Using a USB thumb drive for backups?
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From: JF Mezei on 24 Dec 2009 13:38 A small CR2032 "pill" battery can pack enough power to kill more than one person... if it is wired to a timer, detonator and bomb :-) One needs to look at how/where the current travels. If it travels between two points on the skin, then it may burn the skin, but may not affect heart/brain. But if it affects nerves that control heart, then any voltage could cause problems. It also depends on how the current is transfered. Thsoe resscusutator pads are designed to have a large surface area transfer the pulse, so that no portion of skin gets sufficient amerage to cause a burn. But remove the paddles and just stick copper wire ends onto the guy's skin, and there will be severe burns areound where the wires are in contact with skin because all of the current will pass through a very small area of skin.
From: JF Mezei on 24 Dec 2009 13:40 >> Do you think there's no difference between a 12-volt car battery and eight >> AAA batteries wired in series? If they are nicad or nimh batteries, those AAAs may be able to give very high current. If their are alkalines, then the barry's own resistance prevents high current flow. recheargable batteries can (and have) caused fires because they do allow enough current to flow in a short circuit to heat the wires to a point where they ignite the insulation and anything near it.
From: E Z Peaces on 24 Dec 2009 19:09 Fred Moore wrote: > In article <hgrg92$tk5$1(a)news.eternal-september.org>, > E Z Peaces <cash(a)invalid.invalid> wrote: > >> Technically, it's a solenoid if it mechanically engages the gear of the >> starter motor. In that case, it must be attached to the starter motor. >> If it has no mechanical function, it's really just a contactor, but on >> vehicles they are commonly called solenoids anyway. A contactor is a >> relay built to control motors. > > Well, according to the dictionary which comes with the Mac a solenoid is > 'a cylindrical coil of wire acting as a magnet when carrying electric'. > Many cars have 2 solenoids--one to close the circuit and one to throw > the Bendix gear between the flywheel and the starter motor cog wheel. > Some cars combine these functions to save money in the design. You're right about the definition of solenoid. I didn't know the meaning was so broad. The print version says it dates from early in the 19th Century. The print version goes on to say, "especially such a coil surrounding a moving iron core and used to operate an electrical switch or relay." I agree about the moving core but not that it's normally a switch. A heavy-duty magnetically operated switch is a contactor. I think in most cases the core is stationary. If it moves,the device is a solenoid-type contactor. To me, "solenoid" connotes a mechanical function such as firing machine guns or shutting off water. I think the magnetic switch for a car starter was not called a solenoid until about 1950, when the engagement function was added. For many decades, some cars have used inertia instead of a solenoid to engage the starter gear.
From: Richard Maine on 24 Dec 2009 19:30 E Z Peaces <cash(a)invalid.invalid> wrote: > You're right about the definition of solenoid. I didn't know the > meaning was so broad. The print version says it dates from early in the > 19th Century. My paper OED (hey, the thing takes over 4 feet on my bookshelf - might as well get some use from it on occasion) has citations from 1827, which pretty much agrees with your "early 19th century." -- Richard Maine | Good judgment comes from experience; email: last name at domain . net | experience comes from bad judgment. domain: summertriangle | -- Mark Twain
From: E Z Peaces on 24 Dec 2009 23:24
JF Mezei wrote: >>> Do you think there's no difference between a 12-volt car battery and eight >>> AAA batteries wired in series? > > If they are nicad or nimh batteries, those AAAs may be able to give very > high current. If their are alkalines, then the barry's own resistance > prevents high current flow. > > recheargable batteries can (and have) caused fires because they do allow > enough current to flow in a short circuit to heat the wires to a point > where they ignite the insulation and anything near it. I think NiMH are comparable to new alkalines, but an alkaline's internal resistance increases as it discharges. NiCds typically have lower internal resistance. |