Battery Voltage

[El Jefe]

well, I was planning on drilling two holes for contacts in the battery cover, to allow a base with an extra battery to be tacked on easily.

This would work, I added four Li-ion cells on the back of my PSP and tripled my battery life!!!

Were they the same voltage as the original?
Is it necessary to have the same voltage on batteries in parallel?
like if there was the normal 3.7v but with a 5v tack on, would that cock things up?

 

[bennollan]

well, I was planning on drilling two holes for contacts in the battery cover, to allow a base with an extra battery to be tacked on easily.

This would work, I added four Li-ion cells on the back of my PSP and tripled my battery life!!!

Were they the same voltage as the original?
Is it necessary to have the same voltage on batteries in parallel?
like if there was the normal 3.7v but with a 5v tack on, would that cock thinks up?

All Lithium ion battery cells operate at the same voltage so just remember to hook them up in parallel to each other.

 

[Yoyobuae]

IIRC, lithium cells can be damaged quite easily if they are charged over the maximum safety point (over the maximum voltage the can take).

Also if you have discharged cell (with a low voltage) and connect it on parallel with a charged one (higher voltage) probably charge would flow (current) into the discharged cell. This current may be high enough to cause damage (there is nothing slowing it between one cell and the other, just low resistance conductors).

If you can it would be wise to match the voltage on both cells via charging/discharging one/both of them until it matches. Or perhaps connect them first thru a resistor of appropiate value (lowering current to safe levels), leaving them there until voltage (across resistor) drops to near zero.

 

[Polossatik]

I had a reply from Mweston, I copy it here in full. I will ask some more on the charging part and relay when recieved.

"Hi, The battery charges to 4.2V and can safely discharge down to 3.0V although we need to make something in the OS that will shut the system down at safe levels. Both the TI power management chip and the battery have built in protection to not let the battery drop below 2.7V but we don't want to go anywhere near that to guarantee long life of the cell itself. Unfortunately, with my basic kernel, there is no way to shut the system down automatically. It's something that needs to be added soon and lots of work is currently being done in regards to power management and this will be an important one too. During my testing I have found that the time it takes for the battery to go from 3.3V down to 3.0V is about 5 minutes with a kernel idling at 500MHz and the LCD at full brightness. For longer battery life, I wouldn't be opposed to setting the off point at around 3.2-3.3V and the battery fuel gauge will also be useful here as that will represent 0-1% of life left. If you always force a shut down or suspend at 1%, you can trade off those few extra minutes for a more durable battery which is something I have considered the best idea all along. Michael"

 

[Polossatik]

Micheal confirmed that the pandora battery datasheet states that 4.20 v is the recommended charge voltage and every charging chip he looked into uses also 4.20v, it looks like the 4.10~4.15 v was mainly applicable to older battery's and 4.20v is the current value to use.
So basically all now depends on the OS to avoid draining the battery below 3.0 and start with gracefully shutting down the system at 3.3v and then we can enjoy a long lifespan for the pandora's battery. B)

 

[Tor]

I would, if I can configure this myself on my own Pandora, put the switch-off much higher, maybe 3.5-3.7 volts. My Palm PDA turns off at 3.76 volts and that'll get a lot of charge out of the battery and it lasts for a very long time (I have one which is 5 years and still going strong with not much capacity loss).

 

[MWeston]

Your Palm PDA probably has a 4.1-4.2V cell that charges up to 5V (or something higher than 4.2V anyway) and so it runs down to 3.7V. I'm pretty sure that is what is in my Zodiac. (Nope, must be thinking of something else)

Pandora uses a 3.7V cell that charges up to 4.2V and runs down to 3.0V safely.

The battery runs for hours at the 3.7 - 3.8V level so I don't think you will want to cut this one off that high or you will only have about 4 hours of battery life at best.

 

[Yoyobuae]

Any chance that the Pandora battery actual voltage would be visible (perhaps with command line tool)? Or perhaps a nice graph of Voltage vs Charge% ?

I found some interesting tips:
How to prolong lithium-based batteries
Charging lithium-ion batteries
How to Extend Your Laptop's Battery Life?

It would be nice applying these tips for my Pandora batteries. My reviewed plan:

• Main battery - Charge up to 3.92V max (unless I really need the full capacity), use normally after but trying to avoid too deep discharge.
• Extra battery - Maintain in "storage mode". Store at 40% charge. After 3 weeks, do the discharge/charge again procedure (too let the control circuit recalibrate). Probably swap main and extra battery at this point.

