Optimizing VOM leads

I use my VOM a lot, mostly with low-voltage hobby work. I'm impatient and hate the hassle of long tangled probe leads and constantly having to change from points to pinchers to hooks. So I spent a lot of time optimizing my leads to the way I work.

The first thing was to obtain permanently coiled leads (like the older telephone handset cords) and fit them with 4 mm banana plugs at each end. With this arrangement I don't have to screw and unscrew the devices at the end of the cords as is the case with many commercially available sets. I managed to find some extra long spring-loaded hooks that accept banana plugs and a commercial set yielded some grippers with a much wider "gape" than an alligator clip.

Still missing was a set of banana probe handles that could take all the probe points I'd acquired over the years. Most of these have a M 3 x 0.5 thread.

A length of 1/4" hex aluminum from the junque boxes provided two 3.5" handle lengths. These were drilled at one end to accept a banana plug and drilled and tapped for M3 threads at the other.

I'll insulate the handles with shrink wrap if the junque box doesn't yield any suitable lengths of silicone tubing. On the rare occasions when I work with the scary stuff like 220, I have a set of commercial heavy duty leads that I use. I won't trust my homemade handles any farther than I trust the stuff that came with the VOMs.

Attachment 33717

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Thanks mklotz! We've added your Optimized Voltmeter Leads to our Testers category,
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Quote:

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Originally Posted by mklotz

A length of 1/4" hex aluminum from the junque boxes provided two 3.5" handle lengths.

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There is a major downside with aluminum. If you don't immediately protect it (within seconds), the bare aluminum surfaces where the pins & banana plugs are mounted will begin to oxidize. That may change your measurements when looking at DCR or straight resistance readings. They would measure higher than they actually are.

Quote:

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Originally Posted by object

There is a major downside with aluminum. If you don't immediately protect it (within seconds), the bare aluminum surfaces where the pins & banana plugs are mounted will begin to oxidize. That may change your measurements when looking at DCR or straight resistance readings. They would measure higher than they actually are.

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I don't think the effect is anything to worry about and probably would require the sensitivity of a Wheatstone bridge to detect. Nevertheless, I did an experiment to check.

I have three 50w 1% precision resistors - 10, 1, and 0.1 ohms. I measured all three of them first with no aluminum in the circuit and then with it in. These were the results...

10: 10.2, 10.3
1: 1.2, 1.2
0.1: 0.2, 0.2

In the days when alloy of aluminium was used with "pop" rivets on smaller aircraft (but still commercial) we used zinc chromate between the rivets and the skin to stop corrosion of, and around, the rivets

Where did you get the coiled leads?

Quote:

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Originally Posted by meyer77

Where did you get the coiled leads?

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Sorry, I don't remember where I obtained those. If you're looking to buy some, they should be easy to find on the net. Just a few minutes yielded these...

https://www.cablescience.com/coils/e...tl-series.html

https://www.mcmiller.com/6ft-coiled-...a-plugs-32846b

Quote:

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Originally Posted by mklotz

I use my VOM a lot, mostly with low-voltage hobby work. I'm impatient and hate the hassle of long tangled probe leads and constantly having to change from points to pinchers to hooks. So I spent a lot of time optimizing my leads to the way I work.

The first thing was to obtain permanently coiled leads (like the older telephone handset cords) and fit them with 4 mm banana plugs at each end. With this arrangement I don't have to screw and unscrew the devices at the end of the cords as is the case with many commercially available sets. I managed to find some extra long spring-loaded hooks that accept banana plugs and a commercial set yielded some grippers with a much wider "gape" than an alligator clip.

Still missing was a set of banana probe handles that could take all the probe points I'd acquired over the years. Most of these have a M 3 x 0.5 thread.

A length of 1/4" hex aluminum from the junque boxes provided two 3.5" handle lengths. These were drilled at one end to accept a banana plug and drilled and tapped for M3 threads at the other.

I'll insulate the handles with shrink wrap if the junque box doesn't yield any suitable lengths of silicone tubing. On the rare occasions when I work with the scary stuff like 220, I have a set of commercial heavy duty leads that I use. I won't trust my homemade handles any farther than I trust the stuff that came with the VOMs.

Attachment 33717

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That is awesome!!

I'll throw this out here for everyone to consider: It's possible to make your own coil cords by wrapping wire around a form, heating it gently and then letting it cool slowly. Plenty of references out there.

One caution: If you do significantly 'high voltage' be careful about choosing wire with appropriate insulation; the 'name brand' meters use a silicone rubber insulation, plus shrouded banana plugs going into the meter sockets.

At a previous job they had spools of silicone rubber covered wire, so I made myself some custom length leads; custom length coiled leads would be just the nuts!!

I was once using a 7,500 V rated Tektronix high voltage probe on a 6000 V laser power supply (4kW industrial laser, not the nuclear fusion ones I later did controls for). Anyway, holding it on the wire and looking at the meter when WHAM! Smoke coming from my hand.

