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Hot weather and PDA's
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Author:  bill_datamaster [ Wed Jul 06, 2011 10:47 am ]
Post subject:  Hot weather and PDA's
Charging Issues with PDA units.

During the hot summer months, we’ve experienced several instances where customers have complained about units not charging correctly. This problem is not (as many think) caused by the charger but by the electronics in the PDA that governs the amount of charge that can be applied to a battery at higher temperatures.

It is entirely possible to reach the condition where the PDA is using power quicker than it’s allowing the charger to run at, with the results that the battery will end up going flat even though the charger is connected. A bigger / better charger will do nothing to solve the problem because it’s the electronics in the PDA determining the rate of charge.

Solutions

Given the problem is entirely due to heat, the most obvious solution is to try and keep the devices in a well-ventilated position and out of direct sunlight. Mounting the device on an air vent is one solution but bear in mind that during the winter it’s hot air normally coming out of these!

Don’t start your shift with a flat battery in the hope that it will charge during the day (it might not) especially if it’s a hot one.

Avoid using power hungry SatNav functions on exteemly hot days unless you really need to.

Finally, try reducing the backlight intensity or even employ the screen saver as this reduces heat and saves on battery power.

Bill :)
Author:  Nidge [ Wed Jul 06, 2011 11:51 am ]
Post subject: 
We found that ours were being fried with them being on charge all day, I take mine iff charge every 2 hours and let it run down to almost flat.
Author:  grumpy [ Wed Jul 06, 2011 3:45 pm ]
Post subject: 
thanks for heads up, Bill. No problems reported so far, but at least now I'll know what solution is, if any come in.
Author:  DMcnelly [ Wed Jul 06, 2011 5:57 pm ]
Post subject: 
Thanks for the heads up Bill, hopefully see you soon!
Author:  skippy41 [ Wed Jul 06, 2011 6:43 pm ]
Post subject: 
Bill another technical question for you.
What is hot weather :lol: :lol:
Author:  Jedidaz [ Fri Jul 08, 2011 9:29 pm ]
Post subject: 
Simple solution that I've used over last 2 years...........

White hanky over the top of PDA or even turn your aircon on. Keeps you both cooooooooooooooooool.

Ours overheat even in winter cos we're soooo busy. LOL
Author:  C.A.E [ Mon Jul 11, 2011 7:57 pm ]
Post subject: 
As Midlander said, you need to allow the battery to drain, and then recharge to gain optimum life of the batteries. Overcharging will eventually kill the battery off, meaning it won't last five minutes between charges.

Charge and then pull the lead for a good few hours and let the battery drain until the warning light comes on. Heat does effect electronics, but only on the hottest of UK days!
Author:  bill_datamaster [ Wed Jul 13, 2011 4:14 pm ]
Post subject: 
Just need to come back on this because the advice given by both CAE and Midlander just isn’t right.

It might have been true back in the days of the old ni-cad batteries but you'd just be wasting your time doing that with a modern Lithium ion type. In fact there’s good technical evidence that that suggests running batteries completely flat in this way can actually cause damage so my advice is don’t do it. Also, it’s totally impossible to overcharge a PDA battery because the battery management system within the PDA prevents this from happening.

Bill :)
Author:  sasha [ Wed Jul 13, 2011 8:07 pm ]
Post subject: 
And I've heard conflicting advice that you should only run on battery power wherever possible, at least in the case of laptops.

Whilst you can't overcharge a Li-On battery once it's fully charged it enters a trickle charge state, as a small amount of power is used the charger keeps topping it up putting strain on the charging circuit within the battery itself. Eventually this leads to failure of the charging circuit even though the battery is still technically healthy.

Best practice appears to be to charge the battery fully then disconnect the charger and run on battery power until nearly discharged, then recharge again. Or just remove the battery and run from an external power source. The worst thing to do apparently is to keep the charger plugged in once the battery is fully charged.
Author:  bill_datamaster [ Thu Jul 14, 2011 9:12 am ]
Post subject: 
You’re always going to get conflicting advice when dealing with something with a limited life cycle but the only people really qualified to give definitive answers are the manufacturers. They set out detailed specifications for the optimum rates of charge in order to prolong battery life. The equipment designer then produces circuitry to do this and for Lithium Ion, this inevitably involves using a method called constant current charging. (Note the word constant!)

On a conventional charger, the charge rate is initially high but as the charge builds, the rate of charge decreases and eventually ends up as a trickle as anyone that’s ever charged a car battery would know. The constant current charger works differently though because it doesn’t slow down. It’s a bit like a flushed toilet that fills due to constant water pressure then having reaches a certain level it turns off.

Our measurements using the common HTC devices over a variety of temperatures show that under normal conditions, most PDA’s charge at a constant 0.4 Amp. If the unit gets hot to the touch, this suddenly drops to half charge rate to protect the battery. If the temperature continues to increase to the point where the unit is difficult to hold, the rate drops again but this time to just 0.05 Amp. Anything much higher than this and it shuts down completely.

Bottom line is, it’s like trying to find the best way to keep bread fresh. You know it isn’t going to last forever and a new loaf doesn’t exactly break the bank so why put up with stale bread or (batteries that wont hold a charge. :wink: )

Bill :)

Oh and PS. Do unplug the charger once it’s charged if you truly believe it’ll help save your battery (and the planet) but don’t come crying when you get to work and find yourself with a flat battery because you forgot to turn the PDA off overnight. :lol:
Author:  Nidge [ Thu Jul 14, 2011 6:22 pm ]
Post subject: 
bill_datamaster wrote:
Just need to come back on this because the advice given by both CAE and Midlander just isn’t right.

It might have been true back in the days of the old ni-cad batteries but you'd just be wasting your time doing that with a modern Lithium ion type. In fact there’s good technical evidence that that suggests running batteries completely flat in this way can actually cause damage so my advice is don’t do it. Also, it’s totally impossible to overcharge a PDA battery because the battery management system within the PDA prevents this from happening.

Bill :)


Bill, I've had my PDA since day one and the battery is still OK where as all the others have given up the ghost. Like I said I unplug my lead and leave it for an hour or so then plug it in again.
Author:  C.A.E [ Sat Jul 16, 2011 11:30 pm ]
Post subject: 
Midlander is doing it completely correctly, and his battery will go on and on.

You must let these batteries cycle in order to maintain life. They do not develop 'memories' like the old nicads, but they are very fragile units and fussy on charging. They must not be allowed to go flat, nor must they be left on charge.

To do this, you allow the battery to drain until power is low, and then recharge.

I will explain the techy bit in a simple a way as I can. These lib batteries work through the passing of electrolytes from anode to cathode and back again (more to it than that but gets the idea across) - just imagine them as neg and pos posts on a car battery for now.

When discharging, electrolytes pass from the neg post to the pos post which creates the energy steadily.

When charging, the higher voltage from the charger causes them to reverse and go the other way. During the charge cycle, they leave the pos post and return to the neg post where they embed themselves causing a chemical reaction resulting in energy. When off charge, it reverts back to the discharge cycle.

If left on one cycle, you end up burning out one electrode prematurely....which means it will not receive charge any more.

If you allow the battery to go completely flat, the electrolytes 'die' as they have no energy to pass to the other post, in order to start the chemical reaction that gives the energy. This results in the battery not receiving charge

That is as basic as I can explain. But it does mean that these batteries must be allowed to cycle to improve battery life - don't think lib batteries are indestructible - they are much more fragile than ni-cad - but benefits of size, weight and length of power, and lack of 'memory' are generally accepted to outweigh the fragility.
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