Voltage Drop Test Video

Hobo,NC

Well-known Member
Location
Sanford, NC
Its slow how about some new fail safe diagnostics... Someone here stated what the voltage on the dist side of the coil should be points closed he said zero. I don't think that was the answer the guy was looking for are what I would have thought it should be.

I had to think about it for a week are so it would be zero if you were preforming a voltage drop test. This test would prove the points and associated parts that complete the ground path were intact and good...

You would have to prove the supply voltage was intact and good to rule out a false reading... In this case the ignition the coil would be the load (resistance) think of the light in the video as a coil...

https://workshop.searchautoparts.co...-ground-side-what-does-it-mean.html?cid=95875
 
Neat video.

If I had to change it, I that that troubleshooting portion at the end, he could had used the terminology to illustrate a voltage drop across the load. Even better, if he had 3 lamps in there so he could show net total.

Still, not a bad video.

I like the poster board with drawn on parts and real components as visual aids.

I think I'm gonna partially rip that off. I'm training 2 new lighting techs, and 2 sound techs this coming month, and this would be a grew signal flow diagram. Way better than me just pointing any talking and trying to keep their attention during training :)
 
Cool video and a great topic since it comes up here so often!

Taking queues from the video, ignoring the minor resistance in
wiring and connections, points closed puts ground on the distributor
side of the coil. The coil would be the load (light) and would
"consume" all the voltage leaving zero or as he said, "close to"
on the distributor side. If it were not, then the points are not
closing or you have a bad connection, etc causing his "unwanted
resistance" in the circuit. Is that not how you see it?

Of course welded together point contacts, slipped points or a
wire touching ground would give you that same reading and no
spark which is why we have to check with points open too.
In his analogy, they are the control device/switch.
 
(quoted from post at 05:00:54 11/03/15) Cool video and a great topic since it comes up here so often!

Taking queues from the video, ignoring the minor resistance in
wiring and connections, points closed puts ground on the distributor
side of the coil. The coil would be the load (light) and would
"consume" all the voltage leaving zero or as he said, "close to"
on the distributor side. If it were not, then the points are not
closing or you have a bad connection, etc causing his "unwanted
resistance" in the circuit. Is that not how you see it?

Of course welded together point contacts, slipped points or a
wire touching ground would give you that same reading and no
spark which is why we have to check with points open too.
In his analogy, they are the control device/switch.

The voltage would be from positive (+) to negative (-)

To check the positive power side voltage drop ground the coil (load) negative are add a load equal to the coil like a head light bulb in place of the coil...

Think about how you check it to get zero you are checking the ground side only.... What you have is the voltage drop on the ground side...

It takes time to play with it, its easier to get a handle on using a bulb as a resistance in the circuit. The bulb is a resistance in the circuit as a bad connection would be in a starting circuit be it the power side are ground side...

The way I learned to do it...

One (1) lead on the battery post the other (2) on the cable end at the bat load circuit, Pass (one lead will stay on the battery post)

Move 2 lead to were the cable wires leave the bat post cable end load circuit, pass

Move 2 lead to terminal end on end of cable load circuit, pass

Move 2 lead on stud of starter solenoid load circuit, pass

Move 2 lead on output side of starter solenoid load circuit, pass

Move 2 lead to starter post, pass

If any fail you issue is between there and the last test... Do the same test to the ground side... The thing you have to remember is the circuit has to be loaded to check voltage drop...

Jessie tell me this

The voltage would be from positive (+) to negative (-) ohms law deduct the resistance.... Why does it not work that way..

I test a 3 ohm coil apply voltage (12V) to one side and ground the other I get 11V on the ground side :?:
 
"Think about how you check it to get zero you are checking the ground side only.... What you have is the voltage drop on the ground side... "

Yes, that's exactly what I want. Good connections and closed
points should drop zero volts or very close to zero.

I don't see anyway to get 11V on the grounded post unless it is not
truly grounded. Maybe I'm missing something, but I don't think I am.
Always willing to listen though!

Your steps make sense. To save time and measurements (and
in my case, possible mistakes) I would divide the circuit in half
and check the middle. That reading, good or bad, would point to
which half is suspect. Divide the suspect side in two and check
that portion in the middle.
Lather, rinse, repeat until I'm down to the problem.
 
