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### Author Topic: power bank DC 19V 5A/12V 2.5A Charge Ports External Battery Charger for Laptops  (Read 2079 times)

#### Contro

• Supporting Member
• Joined in 2007
• Posts: 3,836
##### power bank DC 19V 5A/12V 2.5A Charge Ports External Battery Charger for Laptops
« on: February 14, 2019, 02:15 PM »

After seeing several chinese products I am thinking buy this.
Anything better for similar price ?

https://es.aliexpres...amp;isOrigTitle=true

Why they don't compromise the mAh capacity :  Battery Capacity(mAh): Above 30001mAh

I understand tha 30000 mAh is the same that 30 Ah .

So if output is 19 V DC you can obtain up to 570 Wh
My laptop is 45 W , so I can have working up to 12 hours.

I need the output 12V too. I have bought some time ago 5 led lights of 3W each. If I have 30000 Ah I will obtain up to 360 Wh.
360 Wh / 15 W = 24 hours of lights.
Perhaps more.

When you bought a car battery of 60 Ah you have 12 V  x 60 Ah = 720 Wh

What I don't understand completely is in case of different voltages.

I suppose that when the maker says in the features 50000 mAh express a maximum capacity .
In other part of the publicity : REAL ULTRA HIGH CAPACITY 50000mAh/185Wh: Compatible With Most Popular Laptops and Notebooks
( Can not Charge Laptop with DC Current Over 5A).We Provide 14 Kinds of Connector for Most of the
Popular Laptops (Pls Make Sure the Connector Fits for Your Laptop before purchasing.). Once Fully
Charged. Our K2 Portable Battery Pack Can Charge Your iPhone 6 Plus about 11 Times, iPhone 6
About 17 Times, Galaxy S6 Almost 11 Times.

So.....
185 Wh what is now ?
What voltage applies when refers to 50000 mAh ?

V volts. x 50 Ah = 185 Wh

V = 185 Wh / 50 Ah = 3.7 volts.......

With 185 Wh I was wrong before.....

My laptop will last for 185 Wh / 45W = 4 hours aproximately
And my lights of 3 x 5 = 15 W for 185 Wh / 15 W = 12 hours aproximately .

Seems more secure give the  ??? Wh , because the Ah or the mAh are in relation with the voltage. Or I am wrong ?.

Are maximum values ?

#### Contro

• Supporting Member
• Joined in 2007
• Posts: 3,836
##### Re: power bank DC 19V 5A/12V 2.5A Charge Ports External Battery Charger for Laptops
« Reply #1 on: February 14, 2019, 02:32 PM »
185 Wh / 50 Ah = 3.7 volts

If 12 volts ?

If 19 volts ?

Why they don't give real values ?. I think is 185 Wh independently the voltage.
If voltage varies, varies the intensity and the Ah ....

So if 19 volts : 185 Wh / ?? Ah = 19 volts ---->  we obtain 9737 mAh

#### 4wd

• Supporting Member
• Joined in 2006
• Posts: 5,558
##### Re: power bank DC 19V 5A/12V 2.5A Charge Ports External Battery Charger for Laptops
« Reply #2 on: February 14, 2019, 04:14 PM »
50,000mAh @ 3.7V = 185Wh = Not likely to be allowed on a passenger aircraft, (anything over 100Wh is usually only by permission of the airline these days - anything over 160Wh is a definite no according to the few airline T&Cs I've looked at).

Why they don't give real values ?
-Contro

Power banks are always quoted with reference to the primary cell voltage they use, in this case Li-Poly which is 3.7V.

It also looks good to the marketing muppets if it says 50,000mAh (@ 3.7V) rather than ~30,000mAh (@ 5V * 0.8) because a it's a bigger number.

I think is 185 Wh independently the voltage.

Power = Voltage * Current (of the primary cell in this case)

So if 19 volts : 185 Wh / ?? Ah = 19 volts ---->  we obtain 9737 mAh

You also have to take into account converter efficiency which will be around 80-85% for a very good power bank and is usually somewhere between 70-80% for the majority.

So your 185 Wh might be 185*0.8 in real life after conversion to a higher output voltage.
There's also probably a reduction in efficiency, (greater losses), the higher the output voltage so while 5V output may be 80% efficient, 19V might only be 70% efficient.

It's also why they can't quote figures based on theoretical efficiencies.
« Last Edit: February 14, 2019, 04:28 PM by 4wd »

#### Contro

• Supporting Member
• Joined in 2007
• Posts: 3,836
##### Re: power bank DC 19V 5A/12V 2.5A Charge Ports External Battery Charger for Laptops
« Reply #3 on: February 15, 2019, 03:42 AM »
Magistral !!!!!!!. Wonderful !!!!!!!

Thanks a lot 4wd !