Today I was installing some landscape lighting - basically two legs off of one transformer. One leg is 10 4 watt lights and the other is 8 4 watt lights for a total of 72 watts. The transformer is rated for 88 watts. As I added the last light the entire system shut down. The circuit breaker was not tripped, power at the outlet I was using was 120 volts. Output of the transformer was 7.4 volts. I disconnected the second leg of 8 lights and the first leg started working with a transformer output of 11.4 volts. I reconnected the second leg - it doid not work and the first leg went out. Disconnected the second leg and the first leg started working?
Any thoughts on cause or troubleshooting? Do I have a bad transformer?
Thanks for any ideas you may have
If you used those stab type connectors, make sure they aren't sitting in a wet spot causing more draw or a short. All connections should be waterproof. Those stabs are junk.
If there aren't any shorts or bad connections, then the transformer probably weak I would guess.
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You are working too close too the limit on a piece of crap transformer that doesn't work at max load.
More likely you are over max wattage. The 4 watt lights are probably drawing a tad more than 4 watts resulting in an internal limit being activated.
FWIW: loading the transformer to that level will shorten its life. Get a bigger one or a second one.
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thanks for the thoughts - the idea that I am close to the transformer limit kind of makes sense. When I was connecting the second leg I tested it as each light was added and everything was working fine - right up to the last light which was whenboth legs stopped working. After I posted this I tried disconnecting the last light - still nothing with either leg. In the interest of trouble shooting I may try disconnecting more lights on the second leg to see if it corrects the problem.
Ditto the stab type connectors being bad. Same with those transformers. Those never seemed to put out anywhere near rated amperage and are pricey for what they are.
Now I haven't been watching them too closely lately but.... I would assume they are switching to led bulbs now... If not you can use automotive led bulbs as they are the same socket. Don't buy them at the parts store as they are way overpriced there. Course this only works if your transformer is 12vdc. 12vac would actually reduce corrosion but led bulbs would have have a little flicker.
To prove if it is an overload or transformer issue unhook the first set of ten and hook up the set of 8 by itself. If all 8 work then you have a load issue. If they don't you have a wiring issue.
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It might be that the transformer can't handle the inrush well enough to heat the filaments to where the resistance goes to where it would be for 4W at 12V (about 36 ohms). If you measure the DC resistance of a bulb, it's probably around 4 ohms, give or take, when cold. That means the transformer would have to output enough current to get them hot enough that the resistance increases to much much more than when cold (de-energized), at which point it only has to sustain it - something like 9 times the steady-state current, but for very short duration. I'm sure it's designed to output much more than rated for short duration, but it might be just too much in this case and some internal protection is cutting out before it can get there. Or it's just saturated, and can't get there. Might want to take a current reading on the LV side, if you have a clamp-on ammeter .
It's a possibility, anyway.
It is better to be roughly right than precisely wrong.
So a quick update - I tried connecting just the second leg and nothing. Then I tried the first leg again and nothing so I assumed a bad transformer. At that point I connected everything back up to the transformerand moved on to other things until I got a new transformer. One of the other things was spreading 10 yrds of mulch. In the process of doing that my wife was burying the LV cable in the mulch (the cable between the last light and the next to last light where it previously stopped working) and voila all the lights stated working and have stayed working. I know I'm living on borrowed time but given I am in the middle of the mulch project I'm going to wait and see.
Sounds like something is shorting out in the last section. Just a little movement cleared it for now. Suggest checking that section carefully. Roly