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Maximum possible file size and fastest charging speed?
02-12-2020, 01:29 AM
Post: #1
Maximum possible file size and fastest charging speed?
Hi, I recently tried to load a large program file onto my G2 with ~400mb ROM free and ~200mb RAM free. It appears that 32mb is the maximum size for a single file the calculator can handle. It started warning me about there not being enough space any higher than that. Is this correct? If so, does that mean there are 16 flash pages?

I was also wondering, what's the max wattage the prime can charge from? I know it's not really expected to be charged from much more than standard 5W chargers but can it utilize more than that?
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02-12-2020, 05:31 AM
Post: #2
RE: Maximum possible file size and fastest charging speed?
Does it even use 5 W? Anyway, you can plug it into a 2000 W (5 V) supply and it will charge the same as with the 5 W supply. Li-ion batteries are charged with a CC/CV method meaning that first the current is limited by the charging controller until the maximum voltage (usually 4.2 V) is reached. Then it keeps that voltage until the current is low enough.
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02-12-2020, 06:25 AM
Post: #3
RE: Maximum possible file size and fastest charging speed?
Hello,

I have no clue what is the max file size for apps... I do not remember putting upper limits in place, but it might be that the underlying YAFS file system has a file size limit...
Can you try sending the same app to an emulator and see if there is a limit there on the PC? if no, then it means that the limit is imposed by a component not under our control... If yes, then I might be able to do something about it...

About the battery charging.
I think that the max speed is around 4h for a full charge, regardless of power... This is due to the chemistry of the battery which can not tolerate faster charges.

Cyrille

Although I work for the HP calculator group, the views and opinions I post here are my own. I do not speak for HP.
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02-12-2020, 04:52 PM (This post was last modified: 02-12-2020 05:27 PM by DrDarius.)
Post: #4
RE: Maximum possible file size and fastest charging speed?
(02-12-2020 05:31 AM)SammysHP Wrote:  Does it even use 5 W?
I have never measured the charging current for the fully discharged battery, but for the substantially discharged battery (below 50%, and Prime's accuracy of the measurement of remaining battery charge is rather symbolic, than real Smile ) the charging current remained below 0.5A.
(For the fully discharged battery the current might be slightly higher. The current also depends on whether you have a calculator on or off during charging, since when the calculator is on, electronics and display also take some current from the charger.)

So this would make 2.5W...

I am going to take one of my Primes, drain the battery, and measure the charging current for the empty battery. But it may take a day or two to drain it, since I'm going to use a calculator to do it. I will post an update when I'm done.

(BTW: Prime's battery charging voltage 4.35V; it's written on the battery)
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02-12-2020, 05:32 PM
Post: #5
RE: Maximum possible file size and fastest charging speed?
(02-12-2020 01:29 AM)TheLastMillennial Wrote:  I was also wondering, what's the max wattage the prime can charge from? I know it's not really expected to be charged from much more than standard 5W chargers but can it utilize more than that?

One of my students said that her Prime calculator battery was dead and it wouldn't charge. I plugged it into a computer and it seemed to charge fine. I suspected that she was using a fast charger >5volts. I recommended that she use a computer or the small charger and she's been fine since. Fortunately, it appears that no harm was done to the calculator.
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02-12-2020, 07:31 PM
Post: #6
RE: Maximum possible file size and fastest charging speed?
Cyrille, the emulator accepts files larger than 32mb. In fact I even tested over 64mb without issues. Small request: could you please tweak the spacing allowed for the program size to be displayed? Instead of showing 'mb' it's showing '...' as if there's just barely not enough room.

I'm kinda surprised the Prime doesn't even have 5W charging capabilities. I looked up the max charging speed of the Galaxy S3 and I discovered some people saw a maximum of 1.8A drawn from the charger so the battery itself should be able to handle more than 2.5W. Wes, I don't know why your student's calculator wouldn't charge, I'm using an 18W fast charger and my Prime charges perfectly fine. Maybe it's a placebo effect, but I thought it started charging faster when I used my 18W vs my old 5W. I should test that!
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02-13-2020, 12:00 AM (This post was last modified: 02-13-2020 12:01 AM by DrDarius.)
Post: #7
RE: Maximum possible file size and fastest charging speed?
(02-12-2020 04:52 PM)DrDarius Wrote:  I am going to take one of my Primes, drain the battery, and measure the charging current for the empty battery. But it may take a day or two to drain it, since I'm going to use a calculator to do it. I will post an update when I'm done.
It took shorter than I expected.

From the charger's standpoint, the important parameter is current drawn from the charger, not the current charging the battery. (If the charging circuitry is based on the switcher, they would not be equal.) So, for the measurement I used Ruideng USB current sensor connected between the charger and the calculator (rather than measure current flowing through battery terminals).

I let the calculator run until it turned off by itself. The battery voltage after it happened (measured on the battery removed from the calculator) was 3.061V. It well corresponds to standard 3.0V LiPO cutoff voltage.

The current drawn from the charger measured for the calculator turned off was 0.655A, thus slightly more than I expected. (This is the maximum current; it kept quickly dropping down, and after ten minutes dropped to vicinity of 0.5A.)

Thus, to make sure that the used charger is not overloaded while charging fully drained battery, it has to be able to deliver about 3.3W. Most of the small chargers exceed this value.
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02-13-2020, 12:07 AM
Post: #8
RE: Maximum possible file size and fastest charging speed?
(02-12-2020 07:31 PM)TheLastMillennial Wrote:  I'm kinda surprised the Prime doesn't even have 5W charging capabilities.

Take under account that Prime can be connected to (thus inadvertently charged from) the computer USB port. Not all computer USB ports have high current sourcing capabilities.
Maybe this was a reason for selecting lower charging current...

Darius
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02-13-2020, 05:49 AM
Post: #9
RE: Maximum possible file size and fastest charging speed?
Hello,

We selected the current based on the battery specs.

We did try to use some of the "optimized" charging curves at one point, but stopped because this required active SW monitoring, which was not something we could guaranty during the whole charging sequence...

Cyrille

Although I work for the HP calculator group, the views and opinions I post here are my own. I do not speak for HP.
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