I got a new 7 ch futaba radio with it i also got a tx and rx charger. I plugged the charger in wall socket and tried to operate it but it didn't work after that i read the specification on the charger and it said it require only 120 volt ac the charger which i got got burnt. I have now purchased two local made charger output rating 9v 500mA for  tx and one i have bought 4.5v 500 mA for rx battery. On the original  charger the rating is shown as for tx 9.6Vdc 70 mA and for Rx 4.8 Vdc 100mA. Should i use the new charger as it is to charge the battery or do i have to modify some thing like adding resistance in parallel or in series to decrease the charging current. I would also like to know how to convert a CPU SMPS to charge the battery of Rx and Tx directly because when i am searching the Internet it is only showing me how to convert SMPS to supply different battery chargers .

Ritesh

Ritesh,
you can not charge a 9.6 volt and 4.8 volt batteries with 9 volt and 4.5 volt eliminators respectively. However you can use an SMPS  to charge the Tx and Rx batteries. Use the 12 volt tap from the SMPS  with a resistor in series to limit the charging current.You can use the 5 volt tap again with a serial resistor to charge the Rx battery.

Rao

I guess you a need a step down transformer from which you can plug the charger and then charge your batteries..You can get it locally made..

Dude thats a very stupid mistake man, you are lucky you didnt burn your radio.. Hope you were not charging the battery on the radio ?

Be Safe, these are costly equipments..

You should open up the charger and check what is damaged. Some of them have a thermal fuse that pops protecting the windings. You might get away with just replacing the fuse.

Hi

Not worth going into the details... just buy a new charger.. these are pretty cheap...

http://cgi.ebay.in/GWS-Tx-Rx-Charger_W0QQitemZ110395502620QQcmdZViewItemQQptZLH_DefaultDomain_203?hash=item19b415b01c&_trksid=p4634.c0.m14.l1262

Cheers !!!
Saurabh.

There are subtle differences between tx chargers. Some transmitters have diode built in that changes the charger requirements slightly.

If the manufacturer recommended slow charging for the battery, you should go with that as much as possible.  So replacing a 70ma charger with a 500ma charger is best avoided (at least as the primary method of charging), as repeated fast charging is not recommended.

1. Take a multimeter, put in 20K resistance range. Short the probes, ensure continuity
2. Check between the two Plug points (AC) of the charger.
3. If the charger is good one should get some continuity (may be about 1K)
4. If no continuity, open the charger.mostly if there are no screws, one will have to open it by cutting the cover carefully with a hacksaw blade.
5. Once opened check carefully, for a fuse on top of the winding. if blown replace with a short.
6. If xfer is blown, there are people who rewind it 1:1 in SP road.
refit with good xfmr and seal the cutting with glue.

Question is, other than the DIY aspect, is it worth the effort, when a new one is little over the Rs500 range.  It may be, not sure what it costs to do the winding etc.  If it is just the fuse, it makes more sense.

Wish Ritesh had just bought the exact replacement, instead of substituting with locally available but incompatible ones

buy a new charger if you are not up to DIY stuff .

Quote from: ritesh.sangam on September 28, 2009, 06:36:35 PM
I have now purchased two local made charger output rating 9v 500mA for  tx and one i have bought 4.5v 500 mA for rx battery. On the original  charger the rating is shown as for tx 9.6Vdc 70 mA and for Rx 4.8 Vdc 100mA.

Wow. Funny thing how people confuse between voltage and current. If you have an adaptor of 9V and 1000Ampere capacity, it would drive only 70mA ( or even less) through a battery pack of 9.6V.

The rating shown on your adaptor is a maximum current rating, the transformer is designed to provide. How much current actually goes through your cells is dependant upon the voltage, which if yours is 9V ( in reality it would come to around 11V ), would be enough to charge your battery pack (if not fully ) without damaging.

You should be able to charge your batteries with the 9V and 4V adaptors locally available. Of course i would recommend you to check the voltage of the charged battery packs after charging.

Good luck and see you soon.
-Gaurav

QuoteOf course i would recommend you to check the voltage of the charged battery packs after charging.

More important, check the charging current on a fully charged battery, If around 10% of the rated capacity, you're OK. The initial charge current would be higher but of no real consequence.

same problem is mine ,......why is it 120v ac when in india tere is 220v ac .

how are you people providing 120v ac?

That is the US standard, and a lot of times that is what is available for purchase even locally.  But you can always get a 220v to 110v converter in your local electronics shop, which takes care of the problem, and they are quite affordable too.  Since they have a big transformer inside, these converters are bulky/heavy though.

There are small (20 W) units also available. They are about the same size - or smaller - than the charger.