As a retired spark I can vividly remember using these with pyro it was all we had in those days, we had no fancy battery operated multifunction meters like today As previously stated these were so reliable no worry’s about dead or leaking batteries. You could always feel you had a short as the handle was much harder to turn when meggering out to test for continuity and identifying conductors. Been on the receiving end getting a shock from them much to the delight of work colleagues.
I used to own one of these. Inherited from my dad. They are bulletproof and very well made. The bakelite case has that characteristic smell that I will never forget.
I work in a calibration laboratory, and you'd be surprised how many of these are still in use, we probably still get one or two a month sent to us for calibration.
+risvegliato And the owners know why. You could go through 10 modern meters while this one still ran strong. The gears are beautiful, you can't really burn the components in use, the connections are as heavy-duty as they get, it runs off-grid...
My Megger is not as old maybe 1970. It has still a shorting link. This is used to short the two terminals during transport. As long the link is in the two terminals you can't connect the test probes. I have shorted my two test probes because my Megger can also measure Ohm. There is a little switch Ohm or M Ohm. My two test probes shorted are 0,4 Ohms. I subtract 0,4 Ohms from the 0 to 500 Ohms scale.
The 821418 written on the back of the scale, is the serial number of the device. I believe (if my eyesight serves me well) it also appears on the brass arm near the needle. Good teardown video, very indepth :)
All very interesting but how does it work? I remember using the old hand cranked Meggers when I was an apprentice nearly fifty years ago but I never really knew how they worked. Now after retiring from a career in electrical engineering I think I’ve finally figured it out. If you Google “How does a Megger work” you will find several explanations, none of which make any sense and are obviously written by people who don’t actually know how a Megger works at all. Any feasible explanation must explain the following facts. 1. The indication varies from zero ohms (short circuit) at one end of the scale to Infinity (open circuit) at the other end. 2. The scale spans an angle of approximately 90 degrees 3. There is no spring involved, the needle moves to the appropriate resistance value when the handle is cranked and then stays there when you stop cranking. 4. The resistance indicated is roughly independent of the speed of cranking, only the applied voltage varies with speed. Clearly a Megger works in a very different way to an ohmmeter like an AVO which simply applies a known voltage via a resistor and then measures the resulting current with a conventional moving coil ammeter. So here’s my explanation of how I now think a hand cranked Megger works. 1. The crank turns a generator which produces a dc voltage equal to the test voltage, typically 500V when it’s at full speed. 2. There’s a permanent magnet which creates a uniform linear magnetic field across the armature ie one with parallel lines of force rather like the earth’s magnetic field. Note that this is different from a conventional moving coil meter which has a radial magnetic field. 3. There are two coils on the armature, a voltage coil and a current coil which are mounted at right angles to each other. Let’s assume for the sake of argument that they have the same number of turns although they may not. 4. The voltage coil is connected in series with a resistor (the 4k7 seen in John’s video) and then across the voltage source. So it produces a magnetic field proportional to the voltage. 5. The current coil is connected in series with the current taken by the load, so it produces a magnetic field proportional to the load current and orthogonal to the field produced by the voltage coil. 6. These two fields combine to produce a simple vector sum, ie a field at an angle to the armature somewhere in between the voltage and current fields. If the load resistance is very low the resultant field will be aligned with the current coil, if the load resistance if very high then it will align with the voltage coil. If the currents in the two coils are equal then the field will be at 45 degrees to the armature. The full range of movement of the resultant field relative to the armature is therefore 90 degrees. 7. The armature acts like a little magnet, just like the needle in a compass and rotates to align its magnetic field with the permanent magnet’s field. 8. Once the armature and the hence the needle is aligned with the permanent magnet ‘s field there is no further torque and it remains in position even if the voltage is removed. 9. Voila! Incidentally, I think the other two “capacitors” mentioned in the video are in fact wire-wound power resistors which protect the coils if the instrument is accidentally connected to a live circuit. What I would still like to know is who was the comedian who designed the Megger so that you have to hold it with your hand over the terminals when you crank it.
