Battery Issues

[WizardStan]

So this "fuel gauge" can miraculously Determine what a full charge is the first time but not at any other time?

Nothing miraculous about it.

I thought a Lithium charger charges each individual cel to 4.20 volts . It charges full charge rate to 4.05 volts then trickle charges the rest. The pcb is there to limit over discharging.

You thought wrong. When you apply a load to a battery the measured voltage drops. When you apply a charge to the battery the measured voltage is higher. Depending on what the Pandora is doing the actual voltage measured across the battery can swing by up to 0.2 volts. That's almost a 20% difference. It'd be really confusing to start mupen64 and see your capacity drop from 80% to 60%. It'd spring back up as soon as you got to the desktop but it's still not ideal. Furthermore, voltage drop rate changes as the chemistry of the battery changes over time: where a drop from 4.2 to 4.1 may have once been a change from 100% to 90%, a few years later that could be a change from 100% to 85%. A reasonable estimate based on voltage can be made when the battery is first inserted, hence why removing the battery might help, but it is very imprecise once the battery starts getting used.The proper way of monitoring battery level is to measure the current going in and out. The BQ knows how much is supposed to be in the battery, so as the battery is charged it measures how much goes into it until the charging stops, at which point it goes "ok, the battery now has 4000mah in it". Then, as the battery discharges, it measures the current and subtracts that from what it knows.

If that wasn't the case then why would any battery arrive not fully charged? Why do they arrive partially charged? Wouldnt they have been already fully charged once if they already have a partial charge? Doesn't make sense .

Two reasons: first, lithium batteries are volatile. Shipped fully charged there is a small but not impossible chance of violent explosion. Second, lithium batteries stored at full charge wear out faster than those stored at lower levels: a battery kept at full charge for a year will lose 10-20% of its storage capability vs just 2% if it was stored at 40%. In actual numbers, our battery which lasts 10 hours would only last 6 to 8 hours by now if they had been kept stored at 100%.

 

[hailrazer]

 

>>I thought a Lithium charger charges each individual cel to 4.20 volts . It charges full charge rate to 4.05 volts then trickle charges the rest. The pcb is there to limit over discharging.

You thought wrong

Actually what I said was almost a direct quote from several Lithium charger manufacturers.

That is how most Lithium chargers work apparently. Says so in their manuals and several dozen battery sites online say the same thing. Could be they are simplifying it for people like me who just know the basics.

But the rest is interesting info.

But still wouldn't the battery have been fully charged the first time before it was shipped? Even if it was discharged later for shipping rasons?

 

[WizardStan]

That is how most Lithium chargers work apparently. Says so in their manuals and several dozen battery sites online say the same thing. Could be they are simplifying it for people like me who just know the basics.

The charger is different from the fuel gauge, this is pretty standard. We have two chips in the Pandora, the TWL4030 charges the battery (as well as other things, such as acting as the clock, PWM controller, hardware interrupts, etc...) and returns an approximate capacity based on the voltage (which, as mentioned, varies based on the load level), whereas the BQ25000 chip does the more accurate current tracking I mention. Why they are frequently separate chips I don't know, probably a cost saving measure or something.

But still wouldn't the battery have been fully charged the first time before it was shipped? Even if it was discharged later for shipping rasons?

It could have been. How does that help the device the battery is going into? Even if you were to receive a battery perfectly topped off you would still need to plug it in for the fuel gauge chip to detect a charge and "know" that it was at full power.Like I said, the charging suggestion has absolutely nothing to do with the battery itself; it is entirely for the device to be able to calibrate the power level.

 

[hailrazer]

Now that was some Dang good explaining right there . 

That cleared it up perfectly. It's almost like you know what you are talking about.

One last thing though. Isn't it different for the Li-po's and smart chargers like I use in my portables? They even put right on the package that there is no need for a first time full charge .

 

[WizardStan]

The batteries themselves are probably shipped at (or near) full power. They're banking on them being purchased quickly so they don't have time to start crystalizing, and that they have a sufficiently low total capacity that explosion is almost negligible: an AA battery has about 3 watthour of power vs the Pandora's 16 watthour. Hmmm... you're using some pretty beefy cells though, not AA batteries. Maybe simply the fact that they are solid cells as opposed to the squishy packaging of a custom battery is enough to make them considered safe, not sure. I could be wrong about the fear of explosion during shipping so they just have to charge them at the warehouse (something EvilDragon wouldn't have time or capacity for but a battery manufacturer would) before shipping.

I'm guessing that your portables don't have single digit precision for remaining life, right? How do you know when the batteries are needing a recharge? The simplest smart-charge systems are just voltage based, which is fine as long as you only care if the battery is full or almost empty.

Nice construction by the way. I couldn't tell that those cases weren't custom moulded, they fit so well.

 

[hailrazer]

Thanks

Some of my portables just use Lithium-ion camcorder batteries. But on some I use 2- 3.7v 5000 mAh polymers . I add apcb and a smart charger. They do come pretty well charged it seems.  And I just use a simple led based circuit that tells me when the voltage is getting low, around the 25% range.

Sorry for all the questions and discussion. Just trying to learn more. 

 

[EvilDragon]

No, the batteries arrive 50% charged from the manufacturer.


The manufacturer also discharges and recharges them to 50% each month they are lying around on stock.


Don't ask me why, I can only tell you that's the case

 

[WizardStan]

Sorry for all the questions and discussion. Just trying to learn more. 

It's cool. I learned most of this by trial and error. Back in university I was on the school's solar race team, but there I was working with an engineer who knew exactly what he was building; all I had to do was write the software to do what he told me to do. When the Pandora came along and people had issues with the charging I figured I could take that knowledge and do a driver fix. It took several hacky iterations and Notaz figuring out the best way to implement it before we got something that worked.