Budget clamp meter for auto - Page 1
Forum section: electronics / beginners

author: Peabody
author_rank: Super Contributor
timestamp: August 03, 2023, 09:34:42 pm
content: I need a DC clamp current meter to measure auto circuits (battery current, alternator current, etc.) I don't need it to do anything else, including any AC functions. Does anybody know of a specific meter like that for US$20 or less?

author: bdunham7
author_rank: Super Contributor
timestamp: August 03, 2023, 09:39:41 pm
content: Quote from: Peabody on August 03, 2023, 09:34:42 pmYikes, that's a tight budget for DC clamp. The UNI-T UT210E is $40 and from the reports of others is probably OK for your purpose. I suspect if you did find anything cheaper it would be a total turd, but happy hunting!

author: notsob
author_rank: Frequent Contributor
timestamp: August 03, 2023, 10:31:29 pm
content: you could try looking for something like this on your local market (ebay - craigs etc)https://www.ebay.com/itm/403751013203

author: wasedadoc
author_rank: Super Contributor
timestamp: August 03, 2023, 11:17:50 pm
content: Quote from: notsob on August 03, 2023, 10:31:29 pmThat and similar needs to be connected in series wih the circuit being measured. PITA compared to a clamp meter.Edit: Apparently not the case. See bdunham7's post below

author: bdunham7
author_rank: Super Contributor
timestamp: August 03, 2023, 11:23:29 pm
content: Quote from: wasedadoc on August 03, 2023, 11:17:50 pmNo, the ones I've seen you just place it over the wire and crank the starter. It has an tolerance of +/-50% + 50A or so, but it will tell you if your engine isn't cranking because there's an open circuit, your battery is weak or your engine is locked up. Not too handy for headlights and windshield wipers.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: August 03, 2023, 11:32:30 pm
content: Another vote for the Uni-T 210-E.It's a quite affordable meter and it has the quite rare advantage that is has single mA resolution for DC current.Even that (quite famous with EE nerds) guy that blows up expensive DMM's just to test them has one, and he likes it enough to make extensive modifications to it. He put in a better pre-amplifier / opamp and uses it to pick up line level audio. Quite impressive.It's biggest compromise for that price point is mechanical stability. The clamp itself might have some thicker plastic. Maybe it's worth putting it in a hard case instead of it's cloth bag.

author: Shonky
author_rank: Frequent Contributor
timestamp: August 03, 2023, 11:44:14 pm
content: Another Uni-T 210E vote here. I don't think your budget is realistic.I have one and the low DC current measurement whilst somewhat useful is a bit hard to zero out if you're trying to attach it onto a circuit to measure something like current draw when a vehicle is asleep.

author: Smokey
author_rank: Super Contributor
timestamp: August 04, 2023, 12:13:46 am
content: If you are looking at starter currents and other automotive stuff, you want a clamp probe with a BNC you can put into a scope. A meter will miss the peaks.https://www.ebay.com/itm/111839276074Yes, this is more than $20. If you keep on the ebays, you can get used stuff for the $50 range. Not sure how long you have to wait.

author: mwb1100
author_rank: Frequent Contributor
timestamp: August 04, 2023, 12:36:27 am
content: Assuming you already have a multimeter, this clamp is closer to your price range. But I can't vouch for its accuracy:-allsun AC/DC Current Mini Clamp Meter ProbeLooks like today it's a bit under $30 with a 10% off coupon.I got it to hook up to an oscilloscope (I had the banana to BNC adapter already), but I haven't gotten around to that project yet.

author: Smokey
author_rank: Super Contributor
timestamp: August 04, 2023, 12:44:26 am
content: Quote from: mwb1100 on August 04, 2023, 12:36:27 amThe only mention of bandwidth on this thing is in the title: "50Hz-60Hz LED"60Hz isn't really enough.

