What's The Deal With Charging Time?

[Aurekana]

I'm not sure I'm completely understanding this. The charging circuit/device in the Pandora can safely reach 0.5C, but it would be pushing it too hard? Is it currently set to 0.25C just for safety? I don't quite see the point in charging it below-spec.

It isn't the Pandora or the charging circuit that has a problem, it's the charging block. The Pandora's battery should be able to handle being charged in about an hour if you needed to (although I'm told two hours is the optimal maximum rate for lipo), but this would require a charger rated for over 4 amps, probably closer to 6. I'm looking over the chargers for many of my other electronics, and they all say 2amps. Even the adapters for my external hard drives are all 2 amps. The only one that produces more is my laptop, and even that's only 4amps. Long story short: if you want to charge faster, you need a more powerful charging block, and those just don't exist as off the shelf parts; you'd have to get something probably more custom and certainly more expensive.
I'd write a script to set it to do the 2 hour charge thing, but I am genuinely afraid of the prospect of these chargers burning out or overheating and catching on fire. It's just safer to keep well below the maximum rating and take your time rather than push your luck and risk serious injury or worse.

If all else fails and you really need a high amp power supply, I wonder if you'd be able to adapt a computer PSU (desktop) to supply its 5V line into a PSP charger connector. Those are fairly common and decently cheap, as its not like you'd need anything fancy or rated for high power output...

 

[CPUnltd]

would not surprise me if the PSU idea was doable... I'd go for an HTPC power supply as they are smaller (more portable) than the standard PSUs.

 

[jonjandran]

If all else fails and you really need a high amp power supply, I wonder if you'd be able to adapt a computer PSU (desktop) to supply its 5V line into a PSP charger connector. Those are fairly common and decently cheap, as its not like you'd need anything fancy or rated for high power output...

No the Power Supply has to be a smart charger or else the Li-po's will blow up.

 

[Aurekana]

If all else fails and you really need a high amp power supply, I wonder if you'd be able to adapt a computer PSU (desktop) to supply its 5V line into a PSP charger connector. Those are fairly common and decently cheap, as its not like you'd need anything fancy or rated for high power output...

No the Power Supply has to be a smart charger or else the Li-po's will blow up.

The LiPo charging circuitry is inside the Pandora itself. The charging brick just supplies a certain voltage and current, and the charging circuit does the rest. So as long as the PSU supplies a stable voltage and as much current as you need, everything should be fine.

 

[chris_c]

If all else fails and you really need a high amp power supply, I wonder if you'd be able to adapt a computer PSU (desktop) to supply its 5V line into a PSP charger connector. Those are fairly common and decently cheap, as its not like you'd need anything fancy or rated for high power output...

This is a *really* bad idea, the charging circuit has almost certainly been designed with a maximum input current in mind, attempting to mess around with the power management chips settings and using a much more powerful power brick will almost certainly blow the charging circuit.

You have carefully looked at the changing circuit and the component values haven't you ?

Further more this will void your warranty - the damage will be obvious (probably to the eye!) and you'll be out one pandora...

in short NOT WORTH MESSING WITH for the sake of a few hours off the charging time - that can be easily done while you sleep or are using the unit at home.

 

[Aurekana]

If all else fails and you really need a high amp power supply, I wonder if you'd be able to adapt a computer PSU (desktop) to supply its 5V line into a PSP charger connector. Those are fairly common and decently cheap, as its not like you'd need anything fancy or rated for high power output...

This is a *really* bad idea, the charging circuit has almost certainly been designed with a maximum input current in mind, attempting to mess around with the power management chips settings and using a much more powerful power brick will almost certainly blow the charging circuit.

You have carefully looked at the changing circuit and the component values haven't you ?

Further more this will void your warranty - the damage will be obvious (probably to the eye!) and you'll be out one pandora...

in short NOT WORTH MESSING WITH for the sake of a few hours off the charging time - that can be easily done while you sleep or are using the unit at home.

I am not advocating doing anything to the internal DC-DC power supply and charging circuit. Those can remain as they are, unless WizardStan's improved charging script changes anything. What I am referring to is the External Power Brick - the block-like object on the cord of your Pandora charger that sits between the wall outlet cord and the cord leading to the PSP barrel plug adapter that fits into the back of the Pandora. That little AC-DC converter is rated to output a maximum of 2A at 5V. Since supplying much more current than you need is not bad for the hardware unless you force the current through (if it uses only 500mA, then it will take 500mA from the available pool of 2A. If it needs 3A, then it only has the available 2A to work with). The voltage is the main concern - unless the Pandora has some beefy voltage regulation circuitry, then varying the input voltage greatly from the specified 5V will damage the hardware.

WizardStan reported that the charging circuit in the Pandora should be able to handle the increased charging rate without a problem. His qualm was that no readily available charging brick outputs the needed 5V while supplying any more than 2A. To charge at an increased rate, you need more current, and so the charging rate is right now limited by that 2A maximum output of the brick.