Thank you so much Sir! You just helped me with my Cable insulation resistance measurement homework. I couldn't useful information on how to use the megger. Thanks!!
The handwritten number on the bottom of the scale was the serial number, presumably labeling the unit before the number could be engraved or screened on to the top of the scale.
Can you provide a link for where these could be purchased online? I live in Canada and do not speak or write in Russian. So I'm not sure where to look. Thank you!
You've totally missed the plot on this one, John. The 0.1mfd 1,500vDC Dubilier cap will certainly need changing at this age. This cap is connected in series with the 4,700 ohm resistor, across the generator terminals. The other two components next to the cap are NOT caps, but are wire wound resistors of 50,000 & 100,000 ohms respectively; and I believe that E&V modified the values of these resistors over time, probably depending on the scale-plate range of the instrument in question.
I have one just like this, but has 3 wire wounds and a 4700 ohm resistor, and a large square red capacitor- at least that's what I think it is since I can't make out any of the writing on it. The generator is putting out gangbusters, but I have little to no voltage at the terminals. I suspect the 4.7k or the capacitor?, but I haven't got around to actually testing anything yet Clearly there was more than one way they made these devices.
When I was at collage we used to use these to measure the resistance of other students jeans and ultimately their glutamus maximus by putting two screws through the bench and attaching the appropriate cables. You soon become conditioned to check the bench before sitting down 🤭 Oh, the exuberance of youth!
Hand crank Meghan’s are still made. AMEC model 6503 is a good example. Along with two 6503’s I have an earlier 1250 in mint condition. These are bullet proof, and I like using them much more than a battery generated digital version.
They are still compliant if you want to use them you can so long as as it is in good condition and working as intended and the test leads conform to GS38. Same for the Robin testers, and with the changes to BS7671 with amd2 on IR and RCD testing even more so . So the good news is that you don’t have to buy new testers.
+glenwoofit No voltage multiplier of that vintage. They would rather wind on 10000 turns than use a huge selenium stack several times to get a bit of multiplication. Plus coils have nothing to do in a voltage multiplier.
Those number scribbled on various parts appear to be the serial number. It is easy to tell if it has been repaired of the serial numbers don't match on the various locations.
Invented by *Evershed & VIgnoles* in the late 19th century - this Megger - named the 'Wee Megger' (500V/20Mohm) - was the first production insulation tester. A larger version existed, aptly called the 'Major Megger' (2.5kV/20,000Mohm). Megger is essentially an acronym of the words MEGaohm metER. The company Evershed & Vignoles and its brand - Megger were amalgamated into *The Kent Group* of industries in 1965, which also included amongst many other illustrious brands - the famous AVO (Amp Volt Ohm) multimeter manufacturers and HW Sullivan Ltd (inductors, shunts and galvanometers). In 1970 - The George Kent Group was purchased by Thorn/EMI and later in 1987 renamed Megger, the name of which remains to this day under the now vast Megger Group Ltd. My PAT tester is made by Megger and I still use daily, my trusty AVO - M2006 digital multimeter, one of the first to feature a liquid-crystal digital/analog display. Though we learned our physics and basic electronics at school and used later in the military - the ubiquitous AVO Mod 8, still often found in many workshops around the world and still regarded as one of the most accurate moving coil multimeters anywhere. I've got one of the more rugged, external use 'Field Meggers', with the carrying handles, somewhat square in profile, but obviously the same meter scale and movement. Instead of the push-grip connections, mine has the standard 'loudspeaker' style screw terminals and the casing is made of billet aluminium. Unfortunately mine doesn't work and surprisingly, I've never bothered to dismantle it, but I shoulld imagine that it is pretty much of the same construction inside as this rather sweet 'wee Megger' device that JW is reviewing for us here. Well another excellent tear down there JW and one waits with baited breath for your next suitably laconic review/upload. ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Having just noted the date of this upload, obviously waiting with 'baited breath' would be a somewhat absurd chronological endeavour.