When I got my heart restarted I saw that I was ok but the probe had mostly gone to another dimension leaving my hand black.

So, change of pants and contact Tektronix. They quickly replaced the probe but the rating on the new, identical one was now 5,000 V. Hmmm.

I bought one of the bigger much higher voltage probes.

I have a bookmark file for electronics, VOM's, meggers, thermometers, pyrometers, certain unique hardware; guess what joined recently?

Quote:

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Originally Posted by Toolmaker51

I have a bookmark file for electronics, VOM's, meggers, thermometers, pyrometers, certain unique hardware; guess what joined recently?

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I'm flattered to make it into the Toolmaker library. If you do a lot of battery checking, especially coin batteries, you might want to add one of these...

https://www.homemadetools.net/forum/...0729#post92066

to the reference.

Maybe one of these...

https://www.homemadetools.net/forum/...567#post128212

as well.

It pleases me as well, Marv. In case it's not clear, there are hundreds here, who hang on every word in your posts........ I for one, very glad you 'worked for our side'.

Experience at the mechanical services company (pumps and motors) wound it's way into machinery service. Built a tidy bank of metering as we've both described above. Been going through multitude (spindles, feeds, pumps) of motors far beyond anything I could before. Most are 3ph/ 440v, a few single 240v, two are 50 cycle; but all should run proper rotation first time. Insulation checks, motor windings, grounding, continuity of myriad connectors...the most fun to be had carrying a meter, notepad, and penlight. And a block of foam.

Low volt DC, I guess capability was better, but need didn't go past a nice old Realistic VOM. It's probably 50 years old now. Latest addition is a Power Probe, those are the bomb, as I'm often working alone. Like tracing a defunct back up alarm, 30 something feet away, from inside cab, in the box truck.
Ain't no way I'll start it, trust PARK or NEUTRAL, air brake, even chocks; scooting around a creeper in diesel exhaust. Probed? Maybe 3 minutes. There, it turns out, is no hydraulic transmission switch, but a micro in the shift selector hanging under the dash. That and 12v run a tiny motorcycle-type device, way back over the axle, of minimal annoyance. They are available with increasing decibels beyond finch fart.

Proper electronic components aren't quite in the mix yet. Maybe when itch for plasma cutter kicks in. The Electro Arc Tap Disintegrator comes first, no one around has one.

Quote:

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Originally Posted by mklotz

I don't think the effect is anything to worry about and probably would require the sensitivity of a Wheatstone bridge to detect. Nevertheless, I did an experiment to check.

I have three 50w 1% precision resistors - 10, 1, and 0.1 ohms. I measured all three of them first with no aluminum in the circuit and then with it in. These were the results...

10: 10.2, 10.3
1: 1.2, 1.2
0.1: 0.2, 0.2

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I like your execution, very cool. The reason probe ends, terminals, and test point connections are nickel, gold, or rhodium plated is that they don't oxidize. Because aluminum does it will directly affect readings accuracy. Over time oxidation will change them, they could vary month to month. If you are just going for simple go/no-go it's probably fine but if you are doing current measurement or board level troubleshooting to a schematic your test point readings will vary from indicated values. Aluminum forms and oxide layer immediately after it's machined. It's basically an insulator. You can mitigate this (somewhat) by chasing the tapped holes again, quickly adding battery terminal dielectric gel then immediately reinstall the screws. for the banana ends you can fill the voids with the gel. The gel will prevent more air from reaching the machined surfaces. However, some air will reach them as oxidation is immediate after machining.

More here:

https://physics.stackexchange.com/qu...ce-oxide-layer

Quote:

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Originally Posted by object

I like your execution, very cool. The reason probe ends, terminals, and test point connections are nickel, gold, or rhodium plated is that they don't oxidize. Because aluminum does it will directly affect readings accuracy. <<<<<<<snipped>>>>> Aluminum forms and oxide layer immediately after it's machined. It's basically an insulator. You can mitigate this (somewhat) by chasing the tapped holes again, quickly adding battery terminal dielectric gel then immediately reinstall the screws. for the banana ends you can fill the voids with the gel. The gel will prevent more air from reaching the machined surfaces. However, some air will reach them as oxidation is immediate after machining.

More here:

https://physics.stackexchange.com/qu...ce-oxide-layer

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Recall from decades back, no one has ever seen clean aluminum. Even the marine grades, resistant as they are. The lowest grades, suited for extrusion "look" clean the longest, hence use as trim material indoors and out.

Quote:

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Originally Posted by mklotz

I don't think the effect is anything to worry about and probably would require the sensitivity of a Wheatstone bridge to detect. Nevertheless, I did an experiment to check.

I have three 50w 1% precision resistors - 10, 1, and 0.1 ohms. I measured all three of them first with no aluminum in the circuit and then with it in. These were the results...

10: 10.2, 10.3
1: 1.2, 1.2
0.1: 0.2, 0.2

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I wish you the best.