Radio Scanner/Transceiver

[Intercepted]

How do you test your radio legally?

You don't, you test it illegally.

If you was to make your first call for taxi on the handheld instead of the A/c set and then switch back for reply would Atc know and if so would they mind?

I'm sure ATC would know when I do it, since I'm sometimes outside the aircraft fully visible from the tower. Did they mind? No

[Whopity]

The radio only needs a type approval if fitted to the aircraft, not as a handheld. If used in the aircraft, it is covered by the aircraft radio licence which lists only the frequencies in use not the equipment, so testing it in such circumstances is not illegal. Why should ATC be concerned? Its nothing to do with them! If an Ofcom inspector sees you using it outside the aircraft, you could be prosecuted. They do have purges every now and again, usually associated with events, Silverstone etc.

[BackPacker]

Most chargers are pretty crude devices and have no idea what is hung on the end of them

It's not the charger I'm worried about. It's the NiMH batteries.

I was reading the Wikipedia article on NiMH and it clearly states that a NiCd charger should not be used automatically for NiMH batteries, including an explanation on why this is so.

Nickel

My Bearcat adapter will simply deliver 12V at 500mA and does not seem to incorporate an automatic cutoff once the NiMH voltage drop or any of the other mentioned conditions is detected. The battery pack itself is six NiCDs in series (7.2V, 600mAh according to the print, but that 600 mAh was a long time ago...). There is a tiny print board with what looks like three resistors, a diode and two capacitors, but that mainly seems to be there to power the red LED light to indicate external power. Again, nothing to indicate any form of intelligence to cut off the charging current once the batteries are full.

So as I understand it, if I were to replace the NiCds in this battery pack with NiMHs, I can easily cause the NiMH to be overcharged and thus blow their safety device thinghy. I'm not going to risk that.

[Jan Olieslagers]

I am not an expert on the matter but it seems to me that a very crude charger, like you apparently have, is the least dangerous because it charges slowly, i.e. at relatively low current. Try to find an indication of its charge current, it should be stickered on.

[[edit: actually, you seem to have an ADAPTER, not a CHARGER. There ought to be some charge regulation somewhere, probably in the BearCat? You should certainly NOT load batteries of any kind straight from an adapter!]]

The old rule was to charge with a current corresponding to a ten-hour charge, for example a 1000 mAh NiCad would be charged with 100 mA; because the charging process is less than perfect, 14 hours of charge was the rule.
Using such a charger you should not worry, just recalc the charge time and you'll be OK and relatively safe (relatively indeed: there is NO type of battery that is absolutely free from exploding during charge)
The ones you should distrust are the more recent superquick chargers that claim to fully load in 90 minutes or so: these depend on the characteristics of the battery being charged. Also they apply, by nature, much higher currents. I've a gut feeling this is harder on the batteries, reducing life-time and increasing the risk of overheating and explosion.

[Whopity]

My Bearcat adapter will simply deliver 12V at 500mA

That is the maximum it will deliver. Most chargers have a series resistor, so the load current will depend upon the load applied and not provide anywhere near a constant current. Quite often the voltage on a 12 v charger can be as as hight as 18 volts depending on whether there is a capacitor in the charger or if its output is unfiltered DC.

Beware of fast chargers, they are designed to match the batteries capacity and characteristics and provide short bursts of energy where a high current is drawn for a short period and can result in overheating.

Having used basic chargers on NiCads and NiMHs for years I have never had a problem. All appliances tell you only to use the correct charger which is not surprising when you see what some people plug in, all black blobs look alike!

[IO540]

Having designed various specialist (built-in) chargers in years gone by, I don't think that Wiki article is all that great.

The delta-V method works only on a fast charge, and fails if the battery is already fully charged, which means the charger needs to do a discharge first.

Today, most chargers are equally "good" for NICD and NIMH because they are dumb, and charge at about 0.1C at which rate you can't do much damage whatever you do. The cell voltage of the two technologies is very similar. The better ones detect battery temp rise, which is a very good method but it works only if you are charging at around 0.3C or higher (otherwise there is not enough power around to heat the battery up once it is fully charged) and one has to measure the temp differentially (battery versus charger ambient) which few chargers do.

LIPO batteries are a very different thing and they do require intelligent charging methods. There are loads of chips around which implement that. Some of the chargers are very pricey but very clever.