| |
G0FTD > PSION 12.10.04 00:49l 227 Lines 8688 Bytes #999 (0) @ WW
BID : 747162G0FTD
Read: GUEST
Subj: Revo battery info.
Path: DB0FHN<DB0RGB<OK0PPL<DB0RES<ON0AR<GB7CIP<GB7SXE
Sent: 041011/1608Z @:GB7SXE.#38.GBR.EU #:8546 [Hastings] FBB7.00i $:747162G0FTD
From: G0FTD@GB7SXE.#38.GBR.EU
To : PSION@WW
Psion Revo - Charging/Battery Information.
Most Revos are very reliable and only a few users experience problems with
battery life. This Information is provided for the unlucky few and those
who want the very best life from their Revo batteries.
Psion Revo/Revo Plus - Charging Information:
I've heard quite a bit of misinformation about the Psion Revo with regard
to the batteries and decided to post this information to clear up a few
issues.
Important: I think this information is sound but I would welcome any
additional information or comments - use at your own risk.
How It's Supposed to Work:
The Revo is equipped with two AAA NiMH rechargeable batteries and an
internal charging circuit. This circuit is fed by a 6V DC adapter, usually
by the docking port.
In theory, when you put the Revo on charge it should fast-charge(300-450mA)
displaying red and green LEDs until 85% is reached. Then it should switch
down to a trickle charge (~30mA), displaying just the green LED, until
100% is achieved.
The internal threshold for 'Low Battery' is set to <10% and the 'Recharge'
message appears at <3%. Sound is available until the 'Recharge' message
appears.
Both thresholds are dependent on calculations based on the
chargecalibration point
(more on this below).
Contrary to popular and nervous opinion, the Revo charging circuit is a
precision piece of kit and uses purpose-built charging ICs designed by
one of the world's leading battery manufacturers. However, to work
properly, it is vital that the user follows the first charge instructions
to the letter.
The battery level meter works in the following way :-
The first time the Revo is charged from new, or after a hard reset, the
charge controller senses a chemical change in the cells. It does this by
detecting a sudden thermal change in the pack which occurs at 89% of
actual
(84% of the indicated) capacity. This is a feature of NiMH cells. We'll
call this the charge calibration point. It is absolutely crucial that you
follow the Psion guidelines for the first charge so that the controller
can
detect this accurately.
During normal charging or running, an accurate current reading is obtained
sing a 'gas gauge'. By measuring the current in and out of the cells, the
controller knows where the battery level is in relation to the original
charge.
There is a 30% reserve capacity on the Revo, ie. when you have 0% left on
the indicator there is still 30% capacity left in the cells to retain the
memory. When you charge the Revo normally there are actually several
things
that can trigger the drop-down to trickle charge:-
Detection of the charge calibration point.
Overall Timeout:
A thermistor on the cells reaching a preset temperature.
If the Revo is put on charge at a capacity higher than the charge
calibration point, it will switch down after approximately 5 minutes.
Possible Problems:
When your Revo is brand new or has a hard reset, the charging circuit
doesn't know what the true battery level is and resets it to zero. It must
be charged to 100% after a hard reset so that the level accuracy is
restored - this can take up to 6 hours.
The charging circuit is notorious for not switching down to the trickle
level when it should. This happens especially if you recharge the Revo
when the battery level is already in excess of 84% though the figure will
vary if it hasn't been calibrated (charged) correctly.
If the Revo batteries get hot, a thermistor kicks in and shuts off the
charge circuit -this may be the reason why some people have noticed the
level draining when they have left the Revo on the docking station for a
long time although there is also a timed switch-off even on trickle
charge.
There was a problem with a small number of Revos (8MB, not the new 16MB]
Plus version) that had faulty battery packs. The cells in these were less
than a tight fit and could shake loose causing the terminals to make
intermittent contact. This caused machines to reset themselves without
warning, losing all data. Psion's fix for this was to replace the slightly
undersize cells and fix the new ones securely with a dab of glue.
