Is there a cheap DC Clamp Meter with 200A AND mA resolution? - Page 1
Forum section: electronics / testgear

author: elfer
author_rank: Contributor
timestamp: December 27, 2020, 10:50:11 am
content: I've been looking at DC clamp meters recently, for automotive use. Primarily, I want to be able to verify that rebuilt alternators are capable of producing their rated output, which would be 90-150A, depending on the model. But it would also be nice to verify that a car doesn't have a parasitic drain, which would require measuring 30-40mA with a reasonable degree of accuracy. I have a couple of Uni-T DMMs that I've been happy with so looked at their offerings first. The UT210D would meet my main requirement but the specs quote 2%+/-3 counts accuracy at the minimum 10mA resolution, which I interpret as saying it could be off by 30mA, or 100%, when measuring 30mA. So, for that task, I'd be better off with the UT210E, which resolves to 1mA at a accuracy of 2%+/-8, or 9mA at 30mA, which would be much more meaningful. (And I've found the long thread about the 210E and know it's a popular choice here!). But sadly it won't do the higher currents above 100A that I'm looking for for alternator testing.Before I end up buying one of each, does anyone know a single clamp meter that could meet both requirements? Measure up to 150Aandresolve down to 1mA? (or to 10mA with +/- 1 count accuracy?) It would have to cost less than buying both a UT210D and a UT210E to be worth getting instead, though if it had a Peak Hold feature I could talk myself into spending a little more..

author: Martin72
author_rank: Super Contributor
timestamp: December 27, 2020, 11:05:37 am
content: Hi,A clampmeter with such specs and ranges....and cheap.Tell me when you found one.OK, let´s get serious:Even when costs are not important, I don´t know a clampmeter which could handle both, hundreds of A and also mA, I´m afraid, you must buy 2.At work, I got a Fluke337 and a Benning CM11 and it´s perfect - But costs "a lot".Measuring mA with acceptable accuracy with a clampmeter...I got a UT-210E here, will test it after lunch how it performs in that range against an calibrated BM869s.If it´s "good enough", you should buy it plus another clampmeter.

author: elfer
author_rank: Contributor
timestamp: December 27, 2020, 11:34:27 am
content: "A clampmeter with such specs and ranges....and cheap.Tell me when you found one."That made me laughYou make a good point, I'm probably asking the impossible. The UT210E low current accuracy I'd be happy with but it won't do the high current. I do suspect I'll end up buying two meters.Gruß

author: BravoV
author_rank: Super Contributor
timestamp: December 27, 2020, 01:27:29 pm
content: Your quest is like finding a "cheap" weighing scale than measure few grains of rice that weight probably few grams with 1 gram accuracy, yet it can accurately measure the weight of a car, yet with 1 gram accuracy.If its cheap, I want it too.

author: elfer
author_rank: Contributor
timestamp: December 27, 2020, 01:47:58 pm
content: Yeah. It's just frustrating that the 100A max of the 210E is notquiteenough. I might just start with one of those and be satisfied that "OL" would verify an alternator is providing at least 100A, even if I couldn't verify its max output.(Or I might start with the 210D and know I can always still use an inline DMM to measure parasitic battery drain)

author: fourfathom
author_rank: Super Contributor
timestamp: December 27, 2020, 03:10:30 pm
content: I've got a few DC clamp ammeters (a Fluke, and a couple cheap ones), and when I need to measure mA I use a multi-turn coil through the jaws. This is easy if the wires carrying the current are skinny and have enough excess slack, but pretty much impossible on a car -- you have to disconnect the cable and at that point you might as well use a regular ammeter. You can double the sensitivity of a clamp-meter by passing the positive cable through the clamp, and the negative cable through in the opposite direction. This might be possible with car wiring, but probably not.

author: SilverSolder
author_rank: Super Contributor
timestamp: December 27, 2020, 03:20:45 pm
content: I use the UT210E at 200A like this: I made a "calibrated piece of wood" that holds the clamp open just wide enough to drop the reading by half (about 4mm - 5mm if I remember correctly). I calibrated it by wrapping a wire 10 times around the clamp and running 1A through it from a bench power supply, shaving the wood block down with a hobby knife until the reading was exactly 5A. It works surprisingly well for such a cheap hack!

author: Martin72
author_rank: Super Contributor
timestamp: December 27, 2020, 03:25:41 pm
content: MMD

author: SilverSolder
author_rank: Super Contributor
timestamp: December 27, 2020, 03:34:16 pm
content: Quote from: Martin72 on December 27, 2020, 03:25:41 pmThe calibrated piece of wood stores easily in the pouch along with the meter, ready for use any time!

