|
Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
|
Thread Tools |
19th Oct 2015, 12:29 pm | #1 |
Heptode
Join Date: Apr 2014
Location: Wigton, Cumbria, UK.
Posts: 728
|
Choke test - are these reasonable values?
I have picked up this Igranic C40 Choke but without the benefit of any literature I don't know whether the test values seem reasonable. What do you think?
The Henries reading fluctuates between -3.65 and -4.01H. I didn't expect a minus figure. The reading won't hold steady either. The resistance reading is 15.22M ohms. I was shocked at how high the resistance reads. I know very little about chokes and would appreciate the benefit of your knowledge. Thanks Nick Last edited by SurreyNick; 19th Oct 2015 at 12:48 pm. Reason: Problem with image |
19th Oct 2015, 12:45 pm | #2 |
Dekatron
Join Date: Aug 2003
Location: near Reading (and sometimes Torquay)
Posts: 3,094
|
Re: Choke test - are these reasonable values?
Would that be what your meter does if connected to nothing, perhaps with something touching a lead to add a little mains hum?
Either your meter is broken or your choke is broken, or your are not connecting to it correctly. I would just add that negative inductance is capacitance. If your meter is looking at an open-circuit choke then maybe that is the kind of reading it would show. But check you have the clips attached to the right thing! Last edited by GMB; 19th Oct 2015 at 12:50 pm. |
19th Oct 2015, 1:00 pm | #3 |
Heptode
Join Date: Apr 2014
Location: Wigton, Cumbria, UK.
Posts: 728
|
Re: Choke test - are these reasonable values?
The meter seems fine I have tested it against a known item and it was true. With no continuity, whether something is touching one probe or not, the meter returns to 1.
My meter only reads to a maximum of 20H, but when I test it on a 100H choke it just reads 1, so I don't think it can be caused by that either. Addition Yes. I have just checked the meter on a capacitor on the Henries scale and it gave a minus figure. So the choke is almost certainly open circuit too. Last edited by SurreyNick; 19th Oct 2015 at 1:06 pm. Reason: Addition |
19th Oct 2015, 1:12 pm | #4 |
Moderator
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 21,287
|
Re: Choke test - are these reasonable values?
If the 15.22 Mohm reading is correct then the choke is open circuit.
I'd be inclined to remove the crock clips and probe the inductor terminals directly just in case there's a dodgy connection to the clips.
__________________
Graham. Forum Moderator Reach for your meter before you reach for your soldering iron. |
19th Oct 2015, 1:20 pm | #5 |
Heptode
Join Date: Apr 2014
Location: Wigton, Cumbria, UK.
Posts: 728
|
Re: Choke test - are these reasonable values?
Thanks Graham. I did what you said and the 15.22 Mohm reading is correct. It seems the choke is duff.
Nick |
19th Oct 2015, 1:23 pm | #6 |
Moderator
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 21,287
|
Re: Choke test - are these reasonable values?
Are you testing the right points? I guessing the two brass lined holes are for mounting screws, but what about the two studs? I'm assuming that only one stud is visible in the picture.
__________________
Graham. Forum Moderator Reach for your meter before you reach for your soldering iron. |
19th Oct 2015, 1:38 pm | #7 |
Heptode
Join Date: Apr 2014
Location: Wigton, Cumbria, UK.
Posts: 728
|
Re: Choke test - are these reasonable values?
Yeah I checked those studs Graham. Nothing on them. I came to the conclusion that Igranic used the same casing for a transformer and those would have been used for the additional two terminals. The two brass lined holes are indeed mounting points.
Nick |
19th Oct 2015, 1:46 pm | #8 |
Moderator
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 21,287
|
Re: Choke test - are these reasonable values?
Does it look like it'll come apart easily? If so rewinding looks like a simple job.
__________________
Graham. Forum Moderator Reach for your meter before you reach for your soldering iron. |
19th Oct 2015, 1:53 pm | #9 |
Heptode
Join Date: Apr 2014
Location: Wigton, Cumbria, UK.
Posts: 728
|
Re: Choke test - are these reasonable values?
Just about to have a look. I'll let you know. I may be lucky and find the break near the end of the winding.
