Charging Rx and TX batteries

[BernietheBolt]

Hi all 'Again', I know I am probably pushing my luck by asking for more advice so soon but is it possible to overcharge a Rx or Tx battery when using a JP Nicd mains charger. Mine is a two output type ABCN 174 BU and charges at a rate of 70 mA for my 9.6v Tx and 120 mA for my 4,8v RX

Some of my fellow club members say they leave theirs on overnight or evn longer but are a bit vague when it comes to giving me a definite answer to this question. ie can you leave the batteries on charge all the time, like you can with some tool batteries or must you disconnect as soon as the Led charge indicators go out. Any advice will be appreciated.

[Raptorite]

Hi Bernie,

Whilst I am not overly familiar with the JP chargers, I do believe they come equipped with a cut off circuit, which means that as and when the batteries become fully charged, the charger automatically stops charging. This would appear to be borm out with your statement that the LED's go off.

I personally use futaba chargers on my gear, more often than not I put the gear on charge the afternoon or evening of the day before I am going flying. I have in the past forgotten to take them off charge for a couple of days, particulalrly when the weather has been bad and I haven't been able to get out to the field.

To work out how long it should take to charge a pack from flat, devide the pack size in mah by the charge rate of the charger, so in the case of a 2400mah receiver pack being charged on a 120mah charger, it will take 20 hours to charge from flat. The best you will be able to do is a "best guess" as this calculation doesn't take into account any residual charge remaining in the pack before it is put on charge. Normally speaking, an overnight charge of say 12 to 14 hours is more than enough to fully charge a 2400mah pack on a 120mah charger, as the pack will inevitably have some sort of residual charge.

I hope this helps.

Cheers,
Pete.

[antsis]

Bernie

Pete's right. Many supplied chargers have a current sensing circuit, but many don't. The fact that their charge rate is relatively low allows the pack to be left on for longer than normal without necessarily causing any harm.(although I'm not saying non will be caused)

Most modellers charge their batteries for 12-14 hours. The correct way to work out the charge time is to take the battery capacity and add 20%. Then divide this by the charge rate. e.g. 700mA pack + 20% = 840mA. If your charger is rated at 70mA, then 840/70 = 12 hours.

However, this is not exactly true unless the pack is fully discharged, but in general, is the usual practice. Of course, if you buy a pack with a higher capacity, then the charging time increases.

[BernietheBolt]

charging Rx and Tx batteries

Many thanks both of you. Obviously from what you say, neither of you are not exactly sure whether you can leave them on charge indefinitely, so I phoned JP who confirmed that :- The charger does not have an automatic cut out and the LED's do not go out when the batteries are fully charged. They are lit purely to show charging is taking place.

They suggested that I should always ascertain the approximate state of charge of the battery and as you suggested, calculate approximately the time it will take to fully charge it . There would be no harm done by leaving it on charge beyond that for a reasonably short period but certainly not for much longer periods which I have been doing.

PS I appreciate I should have contacted JP before posting but I did so some time ago when I first used the charger and either I did not ask the right questions or I misunderstood what they told me but I got the impression the charger had a safety cut out which I took to mean it could not overcharge a battery whereas I now know the safety cut out protects the charger and not the battery.

Bernie

[Dedcalm]

If you take one of the standard 2 output chargers apart (I did with a faulty Futaba unit) you will see that it is essentially just a transformer coil with 2 taps off (9.6v and 4.8v) and a simple bridge rectifier. There is certianly no inteligence built in.

I bought myself a Mercury EX charger last year and would certainly recommend the expense of a good charger. Allows you to keep batteries in tip top condition.

Rob

[BernietheBolt]

Tx and Rx charging

Hi Rob. Now I know the JR mains charger is a bit of a hit and miss affair, I intend to get myself a decent digital one with auto cut out etc, as soon as I stop forking out for crash repair which probably means I'll never likely own one!!

Bernie

[Dedcalm]

I found my main problem was that batteries were not lasting as long as I expected, including a good quality high capacity pack I had for the heli.
Once I had the Mercury EX I tested the packs and their capacity was abotu 50% of what they should have been. Guess the old charger was not doing them any good.

Now I can charge any size pack (within reason) correctly and know that it is being monitored by the charger. Also cycling etc is now a simple couple of buttons to sort out.

Good luck with the flying, wish I could find time to do some myself

Rob