Why does a transmitter not work with charger plugged in??

[Kalus]

Just wondering why a transmitter isn't able to function while the charger is plugged into it... and.... is it possible to merely use an AC adapter (at the correct voltage of course) to supply power to a transmitter without interfering or causing grief???

I am using a 2.4GHz computer radio to control a modified Jet Ski as the propulsion for a small boat. I want to be able to plug the transmitter in (into mains power) if the battery runs down in order to still have control of the boat.... without having to shut everything down and wait until it recharges.

Anyone have any ideas on this?????

Ideally I'd want a setup that charges the battery (or keeps it charged) while also supplying power to the transmitter while in use.

[Richard Ingram]

Maybe a protection scheme to keep from possible damaging the tranny with improper voltages. Just guessing though.

[Rodney]

All the transmitters I have (Futaba, Airtronics and Hitec) all work fine with the charger plugged in. When I turn on the transmitter, the charger is no longer charging the transmitter batteries but the transmitter transmits. When you turn on the transmitter, it breaks the circuit from the charge jack to the battery. When you turn off the transmitter, it reconnects the charger circuitry to the battery.

[dmccormick001]

Well, even though I know I'm over my head in this forum with all the real, genuine, electronics experts that lurk around here, I'll take a stab at this one.

For starters, the charge jack itself usually has a terminal in it that is designed to act as a switch, so that whenever the charger's plug is inserted into it, it disconnects the battery from the circuit, and allows the charger's output to go straight to the battery, bypassing the radio. That's why when you plug the charger in it cuts the radio off. So the first thing you'd need to do would be to change the jack so that doesn't happen.

Secondly, most chargers, especially the AC-adapter types, don't provide enough current to run the Tx directly. That's why you can run the battery down too low to operate the radio in just a few hours, but to charge it back up to full capacity, they have to be left connected for several hours. And most chargers have a higher output than the voltage of the battery they're charging, and that might cause you some real problems if you try to power your radio directly from one.

My opinion, just get yourself a bigger capacity battery for your transmitter. I've got a 2300ma Ni-Mh battery in mine that lets me fly pretty much all day both Saturday and Sunday before I need to recharge. For that matter, get two.

[Kalus]

Thanks for the suggestions.

I remember my old Hitec used to just disconnect the charger when the Tx switch was on, but this Airtronics (Sanwa) Tx actually won't turn on while the charger is in the jack. I think I'll just rewire the jack/switch to make it disconnect the charger as per Hitec and see what happens.

[Trevor_G]

The reason for this situation is regulatory. In the UK (and possibly other countries) it is an offence to power an RC Tx directly from the mains.

To ensure compliance manufacturers wire ON/OFF switches so that the battery is either connected to the Tx cct or the charger socket.

As the same basic Tx design is used worldwide. One country gets it then everybody gets it!

Trevor