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  #21  
Old 12-27-2017, 08:01 AM
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Mel Mel is offline
 
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Quote:
Originally Posted by rmarshall234 View Post
Here is an experiment I would like to try but it will be about 2 weeks until I am able...
While cranking the starter motor shut off the master solenoid and see if it actually removes power from the starter motor.
I strongly recommend that you do NOT conduct this experiment. The master solenoid was not meant to be switched "HOT". Being switched off with that much current flowing will produce a pretty good arc, probably damaging the master switch contacts.
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  #22  
Old 12-27-2017, 10:09 AM
rmarshall234 rmarshall234 is offline
 
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Some good comments here and now my own...

It it's not high current but instead high voltage, what is _that_ force called?

The welding explanation would explain why it's hard to remove the wrench but what about it being pulled in? I do like this as a possible/partial explanation however.

One of the reasons it will be a couple of weeks before I conduct the experiment is because that is when my new master relay will be here. Experiment first, replace the old relay (time is service concerns) second.

The fellow that felt the need to comment about my technique should wiki the term self-deprecating humor.

I will conduct the experiment and report back, it seems like a worthwhile thing to do. Besides, the title of the thread is "are we abusing our master-contactor solenoids?".
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  #23  
Old 12-27-2017, 12:26 PM
Mich48041 Mich48041 is offline
 
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A wrench does NOT get pulled in. It might seem that it does, but the only force is inertia while the wrench is being turned. Electric motors convert electricity into motion using magnetism. In order for a wrench to be "pulled in", it must be subject to a large magnetic field. And the only way to have a large magnetic field is by having a large electrical current. And there is no large electrical current until AFTER a wrench accidentally shorts positive and negative together. If it could be done SAFELY, conduct an experiment that demonstrates a wrench getting pulled in.
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  #24  
Old 12-27-2017, 03:38 PM
rv7charlie rv7charlie is offline
 
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The force pulling the wrench in to the battery terminal is the same force that tries to pull you over the edge when you look over a cliff.


;-)

BTW, the force in your example of getting 'hooked in' when grabbing the hot wire in house mains voltage is the same force that your brain uses to make your hands grab something. It's just a few million times stronger.

Last edited by rv7charlie : 12-27-2017 at 03:42 PM.
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  #25  
Old 12-27-2017, 04:29 PM
rmarshall234 rmarshall234 is offline
 
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Originally Posted by Mich48041 View Post
A wrench does NOT get pulled in. It might seem that it does, but the only force is inertia while the wrench is being turned. Electric motors convert electricity into motion using magnetism. In order for a wrench to be "pulled in", it must be subject to a large magnetic field. And the only way to have a large magnetic field is by having a large electrical current. And there is no large electrical current until AFTER a wrench accidentally shorts positive and negative together. If it could be done SAFELY, conduct an experiment that demonstrates a wrench getting pulled in.

Beautiful!! I love it!

could it be the that the Arc of the electrical connection being made is what creates the sensation that the wrench is being pulled in? And, once the arc has been established then the magnetic field has also been established??

Interesting...another opportunity for an experiment.
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  #26  
Old 12-27-2017, 04:36 PM
rmarshall234 rmarshall234 is offline
 
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Quote:
Originally Posted by rv7charlie View Post
The force pulling the wrench in to the battery terminal is the same force that tries to pull you over the edge when you look over a cliff.


;-)

BTW, the force in your example of getting 'hooked in' when grabbing the hot wire in house mains voltage is the same force that your brain uses to make your hands grab something. It's just a few million times stronger.
Sorry, I've got thousands of skydives and have looked over many cliffs and have been hooked up a couple of times, but can't make the same connection as you.
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  #27  
Old 12-27-2017, 05:28 PM
rv7charlie rv7charlie is offline
 
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Different 'forces'. You may not be susceptible, but many of us *feel* pulled toward the edge when we look over a cliff. No real effect unless we step off.

The force when you get 'hooked up'...I don't know how to explain it any more clearly, but that one is real. Just a lot stronger when you grab 120 volts than when you grab a sandwich.
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  #28  
Old 12-27-2017, 09:50 PM
rmarshall234 rmarshall234 is offline
 
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Not sure if you are talking psychology or physics. (But assuming the latter since that is what I thought the thread was about...)

>many of us *feel* pulled toward the edge when we look over a cliff. No real effect unless we step off

Care to conduct your own experiment? I'll provide the parachute and, a reasonable level of training to assure you survive.

>but that one is real

But is it stronger when you grab 240 or 480 volts? And is it the voltage or the current that is the dominate factor? I haven't been to that level myself (although I once got "hit" by 277 volts ) so I can't speak to it.

So many questions, so few answers..
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  #29  
Old 12-28-2017, 06:53 AM
rv7charlie rv7charlie is offline
 
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The interwebs really do have very effective humor and nuance filters.

The 'edge of a cliff' example was intended to be an analogy. Some of us feel a weird psychological 'pull' when looking over a cliff, but gravity only works down; not at an angle or curve. The analogy is to feeling the wrench 'pulled' toward a terminal where it shouldn't be. Now, if either the wrench or the terminal is highly magnetized (and both are made of ferrous metal), they could be attracted. A starter motor or alternator/generator may well have permanent magnets inside, or even residual magnetism (depending on design). But with a lead battery terminal, you shouldn't have magnetic attraction (but the psychological attraction may be there, for some of us).

On getting 'hooked up': the electrical impulses from your brain are quite weak. 120V is a *lot* stronger. 240V is stronger still, etc.

Honestly, I won't attempt to answer whether it's voltage or current that actually causes the 'grab' action, but it doesn't really matter in practical terms because of Ohm's Law. If you grab a 12 volt line, you probably won't even feel it if your hands are dry and even slightly calloused. There isn't enough 'pressure' (to use the old water flow analogy) in 12V to push current (electron flow) into and through your body to trigger your muscles. Electrical safety codes have traditionally used 70V as the threshold between 'safe' and 'dangerous'; requiring any terminals at >70V potential to be protected from incidental human contact.
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  #30  
Old 12-28-2017, 07:37 AM
Tomcat RV4 Tomcat RV4 is offline
 
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You are correct,auto starters stopped using separate solenoids in 50s, in auto conversion,
(Subby) ignition switch worked starter flawlessly with out separate solenoids.when was
last time you burned up starter in auto cause stayed engaged ? Tom
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