Solenoid Continuity Question Please

[konakid]

I have another long topic going about a 72v AC Cushman that I fear is getting unpleasantly complicated.

So, I would like to isolate and ask just one question here about the solenoid.

When the solenoid is disconnected from everything, should I have continuity across the small (primary circuit) terminals? Searching the web tells me I should.

However, I do not have continuity. Nor do I have continuity with a replacement (used) solenoid a repair shop gave me to test with. They both say 48v DC on the label.

Are both solenoids bad? I hope so, because that would mean I have probably found my problem.

This is the type of solenoid in question.

[ThreeCW]

Originally Posted by konakid

When the solenoid is disconnected from everything, should I have continuity across the small (primary circuit) terminals?

Yes, with the solenoid disconnected, you should have continuity between the small, COIL terminals. The small terminals are connected to the coil which activates (connects) the large, PRIMARY terminals of the solenoid.

I tested my previous solenoid (it was completely disconnected after I had damaged it by twisting off one of the large, PRIMARY posts) and measured 330 ohms between the two small solenoid terminals. I then function tested the solenoid by applying 48 volt battery pack voltage across the two small solenoid terminals, and the solenoid functioned correctly (audible clicking of the solenoid and continuity between the two large, PRIMARY terminals). With no power applied to the small terminals, there was no continuity between the two large, primary terminals.

I installed a different make / rating of 48 volt replacement solenoid and with the system completely powered down (via my battery switch), I measure 134 ohms of resistance between the two small, coil terminals.

So I am confident that you should be seeing continuity (with some resistance) between the two small, coil terminals!

I have attached a few photos for your reference:
1) Old Solenoid before removing
2) Old Solenoid after twisting off main post
3) Old Solenoid disassembled (note coil wires were connected to the small solenoid posts)
4) New Solenoid installed

Note - I believe that my old solenoid is either the same as or very similar to the solenoid that you have pictured.

So I am lead to believe that both your old solenoid and the used replacement solenoid are NFG (not functioning good).

[konakid]

Thanks a million ThreeCW,

I find it weird that in all the solenoid troubleshooting guides I have been reading they give you all kinds of tests to run if the secondary contacts are not closing. But I only found one YouTube video that said to test your coil by checking for continuity when totally disconnected. I thought if that was true, that would/should be the first and a simple place to start troubleshooting. So, I thought that advice might be in error.

But I also find it weird that I should be given a replacement "test" solenoid (that a repair shop said was good) - and that it would also have a bad coil - that is, no continuity. So again, I thought maybe that was not accurate advice.

Can anyone else confirm what I thought would be the case, and what ThreeCW also thinks is the case - that a solenoid should have continuity between the small (primary) terminals "out of the box."

[ThreeCW]

I also responded on your other thread. Perhaps this is a solenoid "over-voltage" problem"!

[BobBoyce]

Warning! Complex answer to a simple question. I'm an engineer, so I tend to view things in a more complex manner than most people. I will attempt to limit my response, and to frame it in a way thay you may be able to understand.

Solenoid coils are not a simple resistance. Since they are technically an inductor (coil of wire) that creates a magnetic field in response to applied current, it is more complex than simply measuring continuity.

A multimeter should measure simple resistance of the coil, ie about 330 ohms. However, a multimeter in continuity mode is usually "looking" for a value of less than 200 ohms as having continuity, and a value of more than 200 ohms as being "open", ie no continuity. So a simple DMM continuity test with most digital multimeters will not be a reliable test for a 48 volt solenoid coil. In this case, you would use the resistance scale, ie 2,000 ohm (2K ohm) scale and measure the DC resistance of the coil. On the 2K scale, a 330 ohm solenoid coil would likely read as around 0.330 which is 0.330 K (Kilo-ohms).

Purely resistive testing does not guarantee that a solenoid is good. There can be damage to the coil or coil form caused by heating that prevents the metal core from pulling into the hole through the center of the coil form, preventing the solenoid from actuating, or damage to the contacts or contact mounts, preventing a high current contact from being made. It is entirely possible to read a contact closure on a high impedance multimeter, yet the contact may not carry high current due to excessive resistance.

I know you are looking for a simple answer, but you need to know why the answer may not always be so simple.

I hope this helps.

[scottyb]

That's a very good explanation.

[ThreeCW]

Bob,

A great explanation on CONTINUITY Thanks for getting us "non-Electrical Engineers" straight once again (with respect)! I obviously did not fully appreciate "continuity" vs. "a low resistance value".

So as you say, a functional solenoid's COIL terminal will likely NOT have continuity (i.e. in the case of greater than ~200 ohms of coil resistance).

But I assume that a "functional" solenoid coil (and I used the word "functional" loosely) should exhibit a proper resistance reading ... i.e. ~ 336 ohm for the White Rogers Type 586 SPNO Continuous solenoid (if this is the solenoid that "konakid" is dealing with) as per the attached White Rogers spec. So if the coil resistance checks out, then at least "konakid" could check off that box in his troubleshooting. Conversely, if the coil resistance did not check out, then it may point to a potential solenoid problem.

"konakid" - It will be interesting to find out what the coil resistance readings are for your two solenoids and any function testing results with system voltage applied to your solenoid coil(s).

[kgsc]

I am also thinking that the activation circuit on this beast is not pack voltage hence the 48 volt solenoid. I also agree Bob is WAAAYYYY smarter than me so he knows his stuff. I would think that testing a solenoid in the way you have would say you have a bad solenoid. The results you get I don't think would matter as long as you got something. I would think nothing is an open coil and hence bad. Now all that being said if the activation circuit is 72 volts I wouldn't think a 48 volt solenoid would be happy about that for long so it is possible the used one you got may have been good then got fried..

[radioman]

Another way to test a solenoid is to listen at it when its rated voltage is applied to the coil or the two small terminals. It should go click. If it don't it is bad.

[scottyb]

You can do click testing but, I've had many clicking solenoids that were not making contact or marginal contact that passed a big post continuity test but dropped out when a real load was applied.

Sometimes you just have to take the cap off and see what's going on