Charging rates For tx, rx packs

[nellster]

This is a very basic question, but how do you calculate the correct charge/discharge rate for a battery pack.
I have a general idea, which is tried and tested, (no packs killed yet, thanks to DJL Flapper), but I am wondering what is the correct formula. It doesn't matter how many cells you have. Each has a specific voltage and current and therefore the equation is a mulitiple of this.

"Has anyone any ideas!" Nellster....

[uneverno]

hmmm,
While on its suface it appears to be a basic question, like everything else with this hobby, the answer gets complicated.
1st: Are you talking about NiMH's or NiCd's?
2nd: What size batteries - i.e. AA, AAA (designations here in the States, not sure if they're the same in Euro/UK)
3rd: What's the MaH rating of the batteries? This will affect charging times, but not rates so much.

Being a former car guy, I abused my NiCd's fairly routinely, charging them at rates that would horrify fliers. I did the same with my Tx/Rx batteries. This does shorten the usable life of the battery considerably, but "trains" the batteries to charge/discharge quickly which is what you're after in that situation.

With NicD's and NiMH's it's important to remember to cycle them from time to time and discharge them completely so they don't develop memory. They still do, but if you cycle them they do it much more slowly. If you're using them to power the bird itself, this is even more important. If you're flying a gasser, then treat the batteries as nicely as you can, as they're the only thing between you and a runaway bird - failsafe won't work without power...

As for charging rates, I have a computerized charger, so I plug in the # of cells and it does the rest. I can override the computer selected amperage, but unless I'm in a hurry I don't. Esentially, I trust the computer to have better knowledge of the state of my batteries than I do.

The bottom line is slower is better. Faster heats the batteries up, and unless that goes to far, it's not particularly dangerous (notable exception - LiPo's), but the more heat they get, the harder it is on the batteries.

Sorry for the long response, as I said, not necessarily a simple answer.

[hawkman]

I bought a computer type charger a while back....it cost about £100 sterling and its worth every penny....the basic charger I had...and still use...is set at about 10% of the battery capacity...Ni cad batterys that is....this is ok for an overnight charge of some 12 hours.

I got the expensive charger because I got fed up when a nice evening would occur and my batterys were not charged....with the new charger in auto mode the flight pack and radio pack can be good to go in about 1 hr or so....thus giving me plenty of time to go and fly.

I have set the charger up for a larger Ni cad to power the electrics in my gasser heli....the capacity is 2400 mah...all I had to do was select the mah and the battery type...and then the number of cells...the charger keeps this info automatically...its powered off a car battery too...something to do with DC being the ideal supply.

Its worth spending the money on a good charger....if you are serious about the hobby then do take your time choosing....there are chargers that cater for all types of battery....plus you can cycle the battery packs and get an idea of how its holding its charge.

I dont know af any formulae for charging as such.....I just rely on my charger.

Rob

[uneverno]

Originally Posted by hawkman

something to do with DC being the ideal supply.

DC is most definitely the ideal supply. Anything that plugs into the wall converts AC to DC. A DC signature is a straight line. An AC signature is the top or bottom half of a sine wave, in other words a series of humps with gaps in between them where the opposite side of the wave is cut off. Batteries do not like converted AC as it creates electronic (for lack of a better term) friction within the battery causing them to heat up more than would a pure DC supply, thereby shortening their lifespan.

You can get a really clean AC/DC converter, but they cost hundreds of dollars, and the price goes up almost exponentially per additional amp of output required. Why bother (especially just for radio batteries) when a car battery can be had for 30 bucks?

[Daz(DJLFlapper)]

Hello

Idealy a manufacturer will tell you that the battery pack should be trickle charged to gain the highest charge possible. The average trickle charge is 70-90mah that is .70 amp to .90 amp, so for a 700mah pack charged on trickle this would be 10 hours. 10x70= 700.
Of course the bigger the pack mah the bigger the time on trickle charge if your going to do this. However most of us like to have our batteries up and ready for use as quickly as possible without damaging them.

In all the time I have been involved in the hobby the 10 hour rule is what I have followed and it has served me well. Most computerised chargers require you to program a charge current. Now I like to charge at 1amp, But lets say you got a 2200mah pack. You can then safley say that you can set your charge rate to 2.2amps thus giving you by 10= 2200mah. You certainly will not dammage your packs by following this and the packs will charge quickly enough. I have learnt that the higher you set your charge ampage the greater the temp of the pack, Be carefull if the pack gets too hot bring the ampage down.

I have settled on charge rates of 1-1.5 amp I can charge faster but I have never had any reason to do this. Of course this is for NmHi and the odd Nicad packs. I use the exellant Cellpro 4s charger for my Li/Po packs and its great just plug in and it does it all for me, No settings.

Anyone else got a meathod?

[nellster]

I've had a little look around the web just to clear-up things in my mind. There is a site that gives all the info on batterys, from design use and charging. Lots of useful info like, an AA nimh internal pressure can exceed 100psi if you overcharge by 20%. Thats nice to know!!

www.batteryuniversity.com

Nellster