuit.
> For the RecorderV1 (charging control done in software) the charging
> current to the batteries (thus power drain) rises WITH the voltage.
> The v2 (charging control done in hardware, so maybe completely
> different, and maybe I'm on the woodway again) has a far lower power
> rating (6V instead of 10-12V). So the circuit would deliver far too
> high voltage (which should in second be limited by a second regulator
> inside the archos) and the charging control MAY even drain more power
> than expected.
>
> Regards, Manuel
>
> On Fri, 11 Feb 2005 17:02:08 -0600, Tom Clemmer <t-clemmer@comcast.net>
> wrote:
> > Thanks for the response. I measured the input current to the regulator at
> > 70mA but I might have not done that right. I am an electronic Tech by
> > schooling but have not done that type of work for some years. I have lots
> > of soldering experience,so I don't think I fried the regulator. I did by
> > two when I bought it.
> >
> > Thanks again and I will look at joining the list.
> >
> > Tom
> >
> > ----- Original Message -----
> > From: "Manuel Dejonghe" <limbus@gmail.com>
> > To: "Tom Clemmer" <t-clemmer@comcast.net>; "Rockbox development"
> > <rockbox@cool.haxx.se>
> > Sent: Friday, February 11, 2005 4:35 PM
> > Subject: Re: Archos Car Adapter
> >
> > Hi Tom,
> >
> > I didn't expect feedback from that article so soon :-)
> >
> > There are three reasons why I post this on the rockbox-mailinglist as
> well:
> > - documentation. I would not like to write the same info a second time
> > if somebody else asks next month :-)
> > - knowledge: maybe somebody else has another idea.
> > - correction: maybe somebody else on this list reveals I got no clue
> > about electronics.
> >
> > I strongly recommend you to get subscribed on the list. You will be
> > able to reply to everybody, and you will get anybodies answer,
> > independently of the fact wheter they forgot to add you to the list of
> > recipients or not.
> >
> > Well, in the meantime, I read the papers (specs of the 4940) more
> > throughfully, and thought I should've taken the V12 one, as the low
> > voltage behaviour is better than I expected, but thats another story.
> > I first wanted to wait to see how mine behaves before adding info to
> > the article. My fear was that 10V could be a small bit to weak to
> > charge properly, but it does just very well.
> >
> > So, now to your problem:
> > No, mine is not getting very hot at all. I tested a few times by
> > holding the small package in my hand after having an half an
> > hour-travel (that the most I am doing at the moment) and it was so
> > cold I could not determine if it comes from ambient temperature or
> > not. The black brick I mounted on it is merely a buffer than a
> > heatsink as well. Else I wouldn't have it packaged (and thus
> > preventing from cooling) with the thermo-shrink tube. I just mounted
> > it (the black block) for security as IF the unit drains more power
> > than expected, it would only be for a short while like hard disk power
> > up/spin up.
> >
> > I know from experience that such voltage regulators are allowed to get
> > hot. I've once been told to check the temperature by touching it with
> > a wet finger. If it fizzes, it would be too hot. So that shows you
> > what temperature regulators are allowed to get, and up to which
> > temperature regulators are supposed to work without getting damaged.
> >
> > There is two things that may heat up the regulator in regular
> > operation: to much power drain or input voltage different from what we
> > expected (I assume below 8 volts, or even less, and above 17 volts, as
> > the data sheet says)
> >
> > Now there are two things that is disturbing me:
> > - The first is that yours is getting hot, and not mine. Temperature is
> > usually rised if your device drains a lot of power/current (ampere) or
> > if the input voltage is higher.
> > - The second is, that the voltage regulator is known (or at least
> > advertised) to have a very decent temperature controlling. It would
> > rather stop delivering that current than burning itself to death. I'm
> > just checking the spec sheet to see what may be the cause. I assume
> > "too hot to touch it" is above 75 C
> > Unfortunately, the data sheet does not have a figure showing the
> > result temperature of output current or something like that.
> >
> > Now I can think of two things:
> > - Either you did not pay attention (I admit, I did not warn in the
> > article about that, should add that) to not grill the regulator by
> > assembling it. I absolutely don't know how long it should be exposed
> > to which temperatures during soldering. The data sheet says the max is
> > 150 C, but this is certainly for a longer time, as I know I soldered
> > it with 300-350C. I've been teached to always pay attention with
> > diodes, transistors, triacs and so on (in general, all
> > semi-conductors) to not over-heat them, but I've seen people handling
> > them I would've bet they broke it, and it worked, so maybe it's not
> > that sensible my vater taught me. I actually never killed any
> > component during soldering by accident.
> > - There is more power drain as expected. If there would be a
> > short-circuit between regulator and archos-device, you would not tell
> > me it would be working very well, as there would be no current
> > arriving at the archos anymore. So the only one thing I can imagine
> > of, is that something in the archos broke so in trains more power
> > somewhere, most probably a loose contact then.
> >
> > So I definitely recommend you to measure the load/draining current of
> > the archos as well. Most probably, it will not drain more than 600 mA
> > in ANY case.
> >
> > Unfortunately, I got not enough practical experience, to be able to
> > predict anything.
> >
> > I hope that helps, Manuel (lImbus on irc)
> >
> > On Fri, 11 Feb 2005 14:02:11 -0600, Tom Clemmer <t-clemmer@comcast.net>
> > wrote:
> > > Manual,
> > >
> > > Thanks for the write up in the car adapter using an l4940V10. I
> finished
> > > mine and everything measures good. When I power the Archos, the L4940
> > gets
> > > very very hot, too hot to touch. Now I do not have a heatsink on it but
> > was
> > > wondering if your was getting very hot as well?
> > >
> > > Tom
> >
> >
>
>

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Received on Sat Feb 12 13:34:28 2005


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