# Making a battery to charge my laptop on the road

Discussion in 'Power Electronics' started by CnTrL., May 1, 2018.

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1. ### CnTrL.

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May 1, 2018
Hello everyone,

I guess I am a total noob when it comes to knowing how power works. I want to create a bunch of 18650 cells, they are 3.7 volts. I want to put every 5 in series so that i get 18.5 volts to charge my 19 volts laptop(I guess this is not a problem, if this can a problem please tell so). After that I wanted to put a few of those in parallel to get a higher capacity.
Now my question is: my laptop needs 4.75 A, but a single cell is 6.7 A. Is this a problem if I don't set them in parallel and can this create a problem when I do set more sets of 5 in parallel?

Luc

2. ### kellys_eye

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Jun 25, 2010
Your device will only draw the current it requires, no more. The amperage of the batteries will determine how long they last (under a given load).
What you're doing is creating a power pack that could be defined as 5SxP (5 in series 'x' in parallel). Such battery packs require careful balancing (matching battery capacities) and relatively sophisticated charging and monitoring for safety - else possible battery destruction under charging.

This is not a project for
You would be better served by purchasing a small SMPS power pack that operates from a car battery (or other 12V supply) and has switch selectable output voltages (to suit many standard laptop power requirements).

https://www.ebay.co.uk/itm/Universa...552315?hash=item2a4f72d5bb:g:~0cAAOSwymxVIk0g

3. ### CnTrL.

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May 1, 2018
I would rather just make a battery pack my self to reduce costs. The 12 volt batteries are often very small in capacity and are very expensive. I know how to wire batteries up but I don't quite know how a device reacts to a certain source of power. (Especially how amperage works, I understand voltage)
Do you know if I can use a standard laptop charger from for instance 5 A to charge each 5 batteries only set in series or will this totally overload the charger? Otherwise I might just make a 12 volt battery (because these chargers are more common) and get a transformer which you normally would use in a car. Or if it is do-able I could make my own wall charger for the 19 volt version with a higher A. I am totally in for a challenge I just need to know what I need.

4. ### Bluejets

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Oct 5, 2014
Just buy a spare non oem battery.
Usually give a couple of hours use.

davenn likes this.

755
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Aug 24, 2009
6. ### LukeDupont

19
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Apr 15, 2018
Umm...

Why are any of us here if not to make things that we could just buy more conveniently?

I'd rather learn how to do it myself so that I can gain an understanding of how things work, and make them to my own specifications and needs as I learn and improve.

I'd bet the OP wants to do the same.

CnTrL. likes this.
7. ### bushtech

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Sep 13, 2016
Fair enough, but just at least know what you're getting into. Re. using a bunch of 18650's. Crack open a old non functioning laptop battery and have a look at the setup. Circuit board, sensors, and scarily thick connections between batteries. If you think it's going to be easy to improve or even recreate that, go for it.

8. ### kellys_eye

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Jun 25, 2010
If low cost is your aim then you will never compete with mass produced or, specifically, Chinese delivered, items such as the ones linked to above.
If you could purchase the 18650's at \$1 each you're already losing money on the solution........

9. ### CnTrL.

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May 1, 2018
I don't mean necessarily in a car, you could also be traveling by plane or in a train. That's the reason I want to make a battery pack. I would like to know how I could make a proper charger for it.

10. ### CnTrL.

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May 1, 2018
It doesn't have to be super cheap, I just saw that 12 volt battery packs are very expensive and you would still have to buy a car charger to buy it.
Also I think it would be nice to learn more about how all the different component work and how it works together.

11. ### kellys_eye

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Jun 25, 2010
I appreciate (and understand) your desire to learn - it's almost a drug to some - but in your original post you admitted to
which, whilst being a noob is no bad thing, choosing to start with a project that has the potential to cause much damage and possible injury isn't the way to go!

Seriously, even myself as someone with 50 years of knowledge in electronics wouldn't wish to tackle a job like that as the overall costs would be horrendous in comparison to the commercially available stuff let alone mess with 'explosive' consequences.

