I just upgraded the battery for my Rx. I went from 600mAh to 1200mAh and I want to know for how long should I charge this new pack with my stock charger. From what I can figure, it must have to be twice the time I used to charge the 600mAh one, right?

Multiply the capacity by 1.4, then divide by the output rate of your charger.

Assuming your charger is similar to what comes with a Futaba radio (charges Rx at 100mah), you would have:

(1200mah x 1.4) / 100mah = 16.8 hours

This is the time for a full charge from "dead" battery.

Where does the 1.4 come from? I got the battery today but I plan on using it a week from now, is it ok to leave it uncharged until then?

When I was soldering the leads I provoked a brief short on the battery, perhaps about 1 second long, is this a problem?

G'day Mate,
The 1.4 come from the fact that you need to put 140% in to get 100% out, see here.
http://members.aol.com/davthacker/balancecharging.htm
There are always losses, & this figure allows for that.

Yeah. Loses come from heating mostly, so you need more than 100% to charge a battery.

It is still a subjective value.
Slow charging does not produce as much loss from heat and most batteries are never completely dead when you start either.
On the plus side, if you slow charge at below C/10 you really don't have to worry about over charging.
I do like to cycle my batteries at least once a year to make sure they are still getting the rated capacity and condition them for the season.

About the short I caused? Anyone can tell me if its gonna be a problem?

Noone will have a clue how badly you shorted it.

You can easily tell for yourself by checking it's voltage with an ESV. And you should already have one if you plan to fly safely.

http://www3.towerhobbies.com/cgi-bin...&I=LXWW16&P=ML

I lasted about one second and the battery still works, moves the servos, etc.

It is unlikely that the short hurt your battery. As long as it did not burn off any insulation from the leads or on the jumpers between cells, likely no damage. Check out www.rcbatteryclinic.com for some good advice on the care of your batteries. On the nickle based ones (NiCad and NiMh) the batteries will benefit from a forming charge which is defined as a charge at 0.1C for 16 hours. It may take two or three cycles of this forming charge (discharge at not greater than 0.25C down to 0.9 volts/cell between charges) to bring them up to full capacity.

If you left it some seconds like this, then it going to be a problem soon or later. The short is like discharging in many many many Ampers. Good luck with that. I shorted too a few batteries and it was really awful Oh man, you should have seen that smoke coming out of the battery, it was like a smoke bomb

Now about the charging time, i trust NiCD since in their charge when the battery is on the limit, it produces a little heat but the charger (if it's good) cut off the power supply because the NiCD giving a "V" (you must read a whole article about that. It's whjen the battery's voltage is on the limit and instantly that time, the voltage drops a little, so the charger says READY and the charger cut off). The NiMH are a bit different. The charger doing a whole equation to stop the charging. The NiMH are not giving the "V" as the NiCDs, but like a "U" only widther, so the battery overcharges a little bit more than the NiCDs. About LiPOs, i don't want to use them yet. They are freaky dangerous!!!

This was for just a brief second, the the cable didn't even get hot. I assume that it was no big deal.

I really think it's no big deal.

Hell, I shorted out a LIPO for around a second and that still works great. I don't think you harmed your battery at all.

The cables might have bigger diameter than the installation needs. Always, check the battery's temp if you do something bad, not the cables. Tha cables might leave but the battery not, i've seen it a lot of times, not necesarily with RC stuff but i saw it.

The reason why shorting is so bad is because of the high current. This is hard on the wire AND battery. Ohm's law states that Voltage = Current x Resistance (V=IR). With a little middle school algebra we can see that I=V/R. In a short, the only resistance is that of the wire (and in some cases impedance, but we'll forget about that for simplicity), which is extremely small. 23AWG wire has a resistance of well under one ohm in 6" of wire.

I = V/0.2

You can see how large currents can get with that extremely small resistance value. Considering that 23AWG wire has a max current carrying capacity of 4.7A you can see why it will heat up quickly and be destroyed. This current draw is also hard on the battery itself since current in a short can quickly become well over the battery max current load. That being said, if this was only for a second you are likely fine. Cycle the battery a few times to make sure it's still good and count your lucky stars.

I don't know the specific diemeter of the cable, so i was speaking general. But if the cable's diameter is too small, say 1.5~3mm, sure the cable will work like a resistance, and the battery will giving all that energy to that small cable untill it cuts, so no current pass through it. You think that the battery it will be like the old one, right? You are wrong. There is inside damage in that battery now that it will never be like before. Of course, i don't wanna scare you man, the battery's damage is very low to affect your flight, don't worry.

Also, hey Nathan King, what is your profession? Aouuuuuu [>:] (from the 300 (spartans)) Just kidding Really, what is your profession? [8D]

I am in college finishing up an aviation degree and do electronics repair work to fund the hobby.

I've been to Paphos, Cyprus. My father traveled a lot for business and took me once. It's a beautiful place. It's interesting how linked to Greek mythology that area is - even the name Paphos comes from Paphos, the daughter of Venus. I saw the Petra Tou Romiou, which was breathtakingly beautiful, but I was stuck in the hotel most of the time. []

In most cases, regardless of type of battery, a momentary short will do little or no damage. It is simply a matter of physics, heat is created when a high current passes through any resistance and it is the heat that does the damage. If the current is not so great that it raises the temperature of the conducting media (usually the smaller interconnections between cells on the battery or the external leads themselves) raises above the point where the materieal changes state (melts or burns) little or no damage is done.

Plus that Paphos is the most calm place in Cyprus. The other cities are freakin scaries sometimes. We have some "episodes" you see