Efficiency of power banks

Hi,

Does anyone know what sort of loss is to be expected if I charge my laptop with a power bank.

I am guessing if I get a 65wh battery to charge my 65wh internal batter, I would not get to 100% charge.

I am guessing that I loose in both discharge of the power bank and charge of the internal battery.

So then I think, what size battery do I need to charge a 65wh battery.

Thanks

 

You need a power bank at least twice the size of your phones battery to charge it even once as you loose between 20-40% of the power due to charging efficiency between the power bank and your phone, Just do a Google search for an more in depth explanation.

 

Thanks, I did google it but could not find a decent answer.

I have used a 43wh power bank on a macbook air, I got 70% charge (circa 35wh) on the macbook from 0%, as the macbook is 50wh this seems in line with your 20% plus loss.

 

Well I have a 5000mAh Belkin portable battery and it's enough to charge a OnePlus 6t (3700 mAh battery) one full time + a bit more, so it's pretty efficient (a ~20% loss?).

 

@ Tinderbox (UK), thanks.

I think I was too clever with my search.

I tried:

"How to calculate the efficiency loss when charging lithium ion battery from a lithium ion source"

@jotm, I am also seeing about a 20% loss.

 

You'll lose an additional 15-20% if using a wireless charger such as Qi devices.

 

The first thing that comes to mind is looking for a PD bank vs just your generic power bank for aux devices like phones / tablets that don't draw more than 5v/2A of current for charging or even upwards with QC2/3 outputs. PD will make the jump from 10-20W up to 100W depending on the device you're charging. Also, you'll want to look for something with pass thru charging to be able to charge and power your device at the same time. Otherwise you're looking at charging the bank or using the bank but not both at the same time.

As to efficiency... there's always going to be some loss in the conversion process.. it really depends on your use case though if this is to sit for an extended period of time somewhere w/o a power outlet and keep your laptop going for the duration or if you want an extra supply of juice while gaming while unplugged.

For the OP series the best option to get the most out of it for speed / capacity is the SDoutech @ $49.xx and you'll get your 5V/4A DASH charging speed vs the 2-3 hours @ 5V/2A from a normal power bank since they use the proprietary power method / cable.

For a laptop like Macbook Air / etc. I would be looking at a 30K mah pack to start with if you want to charge the laptop while in your bag powered off. Something with a decent PD rating over 50W should refresh things fairly quickly while it's in your bag.
https://www.amazon.com/CHOETECH-Portable-Charger-26800mAh-MacBook/dp/B08B3GLY4Y $79 + a 20% coupon

 

I'd opt for laptops with easily swappable batteries instead and carry around extra laptop batteries, that way there are no conversion losses, just the minor inconvenience of having to hibernate, pop the battery out and pop a new one in before resuming whatever you were doing. Laptops with internal batteries suck in this regard.

 

If you're not using the right V*A = W for the device then it's possible. W/ PD output though the negotiation happens instead of simply supplying 5V/xA to the device. The power bank I have is 4 ports 18W-A / 15W-A / 100W-PD / 60W-PD and I've verified these with a power meter inline with the PB / device.

The problem with just swapping batteries around is they charge slowly. My battery for instance only charges at 14.5W or less if the laptop is powered off it's ~6W. The time it takes on average @ 14.5W is ~3 hours. By adding an aux power supply like a power bank / usb-PD whether 120V or Car adapter while using the device can extend indefinitely or in the case of the PB another hour or two before the installed battery gets tapped.



As to the PB charging my laptop battery while powered down I can get 2 charges off it which translates to ~3 hours of run time with middle power settings. ~2 hours at max settings.

For instance while using a PB / USB-PD charger in place of my power brick the laptop averages 45W draw as measured by a meter inline. This doesn't hit the 60W for the PD port nor on the USB charger. When a load is placed on the laptop exceeding 45W they are both insufficient in negotiating a stable charge/run to the laptop and drain the battery while either is plugged in. When exceeding 60W though the brick supplies ample energy to the laptop allowing both a loaded level of use and charging of the battery at the same time. So, the 120W brick - 14.5W charge = loaded usage of ~105W.