Hey guys I'm buying some Li-ion batteries, the four-pack version of this one http://www.gearbest.com/batteries/pp_189822.html I'm just wondering if anyone can share what they know about these kinds of batteries and how they will affect my projects.
Current project : very basic Arduino Uno, Ultra Sonic Sensor, Cheap Motor Controller and 12VDC computer fans.
(Fans are rated 0.68ma, driver is rated 0.38ma per channel, I'm using a 9V battery which I hope will not draw
the full 0.68 from the fans)
Next project: Arduino Rovor: Arduino mega, motor driver for arduino mega, 4 DC motors rated at 1.6 volts, Jtron Camera module (5v), TFT LCD (5v), GPRS wireless module for Arduino.
I read Li-ion batteries have a higher voltage when fully charged compared to other batteries.Is this correct?
Ardu-weenie:
Hey guys I'm buying some Li-ion batteries, the four-pack version of this one
...snip...
I read Li-ion batteries have a higher voltage when fully charged compared to other batteries.Is this correct?
Those are Li-ion cells, not batteries - each cell fully charged, will output 3.7 volts as specified. Four of them in series will net you 14.8 volts @ 3400 mAh.
Do you have a charger capable of charging those cells? If you don't, then you need to purchase one; anything else will likely result in an explosion and fire. Even with a proper charger, don't leave the batteries unattended, as explosion and fire is a hazard with lithium chemistry cells.
Personally, I wouldn't go this route, unless space or weight issues made the choice the one I had to go with. I would personally look into a 3 or 4 cell LiPoly RC pack and charger, and preferably a pack and charger by a known brand name in the RC hobby (or at least known brand-names for the cells). Too often you'll see "second runs" or "knock-off" cells used to make packs (or sold loose), which may have been rejects or worse - that may charge once or twice (or more) ok, but at a certain point, burst into flames. That's what one of the major causes of all those "hoverboard" fires were - bad battery packs from no-name suppliers.
Those cells you point to say "NCR" on them - but does NCR make Li-ion cells? If they do, do legit ones look like that picture? Do the prices match approximately? If so - then those cells might be legit, first-run cells, and NCR is a known manufacturer. If not - you might want to look elsewhere.
If you did have to go with loose cells to make your own pack, then if it were me, I would shop a known custom battery pack manufacturer, like this place:
Which is fairly known and trusted by solar enthusiasts and similar off-the-grid people. The reason is because they also sell custom charge controller boards for packs:
...as well as other supplies, materials, and test equipment to custom build your own battery pack and end up with something relatively safe.
Even so - most lithium chemistry cells (mainly Li-ion and Li-poly) can become unstable while charging, and should be handled with care while doing so. For instance, for RC packs, you should charge them in a fire-proof enclosure of some sort, like inside a concrete block on a concrete floor, with another concrete block on top (and even then, don't leave them unattended). While not data, I have read stories about people in the RC hobby who have had fires (one guy's house burned down on a forum thread I read!). Many have had "close calls".
One of the safest lithium chemistry batteries that exist, though, are LiFePo batteries - most of these exist in well-known formats (same size to replace standard SLA batteries), and have built-in management controllers to allow charging from standard SLA chargers - they are basically meant as "drop-in" replacements for many apps that currently use SLA batteries. They are combine the advantages of light-weight and high-amp hours, with the ease-of-use of SLAs - while still being very safe. Their only major disadvantage is their cost, which is several times higher than the original SLA they replace.
Ardu-weenie:
I read Li-ion batteries have a higher voltage when fully charged compared to other batteries.Is this correct?
A li-ion battery is rated at 3,7V but they vary between 4,2V (fully charged) down to 2,75V (full discharged). They are much more sensitive than regular batteries (alkaline), if you overcharge or short circuit them they may explode and if you discharge them below 2,75V they may not charge anymore. To be safe use protected batteries, they have a built in circuit to prevent these cases. The batteries in your link are not protected, so be carefull.
To arrange your batteries there are lot of 18650 battery holders for 2, 3 or 4 batteries, series or paralell. Holders for protected batteries are dificult to get, because protected batteries are some mm higher, normaly you have to cut or bend a little the spring in the battery holder.
