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Old 03-06-2015, 06:08 AM   #1
max384 OP
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External battery banks

I just bought a 15,000 mAh battery bank/car starter. I bought it as both an external battery bank for charging my laptop, as well as a jumpstarter to keep in my panniers.

After fully charging the battery bank, I tested it out on my Lenovo laptop, which has a 4600 mAh battery. It only charged the laptop 42% before the battery bank was dead. By my estimation, this means that there is only about 15% of the advertised 15,000 mAh in the battery bank.

Before I return it through Amazon, I'm going to recharge it and try it again, just in case it needed to be fully discharged first (though I fear this is just wishful thinking).

Regardless of whether I have to return this or not, I want to make sure I'm correct in my understanding. If I have a 15,000 mAh battery bank, I should be able to charge a 4600 mAh laptop battery three times, right? Or is it not quite that simple?
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Old 03-06-2015, 06:37 AM   #2
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I have always thought of batteries as buckets of water.
With that in mind I would thing that the two buckets you hooked together would do nothing more than equalize their, um, water???
YMMV...I'm not an expert ( obviously )
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Old 03-06-2015, 06:47 AM   #3
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Quote:
Originally Posted by papaduc View Post
I have always thought of batteries as buckets of water.
With that in mind I would thing that the two buckets you hooked together would do nothing more than equalize their, um, water???
YMMV...I'm not an expert ( obviously )
This is more than just a battery. There are three charging outputs on this battery bank. There is a USB (5V, 2A), a 12V, 2A, and a 19V, 3.5A (and a separate car starter output). The battery bank drains completely while charging the laptop. They do not equalize.
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Old 03-06-2015, 06:47 AM   #4
Manuel Garcia O'Kely
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Too much info to cover in one post. Does your 15 amp/hour battery have an inverter to 120 volts? In conversion are great losses, and your laptop charger is also lossy. 30% efficiency in that chain seems about right.
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Old 03-06-2015, 06:48 AM   #5
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How are you connecting your laptop to it? Is the power conversion DC to DC? Or is it DC to AC (120V) and then back to DC?

Laptop chargers are pretty inefficient (put your hand on one, all that heat is losses). So are small inverters (DC to AC).

If you are doing DC to AC to DC, I wouldn't be too surprised if you're turning 50% of the energy into heat and only getting 50% to your other battery. Still, you would think you would have charged your laptop at least once....
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Old 03-06-2015, 06:49 AM   #6
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Quote:
Originally Posted by Manuel Garcia O'Kely View Post
Too much info to cover in one post. Does your 15 amp/hour battery have an inverter to 120 volts? In conversion are great losses, and your laptop charger is also lossy. 30% efficiency in that chain seems about right.
Quote:
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How are you connecting your laptop to it? Is the power conversion DC to DC? Or is it DC to AC (120V) and then back to DC?

Laptop chargers are pretty inefficient (put your hand on one, all that heat is losses). So are small inverters (DC to AC).

If you are doing DC to AC to DC, I wouldn't be too surprised if you're turning 50% of the energy into heat and only getting 50% to your other battery. Still, you would think you would have charged your laptop at least once....
No inverter. Its output is 19V DC 3.5 A, straight to laptop charging port, completely bypassing the laptop charger.
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Old 03-06-2015, 06:50 AM   #7
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Wow, 2 replies while I was typing.

Care to share part numbers? Might be easier...
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Old 03-06-2015, 06:53 AM   #8
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Quote:
Originally Posted by ig_88e View Post
Wow, 2 replies while I was typing.

Care to share part numbers? Might be easier...
This is the battery bank:

http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1

I am using it to charge a Lenovo Yoga 2 11" laptop. It uses 20V 3.5A input. However, the voltage rating is +/- 5%, so anything from 19-21V is acceptable input.
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Old 03-06-2015, 07:16 AM   #9
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Quote:
Originally Posted by max384 View Post
This is the battery bank:

http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1

I am using it to charge a Lenovo Yoga 2 11" laptop. It uses 20V 3.5A input. However, the voltage rating is +/- 5%, so anything from 19-21V is acceptable input.
That's not going to do the job. The capacity is not there. Using a 19 volt output means that your voltage drop causes charging to stop.
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Old 03-06-2015, 07:18 AM   #10
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Lots of info here.. I spent more time than I should have poking around trying to learn about Ah ratings not too long ago..

http://batteryuniversity.com/learn/
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Old 03-06-2015, 07:36 AM   #11
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Quote:
Originally Posted by Manuel Garcia O'Kely View Post
That's not going to do the job. The capacity is not there. Using a 19 volt output means that your voltage drop causes charging to stop.
Isn't the amp hour rating a measure of the capacity? If so, it's roughly three times the capacity of my laptop battery.

Are you saying that the lower voltage will cause the battery bank to stop charging before it runs out of juice? The charging didn't stop until the battery bank was completely dead.

Using my multimeter, I just measured the voltage coming from the laptop charger at 20.2 V, and from the battery bank at 19.4 V. This is 3.96% lower than the supplied 20.2 V, and only 3% lower than the recommended 20 V, which is well within the 20 V +/- 5%.

Quote:
Originally Posted by A-Bone View Post
Lots of info here.. I spent more time than I should have poking around trying to learn about Ah ratings not too long ago..

http://batteryuniversity.com/learn/
Thanks for the link.
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Old 03-06-2015, 07:38 AM   #12
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Were you charging it with the laptop on or off?

If it was on it can draw a lot of power especially if it has a discrete GPU which would explain some of it but nothing that large...still very fishy.
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NikonsAndVStroms screwed with this post 03-06-2015 at 07:43 AM
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Old 03-06-2015, 07:42 AM   #13
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Were you charging it with the laptop on or off?

If it was on that huge difference VS how big it claims to be still seems off but depending on what you were doing/settings it can draw a lot of power which would explain some of it.
The laptop was on. It took thirty minutes to charge to 42%. My battery normally lasts about 5 hours with normal use (and this was less than normal use; just sitting there). So, that would add, at most, 10% onto the 42%. I didn't include this, because I didn't want to muddy the waters, and 52% is still WAY off from where I think it should be.
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Old 03-06-2015, 07:43 AM   #14
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The big question I have is, though, am I thinking about this correctly? Should a 15,000 mAh battery bank charge a 4600 mAh battery roughly three times? Is this simple math correct? Or is it more convoluted than this?
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Old 03-06-2015, 07:43 AM   #15
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Quote:
Originally Posted by max384 View Post
The laptop was on. It took thirty minutes to charge to 42%. My battery normally lasts about 5 hours with normal use (and this was less than normal use; just sitting there). So, that would add, at most, 10% onto the 42%. I didn't include this, because 52% is still WAY off from where I think it should be.
Was this it:

http://www.amazon.com/Foxnovo%C2%AE-.../dp/B00E9P9A4O

There are more than a few 1 star ratings so you might have a dud.
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