Fuses in radios.

[Henderson,Eric]

In my radios, in particular the computer radios, the fuse is probably the weakest link. The only times I ever blew a fuse was when I did something dumb with the back off, or shorted a charge plug, or used too high a charge rate. In all of these cases the radio stopped working until the fuse was changed. In my latest JR (a 10X) I noted that the pack has its own fuse. Sure enough I managed to eventually blow the battery fuse. (Broken insulation on tip of charge plug). The radio, however kept on working because there is another fuse in the radio beyond the battery.

Looks like they have changed things a bit! This was my first JR with a modular battery pack. (Usually it is a battery specific, of regular servo type, plug). The fuse is surface-mounted on a board in the battery case. Apart from the previously mentioned direct short, the fuse can also blow with a Hobbico field charger if plugged in when the pack is very low. To combat this I shunted the surface fuse. It always seems to blow at the beginning of the charge and is obvious because the "light" does not go on.

I have seen, and heard, of pilots soldering a wire in place of the fuse in their radios. The logic being that the cost of killing a radio was a lot less than the cost of killing a plane due to an unnecessary fuse outage. Of course, the wisdom of this practice depends upon the source and cause of the fuse failure.

The battery "module" has a couple of weakness from my point of view. First of all the pack can unplug under its own weight if the radio is not handled gently. The back can be popped open when using an add-on folding radio stand. The fix is to cut off the lip of the flip-lid on the back of the case, because it snags the hard surfaces. The second thing to watch for is that radio switch does not turn off the TX pack charge circuit like most of the radios that we know. Thus the radio can be on and still be charging. The intent was to have battery packs that can be charged "outside" of the radio case. It does allow easy swapping in of freshly charged packs that will let you fly "all" day.

Last but not least, replacing the batteries with 1850 mAh NiMH's gives you not only great duration but very low self-discharge and no battery memory.

Regards,

Eric.
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