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Battery charging and output voltage regulating please help

Maskot

Aug 7, 2013
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I have a project that I've setup and it works from a power adapter and it takes a 12V input. I want to go wireless so I'll need to setup a battery system.

My question are as follows:

1. How do I link up rechargeable batteries in parallel so that they all charge fully without any problems?
2. How do I regulate the output voltage of the batteries to be 12V?
3. How do I setup a system that will allow me to charge the batteries and deliver the regulated voltage to the project at the same time?

I'm a complete noobie and don't know how to do any of this, the only things I can do are solder and put things together.

Useless image to put a visual to my ramble. Thank you if you can help.
Untitled.png
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Perhaps the easiest way is to use your external adapter to charge the batteries and the batteries to power the equipment. The battery's voltage would be regulated with a regulator.

Without knowing what type of batteries you want to use, all I can suggest is that you use a charger that is appropriate for the type of batteries you choose.

If your batteries have a large change in voltage between fully charged and fully discharged, then a switch mode regulator will likely be more efficient. Remember that your batter voltage must always be higher than the voltage your circuit requires, or the regulation will be either complex or just plain won't work. With switching regulators you can also increase the voltage, but in this case the battery voltage should always be less than the voltage your circuit requires.
 

Maskot

Aug 7, 2013
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Perhaps the easiest way is to use your external adapter to charge the batteries and the batteries to power the equipment. The battery's voltage would be regulated with a regulator.

Without knowing what type of batteries you want to use, all I can suggest is that you use a charger that is appropriate for the type of batteries you choose.

If your batteries have a large change in voltage between fully charged and fully discharged, then a switch mode regulator will likely be more efficient. Remember that your batter voltage must always be higher than the voltage your circuit requires, or the regulation will be either complex or just plain won't work. With switching regulators you can also increase the voltage, but in this case the battery voltage should always be less than the voltage your circuit requires.
I'll be using Lithium Ion batteries, but I need a lot of amps, so I need a lot of batteries. Having the batteries removable would be a hassle, I did setup a switch in the case so I can setup a charge and discharge mode. I need a good parallel battery regulator since I know all of the batteries won't charge the same way.
Untitled2.png
 

BobK

Jan 5, 2010
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There are no 12V Lithium cells, so, most likely each battery will have to be 4 cells in series, giving you a nominal 14.7V. You would need a very complex charging system to charge these in place.

Bob
 

Maskot

Aug 7, 2013
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There are no 12V Lithium cells, so, most likely each battery will have to be 4 cells in series, giving you a nominal 14.7V. You would need a very complex charging system to charge these in place.

Bob
What do you suggest I do? I need a lot of capacity.
 

(*steve*)

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I suggest you use large cells built up into a large battery with a balancing charger. We can't suggest how large unless you can tell us the maximum current required, the average current and the required time between charges.
 

Maskot

Aug 7, 2013
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I suggest you use large cells built up into a large battery with a balancing charger. We can't suggest how large unless you can tell us the maximum current required, the average current and the required time between charges.
The power supply that I use to power it is 12V 4A, I had a 4800mAh lithium Ion battery laying around, I plugged it in and it was drained in less than an hour, probably just a crappy battery.

I blame the power sucking on the design of the PCB and use of components, but I don't have the knowledge to streamline it.

The max current is 48 watts, the average current should be 48 watts since it's a power supply, the required time is as little as possible with a long use time.

I also have a 12v-5v converter to power a usb connector, max draw on that is 7.5 watts.

The holy grail would be a battery that charges in 2 hours and lasts 8 hours, size and weight do not matter.
 

(*steve*)

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you need 4AH x 8 = 32AH.

I'd look for a 40AH, 4 cell LiPo battery and charger. This would be something similar to a pack used for an electric bicycle. Expect something the size of 3 house bricks (but significantly lighter).

I had a 24V 10AH pack that, with charger, was about the size of 2 house bricks. You want twice the power. Mine recharged in 2 to 4 hours and discharged in 20 minutes to an hour :D
 

Maskot

Aug 7, 2013
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you need 4AH x 8 = 32AH.

