Hammond 193J 10H choke test at 6.2H - Page 1
Forum section: electronics / beginners

author: pwnell
author_rank: Regular Contributor
timestamp: January 28, 2021, 06:55:48 am
content: I have a new Hammond 193J 10H choke that I just tested, and it is 6.2H at 100Hz. The data sheet suggests 15% tolerance, so this is clearly not in spec. Any ideas what is going on? I tested it using both the DER5000 and BK879B.

author: dzseki
author_rank: Frequent Contributor
timestamp: January 28, 2021, 07:10:36 am
content: Perhaps the iron core (I assume it has one) lost some of its permeability... But does this cause any issue?

author: pwnell
author_rank: Regular Contributor
timestamp: January 28, 2021, 07:47:39 am
content: How would it have lost its permeability? It is brand new, never used. Just wondering. I am about to build my valve amp so worried that this being 6.2H would not match my design of 10H and cause more ripple in my power supply.Here is the data sheet:https://www.hammfg.com/files/parts/pdf/193J.pdf

author: dzseki
author_rank: Frequent Contributor
timestamp: January 28, 2021, 08:39:54 am
content: OK I missed that it is brand new item, then 100Hz measuring frequency should be the clue, the datasheet clearly defines the exact measuring parameters eg. measured at 60Hz. Obviously the permeability of the core has a frequency dependence...

author: CaptDon
author_rank: Super Contributor
timestamp: January 28, 2021, 02:02:34 pm
content: Those bigger inductors always give weird readings. The reality of it is that the inductance of a filter choke is usually specified at some D.C. current flow like 10hy at 150ma. As you put current through the choke the inductance decreases. I would have expected a 10hy choke to read 12hy 'dry'. If you had an exact known capacitor like 10uf +/- 1 or 2% you could put it across the inductor and ring it with a signal generator to find the resonant point and then calculate the inductance. Power filter chokes have 'slow' iron and the inductance will be very frequency dependent. Set your tester at 100hz and test, then at 1khz and test, you will probably see a difference of 10 to 40% in the indicated value. I think your inductor is not broken.

author: rsjsouza
author_rank: Super Contributor
timestamp: January 28, 2021, 02:15:36 pm
content: @blueskull, 5 and 10H choke inductors were very common in old vacuum tube equipment.The power supply was comprised of dual electrolytic capacitors (25, 50 or 100uF) and the inductor in the middle. At the time, larger value electrolytics were much more expensive than heavy iron.

author: TimFox
author_rank: Super Contributor
timestamp: January 28, 2021, 02:49:55 pm
content: My guess is the DC bias suggestion. For normal ferromagnetic material, looking at the magnetization curve (from zero), one sees a medium "initial permeability" near zero H, reaching a maximum permeability somewhere up the magnetization curve, then falling off as you approach saturation. Filter chokes such as this Hammond have an air gap to determine the inductance, reducing the effect of the change in permeability.

author: The Electrician
author_rank: Frequent Contributor
timestamp: January 28, 2021, 03:29:01 pm
content: TimFox is quite right. The permeability of iron when the measurement stimulus is small, as is the case when measuring inductance with a meter that only applies a voltage of .6 volts (your DER5000), is lower than when a larger voltage is applied. Here for example is a typical BH curve:The spec says the inductance is to be measured with 50V @ 60 Hz and 200 mA DC current applied.

author: The Electrician
author_rank: Frequent Contributor
timestamp: January 28, 2021, 03:35:08 pm
content: Quote from: CaptDon on January 28, 2021, 02:02:34 pmThe inductance increases for a while as you put DC current through the choke (starting from zero current), reaching a maximum at a certain current, then decreases as saturation is approached. See the BH curve in the precious post.

author: bsfeechannel
author_rank: Super Contributor
timestamp: January 28, 2021, 03:58:25 pm
content: The nominal value of a choke's inductance must be measured at their rated condition, i.e., direct current, AC voltage and frequency. Have a look at one of theirdatasheets.Measuring inductance at a different frequency from what is rated, for instance, will result in wildly different values.

author: TimFox
author_rank: Super Contributor
timestamp: January 28, 2021, 05:15:36 pm
content: IET has posted the manual online for the General Radio 1633A Incremental Inductance Bridge that is the classic way to measure such components. It works at discrete frequencies from 50 Hz to about 15 kHz and applies DC from an external power supply.

author: TimFox
author_rank: Super Contributor
timestamp: January 28, 2021, 05:19:29 pm
content: Quote from: blueskull on January 28, 2021, 02:19:30 pmAlso, vacuum tube rectifiers (e.g., 5Y3 and 5U4) had serious limits to peak current, and the manufacturers specified maximum filter capacitance values in the range mentioned by rsjsouza.

author: pwnell
author_rank: Regular Contributor
timestamp: January 28, 2021, 05:39:48 pm
content: I see adding DC bias would be tricky considering the large choke:https://www.voltech.com/Articles/104-160/1_Considerations_For_Accurate_High_Power_Inductor_TestingYes this is part of a power supply design for a valve amp and has several 32uF - 100uF caps and other 1H inductors to reduce ripple as much as possible in the B+ line.

