# Voltage from nowhere.



## AVB (Nov 28, 2014)

I got something that doesn't make any sense to me.

It is on lawnmower. I having a voltage reading across a solenoid (basically a Relay) when none being applied. One side is ground to the frame and when testing on the positive side when no apparent connection B+ made. Ie the ignition is run mode and not start mode.

No it not a wire short the circuit. As after I replace both battery cable ends the circuit works correctly. I know that both battery terminals were corroded but don't explain the fathom voltage reading. No complete voltage circuit even to produce a voltage drop across a resistive bad contact. Ignition would be like a light switch in off mode.


----------



## AVB (Nov 28, 2014)

Also I meant to say there is no capacitor in the circuit just the solenoid. Without voltage there is a 11VDC reading and then when I apply 12VDC I get 12 VDC.


----------



## Done_Fishin (Oct 10, 2006)

At first I thought we were maybe talking about low voltage readings which can be caused by different types of metals being connected together .. however these are normally in the form of millivolts ..

Is this voltage being seen only when the battery is connected ?? If the battery is removed does the voltage disappear ?? It could just be that there is a high resistance circuit somewhere in parallel with the open circuit towards the battery .. 

I am assuming that you are using a digital multimeter which has an internal resistance about 10 ΜΩ .. you are seeing a voltage of 11Volts so somewhere there must be a resistance approaching 1 MΩ towards the battery .. 

try using an analog multimeter, they have a much lower internal resistance of around 30 ΚΩ / Volt / Range (if my memory serves me well) the voltage reading on the 10 volt scale will fall to less than one volt since most of the voltage will drop across the larger "hidden" resistance. 

Just remember that when using test equipment, the equipment being used will make a circuit (create resistance across) what you see in your mind as an "open circuit" thus creating a new circuit and as such puts errors into your calculations .. different types of equipment create errors according to their internal resistance.


----------



## AVB (Nov 28, 2014)

I knew there were bad electrical connections are the battery so voltage drops would be apparent if I was testing from the battery negative terminal but I was getting this reading when testing the solenoid circuit independent of the battery terminal.

When testing the solenoid I was grounding at the solenoid ground point and testing at the B+ input to it at the ignition which was an open circuit. Now with the meter + lead across the B+ input and the negative lead connected the solenoid ground at the solenoid itself the voltage was appearing with no voltage input.

Anyway I got the mower working now so I just leave it as a fathom reading. Never had a reading like this with my Wavtek DVMM meter but it retired itself after 20 yrs and the Tenma auto ranging meter is newly put in use.


----------



## Done_Fishin (Oct 10, 2006)

Glad you got the mower sorted .. Phantom voltages are never really Phantom .. there is always a reason .. probably need a circuit diagram to understand exactly where this one was coming from ..


----------



## Wrench97 (May 10, 2008)

I've had strange reading across switches and solenoids due to internal moisture when using a digital meter.
On one particular 1980's model Ford truck with a 2sd rear and electronic speedo the speedo read wrong in high range usually this almost always meant a bad air switch on the front xmember however when testing with a normal test light the light never lit up and circuit would then work correctly for a day or 2, then I noticed if I tested it with my new at the time digital volt meter I would get 8.x volt reading at the speedo head connector however if I used a test light on the circuit at the same time the reading dropped to 0v then worked correctly.
The incandescent lamp in the test light pulled enough current through the switch to burn off the moisture that was completing the circuit for the digital voltmeter and digital speedo..........................
Bottom line always try to test a loaded circuit if you see something strange load the circuit with something as simple as a incandescent lamp and retest.


----------

