Where is the other 6 volts

[Cryoman]

Wanted to install a usb charging station by the light switch in the bedroom. Figured power to the switch would be a good place to tie in to the 12 volts. When i measure across the switch i only get 6 volts. Anyone know where the other 6 volts is getting dropped?

[notanlines]

Any chance it is a rheostat?

[Cryoman]

No rheostat. Its the typical white green wiring and an on off switch.

[Frank G]

My first thought is they broke the Hot at the light and ran the wires to the switch, so there is a lamp between the hot+ and ground, therefore the reduced voltage.

[SummitPond]

Maybe I'm thinking wrong, but shouldn't there be a near-zero voltage drop across the switch. The voltage drop should occur across the load.

[xrated]

You don't measure voltage ACROSS the switch! Measure from one lead of the switch to the negative....and there will be 12 volts. If there isn't 12v at that lesrs, try the other lead and to negative.

[flybouy]

You have to read voltage from positive to ground, i.e. no resistance. Reading across the switch you are reading the voltage drop created by the device being switched (a light according to your post) so the resistance of the bulb, wire and anything else between the switch and ground is causing the voltage drop.

[Cryoman]

I understand about measuring between plus and minus wire to get 12 volts and that's the way i connect my charging station. But while i had the light switch out of the wall i measured across it with the switch in the off position and i should get 12 volts. To get less would mean voltage is being dropped across another load somewhere but the DVM i am using has a very high internal resistance and is not connecting the circuit to allow any current flow. Where is the other load that is dropping 6 volts. Maybe I'm overthinking. Everything works so why worry.

[Frank G]

I understand about measuring between plus and minus wire to get 12 volts and that's the way i connect my charging station. But while i had the light switch out of the wall i measured across it with the switch in the off position and i should get 12 volts. To get less would mean voltage is being dropped across another load somewhere but the DVM i am using has a very high internal resistance and is not connecting the circuit to allow any current flow. Where is the other load that is dropping 6 volts. Maybe I'm overthinking. Everything works so why worry.

The Light(s)

[cavediver]

Measuring across the switch your reading the same wire. The voltage drop might be coming from your bulb, if it is an incandescent bulb. That is a resistor, a controlled short circuit.

Jack

[Canonman]

Just a "maybe" but your lights should be LED. The light fixture is equipped with a transformer to allow the LEDs to work on 12v. Maybe? you're seeing the transformer??
I haven't checked this on the Cougar but it's become an interesting question:)

[xrated]

I understand about measuring between plus and minus wire to get 12 volts and that's the way i connect my charging station. But while i had the light switch out of the wall i measured across it with the switch in the off position and i should get 12 volts. To get less would mean voltage is being dropped across another load somewhere but the DVM i am using has a very high internal resistance and is not connecting the circuit to allow any current flow. Where is the other load that is dropping 6 volts. Maybe I'm overthinking. Everything works so why worry.

I'll say it again......You do NOT measure across the switch terminals! That is the part of a circuit called the "Switch leg". The 6 volts you are seeing, doing it this way is a pretty common voltage as you are getting your reading towards the negative wire THROUGH the LED in the switch, which is in series with a resistor of some value. Most likely, there isn't a negative wire in that switch box and you will have to find another source for your 12VDC.

[flybouy]

I understand about measuring between plus and minus wire to get 12 volts and that's the way i connect my charging station. But while i had the light switch out of the wall i measured across it with the switch in the off position and i should get 12 volts. To get less would mean voltage is being dropped across another load somewhere but the DVM i am using has a very high internal resistance and is not connecting the circuit to allow any current flow. Where is the other load that is dropping 6 volts. Maybe I'm overthinking. Everything works so why worry.

Let's try this another way. When you test across the switch you do not have a direct path to ground. You will have to go thru the device to get to the ground therefore the resistance is reducing the potential to that ground.

[Steve/]

Well, I guess you have led lights. With the meter across the switch, it is acting like a switch with 1 to 10 meg ohm resistance , until the led get a high enough voltage applied to them they will have 1 to 10 meg ohm so then you are measuring across half the voltage divider. With incandescent bulb I would think you would see 12 volts as they would be less than 100 ohms.

[Cryoman]

Well, I guess you have led lights. With the meter across the switch, it is acting like a switch with 1 to 10 meg ohm resistance , until the led get a high enough voltage applied to them they will have 1 to 10 meg ohm so then you are measuring across half the voltage divider. With incandescent bulb I would think you would see 12 volts as they would be less than 100 ohms.

After thinking about it for a few days that's the conclusion i came to. Internal meter resistance is close to the off resistance of the LED lights. Situation normal.

[rjniles]

The 2 wires at the switch are a switch leg. You do not have the ground. If you measure from 1 of the wires to a metal part of the chassis you will get 12 volts.

[larryflew]

The 2 wires at the switch are a switch leg. You do not have the ground. If you measure from 1 of the wires to a metal part of the chassis you will get 12 volts.

Just to reiterate what was said many times on many ways!!!! You can't get your voltage reading across a switch.

[Steve/]

Just to reiterate what was said many times on many ways!!!! You can't get your voltage reading across a switch.

That could be a misleading statement. The reading that I get across a OFF switch maybe closes enough that I do not have to look for someplace else to get a better reading of the battery. I am assuming that the switch is in front of me and easy to measure.
If the switch is use to turn on and off a incandescent bulb that had a 100 ohms filament. I would expect to see 11.999 vdc if the meter I have is 10 meg ohm input resistance. (battery is at 12 V) The reading is only off 0.001 Volts. That good enough for me.
If I do not like or understand the reading that I get across a switch, I will measure someplace else.
I would as the OP did wonder why I got a reading of 6 volt. Half of my input voltage, it is not what I would expect. Maybe 3 volt or 9 volt but not half.

[rjniles]

If you measure across a closed switch you get zero volts, the switch is a short circuit. It is like like measuring 2 points on the same wire.
If you measure across an open switch, you see some voltage. You have 1 lead at 12 volts. The other lead is connected to ground through the load. The voltage you see will depend on the input impedance of your meter and the resistance of the load. Cheap meters have a low input impedance and will cause more voltage drop.

[Scott228]

Wanted to install a usb charging station by the light switch in the bedroom. Figured power to the switch would be a good place to tie in to the 12 volts. When i measure across the switch i only get 6 volts. Anyone know where the other 6 volts is getting dropped?
You can’t read voltage across the switch. Need to read from switch wire to ground.

[Steve/]

Just for grins, not only can you measure voltage across a switch with a low impedance load. A low impedance load is basically tying one end of the switch to ground. You can also measure the current going to the load by measuring across the switch. The switch must be off in both cases.

[xrated]

Just for grins, not only can you measure voltage across a switch with a low impedance load. A low impedance load is basically tying one end of the switch to ground. You can also measure the current going to the load by measuring across the switch. The switch must be off in both cases.

You might want to add a disclaimer on that one (bold print above). Many times, there is a 10A maximum limit on measuring current with a meter like a Fluke and others. Hopefully, the internal 10A fuse would blow if the current exceeded 10 amps, but it's not something that someone without good knowledge of meters/electricity should do!