Anyone ever repair a clamp meter? - Page 1
Forum section: electronics / repair

author: bitbanger
author_rank: Regular Contributor
timestamp: August 04, 2019, 05:12:23 am
content: Picked up this Amprobe AC50A leakage current clamp meter on the cheap to diagnose some GFCIs and I get zero AC current measurement. Open it up to find the case screw had at some point pierced/shorted the enamel wires leading to the pickups in the clamp. Wire is crisp and burnt. Meter works otherwise, with no visual signs of damaged PCB components.First, is there typically anything special about this enamel wire? How particular if at all do I need to be about matching gauge and length?Second, to get to the magnetics I need to split the yellow jaw casings, which were either ultrasonically welded or glued together. The wire is burnt/broken right at the jaw casing entry, so I'm not left with any splicing option. Any tips to get this cracked open? Here are some quick pics:https://imgur.com/a/ELvENNkThanks!

author: techman-001
author_rank: Frequent Contributor
timestamp: August 04, 2019, 07:27:36 am
content: Quote from: bitbanger on August 04, 2019, 05:12:23 amYes, I did instrumentation repairs for a few years.Proper way, about as neat as you will get:1) mount the pickup securely on a vertical mill and align a small cutting wheel with the ultrasonic join. Follow it all the way around for a neat cut.2) repair3) glueNext best way:1) a small cutoff wheel in a Dremel tool to cut the weld open. Problem is the speed is too high and it will melt the plastic and look pretty horrible but with steady hands and lots of caution and time it can be done.2) repair3) glueNasty way:1) Use a box cutter and do the same.2) keep bandages and super clue on hand for the inevitable horrific cuts when you slip.This way is pretty nasty, even if you survive with all fingers intact, the pickup will have deep scratches everywhere where you ran off track. Strongly advised against.Really horrible way:1) burn thru it with a soldering iron.This ruins the plastic and the soldering iron. Strongly advised against.

author: BurningTantalum
author_rank: Frequent Contributor
timestamp: August 04, 2019, 08:26:10 am
content: Dremel make cutting discs for plastic. They work rather well as long as the speed is slow.BT

author: Assafl
author_rank: Frequent Contributor
timestamp: August 04, 2019, 10:15:20 am
content: Sometimes, clamping an ultrasonically welded device in a vice and “squeezing” it causes the joint to break cleanly.Especially if the jaws are perpendicular to the joint.Sometimes it takes many attempts to get it to split. Don’t force too hard.

author: cbutlera
author_rank: Regular Contributor
timestamp: August 04, 2019, 01:18:04 pm
content: Just some thoughts. I've never repaired one of these myself.You don't have to cut along a seam. If it were me, I would try cutting along the outside perimeter of one of the C shaped sections covering the core with a junior hacksaw. That would avoid having to cut the handle in half, and messing up the pivot. Having done that, it may be possible to pry the C section open a little, to get the hacksaw between the case and the core for the inside perimeter cut, otherwise I would resort to the Dremel for the inside cut.Another crazy sounding alternative is to cut it with a disc of plain paper mounted in a Dremel, on the usual cutting disc mandrel. You may get through quite a few discs. On the few plastics I have tested this with, it works better than it has any right to. It doesn't melt the plastic, and makes a very narrow cut. I saw the idea on that darned channel that eats your life away.If the paper disc idea works, or if you have a mill, it may be neater to just make two cuts on the inside perimeters of both sides. The piece you remove will be shaped like a short piece of tube sliced in two, if that makes sense.As for the wire, wait to see what you are up against until you get in there, it may be a lost cause. The wire itself doesn't need any special characteristics, just replace with a similar diameter enamelled copper wire. If you need to rewind the coil, take photos of the old winding first and count how many turns there are and where they are positioned.

author: bitbanger
author_rank: Regular Contributor
timestamp: August 04, 2019, 06:34:48 pm
content: Thanks for the replies everyone - as one person implied the plastics may turn this into a lost cause. I think the magnetics should be fine, just two wires burnt up.Curious, why on Earth would they use enamel wire for this? Is it simply because that's what's used to wind the coil, and so it's cheapest to simply extend it out of the clamps? For something that flexes so much, stranded wire would seem to make more sense, at least for the movable jaw. Then again, price point (though the reason I'm attempting repair is that these go for a premium on eBay so this is my best shot at having one for occasional use).No easy access to a mill, unfortunately. One of the bitter sweetnesses of leaving work in industrial electronics (you're usually in a place with a machine shop).I've had my share of sliced thumbs, so it's low speed cutter for me!Thanks all, I'll keep you posted.

author: techman-001
author_rank: Frequent Contributor
timestamp: August 04, 2019, 08:27:56 pm
content: Quote from: bitbanger on August 04, 2019, 06:34:48 pmI think it's just the usual junk, copied by experts at copying (from something better) by people with no real engineering training or experience just to make a quick buck then resold outside China by people also after a quick buck via a massive markup on Ebay.Sadly nowadays price has almost no relationship to quality and buying quality has become harder than ever.Luckily in your case you can replace the flexible section with wire suitable for the task