Take the advice given above re a second battery and/or the laptop adapter (car) and have another think about what you'd like to tackle as an introduction to power electronics - build a small variable power supply for example..... something that you could use in going forward with 'learning' about the subject.

We rarely try to discourage enthusiastic builders but there are some areas of construction where lack of knowledge/experience can prove harmful and we're dead set against 'helping' those to hurt themselves.

12. ### CnTrL.

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May 1, 2018
I wouldn't say I have no experience with soldering and building electronics, batteries are a new area for me something new for me. I will make sure I have all my researching done before I start building
Coming back to my question can I use a laptop charger from let's say 5 A to charge a battery pack from 27 A, or would this totally overload the charger? (both of them are 19 v) If not what kind of parts would I need to make a proper wall charger for this?
Or could I take out every set of 5 batteries in series (so that I get the 19 volts) and charge it with a laptop charger? The batteries in series are 6.7 A, would this overload a 5A 19 volt charger? I am planning on using the panasonic NCR18650B 3400 mAh batteries.

Last edited: May 2, 2018
13. ### CnTrL.

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May 1, 2018
This is what I am planning on making would this work and what kind of materials can I use to power it, wehter there is a cheap charger for this (up to \$20?) or else I would like to make it my self.

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14. ### CnTrL.

14
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May 1, 2018
I just looked which batteries i currently have in my laptop which are 6 samsung ICR18650-22F cells. If I could buy a device that can charge 18650 cells and buy some 18650 cells (the same or maybe Samsung INR18650-35E because they have a larger capacity and the same voltage) and a "holder" like you see in toys (you can take the batteries easily out). And make a extra connection outside my laptop so I can connect 6 more charged batteries in parallel? Would they both need to be charged if I wanted to cennect them or can I connect them anytime?

Or if this all can't workout just buy 6 Samsung INR18650-35E so the battery inside my laptop gets 1.5 times bigger.

15. ### kellys_eye

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Jun 25, 2010
You have to REGULATE the charging current/voltage as well as provide various forms of protection (over/under voltage, over-current, thermal protection etc) - you can't just connect your power pack to a set of batteries as per the schema you post. Fire will ensue!

There is also the problem of cell balancing i.e. ensuring each cell gets the appropriate charge which means either 'matching' all the batteries or using cell sensors/balancing circuits like this:

the one shown above is for a 3s (three in series) battery pack of 25A (maximum). You would need the appropraite board to match your cell arrangement.

16. ### kellys_eye

4,275
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Jun 25, 2010
Crossed posts.

Why not simply get a second battery for your laptop and carry a charged one around with you? This contains (1) the batteries (2) the protection (3) the regulation (potentially) and (4) comes with its own case.

What it DOESN'T come with is a fire extinguisher because none is required.....

but if you're doggedly determined to build your own then there are many instructables on the subject such as:

http://www.instructables.com/id/DIY-Professional-18650-Battery-Pack/

17. ### kellys_eye

4,275
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Jun 25, 2010
bushtech likes this.
18. ### Hopup

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Jul 5, 2015
Only use quality 18650 I have heard lot of bad things about the cheap ones. As said already you need proper battery protection and charging, not the best project for learning electronics since if you make mistake there will be fire.

19. ### Externet

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Aug 24, 2009
Better choose a simpler project to start getting out of the 'total noob' condition. The most convenient approach for your laptop on the road is, as suggested, get extra battery packs for it.

Have you thought of gluing a 20V solar panel sized to the laptop lid ? Will take longer to charge, but could give you some learning experience too.

20. ### Audioguru

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Sep 24, 2016
You need a complicated lithium battery charger circuit that is designed and wired so that all your lithium cells are balance-charged. Your laptop has the complicated charger circuit inside it and the laptop "charger" is simply a power supply for it.

Your simple idea will probably cause a lithium explosion followed by a VERY HOT fire.