adjustable dc regulated kit not working

Thread Starter

ninjaman

Joined May 18, 2013
341
hello

i bought this,
http://www.ebay.co.uk/itm/PCB-LED-0...054158?hash=item43de84cd8e:g:dIYAAOSwBahVf9Qv

put it together following the schematic and it doesnt work. i am using a 19v 3A laptop supply though. and it says 24v input.

is that why? i thought that you could use any dc supply, the output would be limited though if not 24v.

also, i am not to sure how to test this to find where the fault may be. any suggestions on testing a circuit?

thanks
simon
 

TheButtonThief

Joined Feb 26, 2011
237
It appears the project is based upon a linear voltage regulator so you're not going to get a higher output than what you put in. Also, the module takes an AC input, not DC. Rectify 24VAC and you'll get something close to 32VDC, feed 32V to the regulator and you'll get a max output of 30V (with all linear regulators, there's loss). You could feed a DC voltage to the input but remember if it's lower than 32V then you're not going to get 30V at the output, if you feed 19VDC then you're only likely to get around 17V max at the output.
 

Thread Starter

ninjaman

Joined May 18, 2013
341
what would be best to use as a load, i am guessing a high power resistor would be best. i have no experience of this. i have a book that shows how to design and build a power supply. all i need is a 0-30v dc supply the current does change from 0.5A to 1A and thats all.
 

TheButtonThief

Joined Feb 26, 2011
237
Your load doesn't need to draw very much current if it's just for the purpose of testing. I'd draw about 200mA, just use a resistor.
 
Last edited:

Thread Starter

ninjaman

Joined May 18, 2013
341
at the moment with a 19 volt 3 amp dc supply i get 400 millivolts at the output. my reasoning is that output voltage over the 200 milli amps mentioned above gives 2 ohm resistor(?) would this be right?

thanks
 

dl324

Joined Mar 30, 2015
16,845
The silkscreen on the board indicates input is 24VAC. That appears to be the input for the 7824 regulator, so you need to provide at least 27-28V DC. With less than that the regulator won't function.
 

Thread Starter

ninjaman

Joined May 18, 2013
341
cool, cheers dl324 and button thief. im thinking of just getting a dc dc step up booster for a few pounds. it wont change current but should provide the 30 volts.

thanks
 

AnalogKid

Joined Aug 1, 2013
10,986
Putting a switching boost converter in front of a linear regulator seems like a lot of unnecessary complexity. If you are going to buy something, what about getting a 24 Vac output transformer and connecting it to the board as the instructions suggest?

ak
 

takao21203

Joined Apr 28, 2012
3,702
Pretty nonsense these don't normally need extra standby load. Put a led if it doesn't Have one.

Bypass the bridge rectifier. It's not clear if it works even with lower DC.

Otherwise need to look item description

24 volts AC

Anyway it could be bad if the transformer goes down under load and you don't receive 30v anymore.

I'd try bypassing the bridge rectifier
 
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