Stupid Laptop Charging Question

[Ben]

Possibly a stupid question, but does anyone know if there's a problem going directly from the USB port on an external LiIon battery pack to a laptop charging port using one of these adapters:

https://www.amazon.com/Onite-Famale-5-5x2-1mm-Connectors-Cables/dp/B010VDOSOE/ref=sr_1_9?ie=UTF8&qid=1513010267&sr=8-9&keywords=usb+to+power+cable+laptop

I would ideally want to do the direct battery pack to laptop connection if there were, for instance, a power outage or whatever, since I have a bunch of the LiIon packs laying around and thus wouldn't have to fire up a generator just to charge a laptop using the laptop's regular AC adapter.

I haven't found any kind of charge controller that would fit between USB and a laptop power cable such as at the above link. Unless maybe one of the 20 buck charge controllers for solar panels would do it?

I could, of course, just use one of my regular UPS units to charge the laptop, then just plug them into the genny, but am looking at a way to use the portable battery packs to do it, just to have an alternative charging method available.

[dogmush]

That LiIon battery probably puts out 5VDC into the USB cable.  The two Dell Laptop power supplies I have handy output 19.5VDC.  It's unlikely the charge controller on your laptop would see the 5VDC doming into the charge port as useful, and as a result probably wouldn't charge the battery.

I'm unsure what the Charge controller voltage range is, but I'd be surprised if it was that much.  Check your power supply to see what your laptop normally gets.

[Ben]

Well, the power supply for the little laptop that I would do this with is input 1.2 amps and output 20v 2.25 amps. My larger laptop, where this likely wouldn't work, is input 2.5 amps, output 20v 8.5 amps

[Hawkmoon]

Amps isn't the issue -- notebook computers pretty much all need 19 volts. USB is 5 volts. You can't charge a 19-volt battery with a 5-volt input. The best you can get out of that is to bring the notebook from "dead" to "mostly dead."

[Ben]

Amps isn't the issue -- notebook computers pretty much all need 19 volts. USB is 5 volts. You can't charge a 19-volt battery with a 5-volt input. The best you can get out of that is to bring the notebook from "dead" to "mostly dead."

I was kinda hoping it would work as a backup emergency "trickle charger" in the same way I use a 3.5 amp charger on my car battery, but I guess not. 

Oh well. UPS and generator is it I guess.  I can always use the power bricks with my phone and tablet I suppose (as I do anyway when on the road), since they are direct connect. I'd just rather surf something with a keyboard in a power outage rather than a tablet or tiny screened phone.

[Hawkmoon]

I was kinda hoping it would work as a backup emergency "trickle charger" in the same way I use a 3.5 amp charger on my car battery, but I guess not. 

Oh well. UPS and generator is it I guess.  I can always use the power bricks with my phone and tablet I suppose (as I do anyway when on the road), since they are direct connect. I'd just rather surf something with a keyboard in a power outage rather than a tablet or tiny screened phone.

Agreed. That's what Bluetooth mouses and keyboards are for. Each has its own batteries, so they don't suck the life out of the computer. Or you could just get a USB hub and use your regular keyboard and mouse.

[KD5NRH]

IIRC, somebody used to make a 12V laptop, as well as a DC-DC converter to run other laptops off 12/24/48VDC, specifically for solar and battery systems.  Eliminates a couple steps in the DC-AC-DC mess of trying to run one off its regular power supply in off grid systems, so you can just use a deep cycle battery (or several) and a cheap charge controller as your UPS.

[Hawkmoon]

I guess you could wire up a 12-volt battery and a 6-volt battery in series. I imagine a computer will run on 18 volts even if the label says 19.

[Firethorn]

Buy 5 18650 cells with a charger.  Build a pack with them in series.  Should get you close enough.

Or try something like this:
https://www.amazon.com/MAXOAK-Portable-External-Smartphone-Notebook/dp/B078DRJQ7G/ref=sr_1_2_sspa?s=electronics&ie=UTF8&qid=1513049285&sr=1-2-spons&keywords=external+laptop+battery&psc=1

[Ben]

Or try something like this:
https://www.amazon.com/MAXOAK-Portable-External-Smartphone-Notebook/dp/B078DRJQ7G/ref=sr_1_2_sspa?s=electronics&ie=UTF8&qid=1513049285&sr=1-2-spons&keywords=external+laptop+battery&psc=1

Well see, now we're back to my OP. A couple of my power packs are the size of that one (they're actually LiIon jump starters for my vehicles). The one in the link comes with the adapter kit that I was asking about, so now I'm back to wondering why that wouldn't work. Maybe I'll just spend the ten bucks on the adapter kit and see what happens. I've got a USB output meter, so I think I'll check the output of the various ports on my bigger power packs.

