Low cost battery supply.

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ahull
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Re: Low cost battery supply.

Post by ahull » Fri Jan 08, 2016 8:56 pm

mrbwa1 wrote:Thanks for the extra info @ahull!

I just am not that familiar with the 18650 cells. I would imagine their Current ratings are in line with the intended use: Laptop batteries. and I agree about charge/discharge rates. The accepted rule for 3S Hobby Lipo packs is 1S (Charge a 2700Mah pack at 2.7A), however I usually charge them at a lower rate, especially the first time when I have to discover what the true capacity is. I suppose I should get busy and build a battery temp probe so I can feel a little better about that 1S rate (it's not like it's hard since I have all the parts laying around...
Adding a temperature probe to a fast charger is, I would suggest, essential. Interestingly camera batteries generally include a 10k Ohm PTC thermistor as a built in probe, and most quality chargers check this ptc to ensure the battery is not overheating. I tore down a cheap clone Canon NB-4l Battery a couple of years back, and you can see the results here. One of the things the clone battery makers do, is substitute a 10k resistor for the 10k PTC thermistor.
- Andy Hull -

darth_llamah
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Re: Low cost battery supply.

Post by darth_llamah » Sat Jan 09, 2016 9:22 am

ahull wrote:One of the things the clone battery makers do, is substitute a 10k resistor for the 10k PTC thermistor.
One of the things the smatphone maker did (maybe still does) was to susbstitute thermistor with a resistor to detect counterfit batteries- different resistance than expected=no charging. Battery was charged with 1/3C (PC USB) or 2/3C (AC charger) current, after less than a year it started to be swollen.

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mrmonteith
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Re: Low cost battery supply.

Post by mrmonteith » Thu Jan 28, 2016 6:36 pm

I was looking around for discussions about powering my projects. I already bought a single-cell 18650 charger battery banks like they use for cell phones.
http://www.ebay.com/itm/Portable-USB-Mo ... 4647912f14
I can't complain for $.70 and free shipping and I got a bunch of 5800mAh 18650 for like $.36 a piece with free shipping. So what can I say for slightly more than $1 plus the cables. I got them for like $1 a piece. These can supply a max of 1A which is far more than I would need anytime soon.

Only gotcha was it was purple. My wife saw it on the table and knew what it was and snatched it up for herself. :roll: lol At her work inside it drains her phone terrible. So needed it for emergency. Oh well, it was a feather in my cap for her so she doesn't complain any about my odd purchases. lol Just had to order myself more now. Keep this up I know what I'll get everyone for Christmas this year. lol

My next though was for something smaller. Everyone seems to be pointing to LiPo power. But then I started down another rabbit chase about supercaps. i just started down this trail so not sure if they can be used solely as power or like in this article:
http://www.digikey.com/en/articles/tech ... nsor-nodes

I'd love to see some pics of others that have powered their projects in various ways.

Michael

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mrburnette
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Re: Low cost battery supply.

Post by mrburnette » Thu Jan 28, 2016 8:21 pm

mrmonteith wrote: <...>
But then I started down another rabbit chase about supercaps. i just started down this trail so not sure if they can be used solely as power or like in this article:
I'd love to see some pics of others that have powered their projects in various ways.
Michael
@Michael,
The resulting power-consumption profile resembles a series of pulses of varying height depending on the number of modules that need to be active at any one point. Although the current consumption is to a large extent predictable, it does exhibit large swings over the lifecycle of the system. Battery cells and energy harvesters do not necessarily work at optimum efficiency in this type of environment.
Supercapacitors, otherwise known as double-layer capacitors, provide a good match for designs that have ‘bursty’ power demands. Their ability to reduce the peak power demands on the chemical battery are also likely to extend its lifetime, a critical factor in consumer electronics devices, although there is a clear tradeoff between the energy lost through self-discharge versus the problems caused by continual battery charging.

