Moving to Lithium

[PJ-27]

Bitza needs new batteries as the old ones are dead but given that Lithium batteries are becoming more and more reasonably priced, most chargers that do enough NiMH cells also do Lithium and the 40% discount from FlightPower they may be an option.

Never used Lithium before though, so could do with some noob advise!

In terms of NiMH we would get 2 x 9.6v packs at over 3000mah, what would the equivalent be in Lithium?

Would we require the same voltage / mah?

What are the general advantages / disadvantages of Lithium?

Considering I could get the NiMH option for about £35 how big is the price gap?

Just to confirm are the cells 3.3v?

Cheers!

[gizz]

Re: Moving to Lithium

An advantage is the possibility to draw high amounts of current from the cells, 50C on some cells spring to mind, low weight/ capacity, the voltage stays roughly the same untill it's nearing empty when it dips faster.
The disadvantage is the need for specific chargers but then again most chargers today can charage both li and nimh/cd.
The biggest disadvantage when comes to lithium is that they are very sensitive when it comes to overcharging or draining them too much aswell as they are quite fragile. I'm, generally speaking about LiPo's as im unsure about LiFe.

A fully charged cell of LiPo is 4,2V but generally specified as 3,7v / cell.

A 5p Lipo is at 21v, 4p at 16,8v fully charged. There are packs with roughly 3000 mAh aswell which should be enough

[robotic_ants]

Re: Moving to Lithium

Not suprised FlightPower is giving away a 40% discount, they haven't got great reviews on rc froums.

[PJ-27]

Re: Moving to Lithium

Thanks for the help.

I like the look of this;

http://www.flightpower.co.uk/index.php? ... cts_id=150

With the discount it's quite a good price.

[mattsdragons]

Re: Moving to Lithium

lithium batteries are very good yet what puts me off them is the sensitivity and they seem to like catching fire and exploding... NIMH's FOR ME!!!!!!!!!!!

[team_orr]

Re: Moving to Lithium

also remember that with Lipo's and stuff you need special charging and safety equipment, i seem to remember last time i checked that you needed to bring a special bag to charge them in, salt in case it catches fire and other such things, however i only use Lipo in antweights so you might want to check that in the rules, even in antweights i have seen some nasty incidents with lipos so be careful. Not to put you off though, as there are many benefits as well, just take it easy :wink:

Jack

[jonny]

Re: Moving to Lithium

almost the same as that flightpower but better:

http://www.hobbyking.com/hobbyking/stor ... duct=16485

[maddox10]

Re: Moving to Lithium

Depends on what you want from the Lithium packs.

But if you go for Lipo, make sure the speedo has a good low voltage cut-off. (some advice a cut-off at 80% of the capacity)

Draining them below a certain voltage that combined with our wish to charge as fast as possible can be devastating.

LiFepo4 (A123) is less prone to dangerous charge/discharge mishaps, but ain't invurnable either.

[typhoon_driver]

Re: Moving to Lithium

You will need a charger that can charge lipo cells along with a method of balancing them whilst charging. A lipo sack can be picked up for under a tenner on ebay. Lipo cells only explode if you mistreat them which would probably damage nimh cells anyway if treated in the same way.

I don't bother with a voltage cut off in boner (although there is one in the brushless esc). Easiest way to make sure over discharge is never a problem is to overspec the pack. A 3Ah lipo pack with 5 cells would do exactly what you are after and would discharge very little from just two drill motors.

The other important thing with lipo cells is that they have to be removable for charging purposes (it's in the rules) and they should be full enclosed as being punctured is what is likely to set them off. You need to put a fuse in line with the lipo pack as well which is just lower than the short current from the pack.

A123s will do the job happily for Bitza as well but if you are planning anything high powered in the future then you might as well jump on the lipo bandwagon.

Add me on msn xzibit206 'at' hotmail.com if you want to talk in more detail.

[mattsdragons]

Re: Moving to Lithium

You will need a charger that can charge lipo cells along with a method of balancing them whilst charging. A lipo sack can be picked up for under a tenner on ebay. Lipo cells only explode if you mistreat them which would probably damage nimh cells anyway if treated in the same way.

I don't bother with a voltage cut off in boner (although there is one in the brushless esc). Easiest way to make sure over discharge is never a problem is to overspec the pack. A 3Ah lipo pack with 5 cells would do exactly what you are after and would discharge very little from just two drill motors.

The other important thing with lipo cells is that they have to be removable for charging purposes (it's in the rules) and they should be full enclosed as being punctured is what is likely to set them off. You need to put a fuse in line with the lipo pack as well which is just lower than the short current from the pack.

A123s will do the job happily for Bitza as well but if you are planning anything high powered in the future then you might as well jump on the lipo bandwagon.

Add me on msn xzibit206 'at' hotmail.com if you want to talk in more detail.

i thought that was the same with all batteries?

[psychostorm]

Re: Moving to Lithium

I thought that was the same with all batteries?

Not a written rule, more of an unwritten rule. It's listed in many a battlebots build guide to make batteries removable within 1 minute.

[mattsdragons]

Re: Moving to Lithium

so they can be left in if you please? but its better if you remove them since if they catch fire, its only the batteries what will go and nothing else inside your bot?

[typhoon_driver]

Re: Moving to Lithium

7.8.5 Inspection
LiPo batteries must be removed from the robot, inspected and placed into a LiPo sack prior to and during
the charging process.

It's a written rule.

[psychostorm]

Re: Moving to Lithium

so they can be left in if you please? but its better if you remove them since if they catch fire, its only the batteries what will go and nothing else inside your bot?

Allow me to clarify:
All Lithium batteries have to removable, as stipulated by the FRA rules.
All non-lithium batteries can be charged in the machine , but is advised to be removable for precisely that reason.

[robotic_ants]

Re: Moving to Lithium

What sort of Ah would you need for a big spinner like LS4 or Buzzbar? Still not confident what size of LiPo to go for.