Warm up RPMs?

[DRFoster]

I went out and bought a "heavy duty" timer rated with the following:

15 amps
(1875 watts)
120 volts AC
"R" resistive

15 amps
(1875 watts)
120 volts AC
"H" inductive

500 watts
"T" Tungsten
1/3 H.P.
120 volts AC
60 Hz

Any opinions as to whether this should suffice for controlling a block heater? I guess my question boils down to the difference between the "R", "H" and "T" ratings and which one applies here.

I plan on it setting the timer to turn the block heater on about 2 1/2 hours before my normal starting time (for snow removal.) Should that be sufficent? Too long?

 

[TWINKLE_TOES]

Dennis,

With respect to electrical contact points making and breaking.
(R)
Purely resistive loads are the easiest the current at mating is E/R the same as steady state.
(H)
Inductive loads, generally motor loads, are tougher. Inrush current to a motor is about 4 times running. Opening contacts to inductive loads is a tougher job because of the high voltage produced by sudden release of the energy stored in the inductor.
(T)
Incandescent (Tungsten) lamp loads, heater loads are related to the temperature of the filament. And are one of the hardest loads to switch. A lamp that gets hot enough to emmit light will have an inrush of 7 to 10 times running current. A heater load because of lower filiment temperature will have a lesser inrush.

The fact that your timer is specified for the different loads is an indication it probably a pretty good one/w3tcompact/icons/smile.gif

Your load is (T) but probably not Tungsten but Nichrome. The inrush current will be less and the contact rating of the timer is adequate for the 400-800 watts John suggested.

The failure mode for exceeding the contact rating is reduced cycle life and in your application should never be a problem. Once a day every day for 10 years is not a big number in terms of cycle life. Contact welding can occur anytime if the rating is grossly exceeded. Your fallback in this case should be the thermostat on the block heater. I don't own one so I don't know that this is how they are designed.

<font color=blue>500 watts
"T" Tungsten
1/3 H.P.
120 volts AC
60 Hz</font color=blue>
There is a bit of a contradiction here 500 watts is not equal to 1/3 hp. 1/3 hp is about 250 watts.

 

[EdDekker]

An X10 controlled recepticale in the garage and an X10 controller in the house would give you the remote control (possibly even a timer).
see http://www.smarthome.com/x10map.html





Ed