author: elfer
author_rank: Contributor
timestamp: December 27, 2020, 03:38:35 pm
content: I don't know how well I'd be able to replicate that but I love the idea! There'd be no harm in me giving it a go anyway

author: SilverSolder
author_rank: Super Contributor
timestamp: December 27, 2020, 03:45:39 pm
content: Quote from: elfer on December 27, 2020, 03:38:35 pmI'll take a picture and an accurate measurement and post here a bit later on. It's my favourite hack of 2020!

author: Martin72
author_rank: Super Contributor
timestamp: December 27, 2020, 03:57:20 pm
content: mA current measures, comparing Brymen 869s calibrated vs UT210E, first a normal resistor, then a electronic ( chinese crap) load with 10mA steps.10.00mA/12mA15.10mA/19mA20.22mA/21mA25.06mA/26mA30.42mA/34mA35.25mA/40mA49.01mA/47mA59.11mA/59mA69.10mA/68mA78.95mA/75mA88.90mA/86mA98.96mA/98mARange Brymen: 400mA(probably), range UT210-E : 2ABefore every measurement, I´ve pressed the zero-button of the clamp.Values are depending of the position wire-jaws.Martin

author: elfer
author_rank: Contributor
timestamp: December 27, 2020, 04:14:41 pm
content: thanks Martin. Those 210E results are more than accurate enough for my needs. If only the 210D could be relied on to be within +/- 10mA at those sort of currents it'd be close enough for me.

author: Trader
author_rank: Frequent Contributor
timestamp: December 28, 2020, 01:13:15 am
content: Quote from: elfer on December 27, 2020, 04:14:41 pmAFAIK you can hack the 201E to 1,000A and 10,000 counts.

author: elfer
author_rank: Contributor
timestamp: December 28, 2020, 01:50:56 pm
content: Quote from: Trader on December 28, 2020, 01:13:15 amI'd seen that increasing the count was possible but missed that one could increase the max measurable current. That's something I could potentially explore. It could be a fun winter lockdown project learning how to read and write to eproms!

author: elfer
author_rank: Contributor
timestamp: December 28, 2020, 01:53:22 pm
content: Just to thank everyone for taking the time to reply and offer advice. I've ordered the 210E for now and will see if I can get by with just that

author: SilverSolder
author_rank: Super Contributor
timestamp: December 28, 2020, 02:34:45 pm
content: Quote from: elfer on December 28, 2020, 01:50:56 pmIt may be possible to reprogram the computer inside it to go up to 1,000A but will the Hall effect sensors in the clamp be up to the task with a 10x overload?

author: kbrill
author_rank: Contributor
timestamp: December 28, 2020, 09:09:01 pm
content: Have made charging system and parasitic measurements on a variety of vehicles . Charging system measurements are easy and even low cost clamp on probes will work fine . Consistency of reading is more of an issue with oversize aperture .Low level parasitic measurements are more frustrating as probe head size and geometry make placement over wires in the available space difficult and sometimes impossible . Often I must try a variety of probes in order to find one that will fit .It is very tempting to purchase a higher amperage range instrument than necessary . resist the urge and look for smallest head and aperture .

author: Hydron
author_rank: Super Contributor
timestamp: December 28, 2020, 11:19:45 pm
content: Certainly worth getting one and having a go at an EEPROM hack - even if >100A doesn't work out the UT210E is worth having for the low range.I would check that it remains accurate at the higher currents (wrap a few turns around it to multiply a known test current), and that any magnetisation from the high currents doesn't cause any offset issues when subsequently measuring low currents.

author: Martin72
author_rank: Super Contributor
timestamp: December 28, 2020, 11:27:54 pm
content: I did measure comparisons UT-210E vs a calibrated high accuracy poweranalyzer and postef it in the Uni-T thread.When I find it, I´ll post a link here.

author: SilverSolder
author_rank: Super Contributor
timestamp: December 29, 2020, 03:24:28 am
content: Here is the "calibrated piece of wood" hack to read 200A with a UT-210E by creating an air gap in the magnetic circuit.Basically, it causes the sensitivity to drop by half so 100A on the display means 200A actual current.The wood needs to be 6.25mm thick (at least on my example).

author: mansaxel
author_rank: Super Contributor
timestamp: December 29, 2020, 09:38:05 am
content: Alternative, non-economical, complicated, not-what-you-asked-for vintage solution:Find an used -hp- 428b for low amps (up to 10A) measurement (better than 5% accuracy on 1mA FSD) and a good modern clamp for high amps.Attached image is a 974a and the 428b both measuring a "100mA" current from a bench PSU. After the required 15 minute warm-up of the valve-based wiggly-pointer meter...

