[Arm-netbook] modifying a 7 inch notebook cabinet toacceptapccard

Tor, the Marqueteur Marqueteur at FineArtMarquetry.com
Tue Jun 13 07:34:46 BST 2017

Hash: SHA1

On 12/06/17 11:07, ronwirring at Safe-mail.net wrote:
>> The upshot of this is that trying to power a device with the 
>> battery/charger combo while charging the battery will confuse any
>> decent charger (and if it isn't a decent charger you SHOULD NOT
>> use it).  The only way around this is a charge controller designed
>> for such use that has three sets of terminals.  One for a source,
>> one for battery, and one for load.  The charge controller is then
>> able to distinguish the load from the battery charge current and
>> charge it intelligently.
> Your lowermost section, I do not follow.
In short this is dealing with a straight-up battery pack, not a fully
integrated power bank with charger.

> Let us assume you somehow are able to get the battery bank into the
> computer's cabinet. Let us say, you use an usb port on the usb
> battery bank to both charge the usb battery bank and power supply
> the pc card. In order to power the pc card, you would have an usb
> cable connecting the power bank and the pc card.

Assuming a schematic that looks something like:

  PC Card-\___
          |   Power supply
- --Battery

This is OK.  If the power bank is designed with internal charge
circuitry (required for USB powered devices because the USB voltage is
too high for Li-ion), then you should be OK.

> I have no power banks. Looking around, it appears power banks have a
> port for getting charged and one for power supplying devices.

In this case, simultaneous charge/draw may have some losses that would
be preferable to avoid, but if the power bank is well-designed it
should be fine.

> In general, are you sure, you cannot charge a power bank and 
> simultaneously have it power supplying a device? If the power bank
> can be charged and power supply a device simultaneously you would
> connect another usb cable from the charger which charges the power
> bank to the power bank.

It's a question of how the charger is arranged.  Laptops do this all
the time.

The schematic that does not work is:

   |           |
Computer       Li-ion charger

The problem here, AIUI, is that the charger can't cut off power to the
battery once it's charged, because it can't tell.  This will degrade
the battery faster, and Li-ion is the most dangerous chemistry to
mishandle.  It's not without reason that there are warnings everywhere
to only use proper smart chargers for Li-ion.

> Else if the power bank gets empty, you would remove the usb cable
> connecting the power bank and the pc card. Then connect an usb cable
> from the charger of the power bank to the power bank. I suggest to
> use a
> https://www.att.com/chargers/att-42a-dual-usb-low-draw-universal-wall-c
if you want to charge the power bank and turn on the pc card at the same
> One usb cable from the charger to the power bank. One usb cable form
> the charger to the pc card.

This can be done.  The most important thing is to make sure the charge
circuitry has only the battery on the battery side of it.

By running off a power bank you will have some extra losses in the
boost then buck voltage conversions, quite possibly upwards of 10%.


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Tor Chantara
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