# Question regarding 3.7v 8000mah battery

#### Frankiebateman

Joined Jun 17, 2017
11
Hi I was wondering if someone could help me here. I've recently bought a battery from eBay 12v 20ah li ion battery. Anyway it was being used in a power bank to charge phones for me to realise I only got 3 charges from it my question is do 3 of these equal what I was supposed to get and if so why will it only charge a phone three times when it should be about 20 hours worth?

Plus on the other side isn't this a 3.7v 8000 mah polymer /Li-po??

It was advertised as li ion battery?

#### #12

Joined Nov 30, 2010
18,210
Things to consider: 1000 MaH is one amp hour.
12V is wrong for a phone. I thought they needed 5 volts? If you use a linear regulator, more than half the power is being wasted as heat.
A switching regulator can be about 80% efficient instead of 42% efficient.
I can't tell the difference between LiPO, LiFePO, or polymer from that label.

#### BobTPH

Joined Jun 5, 2013
2,505
A 3.7V battery rated at 8000 mAH when boosted to 12V would be 3.7 / 12 * 8000 = 2466mAH if perfectly efficient. I suspect your 12V power supply is rated at 2AH, (2000mAH) not 20AH.

Also, an 8000mAH charging a phone 3 times is about right. The typical phone is about 2000 mAH, and again, there is loss of efficiency.

Bob

#### Frankiebateman

Joined Jun 17, 2017
11
Things to consider: 1000 MaH is one amp hour.
12V is wrong for a phone. I thought they needed 5 volts? If you use a linear regulator, more than half the power is being wasted as heat.
A switching regulator can be about 80% efficient instead of 42% efficient.
I can't tell the difference between LiPO, LiFePO, or polymer from that label.
Appolagies on not being clear. I am running a dual usb 12v socket with a 1a and 2.1a socket on there so enables me to charge phones up as you may see on the photo. Is this where I could be going wrong? Or will it still draw 5v? I'm pretty new to all this stuff so I do appolagies if these sound simple lol.

A 3.7V battery rated at 8000 mAH when boosted to 12V would be 3.7 / 12 * 8000 = 2466mAH if perfectly efficient. I suspect your 12V power supply is rated at 2AH, (2000mAH) not 20AH.

Also, an 8000mAH charging a phone 3 times is about right. The typical phone is about 2000 mAH, and again, there is loss of efficiency.

Bob
Thanks for the reply Bob. There are three of these strapped together I'm running a 12v dual usb socket on this so maybe this is drawing too much current out? Image attached

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#### BobTPH

Joined Jun 5, 2013
2,505
Okay, it has 3 batteries, probably in series to produce 11.1V nominal (it will be 12.6V when fully charged).

That makes it 8AH at 11V. You might rate it at 20AH at 5V, though it would be more likely closer to 15.

So, can I assume you are using a 12V to 5V car charger plugged into the 12V socket for charging the phones?

Bob

#### #12

Joined Nov 30, 2010
18,210
Volts are the stable part which you manipulate. Amps depend entirely on the load. The load allows amps to flow.

#### Frankiebateman

Joined Jun 17, 2017
11
Okay, it has 3 batteries, probably in series to produce 11.1V nominal (it will be 12.6V when fully charged).

That makes it 8AH at 11V. You might rate it at 20AH at 5V, though it would be more likely closer to 15.

So, can I assume you are using a 12V to 5V car charger plugged into the 12V socket for charging the phones?

Bob
So they've basically sold me something that isn't true to its description? As it said 12v 20ah? And the dual usb on the enclosure had 5v 1a + 5v 2.1a outputs so I just plug my micro USB into it

Volts are the stable part which you manipulate. Amps depend entirely on the load. The load allows amps to flow.
Thanks for that I'm still taking in all info footage learn from somewhere

Design a boost converter to provide an output of 18 V from a 12-V source. The load is 20 W. The output voltage ripple must be less than 0.5 percent. Specify the duty ratio, the switching frequency, the inductor size and rms current rating, and the capacitor size and rms current rating. Design for continuous current. Assume ideal components.
Thanks but there's one problem. Where do I start with that? Isn't there anything I could buy like that? Lol

#### BobTPH

Joined Jun 5, 2013
2,505
So they've basically sold me something that isn't true to its description? As it said 12v 20ah?
Lol
Yep. That powerbank cannot produce 12V at 20AH. More like 11V at 8 AH. And even then, the 8AH rating of the batteries is probably a lie as well.

Bob

#### Frankiebateman

Joined Jun 17, 2017
11
Yep. That powerbank cannot produce 12V at 20AH. More like 11V at 8 AH. And even then, the 8AH rating of the batteries is probably a lie as well.

Bob
Darn Chinese! Lol OK so now I have got to the bottom of the battery situation would you say the 18650 batteries are better to work with in this type of situation? Maybe look at building my own batteries and testing the cells before they get installed?

Maybe you will get some framework from this which I wrote for serious noobies.