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RalfyFM

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Posts: 1
Reply with quote  #1 

Hello,
     So far in my solar DIY project I haven't come across any particular problem except the one that happened this week and I can't even be sure it's the 12v system that's the problem.
     I charge a 12v battery system via solar and because I'm in a UK winter top up occasionally using a battery charger.
     From this system I have a 600w inverter (I have a few independent solar installations so for this one I don't need a large inverter). Off of this inverter is a mains distributor. Plugged in to this was a laptop charger, but no laptop connected, and a NiCd/NiMh battery charger with no batteries charging.
     My wife luckily came home earlier in the week to discover smoke in the kitchen, switch everything off and so save the house catching fire. Both transformers, the laptop and the battery charger, had melted. The battery was being charged from the mains at the time, as well as a tiny amount from the solar panels (it was an overcast day), as I have done previously. So I have several probably clueless questions

1. Why did the transformers burn out if nothing was actively going on at the other end? 
2. What is more likely to be the problem, the inverter or the distributor? I have a mains socket tester being delivered this week but not sure if that will tell me anything
3. I have a smoke/gas alarm fitted to the battery (that was squealing when my wife got in, and rightly so). Very similar to this http://www.ebay.co.uk/itm/MQ-2-MQ2-Smoke-Methane-Gas-LPG-Butane-Hydrogen-Gas-Sensor-Detector-Module-/232201325115?hash=item3610470a3b:g:6T0AAOSwUKxYc3JD. This is great for the alarm but obviously useless as it wasn't actively shutting everything off. I'd like to use this so that were it to detect a problem again it permanently disconnects both charging and any power draw from the battery until it is reset. Can anyone advise on how to do this please? I've been looking at relays but these would switch again once the sensor stopped detecting gas/smoke. What do I need ffor a permanent but "resettable" switch?
4. Obviously I would like to prevent any problem so the alarm and isolator needn't ever be used. I have fuses in line for both charging and to the inverter but they didn't blow because the high resistance heat problem was way down the line, so the fuses never got hot enough to break. I'm thinking a mains RCD from the inverter to the distributor. Would this detect resistance build up?

Sorry for the lengthy discourse and multiple questions. This has become an impediment to my solar DIY project to the point where if I can't solve it then it may have to be ripped out (unless I can prove the problem was with a faulty 240v mains distributor).

Regards,

Craig

stmbtwle

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Posts: 2,545
Reply with quote  #2 
Scary! Glad it didn't turn into a real fire!

I've never heard of that before. If I read it correctly everything that was damaged was connected to the mains distributor. I'd start there and check the voltage with the inverter running. If the voltage is appreciably higher than it's possible the inverter has failed and destroyed the transformers. If the inverter has failed also check the batteries and their charger.

Even with no load on them, transformers do have a small amount of current going through them. A short in the windings can cause them to overheat and melt. IF they are touching I suppose the heat from one could cause the adjacent one to also fail.

Another possibility would be a mains spike (lightning?), feeding through the battery charger and inverter to the transformers. Lightning can cause all sorts of weird damage.

I'd replace the fuses with the smallest that will carry the normal load.

You could install a relay so that when energized it causes a short from the fuse to ground, blowing it. The power would then stay off till you replaced the fuse. It's an "old school" trick but it works. I'm sure there are other devices but I'm not familiar with them.

Please let us know what you find so we can all learn from your experience.




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Willie, Tampa Bay
colinmcc

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Posts: 139
Reply with quote  #3 
Almost 100% certain your inverter had failed and was putting out a modified square wave, which transformers hate, probably one half of the sine wave generated had died, leaving you with  'pulsing DC'.  

About 40 years ago in the 'disco era'  I was commissioning engineer for an British company and we were installing a curtain of light 'round a dance floor in Paris, France. It consisted of several hundred potlights, each with a 6v toroidal transformer and bulb. I still remember the stink as one of the thyristors in the sound to light machine failed and the windings in all those transformers melted.

Had to take them all down, strip out the transformers, get new ones shipped from the UK, fit them, took a week and for a $5.00 thyristor several thousand $ of cost!  The club was in 'La Defense' a high rise area of Paris, the club got so rough, I recall the DJ calling in and requesting money to rent a suit of armor to wear while working, he apparently had had bottles and worse thrown at him! Fun days!![biggrin]
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