Cells test 50 OHM

[Mike K]

Recent find , cost me 1$. Not sure what this was used for ?

[Jakko Westerbeke]

Going by the text on the label, it’s for testing some kind of batteries for electric firing circuits — that is, the wiring needed to set off electric detonators for explosives used in demolitions.

[Mike K]

Originally Posted by Jakko Westerbeke

Going by the text on the label, it’s for testing some kind of batteries for electric firing circuits — that is, the wiring needed to set off electric detonators for explosives used in demolitions.

Or, could it be a device for testing electrically fired Artillery pieces ? It appears to be just one part of a multi - unit system , with a battery , the resistor limits the current flow in the circuit.

[Chris Suslowicz]

Originally Posted by Mike K

Recent find , cost me 1$. Not sure what this was used for ?

It's part of the WW2 (and possibly earlier) Demolition Test Set. Basically it's a safety battery box that takes an 'S' (inert for long term storage) or 'X' cell as used in field telephones and the daylight signalling lamps. The 50 ohm series resistor limits the available current to less than that which will cause a detonator or squib to fire, and sealing the box means nobody can fiddle with it.

Used for testing firing circuits (demolition and also electrically fired artillery) safely.

What you have is the battery box that goes in the wooden case containing the rest of the equipment.

https://www.worthpoint.com/worthoped...1944-275492158

That one appears to be missing the piece you have, unless the army modified it to use the bare battery.

Best regards,
Chris.

[Mike K]

Ah, that makes sense. But you would have to make sure the firing fuse wasn't active . you wouldn't want to accidentally fire the detonator in the demolition charge or the Artillery piece.

Good old Wheatstone bridge.

[Chris Suslowicz]

Ah, that's the entire point of the 50 ohm resistor: it cannot supply enough current to set off a detonator or squib while the Wheatstone Bridge is sensitive enough to measure the resistance of the complete firing circuit (including detonator, etc.).

There's currently a "Continuity Tester" on eBay as well, which uses an "800" (3-volt lantern battery) and a buzzer and is only for testing the cabling - it specifically warns against testing demolition circuits because they WILL go off.

(I have a detonator/squib tester that is a piezo-electric crystal and a neon - the energy supplied is nowhere near enough to warm up the bridge wire in the item being tested - though I suppose if that was open circuit inside the pellet the voltage might do it (instructions warn to put the item under test in a suitable container for safety).)

"Notes On Electricity (date)" is your friend, originally a small pocket book (1915), later a series of pamphlets "Notes on Electricity as applied to Service Apparatus" (I think), which covers telephones, gunsight illuminating gear, firing pistols for field artillery, and demolition kit. I have some of the books and pamphlets.

Best regards,
Chris.