Question Battery Life Ashida

[Darkside19]

Hey guys.
I just want to know, how is your battery life of your Ashida and which batteries do you use. I bought the Vapcell F60 6000mAh 21700 batteries a while ago and "only" get close to 3 hours of battery life out of my Ashida. Still not sure if this is good. I think for 12000mAh it should hold 4 hours to 4,5 hours. What's your opinion and how long do your ashidas last? (I use the IPS panel with brightness at 80%, Volume about half to max and have a rumble motor installed). If I try to charge and play it do not work like I want it to, it discharges faster than charging it (use 30W Anker Adapter via USB-C, charge current set to 3006 mA)

 

[YveltalGriffin]

Hey, this isn't a direct answer to your question, but I hope it's helpful for you and anyone else trying to crunch the numbers on portable battery life. The key thing to know is that advertised 18650 and 21700 cell capacities are calculated based on a full discharge down to 2.5V.

The PMS2 uses a buck converter for the 3.3V rail. As a result, it has to cut off the cells above 3.3V. I don't know the exact cutoff voltage (Gman or Aurelio could tell you) but the result is that a massive portion of the advertised battery capacity goes unused.

This is the Vapcell F60 discharge curve. At low discharge currents, with modern cells like this, the curve is relatively flat. A Wii portable draws around 10W, which works out to less than 1.5A per cell with a 1S2P pack like the Ashida's. So the relevant traces in the plot are the red (1.2A) and yellow (2A) ones.

By cutting off at 3.45V, you are sacrificing 40% of the cells' advertised capacity (the red area under the curve). The effective capacity per F60 cell when cutting off at 3.45V is only 3715mAh, not 6000mAh!

That's 13.4Wh per cell. Assuming your portable draws 10W, a 1S2P 26.8Wh pack will run it for 2.68 hours. This matches the behavior you're seeing. A fully exercised cell (nearly 6200mAh at these low C-rates!) provides 22.3Wh. As you said, that would work out to 4.5hrs.

This is why I use buck-boost regulators for the 3.3V rails in my portables. They allow you to discharge below 3.3V, all the way down to 2.5V if you want. Since most portables run at very low C-rates, the cells have no problem discharging fully, with no sharp knee in the discharge curve. And since most portables aren't played a ton (relatively few discharge cycles), discharging deeply won't have an appreciable effect on cell health over time.

Btw, Vapcell just released some new 6250mAh 21700 cells. Might be an easy way to increase runtime ever so slightly without a PMS change.

 

[fdraghi]

That's insanely good data... I wonder if there's a good reason why the PMS was designed with a converter instead of a booster...

 

[Stitches]

That's insanely good data... I wonder if there's a good reason why the PMS was designed with a converter instead of a booster...

My guess would be because most off the shelf li-ion charge/discharge protection chips have their maximum discharge voltage set to 3.2v, which is just below 3.3v. Safely cycling a li-ion cell down to 2.5v requires some additional handling, and not all cells support going down to 2.5v. Some will die and become a fire hazard at 3v, so 3.2v is kinda the safe standard.

For the PMS to full cycle the cells, it would require creating and maintaining a compatibility database and then dealing with the inevitable "I got these cells from my dad's tesla and the PMS killed them" emails.

 

[YveltalGriffin]

2.5V really is the industry standard cutoff voltage for cylindrical cells. A few cells have cutoff voltages of 2.7V or so, but they are outliers.

The most common DW01 protection IC, used in virtually all eBay/AliExpress PCMs, has an overdischarge threshold of 2.4V - 2.5V.

A threshold of 2.9V would only sacrifice ~10% capacity instead of 40%, while providing very wide safety margin for all cells on the market.

I can't speak to why the PMS2 was designed the way it was, and I'm not criticizing its architecture. Many low cost consumer devices behave the same way and cut off at 3.4V or so.

But in mobile devices that are trying to achieve the best possible battery life, like phone/tablets/wearables, using a buck-boost for high voltage rails is incredibly common-- it's standard practice! There aren't any additional safety concerns when doing it. This is important context for folks who want to extend their portables' runtime as much as possible

 

[Gman]

That's insanely good data... I wonder if there's a good reason why the PMS was designed with a converter instead of a booster...

The pmsv1 had battery drain issues so we wanted a conservative bullet proof design with the pms2. And there hasn't been any trend of issues after years of use. It can be more efficient and longer battery times, ofcourse. We have been slowly developing new tech taking into account what we have learned, and how we can improve.

 

[fdraghi]

Thanks @Gman, yeah I understand... Don't get me wrong, I'm happy with the PMS2, and I'm now happier knowing that there's potential, if something like a PMS3 were ever to be a thing, to extract 1~ish hour more (actually way above 1 hour running gamecube) with the same batteries. I'd upgrade to it in a heartbeat.

 

[Darkside19]

Hey, this isn't a direct answer to your question, but I hope it's helpful for you and anyone else trying to crunch the numbers on portable battery life. The key thing to know is that advertised 18650 and 21700 cell capacities are calculated based on a full discharge down to 2.5V.

The PMS2 uses a buck converter for the 3.3V rail. As a result, it has to cut off the cells above 3.3V. I don't know the exact cutoff voltage (Gman or Aurelio could tell you) but the result is that a massive portion of the advertised battery capacity goes unused.

This is the Vapcell F60 discharge curve. At low discharge currents, with modern cells like this, the curve is relatively flat. A Wii portable draws around 10W, which works out to less than 1.5A per cell with a 1S2P pack like the Ashida's. So the relevant traces in the plot are the red (1.2A) and yellow (2A) ones.

View attachment 38472

By cutting off at 3.45V, you are sacrificing 40% of the cells' advertised capacity (the red area under the curve). The effective capacity per F60 cell when cutting off at 3.45V is only 3715mAh, not 6000mAh!

That's 13.4Wh per cell. Assuming your portable draws 10W, a 1S2P 26.8Wh pack will run it for 2.68 hours. This matches the behavior you're seeing. A fully exercised cell (nearly 6200mAh at these low C-rates!) provides 22.3Wh. As you said, that would work out to 4.5hrs.

This is why I use buck-boost regulators for the 3.3V rails in my portables. They allow you to discharge below 3.3V, all the way down to 2.5V if you want. Since most portables run at very low C-rates, the cells have no problem discharging fully, with no sharp knee in the discharge curve. And since most portables aren't played a ton (relatively few discharge cycles), discharging deeply won't have an appreciable effect on cell health over time.

Btw, Vapcell just released some new 6250mAh 21700 cells. Might be an easy way to increase runtime ever so slightly without a PMS change.

Wow thanks, never thought about that, I ordered the new 6250mAh to get maybe another 15-20 minutes

 

[Stitches]

Man my figures are hella outdated...................

 

[Darkside19]

got the new batteries and try the battery time now