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Electricity Can be Difficult
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Jan 20, 2017 08:07:47   #
jerryc41 Loc: Catskill Mts of NY
 
Over the past few week, I've been working on a wooden box to hold two hard drives for backing up. I want to turn them on and off individually and also have a fan, just in case. I'm using the connectors and power plug from a Sabrent disk case. I have two small 110v switches to turn each fan on and off. My plans have been changing as I work on this, and those switches were a mistake. Simple toggle switches would have been better. I discovered something surprising about how the switches work. When I turn the switches on, only one leg completes the circuit. The other leg is always live with power.

Originally, I was going to use two Sabrent power supplies and run 110v to them. Each switch would light up when I turned it on. Then I realized that I could change the wiring and use just one power supply. Getting all three components to turn on and off individually has been a challenge, but I finally got it. When I get around to completing the wiring, it will be finished, and I'll post some pictures.

I hesitated to disassemble the Sabrents, but my computer has a drawer to insert drives right in the front, so I don't need them.

https://smile.amazon.com/gp/product/B00SSFRES0/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

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Jan 20, 2017 08:26:05   #
SonyBug
 
If you switch only the hot side and pay attention to polarity, then all of the wires will be "cold" up to the back of the switch. Only the one wire will be hot...

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Jan 20, 2017 08:41:51   #
boberic Loc: Quiet Corner, Connecticut. Ex long Islander
 
nikonbug wrote:
If you switch only the hot side and pay attention to polarity, then all of the wires will be "cold" up to the back of the switch. Only the one wire will be hot...


Black wire is hot, white is neutral green (or bare) is ground. Get a book(if you don't have one) about basic wiring. If you want to control both gizmos with one switch you need something called a switch loop. Same as controlling 2 outlets with 1 switch. My house has many switch looped outlets.

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Jan 20, 2017 08:50:13   #
jerryc41 Loc: Catskill Mts of NY
 
Thanks, all.

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Jan 20, 2017 09:21:09   #
davefales Loc: Virginia
 
jerryc41 wrote:
I discovered something surprising about how the switches work. When I turn the switches on, only one leg completes the circuit. The other leg is always live with power.



Sounds like a standard single-pole switch, common in homes.

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Jan 20, 2017 13:35:48   #
Ring Loc: Reed City Michigan
 
Single-Pole Double Throw Center Off. Will select either or neither!

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Jan 20, 2017 14:11:11   #
G Brown Loc: Sunny Bognor Regis West Sussex UK
 
The UK uses 240v it can kill you.
Darwin was English.
:-(

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Jan 20, 2017 15:21:47   #
TriX Loc: Raleigh, NC
 
remember that hard drives (not SSDs) use both +5 volts and +12 volts, so you will need to switch both if you plan on a single power supply. If you want to switch the drives individually so that either or both can be on, then you'll need a double pole, single throw (DPST) switch for each drive plus a 3rd switch (which can be a standard single pole, single throw, SPST) for the 115VAC for the power supply. If you wire the fan directly to the +12v out from the supply, then it will come on whenever you turn on the main power. I'll draw you a schematic if you like... Also, are you sure the power supply will support both HDs simultaneously? Might be easier to use the two supplies as originally planned.

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Jan 20, 2017 18:00:30   #
jerryc41 Loc: Catskill Mts of NY
 
TriX wrote:
remember that hard drives (not SSDs) use both +5 volts and +12 volts, so you will need to switch both if you plan on a single power supply. If you want to switch the drives individually so that either or both can be on, then you'll need a double pole, single throw (DPST) switch for each drive plus a 3rd switch (which can be a standard single pole, single throw, SPST) for the 115VAC for the power supply. If you wire the fan directly to the +12v out from the supply, then it will come on whenever you turn on the main power. I'll draw you a schematic if you like... Also, are you sure the power supply will support both HDs simultaneously? Might be easier to use the two supplies as originally planned.
remember that hard drives (not SSDs) use both +5 v... (show quote)


The plot thickens!

I can't power them at the same time because my backup program looks for the G drive. With two running, I would have G and H. I hope to have some time to play with this tomorrow and see how the switching works. Luckily, my life doesn't depend on getting this working in a timely manner.

As for the fan, that's why I have a separate toggle switch for that.

Both simultaneously won't be needed, and the power supply probably would not power both. I was going to use two power supplies, one for each drive, but I couldn't figure a way to power the fan without powering both drives. With one power supply, I have the common ground and a hot wire for each device. Basically, power goes from the Sabrent "brick" to each drive, using the Sabrent cylindrical plugs to each circuit board from the Sabrent hard drive enclosure.

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Jan 20, 2017 18:34:44   #
TriX Loc: Raleigh, NC
 
jerryc41 wrote:
The plot thickens!

I was going to use two power supplies, one for each drive, but I couldn't figure a way to power the fan without powering both drives.


If you use a DPDT switch with a center off position to select which of the 2 power supplies to activate, you can use the second section, with both of the "on" poles wired together, to turn on the fan when either power supply is activated. Sent you a crude schematic via PM (this assumes a 115 VAC fan)

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Jan 20, 2017 19:07:13   #
G Brown Loc: Sunny Bognor Regis West Sussex UK
 
TriX wrote:
remember that hard drives (not SSDs) use both +5 volts and +12 volts, so you will need to switch both if you plan on a single power supply. If you want to switch the drives individually so that either or both can be on, then you'll need a double pole, single throw (DPST) switch for each drive plus a 3rd switch (which can be a standard single pole, single throw, SPST) for the 115VAC for the power supply. If you wire the fan directly to the +12v out from the supply, then it will come on whenever you turn on the main power. I'll draw you a schematic if you like... Also, are you sure the power supply will support both HDs simultaneously? Might be easier to use the two supplies as originally planned.
remember that hard drives (not SSDs) use both +5 v... (show quote)


Not quite 'lick your fingers and see if it tingles'....My Father ran signals and telegraph for British Rail: Euston, London To Glasgow, Scotland out of a single signal box at Preston. He talked switches just like that!

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Jan 21, 2017 08:41:13   #
jerryc41 Loc: Catskill Mts of NY
 
TriX wrote:
Sent you a crude schematic via PM (this assumes a 115 VAC fan)


Nope! 12v, 120mm computer fan, with blue LEDs.

https://smile.amazon.com/gp/product/B0026ZPFCK/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

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Jan 21, 2017 12:08:49   #
TriX Loc: Raleigh, NC
 
jerryc41 wrote:


Edit: will send you a PM with a revised schematic shortly...

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Jan 21, 2017 13:26:58   #
pounder35 Loc: "Southeast of Disorder"
 
G Brown wrote:
The UK uses 240v it can kill you.
Darwin was English.
:-(


So will 120v. It's the current that will kill you. Not the voltage.

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Jan 21, 2017 13:32:13   #
TriX Loc: Raleigh, NC
 
pounder35 wrote:
So will 120v. It's the current that will kill you. Not the voltage.


Either one will do it. Fibrillation is the issue - your heart just isn't capable of beating at 60 (or 50) Hz. Very high voltages have other issues, but the majority of people electrocuted are killed by AC line voltage (115/230 here in the US, 240v in some other countries).

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