12v 7.2ah

[paul (dig-it-up)]

hi just a quick question on charging those pb 12v 7.2ah batterys. i have a imax b6 charger just wondering how much amps i could put safely through the battery as i think these batterys need a slow charge at least 22 hours on a trickle /or can i up the amps to about 5 or more for a  quick  charge? any ideas  dont want to blow my shed up lol cheers

[Klippy]

Hi Paul, they'll take .1C quite happily, but .5amp to be safe. The trick is not to let the voltage go over 14Volts, once again, to be safe I use 13.8volts. If you go over voltage or over current you fry the gel inside and they die! Then you cut the lugs off and use them as weights in the shed!

[paul (dig-it-up)]

ok cheers tony. thanks for the info m8

[Wingman]

Paul, You can buy an automatic plugtop type charger for those for about £12 and there's no risk of boiling the battery - I leave mine connected to the battery all year round so the battery is always ready to go. 

[paul (dig-it-up)]

thats a good idea wingman were do you by them from ?

[Wingman]

I got mine from my local hardware shop but a quick google brought up this
 gell cell charger for £14.20

Edited By Wingman on 19/04/2010 18:28:39

[Peter Beeney]

   Recently there was a similar sort of thread, entitled Charging 12V Power Panel Battery, by Ian W. At the time I made a contribution to the general theme. This was concerned with the actual construction of the flight box, as apposed to the battery charging. With respect, I wondered if it may be worth repeating here, but just simply as an ‘add on’.
   You may, of course, feel that these precautions are unnecessary, and that fine, however there are a very small number of incidents with modellers batteries, which in general seem to become highlighted. The first paragraph was related to the question of using the engine starter connection plugs for charging.

   This is what I posted. ----

     One way of ensuring at at least a degree of safety in charging your 12V battery is to have a dedicated input socket on the flight box and the appropriate plug on the charger leads. One reason for this is that, if the starter uses two 4 mm plugs, sooner or later you will connect them, (the charger leads), the wrong way round. When this happens, any reversed bias diodes in the charger then become forward biased. It’s then possible that the circuit impedance may become very low, which might then make the term ‘hot wiring‘ quite obvious.
    Run a separate pair of wires internally in the flight box from the socket to the battery, and on the positive leg, as near to the terminal as you can, fit an in-line fuse holder. The type designed for the continental automotive fuses are good. Put a 10 or 16A fuse in this. The reason for this is to protect the wiring in the event of a short circuit occurring in the charger. The relatively heavy fuse rating will carry any normal current. If a short circuit happens the impedance will undoubtedly be low enough to allow the instantaneous fault current to be at least towards the hundreds of amps, rupturing the fuse very quickly indeed.
    This would be normal practise in the full-size electrical world, but there are exceptions and I have seen evidence of this. Modelling wise, recently a friend and fellow club member was charging his 12V flight box indoors. He was alerted, after about a couple of hours, by a smoke alarm. I have the photographic evidence of the carnage caused, and copies of the letters I wrote to the manufacturer concerning this, all without any replies, as always, I might add. The problem was simply the very poor standard of construction, and the quality of some of the components, of the charger, which had resulted in a short circuit and the resultant very heavy current catching the charging lead alight. And his carpet. As he said, had he been out at the time, he could have so easily have come home to find it all a smouldering heap of rubble! At the time he was, to say the least, a bit shaken; as you can imagine!
    If you wire up any secondary battery, it’s always a good idea to fit a fuse to cover the wires. They can be, in these extreme circumstances, a fire hazard. That’s why you have the diode in the tx charging circuit. Even these batteries, in the right conditions, might easily be capable of setting those lightweight wires on fire. This would be very unusual, but not impossible. My MPX tx has a 2A fuse in the charging circuit, not to protect the battery, to protect the wiring.
    Please, on no account consider this to be any sort of scare story. It’s just what I see as good working practise. I don’t normally lecture on these things but here I see this as a little safety point which is not usually considered. I’ve carried a 12V lead-acid battery in the back of my car for modelling purposes since before history started, well, a long time anyway; this is connected to the car charging circuit and I protect the wiring with a fuse at both ends. I’ve popped a fuse a couple of times, when I’ve donged the croc clips together, but this will never cause me any burning concerns!
    If your battery uses the standard push on ‘Lucar‘ type connector, you can obtain a ‘piggy-back‘ adaptor, enabling two connections on to one.
    One other thing, it may be a plan to use fairly heavy duty wires on any wiring you do yourself, the starter etc. We overcame a heli pilot’s starting problems in one go, once, just by re-wiring his flight box.
    Hope this may be of at least some use.                PB  

[Klippy]

Excellent advice Peter. People often don't realise the amount of energy that can be released in a very short period of time.

[paul (dig-it-up)]

thanks for all the advice much appreciated regards paul