John, It was quite common practise to date stamp electrolytic capacitors with year of manufacture back then, perhaps that ancient Dubilier electrolytic might bear a bit of further investigation.
Hi John, can you point me the right way....i have just got one of these from the dark ages,,,it has 2 ranges, thousands and Mega i think...the pointer appears to do what it should, but i put a DC voltmeter across the terminals, on low it read about 30 volts on high it reads about 250 volts dc, its a 500 volt megger....what do you think, i think the low one could be right might just use 30 volts similar to a multi tester but i think on high it should read 500 volts...used a digital and analog meter, same with both.....Fred in essex.
I have a couple of these old meggers, that I set up for my kids science class for them to learn how to generate electricity and to activate old telephone ringers and florescent lamps
I inherited one from my dad recently its a pre bakelite one in a huge wooden box, from the serial number I have guestimated it to be circa 1916, I am now trying to sell it.
I was given one of these about 30 years ago. Have used it for the first time in years today to test the heating element out of a washing machine to see if the heating element's insulation is failing which it is. From what I gather, the needle floats so there's no way to steady it I presume?
i am having one like this. But supplied by GEC of London. 500V. With original box. It's my dad's (Died in 1972). He used in early 1950s. Ok. How many cranks needed for this. And formulas i want.
The number under the scale is the serial number. And the shellac covered components look like inductor coils to me... The 5000 is probably the number of turns
+mc349iii Attach an apprentice across the terminals and see how loud they yelp when you crank the handle? This may or may not be an approved method related to me by a really old school electrician - As in he was really old, and one of his last jobs was in a school
I still use mine for measuring immersion heater elements in situ. the one I tested recently hadn't effectively disconnected from the supply, blowing the megger fuse. I replaced the fuse but found that it no longer measures the low resitance scale (ohm) (megohm) the megohm scale is ok. Can it be repaired?
Those square section brass plungers to make the connections seem a weak point to me in terms of conductivety. As you manipulated them it was clear they were a very loose fit in the brass housing with the latter presumably connected to the internals - I didn't see any connections to the brass plungers themselves. I would think this would make a rather uncertain connection - safe for low resistances but could cause a false high one (possibly!)
diymostthings The brass slugs are connected to the shell they ride in via the tension spring (much like on brushed motors). There is positive grip on the cables by the guillotine action of the slugs trying to relax against the wire passing through the housing and the slugs themselves. These hand crank meggers would be tested in short circuit to make sure that the ground point and the wiring from it are actually working. When testing, the crank is spun at at least 60rpm (one rev per second) to ensure enough voltage is developed. There is a speed limiting clutch inside to prevent over-voltage from spinning the crank too fast.
I have the same type of instrument and works fine.The only problem is that the output voltage does not reach 500v dc as it should do.It reaches 290v only.Any idea what could be wrong in it?
Biddle wasn't a brand that was ever sold in the UK, I have not seen or used any of their items. Instruction manual for that one available here: www.biddlemegger.com/biddle-ug/21159Series_UG.pdf
i realy like old technics stuff. there was a time in there was not the goal for construct diveces to get out of order after the warrenty. i hate the idea to replace technics there are fully function and can be used. but uneccesary work for low money to create waste and destroy the envioment and healthy of all living things on the planet and wastiny recources is the ghost of the time :( another point is , it is not nessecery to bring every minit a new produkt on the market and all stupid people must have a new one .
Megger is a contraction of MEGohm metER + an extra G. In many regions of the UK, the final R of Megger would be pronounced. It just so happens that John's regional accent (circa London, possibly Kent) doesn't.
(9:55) - It's not a "job to tell" at all. Distinguishing plastic from glass, is one of the most simple, easiest task to do. And you call it: *_"A JOB TO TELLL ?"_* I'm sorry but SHAME ON YOU John, here. Identifying whether a lense or some clear sheet is glass or acrylic or any other type of plastic is just too easy to mention. Shame on you. That's all I can muster. >
