Rechargeable Power Supply Question

[Kouki]

I have a basic knowledge of electrical circuits and electronics, but I need help with this next project of mine. I will be building a fan box with a computer fan. The fan runs on 12VDC, and I'd like the power source to be battery, with the option of an AC plug for times when recepticals are near. As well as to charge the battery, obviously.

I've been looking at battery packs, chargers, converters and the like, but I'm lost now. I know I'd like the charger to be "smart" or "rapid" so the battery can be plugged in for long periods of time without overcharging.

Could someone please let me know what type of battery/charger this would require, and where I could find one? Ideally I like it to function like a cell phone. All you see is a plug in, and the battery pack would be soldered within the unit.

This seems basic to me, but I'm having a time trying to find the right components.

 

[kellys_eye]

You need to supply more specifications.

How much power does the fan use?
How long do you want to fan to run, on battery power, for?

This data is required to determine the size of battery and the consequent charging system to be used.

 

[Kouki]

The fan uses 3.36W and current is 0.16A. I can't see it having to run on battery for more than a few hours. So nothing too big would be needed.

 

[kellys_eye]

so around 12 watts total consumption as a maximum perhaps?

This would allow the fan to run for 3(ish) hours before recharging and equates to a 1Ahr battery at 12V - the smallest rechargeable battery you could find would probably work! If 'size' is an issue (often is.... giggidy) then you need the modern lithiums but how about finding an old battery power tool that originally used a 12V pack?

You could salvage the connectors from the tool to fit in your case with the fan, use the battery to power it and the tools original charger to recharge it.

 

[Kouki]

I thought about doing that, and I could for this one, but if this project works out, I'll be making more. So I was hoping to find a source that sells these parts. I've looked through Arrow and Digikeys websites, and I didn't see a set up that had an integrated charging port. But I may have overlooked something.

Thank you for the quick replys and help thus far though, all good information.

 

[kellys_eye]

You could always use the ubiquitous 18650 cell - there are many simple charging circuits for them and along with a boost converter to raise the output to 12V it would use the most modern/common parts.

charger board:

http://www.ebay.co.uk/itm/2-Cells-S...482399&hash=item43fc8cb8d2:g:5hcAAOSw9GhYeZ4a

boost board:

http://www.ebay.co.uk/itm/5W-12V-US...850370?hash=item2a517e2e82:g:KS0AAOSwr81UQN5e

 

[(*steve*)]

If going for a lithium battery, a single cell solution is great because it means there is no need to balance charge, and you can probably use a ubiquitous 5V phone charger.

 

[Audioguru]

If going for a lithium battery, a single cell solution is great because it means there is no need to balance charge, and you can probably use a ubiquitous 5V phone charger.

No.
A "cell phone charger" is simply a 5V power supply to feed the charging circuit in the phone. The 3.2V to 4.2V lithium battery cell will overcharge and blow up and/or catch on fire without a charger circuit.

 

[(*steve*)]

I thought someone might misread what I said.

You still need the correct charging circuit as suggested by @kellys_eye but your power source can be a ubiquitous 5v phone charger (which is a power supply, not a charger).

Perhaps @Audioguru you could try to be helpful and add clarification rather than just sniping.

 

[Audioguru]

The cheap Chinese charging board (the ad said 2 cells but a thumbprint photo showed a jumper to make it for one cell) has no spec's and might not work with a 5V input.
An 18650 cell with low voltage cutoff must be used so that the cell is not ruined by its voltage dropping below about 3.2V.

 

[Kouki]

Ok, so going off of these suggestions, I've found these two circuits that I believe will accomplish what I'm looking for.

Each seems to have a variable voltage output, both capable of reaching 12VDC. So, I would just like to confirm with you all that these are a good bet.

http://www.ebay.com/itm/USB-3-7V-4-...d=192183192848&_trksid=p2047675.c100009.m1982

This one has a protection circuit as well, which I don't think the other does. If so, that'd be my choice.
http://www.ebay.com/itm/USB-Lithium...r-Board-Protection-Boost-Module-/192183192848

 

[kellys_eye]

Either of those will be ideal - you're quite likely to have a small USB charger somewhere you can use for it too.

The items I linked to were 'suggestive' with the aim to provide you with an idea of what was required and, happily, you've found exactly the items required.

Good luck with your project.

 

[Kouki]

Awesome! Thank you very much for the help, I've ordered a few to try out.

 

[Audioguru]

The first one doesn't say much and leaves you guessing. The second one with battery protection has many more features and details.

 

[Electric-T]

No.
A "cell phone charger" is simply a 5V power supply to feed the charging circuit in the phone. The 3.2V to 4.2V lithium battery cell will overcharge and blow up and/or catch on fire without a charger circuit.

I may be under qualified to say this but wouldnt a 4v voltage regulator be useful for this? I imagine most dc power supplies have some sort of limiter in them since they are often used for charging anyways.

 

[Kiwi]

My only comment is how do they build and sell these things for that price?

 

[kellys_eye]

My only comment is how do they build and sell these things for that price?

The $64,000 question...

I can't even POST those kind of modules in the UK for the price they make, sell and deliver them for!

 

[(*steve*)]

I may be under qualified to say this but wouldnt a 4v voltage regulator be useful for this? I imagine most dc power supplies have some sort of limiter in them since they are often used for charging anyways.

Read my reply to audio guru. Unfortunately his reply wasn't very helpful.

You still need a dedicated charger. A "phone charger" is just a power supply, but one that is easily obtainable and suited to power many of these 1 cell lipo chargers.

 

[Audioguru]

You can read about all the things a lithium battery charger circuit must do to prevent the dangerous lithium battery from exploding or catching on fire when it is charging. Datasheets for the Charger ICs also explain all the important steps like sensing a low voltage before charging then attempting a low current charge, sensing and stopping charging when a full charge is detected, current limiting, temperature sensing and more.

Isn't it amazing that the Chinese can build complicated circuits and sell them at such low prices? What are they cutting out? No testing? Maybe most don't work but some of them are fine.

 

[Electric-T]

You can read about all the things a lithium battery charger circuit must do to prevent the dangerous lithium battery from exploding or catching on fire when it is charging. Datasheets for the Charger ICs also explain all the important steps like sensing a low voltage before charging then attempting a low current charge, sensing and stopping charging when a full charge is detected, current limiting, temperature sensing and more.

Isn't it amazing that the Chinese can build complicated circuits and sell them at such low prices? What are they cutting out? No testing? Maybe most don't work but some of them are fine.

Well if they dont cut quality it must be wages. Thats why theyre jumping out of the foxcon buildings