N. |
19th Oct 2015, 2:52 pm | #10 |
Heptode
Join Date: Apr 2014
Location: Wigton, Cumbria, UK.
Posts: 728
|
Re: Choke test - are these reasonable values?
It was so clean inside I'm surprised it's open circuit. I'd swear it was brand new and unused. Just a light layer of rust on the outermost stamping and a slight discolouration to the top layers of cotton thread covering the wire. The cotton was still pure white underneath the outer layers. Sadly I can't find a break near the end of the winding so I suspect it's a rewind job or a new life as a paperweight!
N. |
19th Oct 2015, 3:17 pm | #11 |
Moderator
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 21,287
|
Re: Choke test - are these reasonable values?
That looks like reasonably thick wire, so rewinding by hand is a possibility. You've nothing to lose.
__________________
Graham. Forum Moderator Reach for your meter before you reach for your soldering iron. |
19th Oct 2015, 3:30 pm | #12 |
Heptode
Join Date: Apr 2014
Location: Wigton, Cumbria, UK.
Posts: 728
|
Re: Choke test - are these reasonable values?
A task for a winter's evening in front of the telly I think
N. |
19th Oct 2015, 5:23 pm | #13 |
Rest in Peace
Join Date: Jun 2006
Location: Chard, South Somerset, UK.
Posts: 7,457
|
Re: Choke test - are these reasonable values?
Indeed: which makes me a trifle suspicions of the diagnoses so far.
Nick - this remark may be too late, but better late than never. In my experience, trying to read the resistance of iron-cored inductors of a substantial inductance can often produce a high-resistance indication. Try measuring the resistance again - with a moving coil ohmmeter this time - such as AVO. If that produces a reading in the megohms range, then yes, that choke is definitely O/C. Al. Last edited by Skywave; 19th Oct 2015 at 5:27 pm. Reason: Add quote for continuity & relevance. |
19th Oct 2015, 6:15 pm | #14 |
Guest
Posts: n/a
|
Re: Choke test - are these reasonable values?
And try measuring it now the coil is out of the iron.
|
19th Oct 2015, 6:18 pm | #15 |
Heptode
Join Date: Apr 2014
Location: Wigton, Cumbria, UK.
Posts: 728
|
Re: Choke test - are these reasonable values?
Thanks guys. Did a quick check of the coil with my DMM free of the iron and still o/c. In light of this I'm guessing it isn't worth digging my AVO out of the garage?
Nick |
19th Oct 2015, 6:50 pm | #16 |
Rest in Peace
Join Date: Jun 2006
Location: Chard, South Somerset, UK.
Posts: 7,457
|
Re: Choke test - are these reasonable values?
In that case, Nick, I'd be inclined to state that the coil is O/C.
Of course, there is always the Ultimate Test: connect it to a low-voltage PSU - say 12v. d.c. (you might need a current-limiter in series) - and measure how much current flows in the coil. Zero current obviously proves an O/C: no ifs; no buts; no maybes. Al. |
19th Oct 2015, 7:14 pm | #17 |
Dekatron
Join Date: May 2008
Location: Derby, UK.
Posts: 7,735
|
Re: Choke test - are these reasonable values?
Or, to throw a curve ball, test the coil on a capacitance range .....
A short-circuit is equivalent to an infinite capacitance (since the voltage across it will never increase). If there is a break, the two continuous bits of winding either side of it will act as the plates of a capacitor, with the cotton or enamel insulation acting as the dielectric. So if it shows a sensible capacitance, you will know that there is definitely a break.
__________________
If I have seen further than others, it is because I was standing on a pile of failed experiments. |
19th Oct 2015, 7:37 pm | #18 |
Heptode
Join Date: Apr 2014
Location: Wigton, Cumbria, UK.
Posts: 728
|
Re: Choke test - are these reasonable values?
I'm pretty sure it's O/C, but I will still try the last two suggestions in the morning and report back. No stone left un-turned.... Thanks.
Nick |
19th Oct 2015, 7:42 pm | #19 |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
|
Re: Choke test - are these reasonable values?
If you have a piezo electric lighter, try connecting it up to the winding and seeing if you can see a flash in the dark. It's only ever worked for me once but worth a try.
|