[cordex]

The one in the link comes with the adapter kit that I was asking about, so now I'm back to wondering why that wouldn't work. Maybe I'll just spend the ten bucks on the adapter kit and see what happens. I've got a USB output meter, so I think I'll check the output of the various ports on my bigger power packs.

The linked pack has 12v and 20v outputs in addition to the USB output.   The adapters plug in to those, not the USB ports.

[Ben]

The linked pack has 12v and 20v outputs in addition to the USB output.   The adapters plug in to those, not the USB ports.

Ah - I missed that. I'll have to check the jump starters to see if they have separate outputs.

[Hawkmoon]

Your original post asked about using a USB port to power the notebook. USB is 5 volts. The notebook needs 19 volts. That won't work. You need something putting out pretty close to 19 volts. Lower amps at 19 volts just means it won't charge as fast, but it'll still charge. 5 volts won't help you.

[Ben]

Your original post asked about using a USB port to power the notebook. USB is 5 volts. The notebook needs 19 volts. That won't work. You need something putting out pretty close to 19 volts. Lower amps at 19 volts just means it won't charge as fast, but it'll still charge. 5 volts won't help you.

Okay, got it (my skull is thick and robust). :)

[KD5NRH]

Your original post asked about using a USB port to power the notebook. USB is 5 volts. The notebook needs 19 volts. That won't work. You need something putting out pretty close to 19 volts. Lower amps at 19 volts just means it won't charge as fast, but it'll still charge. 5 volts won't help you.

So you plug a 4-port hub into it, then wire all four outputs in series...

(Waiting for this one to be on one of the lifehacks YouTube channels.)

[Firethorn]

Okay, got it (my skull is thick and robust). :)

Yeah, volts is basically the important first step for anything electrical working.  Devices have a range they operate at, usually +/- 10%.  Most AC/DC adapters today are 100-240V simply so that the company only has to issue 1 worldwide with their device.

So if the laptop says 19VDC, it'll probably work at 17-21 Volts, but much lower and it'll stop working until you give it more voltage, much higher and you release the magic smoke and it stops working permanently.

USB is 5V until you get into some really funky stuff, really recent moves.

https://en.wikipedia.org/wiki/USB#Power_Delivery_(PD)

You CAN get 20V out of SOME USB chargers today, but it's something that requires negotiation, not just plugging it in.

[Ben]

I should probably, for clarity, say that I was only interested in charging the battery with the laptop off, not running the laptop.

[Firethorn]

I should probably, for clarity, say that I was only interested in charging the battery, not running the laptop.

BLUFF:  If you're using lithium-ion packs of any real size capable of outputting 20V, you aren't going to have a problem operating and charging the laptop at the same time.  Lithium-Ion is capable of crazy amperage.  18650 cells, for example, are good to at least 10 Amps.

Running and charging a laptop affects the Amps needed, not the voltage.  To charge a battery, you need to apply a reverse voltage in excess of the battery's output. 

For example, take car chargers.  A car battery outputs 12V*.  In order to charge it, we generally apply a reverse voltage of ~14V.  IE we push against the voltage the battery is supplying to force electricity to go in reverse, charging the battery.

With Amp limited charging, what happens is that the voltage will "float" to whatever level is necessary to maintain the designated amperage.  IE a 2 Amp charger on a battery will supply a lower voltage than a 12 Amp charger. 

So, you mentioned having a 8.5A and a 2.25A laptop.  First thing:  This is a maximum power draw measure, it will generally be lower in actual operation.  Generally speaking, roughly half that capacity is for running the laptop, the other half for charging.

If the laptop can't pull enough juice, it'll use what it can to run the laptop, then use the rest for charging.  Result, slower charging.  For maximum run time on the available batteries, it's probably better to charge while using.

We really aren't worried about the amps because Lithium Ion is a high power battery technology.  That's why such tiny packs(and I have a LiIon Jumper pack as well) can jumpstart a car.  They can safely push hundreds of amps, at least for a short time.

For running the laptop, you just have to get the voltage to within operating range of the laptop.  Especially when off, as the voltage drops, it'll charge more slowly until it reaches a point that charging just stops.

A 20V laptop probably has a 18.5V battery inside it.

*Actually an amount around 12V depending on the size of the battery, the load on the battery, the charge level, etc....