Help needed with schematic for 5V battery charger


  #1  
Old 03-29-15, 12:46 PM
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Help needed with schematic for 5V battery charger

Hello!

I am looking for a schematic to design and build my own PCB or PCM (protected circuit board/module).

It needs the following:
- 5V 2A input
- Charge 3 "14500" (14mm diameter x 50mm height) cells of 800mAh each in parallel.
- 5V 2A output

Might be awesome if the input could be directly redirected to the output when something is connected on both. This so the batteries wouldn't be used for nothing.
When nothing is connected to the output (or I might insert a switch in between) the batterypack will be charged.

Batteryspace.com told me I needed the following devices (and I quote):
"1. A charging board that will allow 5V input to charge a 3.7V Li-Ion battery

2. A PCB that offer over charge, over discharge protection.

3. An output step-up board that step up a 3.7V Li-Ion battery to 5V for output."

I think I need something like this, cause it looks this one does all:
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

I might buy one of these for testing first.
Eventually I want to put the schematic on a board with specific measures; that's why I couldn't buy one which is prefabricated (and eBay usually offers bad quality products).
Software like KiCad and Fritzing should help me with this.

Thanks in advance!
 

Last edited by PJmax; 03-29-15 at 01:00 PM. Reason: removed advertising ? link
  #2  
Old 03-29-15, 12:59 PM
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Welcome to the forums.

I removed a link from your post. It may have been incorrect on your part or it may be construed as advertising.

You have time to correct the link in your post or reply again with the correct link.

What you are looking for is highly specialized. You will probably not get the answer to your question here. You'll probably need to look at electronic hobbyist sites for particular schematics.
 
  #3  
Old 03-29-15, 01:07 PM
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Okay thanks.
Will try on another forum.
It's not advertising, only an example.

Can I leave it here? Maybe someone can help me here. Even when it's only a website, shop or another place where I can ask?
 
  #4  
Old 03-29-15, 01:30 PM
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Hi kk,
I could build what you want, but you are missing a lot of the details and from a circuit design level, far more complicated than first glance.

Designing and building a PCB would require a much more advanced understanding of electronics which I admire you for your interest, but what you outlined will be a difficult place to start.

If you want we can detail where your initial question needs clarification.

Bud
 
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Old 03-30-15, 03:23 AM
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Can we communicate by PM or email? I would like you to help me. If you could design or help me with my needs, I will be paying you for your work
Or do you think my needs are too big? Want the PCB's to be printed/created for a $5 or $10 each.
Maybe it will be better to stick with existing parts?
 
  #6  
Old 03-30-15, 05:12 AM
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Why you want to reinvent the wheel? Just get a Li-Ion battery charger. Or, are you trying to get us to help you with your engineering homework.
 
  #7  
Old 03-30-15, 06:01 AM
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KK, I said I could, not that I would. To put your project in perspective I have access to a company that takes pilot projects and upgrades them to production level. A simple circuit board, which yours isn't, would probably start around $20,000 for the engineering, testing, and UL approval. Probably much more because yours hasn't reached the pilot stage as yet.

As Pilot said, look for assemblies currently available and see what you can put together.

Bud
 
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Old 03-30-15, 10:15 AM
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Okay that's a clear answer.
Let's focus on another solution.
I will look around for separate parts and test them. Hopefully I will find an easy way to connect every part (cause that's one of the plusses of a prefabricated board).

And no it's not for homework (: might be too expensive.

Thank you all.
 
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Old 03-31-15, 12:00 PM
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Okay, I am going to test my idea's at first, that means: with existing PCB's and modules.

Could you guys help me with the modules I would need for the following:
- Input 5V 2A
- Convert 5V to 3.7V (for battery - batteries already have PCB (protection) build-in)
- Convert 3.7V to 5V 2A to power 3 parts (2 working on 5V 100mA and 1 on 5V 1.5A)
- Want to put a switch between batteries and output. When the switch is pressed, the batteries will power the 3 different parts. When I insert power on "Input 5V 2A" the batteries will be charged and immediately power the 3 parts. When the switch is released, the batteries won't be able to power the 3 parts anymore: the whole device is shut-off. If I insert power on "Input 5V 2A", the input adapter will just power the 3 parts and leave the batteries for what they are (cause this circuit is intermittent).

I already have these in my mind:
- 2 or 4 14500 Li-Ion batteries with 1A input max (so I can put them parallel for 2A input and 2A output).

(Sorry for the sometimes weird word usage - English isn't my native language).

Hope you guys have a clue about the idea I have in mind? I need some chargers/converters; all be able to support at least 2A.

Thanks!
 
  #10  
Old 04-01-15, 09:17 AM
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Any reason it must be powered off 5V and not the much more common 12vdc?
On ebay there are many off-the- shelf portable battery chargers for in-vehicle use, for example.
 
  #11  
Old 04-01-15, 10:16 AM
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I'll just share a word of caution with charging and working with Li-Ion batteries. They are sensitive to how they are charged, and most chargers are electronically controlled to provide a specific charge profile - more current up front and less as the cells charge, finally turning off completely once charged. It's important for both the lifespan of the cells as well as safety. Over-charging can result in triggering the internal protection methods of the battery (rendering the battery useless), or in certain circumstances can result in venting or more technically 'erupting in flames'.

Granted, this is a rather rare occurrence, but it has happened... so be careful when you're working on charging circuits for these batteries.

(Sorry I can't provide the electronic skills though to actually answer your question)
 
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Old 04-01-15, 12:59 PM
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There is more to charging lithium batteries than providing them with a fixed voltage. And on the flip side you don't want to just draw on the batteries without some form of control as over discharge will damage them and cause trouble with chargeable chargers that automatically detect the number of cells.

Also, the built in protection in most cells is very basic. It is not charge or discharge control. It's just simple over charge, over discharge and some have thermal for fire protection. You still need control of the charging in addition to the circuit packaged in many cells.
 
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Old 04-01-15, 01:39 PM
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Just for testing I will start with a batterypack with build-in over- and under-(dis)charge.
Got some products on eBay. Just need it one time to work, so I know I'm at the right way.
When it works (eBay stuff mostly works once or a few times, because its cheap) I will get a professional company to help me - especially on the electric part.

Thanks y'all for the heads up and the provided information.

Got some idea's in my head and want them to be worked out, before I will regret I've just left them there.
 
 

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