Help finding 5v battery for space-limited application

[Daravon]

Pulling my hair out becaues I can't think of what will work. I'm building a light meter and my battery has to fit in a 3/8 thick MAX, 2.5 inch long, and 1.4 inch wide volume. That's about 9mmX30mmX75mm.

I need 4.5-5.5v. I would like decent self-discharge and capacity.

A flat cell phone battery fits in there perfect with a gaint 1000mah, but 3.7v is not enough. Two small lithiums would fit, such as Sparkfun's 200mah lithium button cells, but then I would have to use a 7805 voltage regulator, wasting power and requiring a hardware switch--no sleep mode possible then.

I can barely fit 3 AAA in there, which provides enough voltage if I use alkalines or lithiums, but I would have to make a custom battery holder to allow batteries to be changed. 4 sub-AAA nimh's would fit, but now I'm losing capacity. CR123-size batteries won't fit.

Right now I'm torn between making a custom holder and using 3 alkaline AAAs, or tearing apart a rechargeable 9v and stealing the mini-cells out of it. Anyone know the dimensions of the little cells in 9v batteries? Any other ideas on batteries that add up to 5v? I wish there were 2.5V rechargeable button cells.

 

[Mugrunty]

Why not just use a super tiny boost converter to get your 5V? How much current do you need? I forget the chip name, but I had a surface mount 5-pin chip that needed only a cap, diode, and inductor to function. The stand-by current (when not drawing anything at the 5v output) was in the uA range...so self-discharge wouldn't really be effected. Everything was surface mount, so it was pretty stinkin small. I could take a picture of it, or try and find the part number if your interested!

I think this one was only good up to 200-300mA though.

 

[Daravon]

I need only probably 20ma. I'm running a microcontroller, a LCD display, and a light-to-frequency IC.

If all else fails I'll buy two 200ma lithium button cells and use a 7805, however, I had wanted to be able to put the microcontroller in "sleep" mode, turning off the LCD and chip, so that I didn't have to wire in a switch and remember to turn it off. A 7805 will require a hard switch or it will run the batteries down even if the load turns off. If the device is going to operate like this, then any voltage regulator or boost circuit must have very small quiescent draw (microamps).

I never thought of a boost circuit, but if it would let me use my 1000ma lithium battery that might be pretty good indeed. It needs to run the microcontroller though so I don't know how clean the power needs to be.

 

[rmteo]

Depending on current requirement, an even simpler charge pump boost regulator can be used. No inductors, 3 capacitors and a resistor are all that is need. Device (MCP1252-33X50) is about $1 and comes in a tiny MSOP (3mm by 3mm) package and good for up to 120mA. Works great with 3.7V cell phone batteries.

 

[Daravon]

Depending on current requirement, an even simpler charge pump boost regulator can be used. No inductors, 3 capacitors and a resistor are all that is need. Device (MCP1252-33X50) is about $1 and comes in a tiny MSOP (3mm by 3mm) package and good for up to 120mA. Works great with 3.7V cell phone batteries.

Does a device like that put out power that is 'clean' enough to run a microcontroller and digital circuitry on? I honestly don't know. I know some LED voltage regulators use PWM, which is basically blinking the LED on and off fast. Obviously you can't blink a microcontroller on and off. Or rather, you can, but it won't work if you do.

 

[rmteo]

I used an MCP1252 in this project - handheld terminal. It has a PIC18F44K20 running at 64MHz, a graphic LCD, a bunch of LED's, a 24-key capacitive touch pad, etc. Power is a 1200mAH cell phone battery. Quiescent current of the MCP1252 is 60uA - maximum is 120uA.

 

[Mugrunty]

I'm working on a project that also uses a microcontroller. A fuel gauge circuit, to be exact. Since the micro will be on or sleeping all the time, I also wanted a 5v regulator for the LCD display and micro. I found a couple 5V regulators with ULTRA low quiescent currents.

One was the LM2936 ~15uA

The one I picked was the LP2950. It had 75uA, and was capable of 100mA plus of output current. It was in the TO-92 package, so it was pretty small. Since this was my prototype, I didn't care too much about size though.

Still, If I was using a 7000mAh battery and the total current draw was 200uA...the thing would take about 4 years to die from stand-by.

But...I'd probably just use the boost converter in your case. (or if the Charge pump has a low enough Iq). I lost the one I mentioned earlier, lol. I think I left it at school. I'll check for it this weekend. :)

 

[Mugrunty]

Wow, sounds like that Charge pump is pretty cool!! The one I was talking about was actually a PFM boost converter (pulse frequency modulation). The output was smoothed with a typical bulk output cap.