(quoted from post at 20:24:11 11/02/15)
(quoted from post at 05:00:54 11/03/15) Cool video and a great topic since it comes up here so often!

Taking queues from the video, ignoring the minor resistance in
wiring and connections, points closed puts ground on the distributor
side of the coil. The coil would be the load (light) and would
"consume" all the voltage leaving zero or as he said, "close to"
on the distributor side. If it were not, then the points are not
closing or you have a bad connection, etc causing his "unwanted
resistance" in the circuit. Is that not how you see it?

Of course welded together point contacts, slipped points or a
wire touching ground would give you that same reading and no
spark which is why we have to check with points open too.
In his analogy, they are the control device/switch.

The voltage would be from positive (+) to negative (-)

To check the positive power side voltage drop ground the coil (load) negative are add a load equal to the coil like a head light bulb in place of the coil...

Think about how you check it to get zero you are checking the ground side only.... What you have is the voltage drop on the ground side...

It takes time to play with it, its easier to get a handle on using a bulb as a resistance in the circuit. The bulb is a resistance in the circuit as a bad connection would be in a starting circuit be it the power side are ground side...

The way I learned to do it...

One (1) lead on the battery post the other (2) on the cable end at the bat load circuit, Pass (one lead will stay on the battery post)

Move 2 lead to were the cable wires leave the bat post cable end load circuit, pass

Move 2 lead to terminal end on end of cable load circuit, pass

Move 2 lead on stud of starter solenoid load circuit, pass

Move 2 lead on output side of starter solenoid load circuit, pass

Move 2 lead to starter post, pass

If any fail you issue is between there and the last test... Do the same test to the ground side... The thing you have to remember is the circuit has to be loaded to check voltage drop...

Jessie tell me this

The voltage would be from positive (+) to negative (-) ohms law deduct the resistance.... Why does it not work that way..

I test a 3 ohm coil apply voltage (12V) to one side and ground the other I get 11V on the ground side :?:
don't understand the question, Hobo.
 

I test a 3 ohm coil apply voltage (12V) to one side and ground the other I get 11V on the ground side.

Take a 12V lead and hook it to the + side of a 3 ohm coil
Ground the other side negative what voltage should I see on a volt meter one to positive and the other to negative.

I would have thought 12 divided by 3 I would get 4V.
 

OK

It would depend on were they installed there leads :idea:
What would the voltage be if he put one lead on the battery side and the other on the negative side points closed...
 
(quoted from post at 21:54:52 11/02/15)
I test a 3 ohm coil apply voltage (12V) to one side and ground the other I get 11V on the ground side.

Take a 12V lead and hook it to the + side of a 3 ohm coil
Ground the other side negative what voltage should I see on a volt meter one to positive and the other to negative.

I would have thought 12 divided by 3 I would get 4V.
lose but no cupie doll. V/R=amps. 12v/3 Ohms = 4 amps
You should see 12v, assuming that it is a good stiff 12v supply & nothing lost in wires & connections. V= I x R = amps x Ohms =4 x 3 =12v
 
(quoted from post at 22:14:04 11/02/15)
OK

It would depend on were they installed there leads :idea:
What would the voltage be if he put one lead on the battery side and the other on the negative side points closed...

In a perfect world, battery voltage. Assuming no other resistors
in the circuit. 12V system with a 6V coil and a ballast/dropping
resistor would be less of course. Depending on value of resistor.
 

It don't work out that way why I dunno... 12Vs I don't fudge with 6V chit...

The coil is a load you will get a voltage drop... I can not work the math to make it work out never was in the Navy that mite be a problem :cry:
 
"The coil is a load you will get a voltage drop... "

Agreed. As long as there is current flow. (under load)
If it is the only load, it will drop all the voltage.
Just like the single light in the video.
Zero on one side (measured to ground) 12V on the other
side measured to ground.
12V across the light since one side is zero and the other side 12V.
 
Something I have checked with a meter is starter cable resistance..... read from the battery to the starter post. Doesn't matter, tractor, car, airplane... the test is the same. You will read battery voltage until the starter is engaged or powered, then you will read "voltage loss" over the total circuit.

But it matters not if it is a lighting circuit, the test is the same. Voltage loss equals unwanted resistance, then you work to troubleshoot and minimize the loss.

When the circuit purposely employs items of resistance, each must be held to account and purpose.

Good video, I liked it!

duey
 

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