I'm hoping I can keep the both batteries healthy and also distribute the usage between the two, reducing the # of cycles each goes thru.

By the way, how much current will the Pandora charge it's battery at? 1.0C or 0.5C?

 

[Nation.A.List]

By the way, how much current will the Pandora charge it's battery at? 1.0C or 0.5C?

Do you live in a fridge?

 

[mali]

That doesn't mean degrees Celsius

 

[dflemstr]

By the way, how much current will the Pandora charge it's battery at? 1.0C or 0.5C?

Do you live in a fridge?

I guess that he meant Coulomb by "C" (or the speed of light, but that's improbable) which doesn't make any sense either way since current is measured in Ampère (A).

 

[mali]

Wiki says:

This is often denoted as C and signifies a charge or discharge rate equal to the capacity of a battery in one hour. For a 1.6Ah battery, C = 1.6A. A charge rate of C/2 = 0.8A would use two hours, and a charge rate of 2C = 3.2A would use 30 minutes to fully charge the battery from an empty state, if supported by the battery.

 

[Nation.A.List]

That doesn't mean degrees Celsius

I had a vision of a Penguin living in a fridge...... seemed logical to me

 

[MWeston]

Any chance that the Pandora battery actual voltage would be visible (perhaps with command line tool)? Or perhaps a nice graph of Voltage vs Charge% ?

You could write an application that would show something like that and there might be some kind of battery managers in the XFCE package already. The TouchBook has something like that even though it doesn't seem to report properly for whatever reasons. You can poll the battery fuel gauge at any time to read the battery's voltage, current usage (and direction in or out), PCB temp under battery, time until full/empty, current capacity left (percentage), average drain, number of times it has been charged (until battery is removed from Pandora case), and I'm sure several other things I don't log. You can also query the TPS65950 for the voltage from the charger, how much current is being used be the charger (subtract from battery voltage to know how much system is using), and temperature of battery itself. There are many projects here that need work and volunteers will be welcome.

I should mention that you can poll this information from the console right now through an application Notaz made and through kernel drivers. I use it all of the time to monitor current and battery voltage without connecting any external test equipment.

By the way, how much current will the Pandora charge it's battery at? 1.0C or 0.5C?

0.2C (800mA) for a 5-6 hour charge cycle. It can be manually increased or decreased and at some point it would be great to have a driver that would dynamically allocate the current based on system load.

 

[mali]

What a great post! Thanks

 

[Yoyobuae]

Yes, thanks very much for the very detailed post.

I'll be looking forward to playing with the command line tool and trying to cook up a convenient monitoring/logging application for those parameters, if it doesn't exist already. I'll try looking what's available meanwhile.

 

[Tor]

Your Palm PDA probably has a 4.1-4.2V cell that charges up to 5V (or something higher than 4.2V anyway) and so it runs down to 3.7V.

No, it charges to 4.20 volts (when actually charging it will feed the battery with maximum 4.24 volts). The battery itself has a built-in protection circuit that switches off at 4.30 volts. This is the same type of cell that's often called '3.7v'.

 

[borgqueenx]

sorry to gravedig but i didnt find a good answer. correct me if i am wrong but we can set the volts ourselfs somehow on pandora? Or what volt will be standard?
It will help me to decide what external battery pack to buy.

Energizer has the XP battery packs, and they are 5 volt, so if the pandora is 3,7 volt, it will be pretty tempting to buy that battery pack.

 

[mali]

An external battery back has nothing todo with with the voltage of Pandora's internal battery. I've put a quote of MWeston stating the voltage range the USB port accepts for charging in the dev team updates thread a 3/4 year or so ago. Dunno if Chip added it though.

 

[borgqueenx]

An external battery back has nothing todo with with the voltage of Pandora's internal battery. I've put a quote of MWeston stating the voltage range the USB port accepts for charging in the dev team updates thread a 3/4 year or so ago. Dunno if Chip added it though.

if the external battery pack is 18.000mah on 5 volt, then doesnt that mean it can give my pandora about 20.000mah or a little bit more? Since the pandora is(standard lithium) 3,7 volt? (again, not sure what volts the pandora has, heard a couple things here)