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I am confused about how to use LiPo batteries

Hi all,

I am currently working on a new robot and I will soon have to choose a way to feed it with power.

I've been reading about LiPo batteries, but I am still confused about how to integrate this kind of power supply in a robot. Here are a few questions I have in mind :

  • Can I use a LiPo batterie exactly like a standard NiMH batteries ? (guess not, because of the discharge limit). For instance, can use one of OddBot's configurations for voltage regulation (http://letsmakerobots.com/node/3880) directly with a LiPo battery ?
  • I read about ESC, BEC etc. Is a mandatory component to integrate with LiPos or it is just needed to create PWM signals to motors ?
  • Is there a simple way to prevent a LiPo battery to go under the discharge limit ? (zener diode ?)
  • Oh yeah, important one : to your opinion, is it worth it to use LiPo on a classic robot (with wheels or tracks, and DC/Servos motors)

Thanks for reading :)

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Korel's picture

Same for me,I realy appreciate educative comments from you guys. I was also questionning myself about those Lipos. Thanks for your advices guys and  for asking LordGG. :)

LordGG's picture

Thank you guys for your wise and helpful advices ! It is much clearer to me now :)

I'll probably follow fritsl advice for this robot, it already involves enough new technical skills to me (Xbee, comm between picaxes etc.), no need to add more complexity for now !

But I will definitely look into those batteries later, they look pretty cool :)

Thx !

JAX's picture

Smaller and lighter than the equivalent NiMH battery, but they're more finicky about charging. It definitely takes a real charger; you can't just do a C/10 charge rate. Get a balance charger if you're going to use 7.4V or 11.1V packs. They can be had for cheap:

Mystery 2 and 3 Cell LiPO charger: $8.60

Pair that with a 12V 1.5A wall wart and you're in business.

There are cheap Lipo monitors for <$10 or you can build one on the cheap:

 

JAX's picture

bah

hardmouse's picture

Love LiPOs, small size huge power. However, you need to treat them nicely. GOOD charger is a must. I have use Lipo in most of my robots. Personally, I like to keep battery fully charged and have "low voltage indicator" to check them when you don't use them for while. It's a bit tricky to recharge LIPO when they ran out of power.

If you have servos in your robot, I suggest you could use BEC if you are not so sure how to reduce voltage to 6V. I am not professional in here and also not very knowledge in this field but just accroding to my past experience, that's how I learned. There are 14 servos running on following robot with single 2S Lipo and I use that "UBEC". So far it works fine(except my poor code not working well :P)

Becareful thou, I was stupid enough to try to poke a whole on one of the LiPO and it smokes and burned!

MarkusB's picture

I've used Li-Po's many times without any problems, but Gareth is right: Buy good batteries, a good charger and use a voltage monitor (every LiPo has a 3 pin connector for charging and plugging in a voltage monitor). Voltage monitor can be simply a voltage divider, connected to your ADC. If the voltage drops under a given level, a power MOSFET (N channel) will switch off the power supply.

Gareth's picture

I use a lot of Lipos and the number one rule i apply is simply to include a fuse for the max current you expect your circuit to use.

Lipos will supply enormous amounts of current (so stalling a motor for instance can be fatal for the motor or the fets driving them).

I have blown many a circuit - more often or not copper circuit tracks just vaporise into thin air.

ESC_s  give you the opportunity to control a motor (  via PWM  at amazing currents ) and most have a BEC (Battery Elimination Circuit) output for driving 3 to 5 servos.  However problem is motor will only drive in one direction (ie aeroplane types). (you can get dual direction versions ie model cars types).

I use battery monitors "now", small circuit that attaches to the lipo  (they screech a sound and flash leds) as protection for under voltage - if you buy cheap lipos then driving them to low voltages is fatal (ive killed 3 cheap lipos this way)

I also have tiny lipos "postage stamp" size 100MAhr and they are enough to easily power Atmel and Propellor circuits

Ending Note:- Lipos are the best - however treat them with respect. and buy yourself a "GOOD" lipo charger.

fritsl's picture

I can answer the last one: "is it worth it to use LiPo on a classic robot (with wheels or tracks, and DC/Servos motors)": No :)

I freakin love LiPo's, have some the size of wall bricks that can zapp enormous amounts of electric stuff, drive a car and all.. an I have the tinyest light weight, that can still pack an impressive punch! They are COOL!

But all that special charging and do-not-discharge-completely does not at all add up fr the punch you get - when you just need to drive around :)

I can recomend "ordiniary RC packs" 7.2V. These are very very powerful, they weigh a lot compared, but one of these with a 5V regulator, and your robot will drive for ever, ever, ever!! And they are easy to charge/recharge.

I am not saying there is anything wrong with LiPo's, not at all, but if you are starting, you will have enough to think about, and there a standard RC pack is your solid friend - you will not have to think about that part :)

Or just do normal AA's / rechargables, they work wonders :)