View Full Version : Battery Help needed

T Chap
09-15-2006, 03:37 AM
Attached are two pics of some NiMH batteries I am using temporarily till I get some info. I need a single really low profile battery, appox 1.85" x 2.75" as shown(when combining 5 smaller batteries).

It seems the newest and best stuff these days is Lithium ion. Preferrably, a smart battery with it's own management, just plug in the charger and not worry about it. I already put a 2.5mm dc jack pinout on the boards, although they could be 2.1mm just as well, I also just set up the boards to run two wires straight to the battery(s), multed to the pcb(3.3reg) and the dc jack. There is no management on the boards. I got these batteries shown which are 1.2v 1400aH at all electronics, and will solder them together to get 6v for temp use, but need a better solution that is very reliable and headache proof. Google has 90000 possibilities, any body got a suggestions?

PS wire leads are preferred to attach to the header pins on the pcb.

09-15-2006, 05:02 PM
These guys seem to be the business:



Bill Plano
09-15-2006, 10:41 PM

Looking at the photo you submitted, I do not see any solder tabs on the batteries.и DO NOT solder directly to the batteries.и There is a potential for physical damage if the battery gets too hot.и Suggest you stick with commercially available battery packs.и


Bill Plano
09-15-2006, 10:42 PM
Actually this is intended for originator99 not James.

Loopy Byteloose
09-15-2006, 11:06 PM
NiMH seems to have caught up with Lithium in terms of capacity. Mostly I think the Lithium is a bit lighter and smaller. But the huge additionaly cost doesn't seemed justified for most needs. The NiMH often have one cell go bad, so don't solder them together unless you want to throw out good cells with the bad ones when there is a failure. You could easily get AAA cells at 1000ma/H. Those square ones are interesting. But everytime I deal with non-standard battery sizes and shapes, I find I am throwing money away unnecessarily. There is a huge savings by staying with the generic cells [the AAA, AA, C, and D].

"If you want more fiber, eat the package.и Not enough?и Eat the manual."ииииииии

ииииииииииииииииииии Tropical regards,иииии G. Herzog [и黃鶴 ]иin Taiwan

09-16-2006, 09:11 PM
You don't mention anything about capacity or recharge time...

http://www.sparkfun.com har a neat little one-cell Li-ion charger for about $15, and matching Li-ion cells of 100mA(Stamp-sized and so light that you wouldn't believe it, for $6), 860mA($7) and 2000mA($13)

Their two-cell charger is $42, though.
(I like the one-cell charger as it's a small PCB, the size of a stamp, and easily built into any project)

Don't visit my new website...

T Chap
09-17-2006, 01:17 AM
Thanks guys for thegreat info. The 20000nAh seems like it will do the job. I dont care about recharge time as it will get recharged maybe once or twice a year. The power stays off to the device unless a button s pressed, and only an SX, the 3.3 reg, and an Xbeepro is inside, it wont get pressed but maybe 10-30 times a day for 3 seconds average. I was looking at the iPod 2nd gen battery which seems almost identical in size to the 2000mah on the Spaksfun site. The iPod bat is thinner though. Retail iPod batteries are $50 everywhere I saw them though.

I was looking for something at or above 1000, so these will work great. Thanks for the hookup. The Maxs1555 board is interesting, I can probably fit it in there as well if I lose the jacks, or maybe just build my own 1555 circuit.

OT I just got in a tube of LM2937ET-3.3 3.3v regulators. No matter what I put into the pin one, with GND at pin 2, the output is always Vin - .5v . I haven't tried anything over 12 for Vin. I tried every one in the tube, I tried two different supplies, two diferent breadboards. I am thinking the must have been mismarked, and are really 12 or 15 regulators.

PJ Allen
09-17-2006, 05:11 AM
originator99 said...
No matter what I put into the pin one, with GND at pin 2, the output is always Vin - .5v .
Not much to mess up here.и How're you hooking these up?и

[See pic attached.]

Mike Green
09-17-2006, 06:13 AM
Be careful in that rechargable batteries (of all types) self-discharge. That's not a problem over a period of days, but over weeks or months your battery could go dead by itself. Some cells might discharge faster than others and you might have a problem with reverse charging (where some cells are discharged and some are not forcing a charging current through the dead cells in the wrong direction) when your unit is finally turned on.

T Chap
09-17-2006, 06:42 AM
Somebody said...
How're you hooking these up?

The same way as the schematic you posted. 7805's, 7812's, and others are usually all the same pin out, these are obviously mismarked since the whole batch will not produce 3.3v. I haven't tried putting in 24 to see where it really starts regulating. I have hooked up a lot of regulators, this is a first.

