DC clamp ammeters

[Ferguson 2000]

Picotech sell a current clamp which measures from 10 mA to 2 A on it's low range see: https://www.picotech.com/accessories...rent-probe-bnc
The BNC is to connect to their computer devices and there is a 4 mm plug version, they may be available on the internet at lower prices.

Best wishes with the fault finding, Geoffrey.

[David Simpson]

Stuart, you say you have a Boat. A pleasure craft, an ex fishing boat, what ? Length & hull construction, and engine/machinery ?
The reason I ask is because back in the late 70's/early 80's, one of my commercial diving jobs was to examine & sometime change Sacrificial Zinc Anodes on the hulls & rudders of fishing boats. This, along with a past electronics background, led me to do some brief experiments. Used an Avo 8(on DC mA range), a brass rod, and a gash length of insulated copper wire.
Jesus - a damp engine room with a foot or so of bilgewater is one big Lechanchie Cell. Even with the 24V batteries switched off - sometimes 10's of mA were flowing hither & thither. Depending whether I dunked the brass rod into the harbour or just into the bilgewater. I checked the propshaft, the engine block, seacocks, and so on. Never really followed it through, but I learnt that it was common knowledge amongst marine engineering folk. Bonding across flanges for seacocks & engine heat exchanger metalwork, etc., was designed to reduce this phenomenon. As was, obviously, the zinc anodes.

Regards, David

[Boater Sam]

How old is the inverter? You get capacitors with leakage currents after several years, the capacitors are connected to the battery leads all the time even with the inverters off.

[stuarth]

The boat is a 27ft GRP cruiser with a 75hp Yanmar inboard diesel. There are lots of electrical “things” on board, powered from 3x100AH batteries. The wiring loom is quite complex, and mostly out of sight. Disconnecting wires from the loom to measure the current in individual wires is not practical, but I can get a current clamp round much of it, and if I put the clamp round several wire at once and there is no current flow, then all these wires are blameless, and I can quickly narrow down which parts of the loom to investigate.

I can measure the current coming out of the batteries very easily, the problem is where is it going? It’s something after the main isolator for the “leisure” stuff, so that eliminates things such as the automatic bilge pump and engine related stuff. The inverter is new, and on its own isolator. The radio/CD player has a permenant power connection, but the whole thing can be unplugged, so it isn’t the culprit.

The VHF radio has external GPS and/or NAVTEX receivers hiding between the inner and outer GRP structures somewhere, but I haven’t found them yet. There are various other suspects, eg the heating system, the holding tank level gauge, etc. You can see how a sensitive current clamp meter could save a lot of time (and disruption to the wiring loom, trim panels, etc), hence my original question. Which has been answered by several folk on this jolly useful forum, including Buggies and Mark Hennessy, so many thanks to all. I think I’ll order a UT210, and see how I get on with that.

Stuart

[Red to black]

Originally Posted by stuarth

and if I put the clamp round several wire at once and there is no current flow, then all these wires are blameless
Stuart

Not at all, when you clamp around the supply and return conductors the currents cancel each other out, the only exception to this is my earth leakage clamp meter which is designed to check earth leakage currents (ala RCD) around the live and neutral together and even here the earthing conductor has to be excluded from the clamp to make such a measurement.

[stuarth]

Good point. However, the colour coding for the wiring is very simple, red for positive, black for negative, and in many places there are bunches of red only, or black only wires, usually close to the relevant bus bars used for power distribution. Makes it harder to see which wire is for which load except at the (well labelled switch panels) and the load itself, but easier to do the current probe search for missing current. I hope so anyway.

I think the wiring on boats, at least on GRP cruisers, is more ad-hoc than the well planned wiring loom you get on cars. Each boat is more or less hand built to the customer specification, with wires put in for things the customer had specified, and to the places where the customer wanted his or her extra lights, heating controllers, or whatever.

Stuart

[dave cox]

The dc clamp meter is the way to go, given your constraints!

I wonder if you could hack something up with a 'hall probe' to save a few bucks as you don't really need an accurate measurement just a 'where are the electrons going' device.

dc

[dave cox]

Something like Ti's DRV5053 - maybe ??

They do a range of sensitivities, 10's of mA should produce enough field 'very close' but I don't have one to try it with.

dc

[David Simpson]

Stuart, surely a 27 foot cruiser has a DC (12V?) distribution board, with fuses or circuit breakers for several sub-circuits? Thus, like a house's CU, you can isolate them on & off independently. Ones I've seen on leisure craft usually have a hinged & gasketed front panel which reveals the connection terminals or wee bus-bars behind. I guess in the wheelhouse, as you wont have a roomy engine room. Any pictures ?
Why not get a mate to help you - with the engine & its alternator off, you monitor the worrysome current being drawn from the batteries, and your mate unplugs & replugs various radios, satnav, sounder, bilge pumps, engine & water temp senders, running lights, etc. Then you yell when your MM drops to zero mA. I've worked on boat's looming( and aircraft's) in the past, and right enough its a sod. Sometimes rarely you just have to safely cut & re-splice, & re-insulate a suspect wire for fault-finding purposes.
Would the boat's manufacturer not be able to supply a manual or wiring diagram ?

Regards, David

[Sinewave]

Originally Posted by Red to black

Not at all, when you clamp around the supply and return conductors the currents cancel each other out, the only exception to this is my earth leakage clamp meter which is designed to check earth leakage currents (ala RCD) around the live and neutral together and even here the earthing conductor has to be excluded from the clamp to make such a measurement.

And of course the Avo flexiclamp, which can clamp around multicore cable, flex and twin and earth. Though this is an AC only clamp.

Spurred on by this thread I bought one, and now my UT210E has arrived, what a great bit of kit. Will do anything I need for radio work and vehicular stuff too. DC down to a few mA without breaking the wire, brilliant. If one ever requires an all in one meter this is the one to go for.

[Radio Wrangler]

GPS?
Some GPS can take a painful amount of time from cold switch-on to acquire satellites and get going. I wouldn't be surprised if anything with a GPS in it kept some things running whenever it had power available. Off wouldn't really mean off, so it could come up quickly. As a minimum it would store tha last fix and the last ephemeris.

Tried disconnecting the GPS antenna? It's almost certainly got an amplifier in it and it might just be left running.

David

[stuarth]

Well, my UT210E arrived, and I’ve used it to trace the rogue current. It goes down a wire marked at the distribution busbar under the dashboard as “TV”. The TV runs on 12v, and I’ve already unplugged that (switching it off leaves it in standby mode, showing a LED and listening for the remote control commands) so it’s not the TV itself, but there is an amplifier for the aerial fixed to the bulkhead which has a switch (on/off), and a disk aerial on the roof which may also be powered. The wires for all this disappear into a space above the wardrobe which I need to open up to investigate further. I’ll either add a switch for all the TV related stuff, or, more probably, connect it all the the existing switch for the radio.

However, the UT210E is a great piece of kit, it is more than sensitive enough to find my missing milliamps. The jaws are big enough to get round the two cables from the two leisure batteries at once (each one is the size of a car starter motor cable), and small enough to get round one wire at a time where they emerge from the wiring harness at the busbars.

Many thanks for the advice given here.

Stuart

[ex 2 Base]

Recently I also bought UT210E clamp type meter and found it really useful except it hasn't any croc type clip for ohms and volt ranges. Does any one know of a supplier of croc clips with plastic covers that actually/properly fit the probes. There are a multitube of croc clips available but which ones fit with safety? Ted

[buggies]

Personal opinion only - I try not to use any clip assembled test leads. I swap the complete lead and have large crocodile clips, small ones, sharp probes and tiny clips for IC pins. Each lead has standard 4mm plugs and today for example I had one lead with large clip and the other with pointy probe on one meter and a pair of small crocs on another.