Li Batteries

[jlhooper]

These Li cell phone batteries are becoming very common now, indeed I have a drawer full.
Apart fom the obvious "2 in series, regulator combo". Has anyone come up with, or know of a more efficient way of using them for picaxe projects. I have not tried, but would just one of them run a project ?
jeff

 

[Andrew Cowan]

Yes - no problem.

Each is 3.7V - although it may not be enough to program a PIC, 3.7V will happily run a picaxe.

Careful not to overdischarge it or overcharge it, though.

Andrew

 

[MFB]

I would not recommend powering a PICAXE directly from a LiPo battery. Even a small 30mA/h version is able to supply damagingly high levels of current in the event of a wiring mistake, or connecting an electrolytic capacitor the wrong way etc. Even under normal conditionions it would be possible degrade the performance of the battery, by allowing it to discharge below about 2.5 volts.

My approach is always to use a low drop adjustable regulator set at 3 volts; with its low battery detect circuitry set at 3.2 volts. Not only will this provide current limiting but also the PICAXE can be programmed to auto-shutdown the regulator when the low-battery level is detected. The MAX884 regulator chip would provide all the features required.

 

[Michael 2727]

I've just ordered 4 x CR123A Li-ion cells and charger from China.
($24.99 AUD inc Postage)
Look on the internet, there are hundreds of deals going.

At 3.7V they should make a good supply for many picaxe projects.
I am interested to see if the charger (4.2V) can be adapted to
charge other/smaller Li-ion Cells with the addition of a current
limiting resistor/s.
Some of these Li-ion Cells have battery management chips
embedded into the cap/package to prevent below 3V discharging.

The good thing about Li-ion vs NiCad/NiMH is there is very little
self discharge in the Li-ion cells, whereas NiMH can go flat within
a few days/weeks even if not used.

 

[blauer]

Using lipo

Hello

LiPo in use
LiPos are gooood.. Robots in the video run constantly for 2.5 hours with one battery fully charged. Robot size 200x200mm.

http://www.tkukoulu.fi/~tok/robotti.html Big videos

This is robot (sumo idea att this moment) for math-teachers to try to teach programming with basic+PICAXE. If there would be same language and hardware base in math and technology... that would be nice and practical. This is only test jet....

Facts about Lipo.
1. Charge it only with LiPo charger. Then you don't overcharge it.
2. Lipo must not be discharged under its minimum cell value. It can melt or do something else.....
3. Use something to limit current. LiPo batteries give it and plenty. Our PICAXEs are behind 7805.

http://www.rchobbies.org/lithium_battery_breakthrough.htm

Robots battery pack is 3 cells in series = 11.1 volts.
In the robot we made basic voltage-divider with 08M to monitor the battery and flash leds plus reset 40x1=robot stops. Lowest level is 9.6v and cut...

 

[evanh]

Good to see some people using LiIon's at last. Took a long time for them to catch on it seems. The charger is not that big a deal unless you are pushing them hard, only then does it become a risky business. It's just a simple case of voltage limiting as well as current limiting. No need to look for the delta volts that NiMH chargers have to look for.

As for comparisons, the newer NiMH's are way better now and come pre-charged just to prove the point. They kick-ass for holding their charge. Where as LiIon's are on a downhill slope to poor performance from the day they're made.

There is newer LiIon technologies around also but they aren't readily available. Maybe not working quite up to spec, dunno.


Evan

 

[leftyretro]

Having working some with these batteries in the past (R/C electric planes) my main concern is the over discharging of these kind of cells. It can destroy these cells if you allow them to run down below their lower safe discharge value. Some kind of automatic turn off circuit is recommended for any picaxe application. The ADC features on picaxes is a part of the solution but there needs to be away for the picaxe to cut off the load from the battery.

I've destroyed a couple of these batteries by allowing them to over discharge. Over charging can also lead to dramatic failures but most charging circuits for Li batteries have a means to stop the charging when completed.

Lefty

 

[BeanieBots]

All the warnings as above, but also be careful about the difference between LiPo, LiFe and a few other variants. They have slightly different terminal voltages and charging one type to another's end point can give a whole new meaning to "end point"
Over discharge is fairly harmless, it simply renders the battery useless. However, excessive charging volts causes fire. If you are salvaging batteries from other equipment, check with a calibrated meter what that equipment charges to and then make your own charger do the same.