IMO:
This sounds like snake-oil, albeit there is some truth about ESR in the cell creating heat and lost energy. However, unless the super-cap is pre-charged to exactly the same voltage as the open terminal battery, nasty stuff can happen on a difference. An uncharged super-cap is essentially a short... plays havoc with the ESR of the lithium cell and wastes a lots of battery energy. An over-charged super-cap can damage the battery electrodes.
Once the cell terminal voltage and the super-cap terminal voltages are in equilibrium, your system can now be profiled. Were the lithium cell 0 internal resistance, then the peak current loads would have no power loss due to resistance; however, this does not mean that the lithium chemistry could supply the peak current - in which case the super-cap makes sense. I've seen a good use for such capacitance in the ESP8266 devices as the power consumption can go from 70mA to 500+mA during transmit.

The takeaway is to read the lithium cell open-circuit voltage, use a bench supply to pre-charge the super-cap to the same voltage, then connect the battery to the circuit. Double check the polarity!


Ray

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mrmonteith
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Re: Low cost battery supply.

Post by mrmonteith » Thu Jan 28, 2016 9:07 pm

I think they blew their super-cap. I get errors going to the site. lol

Might be something for a good experiment to try. They're cheap enough I can buy one and see. I already have a couple of voltage converters I had planned on using. This way I could see what the super-cap does to the regulator. I can see how the super-cap would be great for when there are spikes in current. Don't know until you try or until you smoke something. lol

Michael

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mrburnette
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Re: Low cost battery supply.

Post by mrburnette » Fri Jan 29, 2016 12:30 am

mrmonteith wrote:I think they blew their super-cap. I get errors going to the site. lol

Might be something for a good experiment to try. They're cheap enough I can buy one and see. I already have a couple of voltage converters I had planned on using. This way I could see what the super-cap does to the regulator. I can see how the super-cap would be great for when there are spikes in current. Don't know until you try or until you smoke something. lol

Michael
@Michael,
One 'kind-of' knows based upon a LiON + super-cap. When a DC-DC converter is thrown in, it is not just one (1) more component that is a black-box, it is a rather complex ti model black-box.

Most DC-DC run 92% - 96% efficient with higher efficiencies being for the higher frequencies and the voltage-delta: closer the voltage difference, higher the efficiencies.

Placement of the super-cap is critical, too... at the battery? After the DC-DC boost/buck module? Oh, yea, boost or buck?

Then you have the traditional LiON droop attributed to aging: http://www.batteryuniversity.com/_img/c ... thium1.jpg and that must create a ceiling/floor for optimum performance.

We could model from sunrise til the cows come home and still be factoring in the "this-or-that".


Ray

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mrmonteith
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Re: Low cost battery supply.

Post by mrmonteith » Fri Jan 29, 2016 1:33 am

Well you lost me totally. Last time I worked seriously with power supplies was the late 80s if that tells you anything? It was all linear regulators. Anyway this will be a good opportunity. My specialty was test and measurement so guess I'll need to fall back on that along the way. So I'll probably have lots of questions.

Michael

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martinayotte
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Re: Low cost battery supply.

Post by martinayotte » Fri Jan 29, 2016 1:35 am

@Ray, your link give us "access denied", so you must be an elite member of batteryuniversity ... :lol:

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martinayotte
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Re: Low cost battery supply.

Post by martinayotte » Fri Jan 29, 2016 1:38 am

mrmonteith wrote:Only gotcha was it was purple.
Thanks for the link ! I've ordered some, but not "purple", "black" ones.
So, cheap, nothing to lose ...

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mrmonteith
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Re: Low cost battery supply.

Post by mrmonteith » Fri Jan 29, 2016 2:28 am

martinayotte wrote:
mrmonteith wrote:Only gotcha was it was purple.
Thanks for the link ! I've ordered some, but not "purple", "black" ones.
So, cheap, nothing to lose ...
Just remember that's just the case. You need a battery too.

Michael

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