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Asked — Edited

Lipo Batteries

I finally decided on the battery to power my build (5000mAh Turnigy LiPo) but since ordering it I've read a lot of disturbing information on these... i.e. they can catch on fire very easily

Is it a bad idea to use it in my build if eventually I will be making it unattended and programmed to recharge itself once it get's low on power?

Obviously a melted robot is not a good thing but more worrying is the house it's roaming around!..

Any advice on this is very much appreciated.

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I use Lipo's in my bots, use proper precautions, fuse all your batteries and if you are going to use a self recharge be sure to also use a good lipo charger with auto shut-off and balancing features.

Another good item might be a recharge bad for lipo's left on permanently while in the bot.

Lipo's can be dangerous but so can every other battery out there if miss handled.

A good alternative to the Lipo is the LiFe batteries check them out.
United Kingdom
I had thought about using a bag as a precaution but from what you have said, it sounds like what I've read is a lot of paranoia.

I have a Turnigy charger which has auto shut off and balancing which is small enough to fit in the bot so all the home base would need is the 12v barrel jack. That side of things is a while away yet but wanted to make sure I have everything I need.

Thanks for the advice.
United Kingdom
Right I now have two LiPo chargers, the Turnigy 12v 2s/3s charger mentioned before (ideal choice for install inside the bot) and picked up an Imax B6 for cheap too.

The Imax B6 bas banana plugs for the battery and the balance port but the Turnigy only has balance port. Is it safe to charge through the balance port?

Ideally what I want to do is fit the Turnigy charger inside the robot, connected to the balance plug on the battery. The batteries +Ve and -Ve wires connected to the EZB and Hbridge and then just charge though the barrel jack (which will be extended to the one on the back of the omnibot torso).

I just don't want to get this wrong. Call me paranoid, or it may be from watching a bunch of videos on youtube earlier where lipos caught fire...
I would only charge thru the balance port it keeps the batteries, well , balanced.

If 1 cell drops below the other and gets to low it will die and you loose the whole battery.

IE: you have a 3 cell battery at 11.1 volts, you use it on something that needs 5 volts so you run it thru a BEC that supplies 5 volts, so your device is happily running along at 5 volts BUT because your batteries aren't balanced equally 1 cell or more can drop below the danger point but your BEC can still supply 5 volts.

each cell provides 3.7 volts when balanced

if 2 cells are providing 3.7 volts and 1 providing 2.2 volts your device will still work great but as the voltage drops across all cells usually equally as soon as you say drop 1 volt per cell

2 at 2.7 volts
1 at 1.2 volts

you still have enough power for the BEC (( 2x2.7)+1.2=6.6) but that low cell is now toast and probably won't recover.

I never let my lipo cells drop below 2.2 volts , I have lipo's over 1 year old working perfectly and always charged with a max of 1 amp with auto amperage control.

This may help or confuse but keep those batteries balanced always if you want them to last.

Dave V.
United Kingdom
Your first sentence was all I needed to read:) (the rest is a bonus).

It's what I thought after doing a lot of reading this evening anyway but I always like to get these things confirmed.

Not sure what the Turnigy 2S/3S balance charger charges at, it come with no instructions but google will help me there.

I have a voltage monitor too which I can set to go to alarm if it drops below a set voltage which I will be using. I also want to use one (or two) of the ADC ports to monitor the voltage within ARC to trigger the return to base/auto charge function I plan on attempting.

That's a great help, it's very much appreciated. Next I just need to see how to use two (or more, these things are tiny and light compared to the old SLA I was running!) LiPos in parallel and charge all at the same time... 20000mAh will easily fit in the Omnibot torso and I'm guessing will only weigh as much as the old 6v 4Ah sealed lead acid that was in there...
@richmr2: use them, theyre totally worth it. I'm using a 2 cell 750mah li-po in my humanoid, they're waaay better than the ni-mh batteries that came with it. The only real danger is improper charging. I use a 1 cell charger to charge the cells individually, then I check them with a voltmeter. Because of that, my cells stay within a hundredth of a volt of eachother. I've never popped one, and you won't either if you keep them balanced :D

@putt putt: I wouldn't take them below 3 volts per cell. Hell, once they get below 3.3v, they start dropping voltage fast....the documentation for all the thunder power and turnigy packs I've had warns that anything below 2.5v per cell causes permanent damage. Of course, that's li-pos, not li-fe packs. I'm guessing damage just means reduced capacity....that would suck have a 3 cell pack with varying capacities for each cell....
what about Lithium Ion (LiON)
I use surplus LI-ion cell phone batteries in whatever series/parallel arrangement is needed for an application. What's nice is that each pack has its own power control board that prevents both overcharging as well as discharging too low. I use iRobot Roomba power supplies to charge them.
United Kingdom
@Kenny, I am sold on LiPos for the build now. I have one 5000mAh 7.4v pack although, depending on budget and space, this may be increased to two or more.

Charging wise I've figured it out now which is great and will work very well with my planned charging station/home base.

However, I also have a LiPo balance port voltage tester which I want to build in to the robot, it's just one of the common 7 segment display types that you plug in to the balance port, but I don't know if it's safe to cut this in to the balance port wiring and have it connected whilst charging, does anyone know if that would pose a problem?

I also thought about using the balance port wiring to go on to two of the ADC ports (2 cell battery) so ARC can monitor each of the cells too, again something I could do with a little advice, or confirmation on.
@Robot-Doc I am really interrested in your re-use of cellphone LiON batteries.
How do you connect them to the ezb (there is 3 connectors on the battery and ezb needs 2 wires: + & -). Could you post a picture of the assembly? Thank you very much.
I use a LiPo 7.4v 1500mAh. This battery was used RC helico (crashed!). Works great on my robot.
@fredebec You only need the (+) and (-) connection, The third connection is not used. Connect as many cells as you require then use a 2.1mm plug and wire the output from your assembled LI-ion pack to then connect to your EZ-B.
Thanks Robot-Doc. Is it possible to use different models of cells simultaneously (all my cells are 3.7V, but go from 1200mAh to 1500mAh)?