DC clamp ammeters

[stuarth]

I have a vehicle (a boat actually) with a small drain on the battery (60mA ish) with everything switched off, and I’d like to use a clamp ammeter to find which of the multitude of wires it’s flowing through.

I have a fairly old AC/DC digital clamp ammeter, but its resolution is only to 100mA, so it’s not up to the job.

There now seem to be available meters such as the Uni-t UT204 with a claimed resolution of 10mA. Is the resolution/repeatability of that extra digit good enough to detect my 60mA, or is it just there for marketing purposes?

Stuart

[Sinewave]

I would think you'd get away with it just fine with the 100mA resolution. What's the accuracy of both? The extra decimal place may make little difference.

[stuarth]

On my existing meter with 100mA resolution, the last digit flickers uncertainly around zero as the DC zero setting is adjusted. A few 10s of mA of actual current through the jaws is not detectable, and certainly not measurable.

My question really is whether the newer meters are an order of magnitude better at measuring low values of DC current, or is the extra digit good for the rather easier task of measuring low AC currents, but of no benefit for DC.

Stuart

[Jon_G4MDC]

Wind more turns through the jaws? Works for me.

[stuarth]

Generally impossible with wires in the main wiring loom, let alone the main battery cables which are the size of car starter motor cables. I might manage a couple of turns with some of the wires, but there's not enough slack for the 10 turns it would need to get my existing meter up to 10mA resolution.

Hence my question about whether more recent meters really have 10mA resolution. Has the technology improved by an order of magnitude?

Anybody here got one?

Stuart

[Trigon.]

>>Has the technology improved by an order of magnitude?<<

I don't think it needed to. My 25 (?) year old LEM PR-30 can easily resolve better than 10mA.

It's not self contained - it plugs into an DVM or scope, but the principle's the same.

Cheers

.

[kellys_eye]

If all you're measuring is the low mA of a 'leak' then an ordinary multimeter in series with the battery leads will do the job. The battery connector should be fairly accessible and easily removed.

Removing fuses at the control panel will isolate the fault.

[Boater Sam]

Put a known load on and measure both.

[duncanlowe]

Another possibility for improving resolution. There may not be enough spare wire in a wiring loom, but you could replace the fuse with a wire link and fuse, giving some length for the multiple turns.

[G6Tanuki]

Why use a clamp-on? There exist nice safe convenient "fuse breakout adapters" that allow you to substitute a DVM for a traditional vehicle low-voltage fuse for just this sort of leakage-detection.

See http://www.gunson.co.uk/product/77068 for example [available in standard-size, mini-blade and maxi-blade]

I've got one somewhere - was brilliant at tracking down the condensation-filled lamp fitting that was causing a continuous drain on the battery in a friend's motorhome.

[PETERg0rsq]

While i do not have any practical experience of the meters you are refering to, I have heard that they do have issues with suseptability to stray magnatism, including the earths magnetic field.

If you rotate them you get different readings!

I agree with others, there are better methods of finding parastitic current drain, but they all involve disconnecting the current path, which can its self re-set a module that might not be shutting down correctly!

For this exact problem I bought (for a few pound) a purpose made tester from china (on an infamouse online auction site), which replaces the blade fuse (the blade fuse plugs back into the tester to preserve fuse protection).
This will fnd the current drawing circuit, if removing and replacing the fuse does not reset the problem module.

[stuarth]

The current through the battery terminals can be measured by turning off the battery isolator switch and connecting the meter across the switch terminals. The question is, which of the myriad of y-splits does the current flow through after that. There isn’t a fuse box as such (as there is in a modern car), there are fuses a bit ad-hoc in the wiring loom, some of which then split to more than one destination. It would not be easy to undo each wire split and measure the current in each wire.

So what I want to do is put a clamp ammeter around each wire after the split to see where a few 10s of mA are going. And for that, I need a clamp ammeter with better resolution than my current (sorry for the pun) clamp ammeter.

Stuart

[trobbins]

Stuart, is there any slack in any of the feed wires to make multi-turn loops? Do any of the feed wires common to a screwed terminal to the battery, or are they all somehow fixed/clamped/soldered in a way that can't be disconnected?
I would also be looking for some type of LEM module that includes DC.
You could also try a clamp on CT, and use a peak detect voltage meter and not too low a loading resistor, and use the step application of battery voltage to try and detect which cable has hopefully some level of in-rush current.

[duncanlowe]

There are clamp meters that will deal with lower currents, we have one at work. I believe its a Chain Arnoux K1, in RS at around £500.

[buggies]

Originally Posted by stuarth

There now seem to be available meters such as the Uni-t UT204 with a claimed resolution of 10mA. Is the resolution/repeatability of that extra digit good enough to detect my 60mA, or is it just there for marketing purposes?
Stuart

I bought this one in May to check my car battery drain (and for true rms heater current with capacitor dropper and diodes - not yet done)
https://www.ebay.co.uk/itm/153000753458
This morning I fed 60mA through a resistor with a couple of DVMs and the clamp meter. With the meter on 2A range and zeroed before clamping a wire, it read 60 +-1 mA. I then rotated the meter and noted the readings at approx 90 degree angles:- 60, 52, 39, 48 so worth zeroing at the same orientaion as measuring. Note this was done in "workshop" with lots of other gear switched on.
For completeness, I placed on kitchen table and checked at the cardinal points with no current as shown in the attached pic.

[woodchips]

I have a clamp meter specifically intended to find earth leakage currents on mains wiring, but can't remember if it is AC only, it is on loan, again. This reads to 1mA I think.

The indicated current will also change as the position of the conductor alters in the jaws.

[stuarth]

Buggies thank you so much! This is just the information I need. Your meter sounds just the job. Other solutions of pulling a fuse or wrapping the wire several times through the jaws are impractical on the boat (and probably not always easy in a car).

Thanks again, Stuart

[mhennessy]

I did an in-depth review of the UT210E a while back: http://www.markhennessy.co.uk/budget...nit_ut210e.htm

It's pretty good for the money - I recommend it

[McMurdo]

I've got one similar to George's. It's not branded Unit-t though, it's a Voltcraft from Rapid.

I bought it to set-up the bias current on audio amplifiers, so when it came I checked the calibration on the bench Thurlby psu. Spot on, when the instructions are followed.

The meter auto-zeros the DC current range when the jaws are opened and closed again. So you need to be able to put the jaws around the wire before the current flows.


Lowest current range ac/dc/true rms is 2A FSD

https://www.rapidonline.com/voltcraf...-meter-64-3330

[broadgage]

I would either use a standard multimeter in series with the battery lead, then turn circuits on and off until the fault is narrowed down.
Alternatively, make up an adaptor consisting of 10 or perhaps even 100 turns of wire to clamp into the meter, and connect this in series with the battery.

Is the boat equipped with an automatic bilge pump ? most are. IME these are a common cause of leakage currents.
Another likely possibility is any modern electronics with a "sleep mode" rather than a true off switch.

60ma leakage can even be narrowed down a bit without use of a meter, simply connecting a low current lamp in series with the battery will help locate the problem.
A 6 volt 40ma lamp will light quite brightly.