Power Hungry. Feasibility questions. Mother Of All Mods.
 

Good afternoon ppcGeeks,

today I was making a write-up about another Raging Idiot bright idea when I realized I might have actually discovered something really cool while brainstorming some possibilities. Although I'd love to jump right in there and get this done I simply can't - because I'm a Raging Idiot and I need some help from the local crowd.

If this is feasible, when I'm done, I'll post results of this mother of all mods.

Here's the first Raging Idiot question:

Opening the back cover you will find 6 battery contact points. The battery itself shows the positive indicator towards the top and the negative towards the bottom.
- (+)
-
-
-
-
- (-)


From this I need to somehow get to 3 points (for a secondary output)
1 positive, 1 negative, and 1 termination.
- (+)
- (T)
- (-)


Is this feasible?

If so, then...
Here's the second Raging Idiot question:

How much power can I get from the phone's 3.7 volt battery and still have ability to use the phone?


I have no idea about Lithium Ion batteries or whether I might be able to get more than the stated amount of voltage out of it.
After all, they advertise stun guns with 900,000 volts working off of three 3 volt batteries.

You could definitly tab a secondary output. In theroy with the correct capacitor you could get higher voltage from the battery if needed. As far as the drain and keeping the phone running I am not sure. One could find out with using resistors to simulate a draw against the battery. This would tell you how many amps can be pulled and still maintain functionality. If you need the power to do something, but do not need the screen to be on ie. standby) you could probally draw a good amount.

Actually capacitors are not capable of stepping up voltage. All cpacitors do is store energy....that's it. You need a transformer to step up voltage.

RI:
For "the drain" on the battery you need to ask this question first:
What are you trying to power and what is it's draw (volts AND amps). Then you can see if there is enough leway on the phone.

I can't tell right now (at work), but if you can run the phone on USB (no battery) then the phone is NOT using more 500mA (that's milliamps). I don't know how many amps the battery is capable of, so I'm no help there. But if you can find that number out you can find out your amperage leway. For volts, unless you want to carry a small transformer around or solder it into your circuit somehow (camera flash transformers are actually very small), you have 3.7v period.



Drew

A rule of thumb about current lithium batteries is that they can be safely charged/discharged at a 1C rate, meaning that a battery can be charged or discharged at it's rated capacity. Say you are using the standard 6700 battery that is rated at 1350 mAh @ ~3.7 volts. This means you *should* be able to charge the battery at a maximum of 1.35 Amps per hour or possibly discharge the battery at 1.35 Amps for 1 hour. However, most of these batteries will have some sort of "smarts" to them and may shut itself off at a current draw less than it's 1C rating, would depend on the application.

I don't exactly what you were thinking of "tapping" the battery for, but if it is an external GPS to be integrated into the back of the 6700, then someone is working on it already:
http://ppc6700users.com/forums/viewtopic.php?t=4494

*And yes there are lithium polymer batteries that can safely discharge at rates of 15C or so, but they aren't too common, especially in the cellphone market (if at all or ever). The charge rating is still roughly at 1C though.

**Just a random link if someone wanted to "play" around with other battery options.
http://www.batteryspace.com/index.as...S&Category=895
Although I'd recommend a lot of reading on these for any sort of DIY projects.

Built-in GPS was in fact the idea.... What else right....
I kind of figured I wasn't the only one thinking about this. But what I have in mind is slightly a bit different (better?) than the one in progress. :)

BTW- it's 3.7 volts that I'll need, which happens to be the exact same as the phone.

If I'm reading this right, you're saying that the "1C, 15C, etc" rating is in proportion to 1? So 15C = 1/15 (or 1:15) of the battery's capacity? So if the phone isn't pulling the full 1.35mA the battery shuts off?

And, if I'm reading this right, your meaning is the opposite (15C = 15/1 or 15:1)? So these "fabled":wink: batteries can discharge at 15 times the rate that they can charge?


This rule of thumb is new to me and I'm just wondering which is your meaning because it is a VERY useful rule.


Drew

Sounds like you've found out you don't need to step up the voltage, but just in case anyone else is reading this with the idea of upping the voltage on their battery be extremely careful.

The reversible (reversible in a strictly thermodynamic sense) voltage of a battery is determined by the chemistry of the battery. That's why alkaline batteries are 1.5 V, lead-acid 2.2 V/cell x 6 cells/battery = 13.2 V, and Li-ion batteries 3.4 - 3.7 depending on the specific chemistry used in the cell.

When discharging a cell irreversibly - any real world application necessarily operates irreversibly - the cell voltage will drop as current increases (less power - P= I x V - is available due to parasitic losses like internal resistance and others). When charging a cell irreversibly, the cell voltage will rise (more power is needed to charge the cell faster).

Things get VERY dangerous if you charge or discharge too fast - that is to say at a higher current. If the cell voltage goes negative or too high other reations can occur. For instance, with lead-acid batteries, trying to charge the battery too quickly can cause the negative electrode to start evolving hydrogen gas which could ignite with a spark.

Li-ion batteries have 2 additional problems.

1) depending on the quality of the battery, charging at high currents can cause dendrites (like stalgtites or stalagmites) to grow. If these grow all the way across the cell to the other electrode, it will short the cell giving a giant current density with giant local heating leading to fires and explosions
2) although manufacturers have moved away from LiHClO4 (Li perchlorate) as the electrolyte since it is explosive, there are still problems with thermal runaway (ask Apple and Dell about their experiences)

Remember your high school chemistry demonstration with what happens when Li (or Na or K or Cs or Fr) reacts with air or water. Also, 3.7 V is a HUGE single-cell potential. Hydrogen and oxygen give only 1.2 V - so there's a bigger driving force for reaction with Li-ion batteries than hydrogen gas in air. They are that volatile. In fact the urban legend about static charges from cell phones causing fires at gas stations are much more likely to be due to fires from the cell-phone batteries. Not to mention meth labs that have burned down from Li fires.

That being said, there are many safety mechanisms built into the cell packs to make sure you can't get into too much trouble. Just don't by pass them unless you know exactly what you are doing.

You can step up AC voltage easily with a transformer (with a proportional loss of current). DC voltage can be stepped up with solid-state electronics, but needs a minimum input voltage to operate.

The danger here is that you try to step up the voltage and either draw too much current in order to match the load's current requirement or accidentally allow the higher voltage to drive current through the cell and overcharge the battery. Either situation could result in an explosion.

So be careful and have a dry chemical fire extinguisher handy!

Whatever number is in front of the C rating is Multiplied by the lithium polymer's capacity. So a 15C battery means that it can discharge safely at 15 times it's rated capacity (example of a 15C battery: http://www.all-battery.com/index.asp...OD&ProdID=1786 ) However, like I stated though, most of these batteries can not be safely charged greater than a 1C rating though.

The "smarts" I was refering to is a protection circit often built into a battery to protect the cells from over discharge (both current and voltage), over charge (voltage), and load balancing between cells if present. (http://www.all-battery.com/index.asp...S&Category=178

If you don't know entirely what you are doing then always get a battery with this protection built in and it probably wouldn't hurt to get a LiPo charge bag if you are going to work with these "hobbyist" batteries. I'd recommend to also keep the charging away from easily flammable materials as improperly charged Lithium batteries can fail and burn at extremely high temperatures (1300+ degrees F).

Try this.......:wink:

http://ppc6700users.com/forums/viewtopic.php?t=4494

Dang~ we have some smart people on this forum.