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View Full Version : Can l daisy chain my 24 v dc



Goldie
02-20-2009, 02:38 AM
Hi

l want to daisy chain my SSR DC power, l have 24v ac bridge rectifier to 24v dc before the SSR, can l use this power source for all or some of the SSR's rather than connecting a new 24v dc to each SSR, l am connecting to 100 string led's to each channel.

hope l have explained ok

synnie
02-20-2009, 03:19 AM
Hi Goldie, im not going to say im an expert on this one but are you using SSROZ or DCSSR's? IF SSROZ they are AC and the triacs wont switch on with DC.If they are DCSSR's then they will work fine.
Are the LED strings series/parallel? i have LED strings which have 7 sections of 10 bulbs, each section pulls 20mA so the string total pulls 140mA. The tree in my pic has 24 of these strings (homemade) and pulls a total of 3.4Amps at 24VDC.They were switched with ULN2803's though.Shall need to do a little bit of counting to see what each string would/should pull.Are the strings complete with their own transformer pack or bought without one? Thats the easy way to see what amps they will pull.
When you rectify the 24VAC have you reduced the voltage also? bridge rectifying Ac will actually give you 1.4 times the voltage at DC. ie 24VAC = 33.6VDC unless its smoothed and reduced to 24VDC....Confused yet????

Cheers Synnie

Goldie
02-20-2009, 09:48 PM
l'm always confused, but l do understand what you are saying, l have a choice of rectifying the 24AC after the SSR with a reducer which would mean every string will need a bridge rectifier plus a resistor or change the SSR to a DCSSR rectify and resistor before the DCSSR, so either do 16 DCSSR's (which l do not have) and 16 bridge/resistors (which l have) or bridge resistors for each DC string l want to use

synnie
02-20-2009, 10:03 PM
Thats what i had lined up to do a couple of years ago when converting LED strings, until i was given the hint with ULN's running from my DIO card.Because i was converting from normal lights to LEDs i had everything worked out to run at rectifried 24VAc to 33VDC.
Just did a quick check with the LED calculator and a rectifried string with 10 LEDs in each section would need a 680ohm resistor per section after the bridge.i suppose i should ask what kind of LED string do you have???

Goldie
02-20-2009, 11:04 PM
l have white on the reindeer but want to put red and blue, plus the flood lights will be red blue and white very Australian lol

synnie
02-21-2009, 01:18 AM
Sounds pretty straight forward then Goldie.When playing with LEDs i always use this little toy, saves a lot of headaches
http://led.linear1.org/led.wiz

Goldie
02-24-2009, 11:51 PM
l was told at one stage that if l use rectified 24VAC because it is not true DC the Triac's should work, is this right ?????

toodle_pipsky
02-25-2009, 04:40 AM
I've been working on the principal (and this could be waay wrong) that it all depends on where you stick the rectifier. I ran LEDs last year off AC rigged stuff (i.e. boards with triacs) - AC to the board --> AC out of the board --> bridge rectifier --> DC to LEDs. If you stuck the rectifier before the board you'd have DC going to the board and that won't work.

I don't know about daisy chaining DC SSRs. Waiting for parts for mine so I'll test it out *boom*! ;)

prof
02-25-2009, 09:10 AM
If it is just rectified (unfiltered) you can put the rectifier in front of the SSR. Since the voltage still drops to 0V at the end of each half cycle the triacs turn off when triggered. In my 08 show I used both methods (before / after ssr) on different led strings - using ozssr boards, and I even ran 2 Ren16s that were fed with (24V) full wave rectified voltage without any issues.

Although you have not mentioned it in your previous posts, if you are chopping off the control modules found on most Ausie light strings to run them from an ssr, some controllers used with leds will have resistors inside them that need to be retained.