Assuming he is correct in that an increased current of 4-5A will not damage the circuitry and will greatly improve the charging time, then I see no concern in using an AC-DC power supply that will provide 4-5A at a steady 5V. I am not sure how efficient my idea would be, but assuming you could monitor the voltage on the 5V rail of the Desktop Power Supply, to verify that it stays within acceptable limits, the 12-16A pool of available current is more than plenty to charge the Pandora with the improved charging script.

I use a bench power supply (adjustable 0-20V, 0-3.3A) to power electronic devices frequently whenever I lose or break their stock charging cord, and have not yet had a blowup (except when I accidentally switched the lines, but that's a big dumb mistake on my part) because as long as the device is supplied with a spec'd voltage and an ample amount of current (and is designed well), it functions just fine.

 

[chris_c]

It's all to easy to inadvertently make magic blue smoke with a bench supply

charging circuit in the Pandora should be able to handle the increased charging rate

I value my Pandora rather higher that risking it on a should! unless they want to publish the charging circuit or specifically state the maximum current it is rated for...

 

[Aurekana]

It's all to easy to inadvertently make magic blue smoke with a bench supply

charging circuit in the Pandora should be able to handle the increased charging rate

I value my Pandora rather higher that risking it on a should! unless they want to publish the charging circuit or specifically state the maximum current it is rated for...

Except for once when I collected all the magic blue smoke and stuck it in a box, I had the best computer on the block for years! :lol:

I agree, it would be useful to take a look at the actual battery charging chip inside the Pandora first to see if all this is even possible, but I was just ranting on how the external power brick itself if overspec'd as far as current won't blow up your Pandora unless you cross the wires. I don't know enough about how to increase the charging rate on the internal chip itself to make much of a comment regarding that.

By the way, if anyone needs pictures of the internals of the stock Pandora external charging block, lemme know; I have it open sitting on a desk next to me.

And here's a link to the Power Management chip in the Pandora: http://focus.ti.com/docs/prod/folders/print/tps65950.html

 

[chris_c]

I've dealt with the twl4030 datasheet and am doing so again looking at the alarm, tell you what its a real brain melt!

Personally I'm more than happy with the changing time - if you can only stick it on charge for 1/2 an hour you're still getting (very) roughly 1 and 1/4 hours extra use (very roughly) good enough performance for me...

 

[Aurekana]

Looking through the twl4030 and tps65950 datasheets, I'm amazed they're able to put so much stuff in such a small support chip. Though I guess all in the name of miniaturization and cramming more stuff into smaller devices.

The charging time could use some optimization, but I guess it works well enough for me. Though I would be in favor of the external battery charging dock someone mentioned a little ways up in the thread. Was thinking of getting something like it for my laptop way back when it had a battery life of roughly 3 hours, so that I wouldn't have to idle while charging the spare. It also makes me want to find some small area in the Pandora case where I can stick a small battery or super-capacitor, so that I wouldn't need to deal with the 30-second downtime while swapping batteries...

 

[WizardStan]

It's all to easy to inadvertently make magic blue smoke with a bench supply

charging circuit in the Pandora should be able to handle the increased charging rate

I value my Pandora rather higher that risking it on a should! unless they want to publish the charging circuit or specifically state the maximum current it is rated for...

Indeed, take my words with a grain of salt, I'm working on a lot of theory and supposition. Looking back over the TWL spec, it looks like max charge might actually only be 1.7a. Maxing it out wouldn't need a larger brick, 2amps is plenty, we'd just have to tweak the registers on the chip. We could get the charging down to about 2.5 hours which should also be well within the lipo's safety parameters. It's not completely risk free still. What the chip says it can handle and what the battery should be able to handle do not necessarily have to line up with reality. If someone wanted to take the risk, knowing there's a non-zero chance that it could blow up their battery, run the battery all the way down and back up 3 or 4 times, at least once with the wifi on playing Mario64 to drive it hard, check the battery to make sure it isn't overheating too much, then maybe we can think about letting Joe Average do it.

 

[chris_c]

what about the long term life of the battery?
would rapid charging shorten the life span?

I personally would prefer battery life span over speed of charging...

I've messed round with that many battery technologies over the years and there’s that much conflicting even plain wrong info out there, I can't remember how lipo's handle fast charging or even if charging over the 4 hours or so would lengthen their lives compared with 2hr charge...

Anyone know for sure - can you back your info up, if you think you do know? - really there’s a LOT of different things said about lipos!!!

 

[WizardStan]

what about the long term life of the battery?
would rapid charging shorten the life span?

It's not rapid charging. 1C is rapid charging, and even that all the literature suggests is completely safe. This is less than 0.5C, the battery can handle it, that much I'm pretty sure about.