Trailer wiring

[Jim Eh.]

Craig,

Is there a special reason to use the 1N4004 diode or can it be substituted with something else?

Reason is my local supplier does not usually carry that particular one.

Thankz,
Jim

[Lee Bradley]

These are the diodes I use http://www.ebay.com/itm/290641207911?_trksid=p2060778.m1438.l2648&ssPageName=STRK%3AMEBIDX%3AIT
Easy to mount, high capacity, easy connecting and only about 90 cents each. Plus four diodes in each bridge. 

[Oonrahnjay]

These are the diodes I use http://www.ebay.com/itm/290641207911?_trksid=p2060778.m1438.l2648&ssPageName=STRK%3AMEBIDX%3AIT
Easy to mount, high capacity, easy connecting and only about 90 cents each. Plus four diodes in each bridge. 

    OK, now I'm confused by two things ....
1)   Do you need a full bridge rectum fryer for this diode arrangement?
2)   (To Gumpy)  Why do you need diodes and the jumper across the coil terminals at all??

      Yeah, I'm easy to confuse .....

[Lee Bradley]

You don't need a full bridge but they are already potted and have nice spade connectors.

[Jim Eh.]

I believe the diode is to protect from a voltage spike back down the circuit when the relay closes. Don't know much about electronics thus my newbie question on the diode type.

[bevans6]

"2)   (To Gumpy)  Why do you need diodes and the jumper across the coil terminals at all?Huh?"

Not gumpy, but I do know the answer to this question.  You recall how in a gasoline engine you use a coil to generate the spark in the spark plug?  The coil in the relay that switches the relay on and off also stores up energy, and the diode shunts off that energy to eliminate issues from that stored energy.  It could cause issues with voltage spikes being fed back to whatever is switching the relay, or cause the relay to hang up and not switch properly.

Brian

[Oonrahnjay]

"2)   (To Gumpy)  Why do you need diodes and the jumper across the coil terminals at all?Huh?"

Not gumpy, but I do know the answer to this question.  You recall how in a gasoline engine you use a coil to generate the spark in the spark plug?  The coil in the relay that switches the relay on and off also stores up energy, and the diode shunts off that energy to eliminate issues from that stored energy.  It could cause issues with voltage spikes being fed back to whatever is switching the relay, or cause the relay to hang up and not switch properly.

Brian 

     Thanks.  I'm stupider about electrical stuff than I thought, I guess.  I still don't see it but I'll take your word and Lee's and Gumpy's on it.   Does "every" relay have a jumper and diode?  If not, why not.  Doesn't every relay have a ground on the coil and energy in the coil?  Isn't it the job of the ground to take away energy?  If I read it right (and I guess I don't), that relay is set to direct energy back to the trigger wire.  Is that what we want?

[bs4104]

Some cube relays have them built in to them>>>Bruce

[Scott & Heather]

Gumpster, I really need to pay you to make one up for my MCI9..... Please?


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[Lee Bradley]

This has gotten a little far afield but coils can produce very high voltages with very little current. When the coil is energized a magnetic field is generated around the coil the rate that the field is generated depends on voltage and current available. When the coil is switched off, the switch opened, the magnetic field collapses much faster than it was generated, the magnetic field collapsing back across the coil winding generates a reverse voltage higher than the applied voltage but less current. This back voltage is not a problem on mechanical switches other than a little arcing when the switch is opened. When solid state switching was introduced, these high reverse voltage created problems as the solid state systems are very voltage sensitive. So a diode has added to drain the reverse voltage to ground and not back to the switch. Most relays are not polarity sensitive but if you have a diode protected relay and hook the coil up backwards it will toast the diode.  Gasoline engine coils also create a magnetic field when the points/switch is closed and the field collapses when the points/switch opens but that would create a single high voltage spark at the spark plug not the best for lighting off the gasoline/air mixture. So they added a condenser/capacitor to the circuit (creating a tank circuit see Tesla). The condenser stores the current created by the collapsing field across the primary windings of the coil while current created in the secondary windings go to the spark plug but when the magnetic field has collapsed the current stored in the condenser flows back into the coil's primary windings creating magnetic field and another high voltage in the secondary and to the spark plug. The condenser/coil continues to charge/discharge until the energy in the system can no longer produce enough voltage to jump the spark plug gap. Shortly thereafter the points close and recharge the circuit for another go.

[Oonrahnjay]

... back voltage is not a problem on mechanical switches other than a little arcing when the switch is opened. When solid state switching was introduced, these high reverse voltage created problems as the solid state systems are very voltage sensitive. So a diode has added to drain the reverse voltage to ground and not back to the switch. ...  

   OK, that's the "back story".  Diodes probably not needed (but likely to be an advantage) for plain switches but probably needed to prevent damage for solid-state switching.  Thanks for the help - I learned something today and I like that.   BH

[gumpy]

Gumpster, I really need to pay you to make one up for my MCI9..... Please?


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I sent you an email...

[Scott & Heather]

Thanks Craig! I'll be in touch


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[Jim Eh.]

Thanks for the schematics Craig. I even put a copy of them inside my enclosure so that WHEN I'm old and senile I can figure out any electrical problem. I just have to remember where I mount the damn box!