Charger setting for Futaba Tx NiMH

[Barrie Dav 2]

Can anyone clear something up for me. My 2.300 mAh nimh TX battery is rated at 9.6v (8 cells x 1.2v). However when charging either with the supplied wall charger or with my A.6 multi-charger, the voltage rises to well above 11v. There is no sign of the battery warming up.

 

My transmitter is a Futaba 7C-2.4 GHz. Nominal operating voltage as indicated in the manual is 9.6v.and the demonstration photos of the LCD panel show 10v. but I cannot find anything which indicates the maximum voltage tolerated by the TX.

 

 

 

[Tim Mackey]

8 cells will show at least 12V fresh off charge - each cell normally peaks at around 1.5 -1.6V so it could show as much as 12.8V.

It will drop off slightly almost immediately.

Absolutely normal.

[Barrie Dav 2]

Many thanks for your reply Tim. So I take it that volts well in excess of 9.6 will not cause a problem with the transmitter.

[Tim Mackey]

You'll be fine Barrie - the manufacturers will have used a regulator designed around their awareness that 8 cells will be 12V+ fresh off the charger.

[Barrie Dav 2]

That's very reassuring Tim. Much obliged to you.

[Peter Beeney]

There is a sort of finale to my post of 02/04/2011 14:24:14, above, relating to ‘eBay, the duff battery, the dodgy battery monitor and the double coincidence’. The laddie was at the patch yesterday and I asked him how he connected the monitor, he said it was into the rx, so it’s now definitely looking suspiciously like an errant little contraption. It’s fixed to the dashboard, underneath a glued on opaque brown canopy; that makes it somewhat difficult to see properly anyway. Connecting up, one red led is lit, the bottom one, so it’s live, but giving the wrong reading. He has a four cell battery, and there is a switch to switch between 4.8 and 6V, but it’s difficult to make out which position it’s in, the pilot was pretty convinced it was 4.8! I’m not so easily persuaded, let’s check it out!

Because it’s sealed in it’s not easy to change anything, but my model has a 5 cell battery so I plugged the monitor into my model’s aileron lead, switched on and bingo!, the top green led is lit! So I suggested that he drilled a very small hole in the base of the canopy, in line with the switch, slid a thin piece of wire in and tried to change the switch. He, of course, was now admitting to feeling like something of a foolish boy. He is a professional man, but, as he said, his knowledge of things electrical is zilch.

The moral? Never take anything for granted the first time around. I learnt a very long time ago that when you were doing safety tests and something was wrong you checked your test instruments first, not the equipment! And that’s not always easy to do!

The lesson, perhaps? Always put the monitor where it’s easy to see! And fiddle with! If possible, near the rx on/off switch; and a good point at which to check it is after a flight and before you switch off. They might give a bit of a false reading at switch on. He mentioned that he tended to recharge as soon as it came off the top green led, but I don’t think that is always necessary. Ideally the Full Scale Deflection, (FSD) of the monitor should be about one volt, from about say 5.4V down to 4.4V, for a 4.8V battery. Eight leds, maybe, so that’s 125 millivolts per led. I reckon you can easily get at least half way down the scale before you even need to consider recharging; but calibrating with a voltmeter is a good idea; I seem to remember doing one in another thread recently and that had a FSD of thirty millivolts! Too tight, that’s erring on the side of caution just a little bit too much!

This is just a tiny little gnat in a big aeromodelling sky, very insignificant, but at least someone’s knowledge has expanded a little. Also saved a little unnecessary expense, perhaps, I wonder how many little situations like this occur every week?

As they say, all’s well that ends well! I hope this is not too far off track, not really tx related, but hopefully topical.

PB