Charging Lipo batteries

[Scooperman]

Sorry if this is answered elsewhere but I couldn't find it.
My son is upgrading his antweight as it is his birthday soon and we will be using Lipo batteries. I notice that I need a charger and Power Unit. I have gone onto Maplin's website http://www.maplin.co.uk/Module.aspx?moduleno=231 and there are several power units. Which one do I need to get? Also, I am looking at the following charger http://www.technobots.co.uk/acatalog/Sh ... 1072_2d001 I asume that this is OK.

Finally, I have some Lipo batteries, not sure if they are good enough. Where can I get more and what do I need exactly.

As you can see my son and I are not experts in any sense of the word.

Thanks

[bitternboy]

Both of these (the 3A unit) are my charging gear of choice and they work swell. Pretty much any form of lipo would work with them I would have thought so this gets a thumbs up from me.

[Scooperman]

Thanks, looks like I'll go with these

[BeligerAnt]

For LiPo batteries, you need to decide between 2-cell (7.4V) or 3-cell (11.1V) packs, the capacity and discharge rate that you need.

2-cell packs are perfectly fine for most applications. I would count 3-cell packs as fairly "specialist" for antweights.

Discharge rate is usually quoted as 15C or 20C, meaning that the peak discharge rate is 15 (or 20) times the charge capacity. So a 300mAh pack rated at 20C is good for up to 6A. For antweights it's not usually a problem unless you use very small batteries that are only rated to 10C. These days most batteries are rated to at least 15C, often more.

As for capacity, up to 300mAh is suitable. You can get away with down to 120mAh if you are stuck for weight or size, but the run time is shorter (and see dischrage rate above).

If you are using a speed controller for motors, try to find one with an automatic cutoff when the battery voltage drops below 5V. LiPos are irreversibly damaged when discharged below 2.5V per cell.

Handle LiPos (any batteries in fact) with care as they can and do burst into flames if short-circuited or over-charged.
Do not charge them in the robot, in case a charger fault destroys your robot!

One possible source of LiPo battery packs that I have used recently:
http://robotbirds.com/catalog/index.php?cPath=63_263

[Scooperman]

Thanks for all that info. I just went on the robotbirds site, but am not too certain as to which battery would be best for my antweight. Could you give me some ideas, there are some very light ones, but they are also a lot cheaper - are they the ones or should I go for a heavier one? also how many cells and capacity?

Thank you

[BeligerAnt]

What motors/servos are you using for drive, and what motors/servos do you have for weapons?
These will determine the amount of power you need.

However, all our robots, running Technobots 12mm gearmotors (or similar) for drive and HPFX/HS-81MG servo flippers or 18mm brushless motor spiners run happily on 2-cell 250mAh LiPo packs, Hyperion brand from Robotbirds. (See link above)

RONNY is a bit strapped for spare weight so uses two of the single-cell 120mAh LiPos soldered into a 2-cell pack. Running time is still OK for competitions and weight is significantly less.

[Scooperman]

Would that be this one http://robotbirds.com/catalog/product_i ... ts_id=4055?

I will be running 2 100:1 Micro Metal Gearmotors and a servo powered flipper, probably.

[BeligerAnt]

Yes, that's the one. Take care of them and they should last a fair while. Usually damage is caused by over-discharge. Do not discharge them below 5V (2.5V/cell). Check whether your speed controller automatically cuts out at 5V or not.