Be aware that - any 18650 cell spec'ed for more than 3000mAh is lying about their capacity. Cheap 18650's have 500mAh to 2000mAh capacity, typically. Some of them are absolutely terrible (the yellow ones claiming 9000-someodd are particularly bad, as you can tell when you pick them up), but the better of the knockoffs are usable. Of course, some care should be taken that you don't have kindling piled around them while charging.
If I'm charging them in place, I strongly favor wiring in parallel, since it makes charging easier (there are lots of single-chip solutions for charging single cells without making a big production out of it. That's less true of series stacks. You can run an AVR microcontroller right off the output of the battery (at less than 16mhz to keep completely within spec - I do 8mhz, using an appropriate crystal - the internal oscillator isn't accurate enough for serial), which makes life easier.
Can't wait until those flexible ceramic batteries that you can drive a nail through during operation without adverse effect become cheap enough to use. There's a lovely video from the company of them cutting the battery into pieces with scissors (it's thin and flat), driving nails through it, and blowtorching it, all while it's powering an LED.
DrAzzy:
Be aware that - any 18650 cell spec'ed for more than 3000mAh is lying about their capacity. Cheap 18650's have 500mAh to 2000mAh capacity, typically. Some of them are absolutely terrible (the yellow ones claiming 9000-someodd are particularly bad, as you can tell when you pick them up), but the better of the knockoffs are usable. Of course, some care should be taken that you don't have kindling piled around them.
This is something I've seen said many times on the forum now, that the batteries can only be trusted for a fraction of the nameplate capacity. This goes against my experience, however, as I've used battery cyclers (I have a Chroma 17020 at the moment) to cycle hundreds of battery packs with thousands of cells. They usually they start with more than their nameplate capacity.
That said, these are all cells bought from reputable manufacturers and used by leading engineering companies. I have no experience with hobbyist sources for cells, and enough people have said things similar to your quote that there must be something to it.
How do you guys know you're only getting a fraction of the capacity, however? Are you actually measuring/integrating the current?
BigBobby:
That said, these are all cells bought from reputable manufacturers and used by leading engineering companies. I have no experience with hobbyist sources for cells, and enough people have said things similar to your quote that there must be something to it.
How do you guys know you're only getting a fraction of the capacity, however? Are you actually measuring/integrating the current?
Yeah, I'm talking about cells bought from disreputable manufacturers and used by people who can't afford the good ones.
The gulf between stated capacity and actual capacity is so great that you can tell they're not even close to spec just from observing battery life.
We have done load tests with some of them, and found the capacity of 4,000 mAh 2014 vintage 18650's with the Ultrafire branding to be only around 500mAh. The 6000mAh yu longs bought later that year were much better, though we never load tested them to see by how much (the setup was a pain - we did it without the aid of a computer, and the chart recorder isn't the most convenient device)
DrAzzy:
Yeah, I'm talking about cells bought from disreputable manufacturers and used by people who can't afford the good ones.
The gulf between stated capacity and actual capacity is so great that you can tell they're not even close to spec just from observing battery life.
We have done load tests with some of them, and found the capacity of 4,000 mAh 2014 vintage 18650's with the Ultrafire branding to be only around 500mAh. The 6000mAh yu longs bought later that year were much better, though we never load tested them to see by how much (the setup was a pain - we did it without the aid of a computer, and the chart recorder isn't the most convenient device)
cr0sh:
One of the safest lithium chemistry batteries that exist, though, are LiFePo batteries - most of these exist in well-known formats (same size to replace standard SLA batteries), and have built-in management controllers to allow charging from standard SLA chargers - they are basically meant as "drop-in" replacements for many apps that currently use SLA batteries. They are combine the advantages of light-weight and high-amp hours, with the ease-of-use of SLAs - while still being very safe. Their only major disadvantage is their cost, which is several times higher than the original SLA they replace.
Heh...if you happen to get the A123 ALM 12V7 it should have an AVR inside (I forget which one).
There have been a few threads about using the Arduino for battery management now. If you find can find an A123 ALM with dead cells, it would contain a circuit board you could reuse for a project like that (battery protection, cell measurement, and balancing).