Power Issues

For a while now ThunderChild has been having issues with its 3 8cell 3000mah A123 battery packs' 1 of which blew at maidstone.
Its a been such an issue' that we're now considering replacing them completely' ether with 2 of these
http://www.robotmarketplace.com/prod...-4600N-24.html

or modifying 3 of these http://www.stuff-uk.net/p-396465.asp...FQjgGwodMzEIaw

I welcome your feedback

Optipower lipo all the way ceros runs 2x5000mah 30c they have been faultless not to expensive with discount. Just my thoughts

Agreed, go to Lipos, ideally Optipower. Dont waste your time/money on Nimh or drill packs, they just wont supply the current needed. Stick a pair of lipos in it, but not cheap ones.

You will also need a proper charger to go with the LiPo's. You can't just charge them with anything. Turnigy Accucell 6 will do the trick, just make sure you use the right settings.

I have recently gone over to LiPo batteries too. for Cherub and Gabriel, (the ones previously suggested) and I have to say they do work well I use a large two channel charger,
http://hobbyking.com/hobbyking/store...ger_800W_.html
It will charge the two packs at 15A each but dose require a power supply that can deliver 75A to power it!
I called it Brutus the battery charger. :)
I do have to say these batteries must be handled with extreme care, as the potential power stored, and chemicals used in them, means they can present a real hazard to yours and others health.
But they are good.

Some more things to know about swapping to Lipo packs:

They can supply WAY more current with less voltage sag than NiMH or even A123 packs, so you might find your ESCs or motors get hotter than before. Batteries used to be the weak link in the system but now they will happily fry your other components if they are under spec for the job.

Lipo packs do not like to be fully discharged and most people recommend leaving 20% charge in them. Fully discharging them can damage cells and in extreme cases, cause a fire.

Use the space and weight saving to add shock protection around the Lipo packs. The foam in exercise mats does a good job.

Using high discharge packs is a smart idea, even if you don't need the current rating. High current packs in the 50C to 65C range have lower internal resistance and don't get as hot. This means they can be recharged sooner (its dangerous to recharge Lipo when hot) and you can usually charge them at higher current. My 4.25AH packs are OK to recharge at 8C, which is 34 amps, very handy when you have back-to-back finals matches.

While everyone loves their Optipower packs, I have been very happy with my Turnigy nano-tech A-SPEC packs. They have performed flawlessly for the last two years and while they might not be quite as good as name brand packs, they are much cheaper.

What about these? http://www.hobbyking.co.uk/hobbyking...Lipo_Pack.html

5800mAh 25C = 145A.
On the low side for a heavy without active electric weapon.

But with a large gearratio to a decent motor for drive, fine.

Two in parallel might be more suitable, but would need careful balancing...

The balancing is mandatory. And the easier way is to recharge and balance in 1 go, as the most chargers are equiped with a balancing port.

Also, the 7S pack as example is annyoing in that respect , most affordable chargers have a 6S limit.
It's easier and probably cheaper to use 4 4000 mAh 4S 25C packs, 2 in series to create an 8S (+/-30V) block and 2 of those in parallel. Creating an 8S 8000mAh battery.

Balancing on every charge is not mandatory from a chemical standpoint (though FRA rules seem to disagree), but it does help to keep your lipos in the best condition. What is done often is use charge only at events, balance charge when coming back home. Most events you won't need to charge more that 6-8 times if you run on one set, so if you have 2 sets that even halfs it. If your cells get so out of whack within so few charges that they need a balance you need to take a serious look at that pack.

Investing in a charger with a proper balancing function that adds charge to cells lacking behind instead of overcharging and discharging those ahead ( which is what cheaper chargers do) is worth considering if you charge and balance at events, but if you have time to spare at home the cheaper balancers will work reasonably well.

A bit if theory on balance charging and how cheap chargers work:

https://youtu.be/wIbHLacozFo?t=6m10s
go to 6:10 for the interesting stuff.

Most new chargers always do a proper charge & balance by default. My Bantam chargers have a fast charge option but that still balances and saves time by only charging up to 95%. I can't see the logic in trying to save time by not balancing - get a charger that puts out enough current to charge your packs quickly and balance every time so the cells never get far out of balance in the first place, so the problem mentioned in the video never happens.

With cheap chargers this problem always occurs. You overcharge and discharge so effectively you keep abusing those cells that got to their end charge quicker. By charging to 95% you avoid the issue all together but then I see no point in balancing as you don't overcharge anyway.

For the record, I don't advocate to never balance, just that balancing with cheap balancers every single time is not making the packs last much longer than charging every time and balancing once in a while.

For best results and longest lasting packs, get a more elaborate charger or charge the cells individually.

My point was "Don't buy a cheap charger" :). If you had a cell go bad during an event and charged without balancing, the remaining good cells would get seriously over charged and risk a fire. The point with the fast charge option is that the last few percent charge is always at a very low current, so you have to wait a lot longer for just a small amount of extra charge.

Then we agree. :) As a rule I check my packs with a lipo checker before putting them on a charger in case one cell is dead or damaged. If so, then I don't even bother with charging.

My actual point was that if you're running 2 or more packs in parallel, you need to make sure the the packs are charged to the same voltage before connecting them up, else they can self balance the voltage between them rather rapidly. I wasn't talking about balancing in the usual sense of balancing the individual cells in the pack

I have 2 nearly new Lipo packs for sale as I bought the wrong voltage :-(
They are optipower 6cell 100c packs I'm open to offers and will be taking them to next event.