Discussion in 'Power Electronics' started by Jirbot, Mar 21, 2016.

1. ### Jirbot

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Mar 21, 2016
Would it be possible to hook up in series or parallel a bunch of Li-ion batteries from old laptops to feed an inverter from a solar system for a possible power system?

2. ### Gryd3

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Jun 25, 2014
Yup!
Although it may not be the best idea unless you are somewhat familiar with it... I'll give you some details and you can see if you want to try, or go for something else...

Lithium Ion and Lithium Polymer are sensitive chemistries that don't like excess heat, and are very sensitive to over-charge and over-discharge... There are also well defined limits to the peak and constant draw of current from these batteries.
So, extra care MUST be taken to charge and use Lithium rechargeable batteries compared to NiCd, NiMh and Lead-Acid.
So, other than the Lithium part, lets talk about battery banks in general.
In parallel, their capacity is added together. (Both their current supply, and mAh rating...)
In parallel, you typically have a lower voltage, but a higher current. All of the cells in a parallel pack are self-balancing.
In series, their voltage is added together, but their current supply is not.
In series, you typically have a higher voltage, but a lower current. The cells do *not* self-balance, so there is a risk with under-charging or over-charging a single battery in a pack, even if the pack is not 'empty' or 'full' ... For a series type pack, it's a good idea to use more forgiving batteries, or you will find that the pack as a whole will degrade quickly and require that one or more cells need to be replaced. You can build a circuit to keep them balanced, but that's extra work
The more cells you have in series, the more likely this problem is to occur with repeated charge/discharge cycles.

3. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
Apparently someone has done this to power a car. He's relatively unknown - Elon Musk.

Now he is attaching them to houses.

Charge management is important if you don't want the whole thing going up in flames.

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4. ### BobK

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Jan 5, 2010
He used old Li Ion batteries from laptops? And then charged \$90K for the car? Brilliant!

Bob

5. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
That's how he makes them so affordable.

6. ### cjdelphi

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Oct 26, 2011
No wonder they never get the milage claimed!

7. ### Herschel Peeler

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Feb 21, 2016
If they were all the same model and in the same condition it would work.

8. ### cjdelphi

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Oct 26, 2011
I've been able to pull 20/ah from the cheapest of lithium batteries probably up to 100a/h from a good 18650 battery from samsung/sony/panasonic etc

The ebay ones that claim 9000mah is total bs, maybe just maybe 800 - 1200 for anything less than \$10 US

9. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
What is your definition of "/ah" and "a/h"?

I am fairly sure it isn't the same as "Ah".

1,096
104
Oct 26, 2011
Amp hours

11. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
then if you claim 100 Ah from an 18650 battery, why is 9Ah total bs?

mind you, I think 9Ah is unbelievably high, and 100Ah in the realm of science fiction for a cell of this size.

12. ### BobK

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Jan 5, 2010
I have some supposed 3600mAH cells. I measured them, with a light draw (20mA LED) at about 2000mAH.

Bob

13. ### cjdelphi

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Oct 26, 2011
What? Where did i say 9/ 100Ah is bs?

A good 18650 battery will pull up to 100Ah (i never said it will give 100Ah for 1 hour, it will pull that much for a brief moment, a few seconds/minute? I never actually tested for that)

Not sure what you think i said....

14. ### cjdelphi

1,096
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Oct 26, 2011
Look you're confusing capacity with current draw

Capacity, 9000mah from a cheap lithium is bs from ebay, it's more like 800 - 1200mah capacity

Brief moments of current draw can be 20Ah but it will only supply that for a few seconds maybe a minute

It sounds like you're confusing current draw and total capacity

15. ### Gryd3

4,098
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Jun 25, 2014
I think the confusion is the additional 'h' you are using...
A good 18650 battery can not provide 100Ah, but may be perfectly capable of providing 100Amps .. not amp hours.
Simply omit the extra highlighted 'h' in the quoted text and it's fine

16. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
hence why I asked what you meant by the united you used.

A. And Ah mean totally different things

17. ### cjdelphi

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Oct 26, 2011
Fair enough; i'll drop the h

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18. ### cjdelphi

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Oct 26, 2011
Although in my defense lol

...... if you're traveling 80mph, are you not traveling at 80mph if you only have enough fuel for a mile?

19. ### Gryd3

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Jun 25, 2014

This is caused only because of how it's typed out.
mph = Miles / Hour
mah = milliAmp Hours

In this instance, let's drop the 'milli' part of Amps, and use the base value of Ah instead to help keep things sane.
To compare the two:
Miles = Measure of Distance
Miles per Hour = Measure of Miles travelled in an hour.
'Range' = Total Capacity of how far can be travelled on a tank/charge. (In an ideal world would be regardless of driving habit / speeds travelled)

Coulomb = Measure of Charge
Amps = Measure of Coulombs per second.
Amp Hour = Total Capacity of how many Coulombs regardless of the rate of change. (Similar to saying you can get 350miles out of a single tank of gas...)

So... if you only have enough gas for a mile, that's your capacity. You can travel as slow or fast as you want in Miles/Hour, but you will not exceed that mile of distance. (Of course driving faster may decrease that range)
Just like a 2.4 Ah battery has it's rated capacity. You can discharge as slow or fast as you want in Amperes (within limits) but you cannot exceed that capacity.

The confusion here is the representation of the units.
mph is a poor comparison to mAh or Ah because you are looking at the letters and not what they mean.
m/h is a better representation of the 'rate of change' compared to mAh which is a PRODUCT of the 'rate of change' and 'time' which gives a total capacity.
If this still causes confusion... say your car can travel 10m/h for 6 minutes. (That is a speed and time... just like the 2400mA for 1 hour)

Last edited: Mar 26, 2016
20. ### BobK

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Jan 5, 2010
Nice explanation, except:
That should be PRODUCT, not SUM.

Bob

Last edited: Mar 26, 2016
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