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We live off the grid and have just installed 26 220V 1.2W LED lights. We are using 220V as the batteries are some way from the house and and thick copper wire is expensive. Everything works on the inverter except the LED lights. We can only use 6 and then the inverter trips out. With everything turned off, adding 1 bulb at at a time and measuring the current, everything is fine until we add the 6th LED light and the current reading starts going crazy, up and down very rapidly until the inverter trips. What is happening here?

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what happens when you add another appliance on the inverter –  ratchet freak Sep 3 '13 at 9:22
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when you plug the 6th one in, have you tried a different LED? or always the same one? –  Steven Sep 3 '13 at 11:38
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Some kind of transient is tripping the 'crowbar' circuit that protects the inverter from overload. Talk to the inverter company, they may have a solution, such as using ferrite core chokes (a type of inductor). –  HerrBag Sep 3 '13 at 12:24
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Are you sure your LEDs are designed for AC? Some are, some are designed for DC. If AC, you may need a harmonic damper circuit (referred to in previous comment). You may need to use a sine wave inverter. See inverter types here: en.wikipedia.org/wiki/Power_inverter –  HerrBag Sep 3 '13 at 12:33
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Can you provide a link to the inverter you are using? Also please describe the power source that supplies the input to the inverter. This information may be helpful in trying to suggest what may be going on with your system. –  Michael Karas Sep 3 '13 at 12:57
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4 Answers

As a temporary fix, I would use an appropriately rated UPS (sized for future computer needs, not just for this LED situation (which is nominally only 31.2 W))

The UPS will cleanup any transients, and depending on "mains failure time", can supply backup power to facilitate an orderly shutdown or bridge switch-overs between mains and batteries

One company that has European UPS products is Tripp enter image description here

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Thanks will investigate further –  Annabel Donald Sep 4 '13 at 12:57
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It is most likely related to the inverter that you are using. Some inverters are sensitive to the kind of load that you put on them, and LED bulbs could easily present that kind of load. The inverter might be better behaved if you give it a better load - like a nice 50 watt incandescent light - along with the LEDs, though that obviously runs your batteries down much more quickly.

A UPS would work if it were always on, but there aren't that many that work like that, and they tend to be expensive.

Another approach is to take the 220VAC and use it to charge a 12V battery in the house, and use that to run 12V lighting. Obviously more of a hassle because you'd need separate lighting circuits, and you'd need to find a 12V battery charger that your inverter would be happy with.

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Maybe the inverter is doing square-wave output and the LED units are reacting to it with current peaks at the voltage rise. Then 6 times that current peak is too much for the inverter to handle well at that one point in time. –  Skaperen Oct 6 '13 at 18:31
    
Certain UPS designs are "always converting" from AC to DC and back to AC. See "dual conversion". –  Skaperen Oct 6 '13 at 18:31
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This is almost certainly from using a "modified square wave" - MSW - inverter rather than a "true sine wave inverter" - the power conversion circuits in AC LED fixtures expect a sine wave input, and the way they behave when fed MSW input is upsetting your inverter.

Red is a sinewave, green is a square wave, blue is MSW

One possible solution, short of "buy a new inverter" (a rather expensive proposition, especially for true sine) would be to feed the light circuits (only) though a small isolation transformer. The inverter power would feed into one side, and you'd feed the lights a much better approximation of a "true sine wave" from the other side. It should be a bit oversized for the load, since the MSW input will cause some heating of the transformer that a normal sine wave would not. However, the load is so small that almost any isolation transformer will be a bit oversized for it. Find the minimum size by looking at the VA (not W - power factor matters, a lot, here) rating of your lamps, and then run a fudge factor for MSW input of about twice that rating.

Unless the VA is absurdly bad for a 1.2W device, something like this for roughly $50 ($40.76 plus shipping) will probably work. You'd also need to mount it in a safe enclosure, provide circuit breakers or fuses, etc...

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Sounds like you're running into trouble with the light's forward voltage drop At 220v and 26 lights, you've got 8.5 volts per light. How many actual LEDs are hooked in series inside each light, what's the drop of each, and what other weird circuitry is hidden within the base?

Ignoring those questions, the fix for voltage drop problems is to wire sets of the lights in parallel. Try two lines of 5, and see if that works.

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I do not believe that the OP is using LEDs that would be wired up in series. They have stated that they are using 1.2W LED lighting fixtures that are designed to run on 220VAC. Such lighting fixtures would be all run in parallel off the output of an inverter designed to output 220VAC. –  Michael Karas Sep 3 '13 at 13:01
    
The 26 bulbs are wired in 3 banks of 6 and 2 banks of 4, obviously in parallel. If we turn on one bank of 4 no problems. If we turn on 2 banks of 4, or a bank of 6 the inverter trips. I will look into forward voltage drop as I don't really understand that. I'm sorry but I don't understand the 8.5v per light, 8.5 volts in total yes but not per light –  Annabel Donald Sep 3 '13 at 13:07
    
@Michael Karas Question doesn't say how the lights were designed, or how they're wired. Thus figured it best to cover this common LED wiring problem. –  Wayfaring Stranger Sep 3 '13 at 13:08
    
@AnnabelDonald LED's require a certain voltage to fire. When you put them in series, a string of them will light up, until you reach the point that (total voltage) / (# LEDs) is less than forward voltage drop. With circuit description you gave, it doesn't sound like this is your trouble. –  Wayfaring Stranger Sep 3 '13 at 13:42
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I don't understand this wire then chain up, they are led bulbs designed to go into standard light fittings. So in theory standard house wiring, standard light fittings and hey presto.......or so I thought. –  Annabel Donald Sep 3 '13 at 14:25
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