How much is too much?

[scdmarx]

Something I learned today and thought this info might be usefull someday.

A good rule of thumb to use for any circuit is:
The amp draw should not be more then 60% of the protection devise, as a
fuse.
Example: 25 amp fuse X 60% is 15 amps.
Anything above this for a prolong time is going to cause extra heat within
the circuit causing a burn out later on. Most radiator
cooling fans pull between 9 and 11 amps on a 20 amp circuit.
If the wire is getting to hot, then either the motor is
drawing to many amps, or the wire is to small to carry the
load.

 

[AApple]

:thanks: :good:
Add to that info that corroded, or loose connections can also create high amperage conditions. :yes:

 

[dan filipi]

Good stuff to know.

 

[WindNWing]

I would like to clear up a common misconception if I may.

A corroded/dirty or loose connection will not cause higher current in a circuit. What it will cause is heat which can melt insulation causing a short to ground or lower voltage to the load and cause a dimmer light or excessive heat in coil or motor windings which can melt the varnish insulation and create a short. It doesn’t matter where in the circuit this happens which means a poor ground can cause the same problems.

The current will actually become lower which can be shown in the formula I = E/R.

I = current, E = voltage and R = resistance

If a bulb has 2 ohms of resistance the calculation would be I = 12/2 resulting in 6 amps of current, if we introduce another 2 ohms of resistance due to a faulty connection the new calculation is I = 12/4 witch will only draw 3 amps of current but the bad connection is producing as much heat as the bulb and the bulb is only seeing 6 volts and the other 6 volts is dropped over the weak connection which results in a dimmer light.

The opposite of higher resistance will cause more current flow. A short to ground ahead of the load will see only the resistance of the wire which is near zero. That becomes I = 12/0 or 12 amps of current which will certainly fry a 10 amp fuse in a hurry.

Loose/dirty/corroded connections are a bad thing. :head bang:

I thank you for your patience.

 

[dan filipi]

Even better stuff, Gary. Thanks for clearing that up!

 

[scdmarx]

I would like to clear up a common misconception if I may.

Please do! I was hopeing for some conversation out of this.

A corroded/dirty or loose connection will not cause higher current in a circuit. .

I agree. This makes sense to me.

What it will cause is heat which can melt insulation causing a short to ground or lower voltage to the load and cause a dimmer light or excessive heat in coil or motor windings .

You have a gifted way with words. :grin: You can make explanations seem simple.
Can you explain to me what exactly is makeing the "heat" at a dirty or loose connection?

I thank you for your patience.

Thank you for yours.

 

[WindNWing]

Can you explain to me what exactly is makeing the "heat" at a dirty or loose connection?

When current is forced through a resistance by the voltage there is a certain amount of power produced which is measured in Watts. A 100 watt bulb will be hotter to the touch than a 40 watt bulb. That wattage is heating the filliment, the fact that it heats it to white hot also produces the light.
In the case of a bad connection, there is no usfull work being done so the energy is given off only as heat. The light bulb and socket are designed to handle the heat but the bad connection isn't, hence the melted insulation that we are all familier with.

 

[joedrum]

who would like windnwing around the next time you had to wire somthing .... :good: k: :mrgreen:

 

[slabghost]

I would! He could stop by and tell me how to fix my wiring. :head bang:

 

[WindNWing]

I’m not so sure guys. For some reason when my left turn signal is on, the light goes out on my volt meter..... :head bang: I have no idea why.

But then the left turn signal isn’t on very often and when it is, it’s not on very long...Yeah, I can live with that. :smilie_happy:

 

[scdmarx]

When your signal goes out and your meter starts blinking, then you know you got a problem.

 

[slabghost]

My left signal indicator light stays on until I use the signal then it stays off. Right flashes normally and my high beam indicator light is on regardless of high or low beam use. But all the lights do work!