Voltages through a solenoid?

[Flatspot]

Fred,
Relay's and solenoids have what is called a 'pick-up voltage' requirement. It takes a certain voltage to pull the relay or solenoid in. There is another voltage that is called a 'hold-in voltage' and that is the voltage required to hold the relay in and is below what the pick-up voltage is.
I'm suspect that with the 'no charge' light on because the pick-up voltage hasn't been achieved and when you rev the engine up the generator/alternator puts out enough voltage for the system voltage to increase above the relay's or solenoids pick-up voltage. If you let the engine idle back down and the no charge light comes back on but the fans keep running that is because the systems voltage hasn't dropped below the hold-in voltage.
Hope that this helps.
LJ

[Gary '79 5C]

  The duty cycle has to do with the control winding. Most intermittent solenoids or relays would heat up and burn out
if left on without any current going through the switch contacts.    06 Bill

Bill, I beg to differ, as the duty cycle has every thing to do with the contol winding, and nothing to do with the switch contact ratings.

I agree with your second comment that an intermittent solenoid will burn out if left ON.  However it has nothing to do with the current thru the switch contacts.

[JohnEd]

  The duty cycle has to do with the control winding. Most intermittent solenoids or relays would heat up and burn out
if left on without any current going through the switch contacts.    06 Bill

Bill, I beg to differ, as the duty cycle has every thing to do with the contol winding, and nothing to do with the switch contact ratings.

I agree with your second comment that an intermittent solenoid will burn out if left ON.  However it has nothing to do with the current thru the switch contacts.

You are both saying the same thing.  I fear this circumstance as I have seen it go to a blood letting. 

[boogiethecat]

FWIW I edited my earlier post for some clarification on what these "solenoid" things are really called.  Just like everyone calling those long skinny oil filled things that make your ride smoother "shocks" when really they should properly be called "shock absorbers", people call the things we're talking about here "solenoids" when really they oughta be called "solenoid operated contactors".  But let's get real and quit picking on words... nobody is gonna go around talking about their "solenoid operated contactor" when they can say the simple word "solenoid" and get the idea across. We're just too lazy, and the short version is too widely accepted!!!

As far as continuous duty vs intermittent duty, the only difference is in the coil windings of the device.  The coils of "Intermittent" solenoids draw more power than those of "continuous" rated solenoids, and if left on for very long at all they will overheat and burn out.  If you're going to leave a solenoid on for more than say 30 seconds, you would be wise to purchase a "continuous duty" solenoid.  It can be left on all day without issue.

None of the above as a thing to do with contacts, contact current, or contact voltage.  

[Gary '79 5C]

Thanks JohnEd,

Absolutely correct. I reread the posts and I am wondering what the he11 I was thinking....  Just spent (3) days watching (5) games Atlantic 10 Basketball Tourney. Came home and thought I could read and think.

What was I thinkin ?

[chev49]

I'm an idiot of course, but i have no idea what the word "Intermittnet" means... my dictionary doesn't speak that language either.

[rv_safetyman]

Kind of fun to read this thread.  I have just finished the second draft of a "relay 101" article for BCM.  Should have the final to them tomorrow. 

BTW, one of the reasons that the magazine is sometimes late: authors who are 3 days past the deadline

Jim

[gus]

Fred,

That blower motor takes 30 amps on a 4104 and I presume the 4106 requires the same since the two buses are a lot alike. That is one huge motor, my lights dim when it first comes on.

A good example of solenoids vs relays is the bus starting circuit. The front panel starter switch closes a relay in the rear of the bus which closes the solenoid on top of the starter which pushes a rod which engages the starter motor gear to the flywheel.