Relay

[blacksnapon]

Technician "A" says a relay is used to control a small amount of current with a large amount of current. Technician "B" says a relay is used to create a voltage drop in a control circuit. Who is correct? 1) technician "A" 2) technician "B" 3)both "A" and "B" 4) neither technician

 

[EnviroCon]

Neither. A relay is a device for controlling a high amount of current with a low amount of current. While there will naturally be some amount of resistance across the contact points of the relay, that's not a relays primary purpose and in most cases the voltage drop will be so small it wouldn't be useful in our everyday world. Resistors are used to "create" a voltage drop.

 

[mrxlh]

neither technician... A relay is used to control a large ammount of surge current utilizing a small ammount of voltage.

 

[O'Rattlecan]

my sister runs relays at track tournaments.

Ryan

 

[Brian_B]

I don't have a sister.

Is that a normally open or normally closed relay? confused

As far as I know a relay is simply an electrically operated switch. A small amount of current flips the switch either closing or opening a circuit (depends on N.O. or N.C.).

Typically it is a higher voltage circuit like driving lights, fuel pump, or AC.

If I ever take mine off-road, I will wire a N.C. relay into the 4X4 system thereby making it a rear wheel drive in low range for tight turns. Control track is great on road though.

 

[Bob Ayers]

Neither technician, a relay is used to switch a large current with a small current.

 

[blacksnapon]

my sister runs relays at track tournaments.

Ryan

But, how much current does she control? It appears we have some very electrical savvy people here!

 

[Bob Ayers]

Typically it is a higher voltage circuit like driving lights, fuel pump, or AC.

Higher current, not higher voltage!!

 

[mrfixit]

But, how much current does she control? It appears we have some very electrical savvy people here!

She's a woman... she controls it ALL!

 

[Bob Ayers]

neither technician... A relay is used to control a large ammount of surge current utilizing a small ammount of voltage.

Again, don't confuse current and voltage, the coils on automotive relays are 12V.

So it should read:

A relay is used to control a large ammount of surge current utilizing a smaller ammount of current

 

[mrfixit]

Higher current, not higher voltage!!

In HIS example, no, but there are many instances where a lower voltage relay controls a higher voltage, like a lovo switch connected to a relay that starts a 480v roller press...

 

[O'Rattlecan]

by current... we mean amperage?

Ryan

 

[mrfixit]

NO that's not what they mean. technically, current IS voltage. Voltage is the amount of current (12 v, 18v, etc) and amps are the FORCE behind the voltage... kind of like a PSI for electricity.

 

[O'Rattlecan]

but on the previous page I heard "not voltage" and am trying to make sense of this.

Ryan

 

[mrfixit]

OK... a relay is used to control a higher VOLTAGE or AMPERAGE with a Lower VOLTAGE or AMPERAGE, but in the case of our vehicles, it is used to control a Higher Amperage with a lower amperage.
Amps are the push, or the pressure, the strength.
Voltage is the Volume, or the current flow.
If you were to take a rattlecan and fill it with paint and put a top on it but no pressure (amps) the paint would not come out. at a low pressure, it just dribbles out... but at high pressure, or amps, it atomizes the paint because the pressurized paint is entering a lower pressure area, and the spray top is the relay...hehe...

 

[Bob Ayers]

NO that's not what they mean. technically, current IS voltage. Voltage is the amount of current (12 v, 18v, etc) and amps are the FORCE behind the voltage... kind of like a PSI for electricity.

Absolutely not! You can have voltage with NO current. Your electrical outlet
has 120VAC, but you don't get any current until you plug a load into it....

The unit for current is the AMPERE, the unit for voltage is the VOLT


The relationship betwen voltage, current, and resistance is called Ohm's Law:

Resistance (R) = voltage (E) / current (I)

voltage (E) = current (I) * resistance (R)

current (I) = voltage (E) / resistance (R)

 

[mrfixit]

Ohm's law states that, in an electrical circuit, the current passing through a conductor from one terminal point on the conductor to another terminal point on the conductor is directly proportional to the potential difference (i.e. voltage drop or voltage) across the two terminal points and inversely proportional to the resistance of the conductor between the two terminal points. In mathematical terms, this is written as:

where I is the current, V is the potential difference, and R is a constant called the resistance. The potential difference is also known as the voltage drop, and is sometimes denoted by E or U instead of V

The voltage drop is the V. the current is the voltage.

 

[Bob Ayers]

E[/I] or U instead of V[/COLOR]

The voltage drop is the V. the current is the voltage.

The current IS NOT the voltage!!!! DO you see I = V (or E) in that equation?

 

[mrfixit]

I retract, bob. I had my thoughts inverted over this truck. my apologies.

 

[Bob Ayers]

I retract, bob. I had my thoughts inverted over this truck. my apologies.

Apology accepted Tom, I enjoy a good technical debate!!