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heavyfletch2nd

Jun 27, 2016
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Hi all ..
I have been taking a interest in electronics for a couple years now so I do have experience with repaires and basic circuits and can use multimeter, but not building my own projects like now so I have purchased a large transformer from ebay for a 12v lead acid battery charging / power supply project and to run DC input chargers etc for my shed, the transformer is 16v AC off load, the problem I am having is when I put a rectifier on it only shows 7v DC, a smaller rectifier sets fire, the transformer is multi tap AC input, very high current AC output of two "FAT" wires. how can I get this 16 v AC high current down to DC without loosing too many volts and amps.

thanks for reading :)
 
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Bluejets

Oct 5, 2014
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Show us the transformer and what circuit /connections you have made otherwise it's just a guess and we can be of very little help.
 

heavyfletch2nd

Jun 27, 2016
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Thanks for the reply .. here are a cupple pics . Pic 1 ,The rectifiers ..the first rect on print pcb circuit i thought would work (came from a 15v curcuit ) used to charge 14.4v battery popped as soon as I turned it on. The second in the pic bolted to the heat sink is taken from a laptop charger it set fire 2 seconds after turning on . The third in the pic are large 70 amp recs wich work but seem to have a large drop out down to 3.47 vdc .. the second pic is the transformer and wires red as live in blk as neutral , when its turned on (off load) 15.9v ac out of secondary I am un sure on current but seems very large , it is going to be a simple power supply curcuit using diods to drop down where needed if I can get the full potential from tranny but worried now about the amount of current from the thing its like a small ark welder lol
 

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Bluejets

Oct 5, 2014
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Firstly, outgoing circuits will only draw what current they require, size of the transformer (large) has no bearing on this.
Blowing diodes or bridges implies you either have it connected incorrectly or the diodes were already blown or shorted out or incorrect voltage etc.
 

heavyfletch2nd

Jun 27, 2016
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Firstly, outgoing circuits will only draw what current they require, size of the transformer (large) has no bearing on this.
Blowing diodes or bridges implies you either have it connected incorrectly or the diodes were already blown or shorted out or incorrect voltage etc.
Firstly, outgoing circuits will only draw what current they require, size of the transformer (large) has no bearing on this.
Blowing diodes or bridges implies you either have it connected incorrectly or the diodes were already blown or shorted out or incorrect voltage etc.
Ok I will pull another bridge rectifier from somthing that I know is working and post the outcome , I didnt expect the 70 amp duel diods to have that result in drop out wich is why I really started this thread before setting any more fires , im no expert by any means this is my first attempt of a project using the few skills I have learned in two years of testing and replacing pcb components , now have learned that current draw is only as required by curcuit and not what is being forced out of transformer i will get back to it .Thanks ;-) appreciate you helping.
 

heavyfletch2nd

Jun 27, 2016
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Ok:-D it is now how i expect it to be with the 1.5v drop out we are now at 14.5 volt dc perfect for a car battery to be charged ,"better safe than wast money" thanks for replying I may ask a few more q's later on when putting together a smothing variable volt/current curcuit for the other half of this project .. thanks
 

Colin Mitchell

Aug 31, 2014
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You cannot connect an ordinary transformer to a battery.

It has to be a battery-charger transformer.
I have written all this up on talking electronics website.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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Please ignore Colin. He is full of half-truths.

You need to do something to limit both the current and the voltage into the battery otherwise you risk overcharging it.
 
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