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Subject: Re: Mystery: Voltage for JBR V1 batteries

Re: Mystery: Voltage for JBR V1 batteries

From: Jerry Van Baren <gerald.vanbaren_at_smiths-aerospace.com>
Date: Mon, 24 Jul 2006 10:29:45 -0400

sfsprs-audio_at_yahoo.com wrote:
> I have an Archos JBR V1 Recorder which I'm using as a car player. I am
> using an DC/DC inverter rated at 2.2A output
>
> http://www.powerstream.com/dc6-12.htm
>
> that takes the car 12V and outputs 6V or 7.5V nominal. I put that
> power into the battery terminals of the Archos. I am finding that the
> Archos isn't working right:

The circuitry is spec'ed for 5.0v +/- 10% (4.5v - 5.5v). 6v is abusive.
  7.5v is very abusive. 9v is felonious assault.

> 1. When the inverter is set to 6V I measure about 5.3V actually going
> into the Archos. It stays on the splash screen for a while and then
> gives the message PANIC ATA -1.

Hard drive probably isn't spinning up or is unhappy with 6v. Note that
the HD is connected DIRECTLY to the batteries, so it is taking the brunt
of your abuse (IIRC, the bulk of the AJR circuitry is running off a
step-down regulator so it is protected).

> 2. When the inverter is set to 7.5V I measure about 5.7V actually going
> into the Archos. It plays normally for a couple of seconds then the
> screen goes all black.

The circuitry isn't happy and is drawing enough power to draw down your
supply to 5.7v, the extra power turning into heat which makes the
circuitry very unhappy and will damage it.

> 3. When the inverter is set to 9V, the screen went all black
> immediately, and stayed black when I use it with batteries which work
> fine.

Ouch! You are lucky it works at all with batteries.

> I also tried putting a 200mfd capacitor in parallel with the power
> source to stabilize it in case the hard drive was using more power
> momentarily, but that didn't help.

Disk spin up takes a lot of current (see the battery FAQ?) for 1-3
SECONDS. A cap cannot supply that kind of current. Batteries can.

> So all of this points to the car inverter just not putting out enough
> power, except one thing: Before I did these experiments with the car
> adapter I was able to run the Archos fine with a home "wall wart"
> (rated 800mA) fed in through the battery terminals, at 6V. After doing
> these experiments (#3 being the culprit I suspect), when I run the
> Archos at 6V nominal with the wall wart it just goes to black screen,
> and when I run it at 4.5V nominal, flickers alot and shuts down
> quickly. So I suspect that I have messed up some of the power
> circuitry somehow by trying to run it with too high of a voltage. But
> it still runs fine on batteries charged outside. The charging circuit
> on this unit was already broke.
>
> To cut to the chase, what I'm wondering is:
>
> - Does anyone have accurate specs on how much current the JBR V1
> Recorder uses out of the battery terminals, max and/or continuous?
>
> - Does anyone have any info on what voltage range is allowable on the
> battery inputs?
>
> - Any idea why the car inverter rated at 2.2A would fail to run the
> Archos at 6V would fail to run it, while the home adapter rated at
> 800mA used to run it successfully? And why does it run right on AA
> NiMH batteries but neither of these inverters works? Could it be that
> the Archos needs "cleaner" power than the switching supply can deliver?

My guess: 6v @ 2.2A is overheating the HD circuitry. 6v @ 0.8A is
making the HD hot but not to the point of operational failure.
Batteries work because they can supply sufficient current at an "OK"
voltage. Note that NiMH batteries are 1.2v/1.4v nominal which is
4.8-5.6v, within spec (nearly). Note that alkaline batteries are 1.5v
nominal (6v total) which is NOT within spec and I would NOT recommend
using them.

> I got another JBR V1 to replace this one, and before I start
> experimenting with it I want to make sure I'm not going to destroy it
> the same way :-!
>
> -Tom

Batteries and an unbroken charger circuitry is the correct answer.

Theoretically you should be able to make an external supply work, but it
is going to be problematic if for no other reason than the wires between
the supply and the AJR will cause voltage drops during disk spin-up
operations. Making it actually work reliably may be impractical (BIG
SHORT wires). Perhaps your best bet would be to put a 5v (LDO)
regulator with sufficient current handling capacity in the battery
compartment and feed it with sufficient voltage (7.5v? 9v?) to allow the
regulator to work. Heat and current capacity for disk spin-up would be
an issue with this scheme.

Replacing your charger IC is going to be MUCH more reliable.

gvb
Received on 2006-07-24


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