According to the Sparkfun site, they are usng the MAX1555 to charge those Lipo batteries. I will get some of the ic's in and make a tiny board to fit inside the remote.

I have tried 5 volts, 9, 24, 5 different LM2937ET-3.3 regulators, all produce approx 90% Vin at the output. Plug in a 7805 in the same holes = 5 volts. I am not using any thing else attached while testing, just inout, GND, and a meter.

Post Edited (originator99) : 9/17/2006 12:07:40 AM GMT

T Chap
09-17-2006, 07:55 AM
Mike you just rained on my parade. I was hoping for a years use with 2000mAh, and after reading up on your suggestion, the battery of choice has the following specs. The implication is, to power a 3.3v regulator with a 3.7v battery will result is approx 8% loss per month, in other words, possible charging every month! That is not acceptable c onsidering 2000mHa in a lead acid would power my circuit for a year minimum. Who knew this would be so difficult.

2C continuous discharge
Excellent long-term self-discharge rates (<8% per month)

Tracy Allen
09-17-2006, 09:09 AM
To get around 3 volts:
1 * CR123 primary lithium (LiMnO2), 3 volts, 1500 mAh, 17 grams
2*AA Alkaline, 3 volts, 2800 mAh, 46 grams
2*AAA Alkaline, 3 volts, 1200 mAh, 22 grams
3*AA NiMH, AA, 3.6 volts, 1800 mAh, 84 grams
1*AA Lithium-Ion (Batteryspace) 3.6 volts 750mAh, 20 grams

Primary EL123 lithium (Li/MnO2, 3 volts) cells are becoming more economical from online suppliers because of their popularity in devices like emergency flashlights, and they are really great in terms of energy per unit weight, long long shelf life, and good performance at extremes of temperature. I can understand well though that you want to use a rechargeable battery for this project. Pb-acid batteries are easy to recharge, but they are terrible on the energy per unit weight spec. I'll be interested to hear how your experiments with the MAX1555 turn out.

The LM2937 is an old regulator design and it is not very efficient. Note that the data sheet specifies the output voltage with a load of at least 5 milliamps, and the output capactor of at least 10uF is required. These things can do strange stuff if they don't have the output capacitor.

Tracy Allen
www.emesystems.com (http://www.emesystems.com)

Mike Green
09-17-2006, 09:25 AM
Seriously consider a switching regulator with an on/off terminal that really shuts it down except for a few microamps. Your pushbutton would turn on the regulator. The SX could keep the regulator on as it initializes itself, then do whatever needs to happen and shut itself off along with the regulator. The regulator could run off 4 AA or AAA batteries. You could use lithium primary cells if weight is an issue, otherwise use alkaline. They're cheap and thermostats and smoke alarms use them for a year for sure. The trick is reducing the off current.

T Chap
09-17-2006, 09:34 AM
I saw the datasheet with the cap and just ignored it thinking it was just typical filtering. I use the 78xx series all the time and never need external parts to see the regulated voltage, these are my first batch of this part. I put the 10uF and it works! Thanks for enlightening the dummy.

As far as the battery, originally I wanted to use a 9v, but it is too bulky and would add over .25" to the device. I then settled on .25" as the max thickness, and the iPod style seemed like a natural fit. There is a trade off for everything I suppose. I really didnt want the customer to have to pull the box a part to change batteries, nor did I want it to die once a month. At first I thought to use an external smart charger, but that has it drawback too. If someone loses the charger and uses a regular unregulated wall wart, then I will get complaints and headaches.

As far as the regulator, it is not in the circuit unless a button is pressed, and the boot up time for every press doesn't seem noticable. The Xbee Pro's modules came in today, pretty cool gadgets. Just like wire right out of the box, I haven't tested distance yet.

Thanks for the help.

Post Edited (originator99) : 9/17/2006 2:44:51 AM GMT

Mike Green
09-17-2006, 09:52 AM
Attached is a datasheet for a ST763 switching regulator. This can provide 3.3V at up to 500ma with only a few parts. It has very low off leakage current and has a shutdown pin that's a CMOS input (very very low current). You could run this off two primary lithium cells or four AA or AAA alkaline cells, tie the shutdown pin through a 1M or higher resistor to the +Vin supply to keep it off. Ground the shutdown pin to turn it on. You could connect an SX pin directly to the shutdown pin if you're careful to keep the SX pin low when it's set to output. To turn it off, just switch the SX pin to input.

Steve Andrues
09-25-2006, 12:19 PM
For answers to goofy battery problems, call Ni-Cad Systems in Hayward, CA. They normally do aircraft Ni-Cd's but do pretty well with one-offs for special projects.