Simple Elec Resistance Question for the Electrical Folks

[CrispyCringle]

Im diagnosing my Jabsco fresh water pump failure. Would not turn on. Turns out a solder connection came loose on the cut-off switch. I resoldered it. But then I wanted to check the operation of the switch with a Ohm meter to make sure it was good.

It does ON-OFF just fine. But doesnt the Ohm reading seem really high for a closed circuit? 2.9 M Ohms? Open circuit is obviously infinite Ohms. Could the high resistance have caused the original solder to fail? Or is that normal. Seems like a good switch would have the resistance of a good wire when closed, near zero for such a short distance?

Thanks in advance.

[thomm225]

Closed circuit or switch will be near zero ohms

You probably have something hooked up wrong.

Or the switch is bad.

Or the meter needs a new battery.

Or the "circuit" isn't really closed.

[CrispyCringle]

Originally Posted by thomm225

You probably have something hooked up wrong.

Closed circuit or the switch will be near zero ohms. (confusing sentence)

Or the switch is bad.

Or the meter needs a new battery.

Or the circuit isn't really closed.

So, I take that to mean -or the switch is faulty- and it should be near zero ohms when closed.

Not sure how it can be hooked up wrong, and battery is good.

[thomm225]

Originally Posted by CrispyCringle

So, I take that to mean -or the switch is faulty- and it should be near zero ohms when closed.

Not sure how it can be hooked up wrong, and battery is good.

Yes, the switch should be near zero ohms when closed.

What you are describing isn't possible with a good meter and switch if you have the meter hooked up correctly.

Btw, I have been an Electronics/Radar/IFF Tech or Tech Manager since 1975. Computer Tech since 1981.

We used Simpson 260 Analog Meters back in the day before the Digital Flukes came along.

[CrispyCringle]

Further investigation- I think the switch is faulty. If I move the soldered terminal around when closed, the resistance goes from near zero to Mega Ohms. Feels sort of loose.

I was mainly just needing confirmation on what the resistance should be for a good switch. $9.75 for two on Amazon.

[thomm225]

Originally Posted by CrispyCringle

Further investigation- I think the switch is faulty. If I move the soldered terminal around when closed, the resistance goes from near zero to Mega Ohms. Feels sort of loose.

I was mainly just needing confirmation on what the resistance should be for a good switch. $9.75 for two on Amazon.

Okay good.

Glad you found it.

[GordMay]

With the switch turned ‘on’ [closed] your multimeter [set on Ohms] should read close to zero; but, certainly 0.5 Ohms or less.

[Locquatious]

Switches are sensitive to heat over exposure time. The heat conducted into the switch will lead to melting of the plastic holding the switch contacts in place. The lead free solder (RoHS) has a higher melting point than leaded solder. When soldering switches, keep the time of heat exposure as short as possible. Consider using leaded solder on temperature sensitive components.

[CrispyCringle]

Originally Posted by Locquatious

Switches are sensitive to heat over exposure time. The heat conducted into the switch will lead to melting of the plastic holding the switch contacts in place. The lead free solder (RoHS) has a higher melting point than leaded solder. When soldering switches, keep the time of heat exposure as short as possible. Consider using leaded solder on temperature sensitive components.

Good point. The switch came from the factory with a bad solder joint. Looks like the solder never flowed and was kind of a ball sitting on the terminal. I wouldn't be surprised if the person doing the assembly had trouble getting a good solder joint and melted some of the stuff holding the terminal while trying to make a good connection. The pump was less than a year old. When I opened up the pressure switch a ball of solder fell out and the wire was not connected. The wire was tinned, but the terminal was not.