author: Peabody
author_rank: Super Contributor
timestamp: August 04, 2023, 04:55:16 am
content: Let me explain what I'm trying to do.The car is a 2012 Honda Civic, which has the infamous Honda two-stage charging system. In normal daytime driving, the alternator puts out 12.3-12.4V, which only charges the battery about 60%. That's still enough to start the car. But if the headlights are on, or any other big current drain, the alternator cranks up to 14.4V.I have a voltmeter installed in the cigarette lighter socket, so I can see what the alternator is doing. Normally, I always drive with the headlights on so I can keep the battery fully charged. But recently, I've noticed that it stays at 14.4V all the time now - whether the headlights are on or not. So that's a malfunction of some kind.So as I see it there are two possibilities. The first is that the computer is sensing the battery voltage as being lower than it really is, or is sensing the total system current as higher than it really is, but nothing is really wrong. The second possibility is that I have a major current leak somewhere when the ignition is on which is equivalent to the headlights being on. If that's the case, I'd like to fix it.So my plan is to turn on the ignition, but NOT start the car, and measure the current flowing from the battery with the clamp meter. With no lights on and nothing running, it would just be what the computer draws, plus maybe some solenoids, so maybe a few hundred millamps. But if there's a major current leak, it would be a lot more.Since posting it occurred to me that it might be possible to do this test by just measuring how much the battery voltage drops when the ignition switch is on but the car isn't running, using my regular meter. I could even try turning on the headlights to get an idea of how big a drop that causes. But the voltage drop may not give me enough information to make the call. I don't know what the drop would normally be if there's no current leak, although maybe someone here could tell me that.I'd just hate to spend $50 on a meter I might use exactly once.The daytime running lights may mess this up if they come on when the ignition is switehed on. So I may need to figure out a way to disable them. There may be a fuse for that.

author: Shonky
author_rank: Frequent Contributor
timestamp: August 04, 2023, 05:13:01 am
content: I wouldn't say that 14.4V all the time is a "malfunction" at all. That's how it should be if anything. Whilst it may be different to what you think is normal, it is more correct than needing lights on to properly charge the battery.I wouldn't bother with a clamp meter to measure currents. Measuring current with ignition on will be indeterminate I'd say. Too hard to tell what's good and what's not.I'd be measuring voltage drops (in particular from alternator body to the battery terminal whilst not charging properly) and checking ground straps everywhere are properly connected.

author: Brumby
author_rank: Unknown
timestamp: August 04, 2023, 11:44:22 am
content: +1 for the UT210E. If you want a high degree of accuracy, I suggest you practice to find out its idiosyncrasies, but that's not difficult.Quote from: Shonky on August 04, 2023, 05:13:01 amCompletely agree here. The 12.3V-12.4V thing sounds more like a malfunction.

author: armandine2
author_rank: Frequent Contributor
timestamp: August 04, 2023, 11:55:16 am
content: may be nothttps://opensiuc.lib.siu.edu/cgi/viewcontent.cgi?article=1011&context=auto_pres

author: Psi
author_rank: Super Contributor
timestamp: August 04, 2023, 12:14:35 pm
content: Old tech, doesn't even need batteries, just rest the cable through the channel at the back and the magnetic field powers the needle showing the amps and the direction of flow.https://www.ebay.com/itm/125328582018?hash=item1d2e2a6582:g:T~gAAOSw6CNiioffI'm mostly joking (about you buying one) but they are kinda useful from time to time.

author: Peabody
author_rank: Super Contributor
timestamp: August 04, 2023, 02:15:31 pm
content: Yes, the 12.3 - 12.4V thing is something Honda did deliberately to reduce alternator load and maximize mileage. But it was and is a terrible idea. Since the battery is never fully charged, it sulphates up and dies prematurely, which more than offsets any mileage benefit you might get. So I'm hoping the computer or some sensor has just gone wonky, and I can now drive without having to turn on the headlights. I would never have that "fixed". But if I really do have something drawing a lot of current that shouldn't, I'd like to get that fixed. But I need some way to tell what's going on.

author: bdunham7
author_rank: Super Contributor
timestamp: August 04, 2023, 03:05:58 pm
content: Quote from: Peabody on August 04, 2023, 02:15:31 pmThe UT210E is probably the appropriate budget tool for this--you're looking for a 5-10A or so draw and that will show up nicely even without precise zeroing. You may find that your battery is borderline and is taking a higher charging current than normal. IIRC there is a current sensor in the (negative?) battery clamp, but I don't know the details or if you could use that to measure current. If there were a problem with that system or pretty much anything other than a higher battery or accessory draw, you would have a warning light on. Running it with the headlights on is the way to go--it is a bit safer and your battery stays happy.