I'd look for a 40AH, 4 cell LiPo battery and charger. This would be something similar to a pack used for an electric bicycle. Expect something the size of 3 house bricks (but significantly lighter).

I had a 24V 10AH pack that, with charger, was about the size of 2 house bricks. You want twice the power. Mine recharged in 2 to 4 hours and discharged in 20 minutes to an hour :D

I've finally figured out a cheap, small, and simple solution! I'm going to take 14500 rechargeable Li-ion batteries that are around 1600mAh. I plan on using at least 20 and put them into simple 4 battery holders all in parallel to give me around 14.8V at 8Ah, then I need a power converter to get a consistent 12v at 4Ah, I have no idea where to look or what to get, so please suggest something specific that I can just google and buy right away. I also need something that will convert down to 5v at 2Ah, again something specific. I don't plan on integrating the batteries fully, so I'm just going to take them all out and charge them up when the thing dies. So is this a good idea and what converters should I get if they're even called converters... I know nothing at all. :( 8 hours was a bit optimistic, but with this setup I'd be getting a reliable and consistent 2 hours.
 

(*steve*)

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Ah is not a current A is a current. Ah is a measure of capacity
 

Maskot

Aug 7, 2013
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Ah is not a current A is a current. Ah is a measure of capacity
I need a converter to go from 14.8V 8A to 12V 4A and 5V 2A.

My project will have 2Ah in a perfect world. Did I get it right this time?
 

(*steve*)

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to reduce the voltage you're best off looking for a suitable switchmode buck regulator.

if your pack has a capacity of 2Ah, and what your powering requires 48W, your pack will last about 15 minutes between recharges.

I thought you wanted an eight hour life which is why I recommended at least 32Ah.
 

Maskot

Aug 7, 2013
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to reduce the voltage you're best off looking for a suitable switchmode buck regulator.

if your pack has a capacity of 2Ah, and what your powering requires 48W, your pack will last about 15 minutes between recharges.

I thought you wanted an eight hour life which is why I recommended at least 32Ah.
So what should I get? You are yet to answer that specifically. Regardless of how much power I have, I only need these buck regulators and I'm good to go, so please help me out.
 

(*steve*)

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It is difficult to search places like eBay, copy links, and respond in that sort of detail while I'm donating plasma. I'll google it for you when I have 2 free hands and a real computer.
 

Maskot

Aug 7, 2013
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It is difficult to search places like eBay, copy links, and respond in that sort of detail while I'm donating plasma. I'll google it for you when I have 2 free hands and a real computer.
Oh, I look forward to that then, thanks for all the help so far.
 

(*steve*)

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OK, on reflection, I recommend you see if your 12V operated device can run from the DC voltage from the battery pack. The reason is that the battery voltage will vary from slightly above to slightly below 12V. It is difficult (and more lossy) to try to produce an output voltage from an input voltage which can swing from above to below the desired output voltage.

If it needs exactly 12V, you might like to consider using a 4 cell battery producing around 17V.

Here is an option that can do voltages between 5V and 12V (you would need two of them). It is rated for significantly higher current than you need, so it won't be stressed. It also seems well encapsulated so you don't need to worry about accidentally shorting anything.

This would also allow you to run your circuit from a ready-made electric bike battery (which should come with an appropriate charger).

You want 48W for 8 hours. That's 38Wh. Assuming 80% efficiency, you need 480Wh.

If you get a bike battery rated as x volts and y Ah, you need to ensure that x * y >= 480.

For example a 24V battery pack would need to be rated at 20Ah or greater.

Here is a 24V 10aH battery and charger. You would require two of these, isolated using diodes to prevent one discharging into the other.

You would also want to put fuses in series with the batteries just in case you have a fault. (A 5A fuse would be plenty)

Here is an example of a 24V 20AH battery.

I don't recommend any of these devices in any way other than suggesting them as examples of what you might consider. I don't suggest that they're the best price. I don't suggest that they're high quality. They should, however, allow you to do some sort of budgetary estimate.

I would recommend you find a local supplier and talk specifics with them.
 
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