On older Revos another problem has been discovered. The battery connection
cable can wear leading to a high resistance that fools the machine into
switching off during high-load conditions (such as playing sound), even
though the battery level is over 50%. D&G Upgrades have a fix for this
potential problem and also do other enhancements including memory
upgrades.
About NiMH Cells in General.
Higher Capacity
The trade-off for these benefits is :-
Lower number of charge/discharge cycles (about 300-500 as opposed to 1000
for NiCds)
No memory effect
More easily damaged by overcharging.
Higher self discharge (NiMH ~2%/day, NiCd ~1%/day)
The Revo is never really off so a little power is used each day just
retaining the clock and memory etc. Psion's estimate of memory retention
while the Revo is unused is 6 weeks maximum when fully charged or 2.4%/day
on average. ChaDis assumes a little heavier usage of 3%/day in its
estimate
of memory retention time during periods of zero use. If you have a Revo+
or Mako then you should assume 6% - this is due to twice as much memory
that has to be powered even when the machine is 'off'.
It is important to note that the symptoms of overcharging NiMH cells are
reduced capacity which looks remarkably similar to the 'memory-effect'
in NiCds. This is the reason why you will see people reporting that NiMH
cells
still have a memory effect - don't believe them - it's overcharging !
When your NiMH cells get old they will lose capacity anyway, but this s
hould only be of the order 10-15% reduction.
Revo Battery Recovery:
If you find that your Revo batteries are not retaining their charge that
well,
it's possible that they have been damaged by overcharging but it is far
more
likely that the charge calibration point is incorrect. However, all is not
lost.
Check your battery performance using ChaDis. It will try to ignore any
periods
while the machine is off by using previous figures obtained for that
particular
1% level drop step.
If you have lost significant capacity, backup your Revo and then let it
drain
until it switches off (turn off the auto-off features). Then perform a
hard
reset and charge the Revo in accordance with Psion's first-time charge
instructions, ie. 6 hours.
Now this bit is very important ! - turn the machine OFF during this 6hr
charge
(or at least pay no attention to the gauge). Do not be tempted to ignore
this
if the gauge apparently reads full.
This may put everything back as it should be and you need take no further
action except to restore your files.
If this doesn't work, drain the cells again and recharge to 20% and then
drain
again. Recharge to 40% and allow to drain. Repeat this a few times in 20%
intervals until 100% is achieved. Then repeat step 2 except for the backup
(which you've already done) to recalibrate the gauge. The repeat + 20%
process
should recover most of the capacity of NiMH cells that have been degraded
due
to overcharging. The reset and complete recharge then recalibrate the
battery
level gauge.
Allow the Revo to drain until it switches off and make a note of how long
this
takes. If this exceeds 8 hours (for screen-on but no activity) then you
can be
certain that your Revo is working correctly again. If your Revo is out of
warranty
and you are fairly competent, you can replace them by removing the Revo
badge on
the top of the machine and moving just two pins.
Revo Battery Charging Tips
Always run ChaDis and recharge with your Revo switched on - if your Revo
charging circuit carries on fast charging when 100% has been reached, at
least
you'll know about it and can take it off charge or consider a hard reset
and
full recharge to recalibrate the gauge.
Try to get into a pattern of charging at set intervals as is practical for
you
and avoid charging when already over 84%. Any level between 10% and 80% is
fine. If your Revo switches over to trickle charge then leave it on for an
hour or two, otherwise take it off within 5-10 minutes of 100% (audible
ChaDis warning) - it should switch down itself within about 5 minutes
anyway.
Remember that it is completely normal for the machine to lose 3%/day
(6% for Revo+/Mako) when unused and plan for periods of inactivity where
possible. The 10-12 hours usage claimed by Psion appears only achievable
if
your Revo is sitting switched on but hardly used continuously. 8 hours is
a
far more realistic target for real use.
- Arthur Ascii -
Read previous mail | Read next mail
| |
