Charging Cell phone form a 9V battery - Page 1
Forum section: electronics / general

author: hamster_nz
author_rank: Super Contributor
timestamp: July 20, 2020, 05:32:48 am
content: Might be worthy of discussion... (but not really).

author: james_s
author_rank: Super Contributor
timestamp: July 20, 2020, 05:48:35 am
content: I mean obviously it would work, but it's a very expensive way to get a partial charge into a phone. Maybe if you're stranded somewhere with a mobile phone, car charger and a pile of 9V batteries?

author: MosherIV
author_rank: Super Contributor
timestamp: July 20, 2020, 07:59:39 am
content: If you look at the capacity of a 9v battery and the capacity of the battery in the phone, you woul realise that the 9v battery would give less tha a few % to the phone.

author: tooki
author_rank: Super Contributor
timestamp: July 20, 2020, 10:16:37 am
content: And that’s before the losses incurred in the car lighter plug, many of which use a linear regulator to burn off the excess voltage as heat!

author: Twoflower
author_rank: Frequent Contributor
timestamp: July 20, 2020, 10:44:18 am
content: The picture says in case ofEmergency. I think it might be possible to charge the phone from dead-as-doornail to able to call a rescue team. Other than that: I totally agree not very useful.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 20, 2020, 01:13:24 pm
content: Quote from: james_s on July 20, 2020, 05:48:35 amOr free for those who work at live events where they regularly change microphone batteries long before they're near dead. Granted, such events are far less common nowadays with the COVID crisis that's going on.Quote from: tooki on July 20, 2020, 10:16:37 amHaven't seen one that bad in a very long time, even the really cheap ones use switchers nowadays.

author: james_s
author_rank: Super Contributor
timestamp: July 20, 2020, 07:09:36 pm
content: Quote from: NiHaoMike on July 20, 2020, 01:13:24 pmAnother source are smoke alarms. My brother used to work maintenance at a retirement home and they legally had to replace all the 9V batteries annually, despite the fact that the smoke alarms were all mains powered with the batteries just as a backup. He gave me a box once of about 400 9V batteries, I used them for all sorts of stuff, eventually a bunch of them failed due to age though.

author: tom66
author_rank: Super Contributor
timestamp: July 20, 2020, 07:11:47 pm
content: Quote from: NiHaoMike on July 20, 2020, 01:13:24 pmA friend of mine had one of these cheap switchers fail and test the OVP circuit on his phone. It had 13.8V on the USB output. Thankfully most modern phones have these protection ICs and it simply refused to charge ("Charger Not Compatible With This Device"), but I can imagine some devices could easily be damaged.

author: james_s
author_rank: Super Contributor
timestamp: July 20, 2020, 07:17:59 pm
content: Quote from: tom66 on July 20, 2020, 07:11:47 pmI've had linear regulators fail shorted and present the full input voltage on the output as well. It's an inherent flaw in non-isolated stepdown regulators lacking a crowbar circuit.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 20, 2020, 10:09:32 pm
content: Quote from: tom66 on July 20, 2020, 07:11:47 pmAnd now the various fast charge standards intentionally boost the voltage when requested by the device. How long before some cheap charger comes out with a bug that causes it to raise the voltage on something other than the proper command? Might the USB standards get amended to require devices to survive up to 20V to cover that scenario?

author: madires
author_rank: Super Contributor
timestamp: July 20, 2020, 10:17:57 pm
content: Hack the charger:https://www.zdnet.com/article/badpower-attack-corrupts-fast-chargers-to-melt-or-set-your-device-on-fire/

author: tom66
author_rank: Super Contributor
timestamp: July 21, 2020, 07:12:10 am
content: Quote from: NiHaoMike on July 20, 2020, 10:09:32 pmThe protocol is alarmingly simple for Qualcomm Quick Charge as well. You just have to pull D+ and D- down separately within a certain time window, and you can get the full 20V. There's no negotiation or communication, and cheap chargers omit the discharge circuitry which can keep the 20V output active for some time, potentially damaging a new device. It is all a bit dodgy in my opinion.

author: james_s
author_rank: Super Contributor
timestamp: July 21, 2020, 08:12:05 am
content: I've never been a fan of using USB strictly for power, and these various nonstandard USB implementations to transfer more power are doubly stupid. If they want to use higher voltages they should have used a different connector.

author: richard.cs
author_rank: Super Contributor
timestamp: July 21, 2020, 09:42:29 am
content: Quote from: NiHaoMike on July 20, 2020, 01:13:24 pmI have seen poundland ones (think dollar store) with a 78L05 in them - it's generally enough to make the phone indicate it's charging but not to deliver much energy, they normally provide 200 mA before the current limit kicks in, and then the thermal shutdown is triggered in a minute or so. This is more in the "fake charger" category really.

author: tooki
author_rank: Super Contributor
timestamp: July 21, 2020, 03:46:55 pm
content: Quote from: james_s on July 21, 2020, 08:12:05 amIn fairness, the USB-IF pretty much did, in that USB-PD requires USB 3. Whether with Type-A/B or Type-C, it's a new connector type.