author: elfer
author_rank: Contributor
timestamp: December 29, 2020, 09:53:13 am
content: Quote from: mansaxel on December 29, 2020, 09:38:05 am

author: Trader
author_rank: Frequent Contributor
timestamp: December 30, 2020, 12:42:44 am
content: Quote from: mansaxel on December 29, 2020, 09:38:05 am@mansaxel, this is an off-topic post, but your HP 974A is an awesome DMM, maybe 26 years old, and seems to be as good as other "modern" 50k/60k counts DMMs (Fluke 189, 289, Keysight U1282A, Brymen BM869s, BM869s, BM789, etc)https://literature.cdn.keysight.com/litweb/pdf/5967-6368EN.pdfReinforce my idea of investing in excellent instruments where you can use them with confidence throughout your whole life.I wonder, what is the First good 50k/60k (100kHz AC, AC-DC, etc...) handheld DMM?

author: mansaxel
author_rank: Super Contributor
timestamp: December 30, 2020, 12:48:01 pm
content: Quote from: Trader on December 30, 2020, 12:42:44 amBest part of the 974a story is that I bought it for about $100I guess because it predates the IEC safety categories and thus won't tick a box in someone's inventory.Quote from: Trader on December 30, 2020, 12:42:44 amThe Fluke 8060 is a worthy contender, even if it's not as many digits precision. But it'll go very high in frequency for its age.Continuing the "vintage" streak, one can argue for the -hp- 427 to be the first good handheld (I'm using "battery operated" as equivalent to "handheld" here, which is a bit of a stretch, but.) since it was made to be quite competent (but not as the 410c), portable, and compact. It is flat within 2% of FS to 1MHz on AC, which few DMM manage today. It responds well to 3,5MHz, but not as flat. It does lack current measurement. (But I've got an Avometer and its german cousin the Elavi 3 to do such things, apart from the 428b, of course) I've removed the battery from mine, and run it as a desk meter.If we're taking the thread back to topic, I'd buy the UT-210E and look for a used AC/DC clamp meter for the higher readings. Or buy another UNI-T.

author: Martin72
author_rank: Super Contributor
timestamp: December 30, 2020, 12:59:10 pm
content: QuoteThe "high-end" solution would be something like this:Benning CM-11plus someone else for higher currents.But there is an all-in-one sloution on the market, if current measuring starting on 10mA is enough:Benning CM-2Measuring range from 10mA-300A......I saw used ones for under 100 bucks in ebay (but not actually).

author: elfer
author_rank: Contributor
timestamp: December 30, 2020, 01:09:11 pm
content: Quote from: mansaxel on December 30, 2020, 12:48:01 pmNo need to bring it back on topic as far as I'm concerned, I'm finding the diversion quite interesting and enjoyableI did order the 210E a couple of days ago, like you say for low current measurements, and yesterday ordered a UT203+ for the higher current. The 203+ is slightly larger but still quite small, and I might even find the additional jaw size useful. It also has a max/min store, which will be very useful as I won't be able to see the meter when I'm increasing engine rpm to a fast idle for proper testing. Best of all it was only £23 delivered. It's coming on the slow boat from China but at least the 210E was from a local vendor and should be with me next weekThanks again everyone for all the advice!

author: Elasia
author_rank: Frequent Contributor
timestamp: December 30, 2020, 01:10:39 pm
content: Quote from: SilverSolder on December 29, 2020, 03:24:28 amIs it calibrated for humidity?

author: wizard69
author_rank: Super Contributor
timestamp: December 30, 2020, 03:48:12 pm
content: I thought for a moment that this EXTECH meter: 380947 would do what you want but it wimps out on DC current resolution. At least they didn't want to spec it below 10mA DC. This one, 380942, does what you need at the low end but max out on the high current end.My net connection seems to be screwed up at the moment but if this post goes through I suggest looking around a bit. Amprobe, Fluke, Flir, B&K and whole bunch of others have a bunch of Meters to consider. The issue is, with respect to clamp ons, is that for the most part DC performance of these meters sucks at low current.At least meters with the wider ranges you are interested in.

author: elfer
author_rank: Contributor
timestamp: December 30, 2020, 04:11:55 pm
content: Cheers, Wizard. I kept finding the same, either DC resolution down to only centiamps or not quite enough at the high end. No matter; I hadn't realised how inexpensively a second meter like that UT203+ could be bought so having two meters is my solution.It's also occured to me that using the meter I want for small measurements to also measure great big currents, and next to an alternator with a great big magnet inside it at that,mightend up not being the best idea if that causes the clamp to get magnetised over time. I don't know if that's a thing but having two separate tools for the two separate jobs seems the better way forward, I've come to think.

author: SilverSolder
author_rank: Super Contributor
timestamp: December 30, 2020, 07:31:56 pm
content: The UT203+ looks good for automotive stuff. 400A should cover many starter motors as well as alternators.