author: mwb1100
author_rank: Frequent Contributor
timestamp: August 04, 2023, 04:57:29 pm
content: Quote from: Smokey on August 04, 2023, 12:44:26 amI'm exposing some of my vast ignorance on electronics here, but does that matter for measuring DC current?(and if I wasn't clear initially, I have little idea of the quality of this clamp other than it matches up with a Uni-T UT211B on AC current to within 10 or 20 counts if I remember right)

author: slavoy
author_rank: Regular Contributor
timestamp: August 04, 2023, 06:01:05 pm
content: Quote from: Peabody on August 04, 2023, 04:55:16 amQuoteDid you check first if all the other conditions are met?QuoteYou can do it easily without clamps, using the simplest ammeter with the appropriate current range: loosen one battery terminal, turn on the ignition, connect both ammeter probes (one to the terminal, other to the battery wire) so that when you disconnect the terminal, the circuit closes through the ammeter.

author: Peabody
author_rank: Super Contributor
timestamp: August 04, 2023, 09:01:06 pm
content: I don't have a meter that will handle current above 500mA.Well I've made some progress. I pulled the DRL fuse just to keep that from complicating things. The battery was at 12.78V with everything off. Then turning on the ignition, but not starting the car, the battery measured 12.4V. Of course all the dash indicator lights were still on, but nothing else. That strikes me as being a bit low. But of course I don't know how much current is causing that drop.However, I think I can find how much current that represents by turning the ignition off and then connecting some power resistors between the battery terminals in whatever configuration drops the voltage to 12.4V. Since I know the voltage and resistance, that will tell me the approximate current the car is drawing when the ignition is on. And that was really all I needed the clamp meter for.Then the question is whether that current level is normal or excessive. And I have to remember that the problem could be the battery - although there's no other indication of a problem there. The battery maintains about 12.8V when left alone for 18 hours, and has no hesitation in starting the car. But it's still a possibility.

author: bdunham7
author_rank: Super Contributor
timestamp: August 04, 2023, 10:13:17 pm
content: Quote from: Peabody on August 04, 2023, 09:01:06 pmThat seems completely OK. There are many things that will cause the charge control to not cut back, so it might not be something to worry about.

author: Peabody
author_rank: Super Contributor
timestamp: August 05, 2023, 06:14:19 pm
content: I finished my test with the power resistors, and it appears with DRL disabled, no interior stuff, ignition on, but car not started, I'm drawing about 2.5A. That's a lot more than I would have predicted, and must be caused by more than all the indicator lights. Fuel pump maybe. Well, I don't know.On the other hand, I think that's a lot less current draw than it normally takes (the headlights) to shift the alternator into high voltage. Even turning on the AC didn't do that reliably before. So maybe there's no current leak after all. Could still be the battery, so I'll get it tested, or buy the Harbor Freight "toaster". But if the battery is ok, I guess I'll just drive it until something definitive happens.

author: Peabody
author_rank: Super Contributor
timestamp: September 01, 2023, 08:40:26 pm
content: I wanted to report that this has all finally resolved. My Civic reverted back to two-stage charging. It's still a mystery why it stayed in high-voltage mode for a while, and why it reverted back. The only thing I can think of is some kind of long-term average of the ambient temperature (the heat wave, now not so hot). But there's no real logic in that - I just can't think of anything else that's changed. I did test the battery with a load tester, and it's fine.But I ran across a guy on a Civic forum who sells a device to disable the two-stage charging system on my 9th generation Civic (but not other generations, or other Honda models). I installed it this morning, and now I have 14.4V again all the time, whether the headlights are on or not. And it doesn't throw any codes. So in the end I didn't need a clamp meter, and nothing was wrong with the car that I could detect.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: September 02, 2023, 01:49:20 pm
content: Quote from: Peabody on August 05, 2023, 06:14:19 pm