Old resistance adaptor plug.

[Tractorfan]

Hi,
Found this little item today for a couple of euros. It's a wirewound resistor inside a perforated metal cylinder with Bakelite end caps. It was used to run a small 110 volts appliance from 220 volts mains when this became the standard supply in France.
The only mark reads: 735.R. and the actual resistance is 720 ohms. No indication as to current rating.
Cheers, Pete.

[Station X]

Won't the current rating be V/R ie 110/735 or about 150mA?

[Lucien Nunes]

Which in turn means the appliance was rated (110)²/735 = 16W

[turretslug]

I'm frequently "impressed" with what was blithely accepted in the past, and this is an intriguing addition to the list! Presumably, one could get a whole range of resistances to suit legacy 110V appliances- this would in turn imply an alarming number of "what could possibly go wrong" eventualities.

[Herald1360]

Only two really.

"It doesn't work"

"What's that burning smell?"

[Refugee]

There used to be a version that chopped the supply at a 50% duty cycle. They were marked for heating appliances only but had a wider power range.
Resistors like that were commonly supplied with 110V AC equipment fans in the early 1980s so that they could be used on UK mains.

[Station X]

Put two in series, add a shorted plug and you've got a low power heater.

[emeritus]

Reminds me that circa 1970 Philips used to sell (for over a fiver) a car power adapter to allow the (7.5V ) EL3300-series cassette recorders to be used in a (12V) car: a ventilated metal box that I think just contained a watty wire-wound resistor to drop the excess 6V, fitted with a lead with a DIN plug for connection to the recorder. An excellent engineering solution that reflects the fact that the current drawn was a pretty constant ~100mA and that the recorders had been designed to continue working with partly exhausted batteries. I had made up my own, and didn't like to mention this to an acquaintance whose friend had made him up a complex electronic voltage regulated 7.5V PSU for his.

[Refugee]

I had an early compact cassette recorder (cheap model).
A lamp limiter and a large capacitor made me an adapter to run it from a model train set transformer with the control also set to maximum resistance.
It lasted for several years.

[turretslug]

I can see a bad situation involving cats and warm places..... At least any suppressor MOVs and X capacitors in the 110V appliance should be pretty effective when fed from that sort of source impedance.

Originally Posted by emeritus

Reminds me that circa 1970 Philips used to sell (for over a fiver) a car power adapter to allow the (7.5V ) EL3300-series cassette recorders to be used in a (12V) car: a ventilated metal box that I think just contained a watty wire-wound resistor to drop the excess 6V, fitted with a lead with a DIN plug for connection to the recorder. An excellent engineering solution that reflects the fact that the current drawn was a pretty constant ~100mA and that the recorders had been designed to continue working with partly exhausted batteries. I had made up my own, and didn't like to mention this to an acquaintance whose friend had made him up a complex electronic voltage regulated 7.5V PSU for his.

Exactly my approach when using a Matsui DA1 DAB adapter in-car- the (very) nominal 6V 500mA unregulated wall wart actually produces around 7.5V with the module's c.400mA load (whether on or standby!), so I simply use a 12ohm 5W resistor to feed it. Acquaintances who had the same thoughts about in-car DAB had ideas about electronic regulators- my response was, why?- a 12ohm resistor will make a good spike-catcher in conjunction with the 2200uF on the input to the DA1, everything within is fed from 5V or 3.3V regulators anyway. I trust a wire-wound resistor far more than silicon junctions in the hostile automotive environment.

[Brigham]

The portable Philishave came with something similar built into the plug, for 110/220v. use.