author: The Electrician
author_rank: Frequent Contributor
timestamp: January 28, 2021, 06:24:38 pm
content: Quote from: pwnell on January 28, 2021, 05:39:48 pmIf you have a variac you can see the effect of larger stimulus when measuring.The DCR of your inductor is 79 ohms (which is so low you can ignore it for this experiment), and the reactance of 10 henries would be 3770 ohms @ 60 Hz. You can determine the inductance by applying a 60 Hz voltage (call it VAC) and measuring the resulting current (call it IAC). The ratio VAC/IAC gives the reactance XL, and XL/377 gives the inductance. Apply various voltages from, say, a low of 1 volt up to 50 volts, calculating the inductance at the the various voltages; report back what you get.

author: rsjsouza
author_rank: Super Contributor
timestamp: January 28, 2021, 06:34:02 pm
content: Quote from: TimFox on January 28, 2021, 05:19:29 pmYes, and that trips folks replacing those massive Tesla-branded dual capacitors with modern ultralow ESR models. Sure, the rectifiers will survive but their lifespan will be very reduced (to kill a vacuum tube you need a LOT of abuse).(photo taken from the internet)

author: pwnell
author_rank: Regular Contributor
timestamp: January 28, 2021, 08:11:35 pm
content: Quote from: The Electrician on January 28, 2021, 06:24:38 pmI will try this and send my feedback.

author: pwnell
author_rank: Regular Contributor
timestamp: January 28, 2021, 08:14:09 pm
content: Can I also measure it this way? I calculate roughly 7V drop over the DCR of the choke when operating at rated levels. Can I hook up my LCR meter while the circuit is live and connected to the load, drawing an expected 100mA?

author: TimFox
author_rank: Super Contributor
timestamp: January 28, 2021, 09:10:11 pm
content: If you are using a DE-5000, I don't think it will tolerate the DC and ripple voltages across the inductor in your example. The ripple voltage is likely to be substantial across the choke, since it is the difference between the macroscopic ripple across the first capacitor and the smaller ripple across the second capacitor. Note that the ripple needs to be calculated at 120 Hz with the full-wave rectifier circuit.

author: The Electrician
author_rank: Frequent Contributor
timestamp: January 28, 2021, 09:43:33 pm
content: Quote from: pwnell on January 28, 2021, 08:14:09 pmYou definitely don't want to connect your DE-5000 to anything that is energized.Set your DMM to measure AC volts and measure the AC voltage across R5. Using Ohm's law, you can calculate the AC current through R5 and L1 (call it IAC). Measure the AC voltage across L1 (call it VAC). As before the reactance XL of L! will be VAC/IAC, and the inductance will be XL/(2*377). The denominator is 2*377 because the ripple frequency is 120 Hz. The ripple voltage and current will not be a pure sine wave but there should be a fairly large 120 Hz component, so this calculation will be a very rough approximation, but an easy one to do.

author: pwnell
author_rank: Regular Contributor
timestamp: January 28, 2021, 10:09:02 pm
content: So I did the simple test with a variac as suggested. See below for the results.

author: The Electrician
author_rank: Frequent Contributor
timestamp: January 28, 2021, 10:15:48 pm
content: Quote from: pwnell on January 28, 2021, 10:09:02 pmQED!

author: floobydust
author_rank: Super Contributor
timestamp: January 28, 2021, 10:22:19 pm
content: I checked a Hammond193MI have-rated 10H 0.3A 63R and I measure 7.6H on XJW01 @1kHz (no reading at 100Hz; 7.8kHz thinks it's a 300pF capacitorand 9.6H on Amrel. I always have trouble measuring inductance when the DC resistance is high, it's a PITA. Most of my meters won't read correctly at all, on relay coils or humongous inductors.I wouldn't measure it in circuit - it's a bit dangerous to yourself and your test equipment.It's not a sine-wave going into it, downstream of a rectifier.Your DMM must be true-RMS as well.I would make a simple RLC circuit with the inductor, inject sine-wave using a signal generator and see what resonant freq. results. Just rolling back to basic principles. Be careful as 10H can easily zap a signal generator from back EMF or resonant voltage magnification. Even then, this is a "no DC-bias current" L measurement.These filter chokes have an air-gap. Also remanence - try reversing polarity, in the case the L meter is not AC excitation, the core is likely magnetized which also seems to upset L measurements for some meters. The Hammond parts are good and I doubt you got short changed.edit: I also have a vintage 193L (5H 57R 0.3A) I can try measure too. It's just that big iron-core inductors are non-linear and have high winding capacitance.

author: pwnell
author_rank: Regular Contributor
timestamp: January 28, 2021, 10:31:52 pm
content: Thanks very much for all the helpful comments. I will see how it performs in my valve amp once I finish building it. Will get some nice waveforms with my Rigol and HV probes and post it.

author: bsfeechannel
author_rank: Super Contributor
timestamp: January 29, 2021, 04:25:09 am
content: https://dalmura.com.au/static/Choke%20measurement.pdf