 

[Illum]

no idea on length and width, but for thickness....

http://www.lenmar.com/Web/Main.aspx?MenuID=4&EntityID=37&ResourceID=9&ProductID=PPU2100B
the power button is a little annoying, but oh well, comes with couple of accessory plugs all joined to a barrel connector
The unit will provide some power with no load to preserve battery power, so to turn it on you'll have to click this tactile button on the top cover for it to power on












Dimensions [L x W x H]
<4" x <2.5" x 6/16"

Powers USB products, charges with USB...I dunno what will happen if you plug the output end into the input end so don't try

5V 7.8WH, so its roughly 1560mah
too thin to be LiCoO2, so I think its Li-Po

Output: 5V 700ma max, Input: 5V 1A

Radioshack has these marked $20, I bought one to power a LED gooseneck light I modded using two CREE XRE P4s and a small resistor, draws 150ma shared between the two LEDs, a very nice little lamp the combination makes:nana:

 

[rmteo]

Will it fit into a 3/8 thick MAX, 2.5 inch long, and 1.4 inch wide space?

 

[Daravon]

No, it won't, but it's still pretty cool, and for 20 dollars a good deal too.

As for the boost convertors---AWESOME. I really wanted to use that big, luscious lithium battery. I think I'll track down an MCP1252--any ideas where to buy?

I need the 5v for the LCD...since my microcontroller will run on 3.3v, I can bypass the boost chip with a diode, and hook its output enable to the microcontroller so the boost chip turns off completely when the chip goes to sleep. The chip should wake up on 3.7v just fine.

 

[rmteo]

Go to http://www.findchips.com/ and type in "MCP1252".

You can get 1000-1200mAH lithium batteries for about $2 each.

 

[Daravon]

Looks like digikey has it and will now ship USPS for only $2.40. I'll just buy a couple from there.

You can get 1000-1200mAH lithium batteries for about $2 each.

From where? Especially now that I know about these boost convertors, Want Moar.

 

[rmteo]

Try here (free shipping) http://www.dealextreme.com/products.dx/category.503

 

[Illum]

Will it fit into a 3/8 thick MAX, 2.5 inch long, and 1.4 inch wide space?

no, it will be 1.5" too long and 1" too fat, but it does give you some ideas about alternative choices.

The MCP1252 looks promising, too bad it only comes in MSOP package...which might pose an issue for us people who are used to thru-hole mounting.
Example of MSOP packaging

I think I'll track down an MCP1252--any ideas where to buy?

Consult the datasheet to see what you need and look up the associated serial numbers

Digikey has MCP1252-33X50I/MS-ND on stock, $1.64 each
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=MCP1252-33X50I/MS-ND

Microchip Direct has MCP1252-33X50I/MS for $1.37 for qty 1-25
http://www.microchipdirect.com/productsearch.aspx?Keywords=MCP1252

Mouser has them listed but they are on order until 12/28
they have MCP1252-33X50I/MS for $1.48 for qty 1-9
http://www.mouser.com/ProductDetail...3X50I-MS/?qs=sGAEpiMZZMsUzhEcHltCubsvjTIdlMwG

 

[Daravon]

I just bought 4 from Digikey--1 of the fixed-output ones, 1 of the adjustable ones, and one extra of each to accidentally fry.

 

[rmteo]

If you need more info (datasheet, app notes, etc.) see here http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en010593

 

[Daravon]

Yeah, the only thing I'm worried about is it's SMD. I can probably solder it with a soldering iron and steady hand, but I'm not exactly sure what to solder it TO. It seems like I need the SMD equivalent to perfboard. Or, I could just point-to-point it in free space...ugly has never been a problem for me.

 

[ifor powell]

If you have a spair pin on your microcontroller you can just use it to drive a "charge pump" voltage doubling circute of your own no need for anything clever just a couple of caps and diodes. Personaly I pinch the high voltage output from my rs232 driver which is on a lot of my projects to drive the lcd.

 

[Illum]

Yeah, the only thing I'm worried about is it's SMD. I can probably solder it with a soldering iron and steady hand, but I'm not exactly sure what to solder it TO. It seems like I need the SMD equivalent to perfboard. Or, I could just point-to-point it in free space...ugly has never been a problem for me.

I'm not sure if there's compatibility between MSOP and SOIC....but if there is..you could use a surfboard:poke:

If your careful enough and want to try deadbug style I suppose you could try to solder it on 8-pin DIP header plugs

You could also consider an SOIC/SOJ to Dip adapter for 8-Pin Products



What you'll end up with either way is a "DIP" chip that resembles a BASIC stamp:grin2: