Best way to locate a fault in garden 12v lighting

[captaincaveman]

Hi Guys n Gals,

I'm a little stumped on a job and was wondering if anyone could advise?

I've got 3 drivers going to 3 sections of garden lights. Two of the three sections are not working (about 10 lights). I presume it's two sections due to the number of lights and I can't find a third section anywhere else. All the cables are buried under the patio flags or within the cavity in the patio wall with no access to connections. None of the connections have enough length on the cables to pull the connections out (so I have no idea where the connections are).

I tried the good working section with the two drivers of the bad sections and the good section still worked so I'm assuming those drivers are ok. The chances of all 10 lights faulting at the same time is unlikely so I'm assuming there is a bad connection(s) somewhere (Although there doesn't appear to be any work done to disrupt them anywhere).

It's a nice patio and the customer is reluctant to have walls opened up and flags lifted so I'm just wondering if there's anything I can do before suggesting that's the only way?

Cheers in advance

 

[Lucien Nunes]

Are they constant current or constant voltage drivers?

If CV i.e. parallel wired, a short anywhere including inside one light will put the driver into overload protect. And you will be able to read it on a meter from the driver end, which might give a clue to its distance. Or, there is a disconnect between the driver and the first light. This will not necessarily show up to a meter because the lights might look O/C anyway. You might have to break into the flex of the nearest light to find this. A TDR fault locator might show the distance clearly.

If CC i.e. series wired, a disconnect anywhere including inside one light will kill everything. This might be hard to trace without breaking into the flex of multiple lights. Or, a short between the driver and the first light (or less lights than will provide the driver's minimum voltage threshold) which might or might not show up to a meter at the driver end. A fault locator might have less luck finding the fault on a series configuration.

The bummer here is that if one or more joints in each dead group is a rusted wreck, all of them are probably going to go the same way over time and the only solution will be to access and remake them all. Let's hope it's a couple of rogue fittings and that replacements are available.

 

[Simon47]

What Lucian says.
Time to tell the customer that it's time to open stuff up or accept non-working lights - and make it really clear that if the lights had been competently installed in the first place you'd have stood a chance of fixing them without the disruption. It's why I really hate hidden joints, and cables that can't be replaced. Even if you find the bad joints, you probably can't pull in longer cables that would allow you to put the joints where they can be accessed behind the lights - so more joints to splice in a bit more cable ...
What's the odds that the electrics were done by the patio builder Any idea how long this has been installed ? There might be a case, if the customer is thick skinned and a persistent b'stard p.i.t.a. like me, for having the patio builder come back and do the opening up and restoration at their expense. But I suspect it's been another bodgit & scarper outfit that no longer exists.

 

[captaincaveman]

It was done about 7 years ago and the builders supposedly used an electrician (though I've heard that one before!). Last time she spoke to the builder hi wasn't helpful so I don't expect anything from that angle.
Thanks Lucian. You've given me a few ideas I shall consider trying! You are indeed a god

 

[marconi]

Did both strings fail at the same time? If so then before digging up anything I would investigate with the customer (and gardener?) why two separate strings of lamps each with working drivers have failed at the same time - the coincidence of failure suggests to me an event which has caused damage to both strings' cabling at the same location at the same time.

Have any 12V led lamps (- I assume LED lamps -) been replaced recently and perhaps fitted in such a way in their lampholder that shorts out the supply or the wrong way round if the lamps are polarity sensitive types and their supply is dc?

I'd also measure the voltage at each fitting to garner information on whether there is an upstream complete open circuit or a high resistance section/point in the string feed.

Then I would remove all the lamps and measure the resistance between the two supply wires at each fitting first with the driver connected and then with it completely disconnected. Measure the resistance of the outgoing feed at the driver location and the output resistance of the driver - take care to measure resistance with the same polarity each time ie red to red black to black or + to + and - to -

With drivers still disconnected and lamps removed measure resistance between the two feeds F1 and F2 ie F1+ to F2+ and F2- and then F1- to F2+ and F2-

 

[Lucien Nunes]

I did not register the reference to 12V (it's only iin the title) so my comments about constant current and series connection are irrelevant.

I'd also measure the voltage at each fitting

I think the problem is that being sealed units, and with all the joints inaccessible, any measurement of anything involves cutting into cables introducing new joints / vulnerabilities. So the trick is to troubleshoot with the minimum possible number of interventions.
But with parallel connection the test sequence is surely to confirm whether there is a short measurable from the driver end, and then continuity to the nearest lamp. One cable chop is more or less unavoidable unless the fitting can be opened non-destructively?

 

[Pretty Mouth]

I'm pretty sure those are constant current drivers, not CV 12V.

 

[marconi]

Picking up on Pretty Mouth’s helpful post above - The drivers are garden zone make. If the plug and go system has been used in the garden it looks like this. Note the last pane which shows a circuit continuity blanking plug when no product is installed which suggest series connection of lamps and constant current scheme. Would be worth checking lamps are properly pushed in and connected And the right lamps have been used for this series circuit to work.

if it is possible to identify the fixtures of a duff string What about taking the lamps out of the working string and putting them in one of the defective strings?

Garden Zone Plug & Go Range​

 

[Pretty Mouth]

An internet search is not showing any garden zone drivers at 12V, but a few constant current ones.

 

[Pretty Mouth]

Just thinking out loud (and probably over thinking it): I assume CC LED lamps fail open circuit? If so, could there be a way of connecting an AC supply to one pole or the other of the circuit, and using a volt stick at each lamp to try to find the defective lamp/ break?

 

[marconi]

Driver 11W - https://www.lights2u.co.uk/exterior-lights-c5/garden-accessories-c97/garden-zone-driver-11w-p3380

I think gardenzone own brand these drivers which are constant direct current at 350mA and loop voltage something like 30 to 80V.

One of the fittings in the wall looks a bit like this:

GZ/Optica3 | Optica 3 Plug & Go 3w LED Ground Light With Optical Lens | Garden Zone Lights - https://www.gardenzonelights.co.uk/index.php?route=product/product&path=59&product_id=131

I cannot find any spare led lamps in the gardenzone website so maybe the whole fitting must be swapped for new when it fails. Are the fittings sealed units ?

 

[Lucien Nunes]

Actually one can just semi-read the driver label in the original pic which seems to give a voltage range and a current in mA so yes, CC. In which case the O/C could be at any one of those tap connectors or any fitting.

I would have a go with a tone generator and tracer before digging anything up. Some experience interpreting the results might be needed. It might not find the fault for various reasons too lengthy to describe here, but if there is a bad DIY joint between driver and pre-made string, it might be just the ticket for finding it

I assume CC LED lamps fail open circuit

Not necessarily. LED chips often fail short, but here the more likely failure is moisture-ingress / corrosion related in which case an open-circuit other than the LED itself is probable.

 

[marconi]

https://cpc.farnell.com/tenma/72-14306/test-probe-0-75mm-red/dp/IN08129

If you have to gain contact with the string feed current conductors, in order to avoid severing the conductors completely perhaps you could carefully peal back the sheath and then use these 0.75mm needle tipped probes to pierce the live conductors insulation? Afterwards a dob of superglue to fill the needle holes and then relay the sheath, cover and bind it well (somehow) to make it watertight. There is probably a tried and tested technique to do just this.

PS: I use these needle probes to pierce the protective conformal coating sprayed over circuit boards to gain contact with the metal on components and tracks.

 

[captaincaveman]

Ok! There's a wealth of helpful insight there. Thank you sooooo much

I'll try and formulate a plan during the week with the suggestions above and book a return.

I might start with Luciens suggestion by breaking into the cable(s) at the driver end and using my socket & see tracer to check continuity to each lamp. Hopefully that may narrow it down at least. If that fails I may voltage test at the wall cables as they're reasonably protected from the elements and I think the owners can afford a couple of weatherproof connections (if I can't get spikey probes - nice tip Marconi). I don't think the lamps themselves can open up unfortunately :/

I'll look at the other suggestions in least destructive order lol.
I'll let you know how I get on. They won't dismantle the patio so I'll either succeed or pass it on but I don't like giving up!

Cheers

 

[adonis2]

I used to just use a pin pushed into a (12v) cable to check for breaks in the wiring of motorbikes just clip or touch the probes of a multimeter on it.